: Removing the dowels



Loose screw
02-18-05, 03:00 AM
What is the best was to get the head alignement dowels out of the block so I can finish Time-sert-ing all the head bolt threads. From what I have read they are in very tight and don't want to come out easily.

zonie77
02-18-05, 08:01 AM
We wound up cutting them and then installig new ones.

dkozloski
02-18-05, 11:21 AM
Take a TIG welder and build up a lump on the dowel that you can get a hold of with vicegrip pliers and twist them out. Replace them with new ones. This is also a very good way to remove twisted off bolts and studs except that you build up a lump and then weld on a nut that you can get a wrench on. Drop a thin washer over the lump before welding on the nut to protect the base metal. If it doesn't work the first try you can do it again. I have removed hundreds of eroded and broken exhaust studs in aircraft engines using this technique and it worked every single time.

haymaker
02-18-05, 12:00 PM
What is the best was to get the head alignement dowels out of the block so I can finish Time-sert-ing all the head bolt threads. From what I have read they are in very tight and don't want to come out easily.
This is a common problem and Iím not too sure anyone has a good answer. I have removed them from cast-iron as well as aluminum engines and I still donít have an easy way. Maybe someone has built a tool that makes the job a snap but I havenít seen it.
If you can find the new dowels, your half way home because removing the old dowels isnít that difficult. Spray some penetrating oil around the old dowels before you start.
Find a bolt that will just barely screw into the old dowel, now find a flat washer that will fit over the old dowel and place this washer over the dowel so it rests down against the block surface (the washer helps prevent the edge of the vice-grip nose from marring the block deck surface). Run the bolt down into the old dowel about ĹĒ(the bolt keeps the dowel from crushing). Snap your trusty vice-grips onto the old dowel and twist the dowel as you lift on the vice-grips. One of the old dowels in my N* came out easy but the other one was a lot harder to remove. If like me you want to try and reuse the old dowels, give this a try. Cut a piece of emery cloth about ĹĒ wide and 1 ĹĒ long. Wrap the emery cloth around the dowel with the sanding surface turned inward toward the old dowel. Snap the vice-grips in place over the emery cloth wrapped dowel and twist as you pull up on the vice-grips. If you donít chew the old dowels up too bad you can use a file to remove the vice-gripís marks. Donít remove any more material from the old dowels than necessary just the ridges mad by the vice-grips. When reinstalling the old dowels turn them end for end so the fresh unmarred end is up toward the cylinder head. If after removing the old dowels you are uncomfortable reusing them, locate and install new ones.
Good luck.

BeelzeBob
02-18-05, 04:43 PM
First, forget reusing the dowels. Get new ones from the dealer parts counter.

Crush them with vise grips, grab the crushed section and hammer upwards on the vice grips....

Use a slide hammer and a large tap. Tap the tap into the ID of the dowel to serve as an anchor and then attach the slide hammer to the tap to yank them out.

The dowels are designed to be a very tight press into the block so that the press load is always there even when the block heats up and the aluminum hole expands more than the steel dowel. Gently heating the aluminum deck in the area of the dowel with a propane torch helps some to relieve some of the press load on a room temperature block.

Bottom line is that you have to get pretty medieval with them to get them out....it usually isn't pretty for the dowels.

haymaker
02-18-05, 05:21 PM
Forget about the heat. You donít need it. It will only make the job that much more difficult. Be very careful if you decide to us a tap chances are you will run the tap in too far and expand the dowel in the block. Then when you get to hammering and prying on the tap you run the risk of removing a good 1/8Ē or better of the surrounding aluminum.

dkozloski
02-18-05, 11:26 PM
When you TIG weld on the dowels or studs they get much, much hotter than the aluminum. Even though the aluminum has a greater rate of expansion the steel still forces the base metal aside and/or the steel collapses. When the dowel or stud cools it will be a looser fit than before. I have seen many studs that were twisted off in the first attempt at removal that spun out easily after the nut was welded on. Don't be timid. Make the first effort your best shot. There was a time when I had more business pulling other mechanics chestnuts out of the fire from broken studs, dowels, bolts, drills, taps, and easy-outs, than I did from aircraft work. I was never stymied. I extracted everything from 4-40 screws broken off two threads below the surface in a multi-thousand dollar helicopter gearbox to 7/8 studs sheared off in a drive coupling. For many years I was the local "last resort". There was really good money in it. To extract small screws you sharpen a .040 tungsten electrode to a needle point and use .025 stainless steel safety wire for filler rod.

BeelzeBob
02-19-05, 12:03 AM
The "standard" removal tool for the dowels at the engine plant and in the experimental build and teardown area for Northstar engines is a tap welded to the steel rod of the slide hammer.....it works like a charm. The slide hammer usually has a tee welded to the end of the slide so that the tap can quickly be turned into the dowel and then just popped out. If you use a bottoming style tap you can cut three or four good threads into the upper part of the dowel before even entering the part of the dowel that is in the block.

Not that this approach is without potential pitfalls and you do have to observe some cautions (like with any approach) but it is , by far, the easiest way to get the dowels out.

dkozloski
02-19-05, 12:19 AM
The problem I would have with the tap in the slide hammer is that taps are either high carbon or highspeed steel. Either is very brittle and easy to break off in the dowel. Then you are in real trouble trying to get that out so you can try something else as they are much too hard to drill. If you are going to try this method I would use a good sharp plug tap followed by a sharp bottoming tap to get the maximum number of threads to engage and then screw in a threaded slide hammer adapter machined for that purpose from a high strength bolt. Make your first effort your best shot. Get tooled up right to start with so you don't have some self created catastrophe to deal with. If you can screw a bolt into the dowel use a piece of all-thread instead, stack washers on it that are bigger than the dowel, then draw the whole works out with a nut screwed down the all-thread. Be deliberate. Think out every move. A few minutes of careful preparation can save hours, if not days, of frustration.

Loose screw
02-19-05, 02:32 AM
Thanks for all the great feed back and sugestions. I did get them all out and it took only about 12 minutes for each, and 10 minutes of that was heating up the block with two propane tourches.

What medothed did I use? First penetrating oil was appiled to each but some were so tight that the dowels had formed a very good seal with the softer block and the penetrating oil never could penetrate in. Heating the area for ten minutes (with two tourch) did allow re-applied oil to get in. Inserting a close fitting bolt into the dowel to prevent the dowel from deforming was a great suggestion given here - thanks. It also made the clamping force of the vice-grips very solid and resulted in a slip proff grip with a sharp new pair of vice-grips. I couldn't find a bolt handy that fit right, but I did however find that the handle of a very cheep 3/8 rachet was a very tight fit, the handle was knerled and had to be hamered in about 1/4 deep, then the vice-grips were applied very tightly. The rachet endup serving another useful function as well - I could pull up on the end by hand and together with first gently hitting the vice-grip with a hamer to brake them loose and then moving the vise-grips back and forth while lifting up on the ratch with this alone they all came out in less than two minutes each (heating time of 10 minutes each not included) very cleanly. The rachet handel was easily hamered out of the dowel.

At the time I thought a tap could be used very well with a long enough bolt to accomplish the same result and be more professional. A slide-hamer would be nice but not neccessay as the force need to pull the dowel out is greatly reduced if the dowel is moved by the back and forth by the vice-grip movement.

In the beginning did try one time to pry up on the vice-gips, carefully placing a pry bar under the vice-grip ---- but could clearly and early see that this is a bad approuch, it is far to easy to damage the block and it takes too much force, the dowel would not move (if you are not rotating the dowel at the same time - but if you are rotaing the dowel at the same time the pry bar can move and scratch the block even with a protective plate something bad seemed ready to happen) it seemed too dangerous for me.

I found heating the block very well necessay and I highly recomend it, take your time once hot adding a few more drops of oil inside and out helps to cool the dowel and lubracate it, then hammering in the rachet handle or tight fitting bolt and then apply the vice-grips last. This work surprising well compared to a cold block where I couldn't get any of the dowels to even move in any direction in or degree applying a great deal of force.

Thanks guys!

haymaker
02-19-05, 05:19 PM
Glad you got them out without too much trouble. One thing great about this forum is the free flow of ideas. Hard to go wrong if you listen to bbob or dkozloski those cats have been around the block more than once. Good luck with the rest of the repair.

Loose screw
02-20-05, 12:51 AM
You learn who the real experts are here very quickly and they are so helpful every time. Thanks for the encouragement, I finished Time-serting the last head bolt thread this afternoon - all went very well so well that I thought you could probably perform ALL of the tasks (drilling, taping and driving in the serts driver) using a slow speed 1/2 drill with a clutch or just don't tighten the chuck TOO tight so it can still slip and then reverse the motor a few time as needed - I have done that on other projects and it has worked very well and fast being sure to use plenty of cutting fluid. And of course GM is not cutting or rolling threads by hand but with power driven taps. The Time=sert tools appear plenty strong to handle it if done with some common sense. Just stop and revese frequently and always befor it binds and stops it self.

One additional recomendation I might add is to use Liquid Wench with PTFE Super Lubricant & Penetrant in a greenish blue and white can (not the yellow one every shop has for freeing rusted parts) as your cutting oil, it really works well, makes clean cuts, reduces friction and heat plus it lets the chips move out of the way better and is a time saver. Or maybe someone knows of an even better cutting oil? Obverously, I am no expert. - but make sure to use a good strong solvent (like Berryman B12 caburator cleaner - very mean stuff) that clean down to the bare metal and leaves no residue, use the one that comes in a spray can to wash the PTFE and all chips out completly.

One question/problem I did have - now that the head bolt threads are all done I took a much closer look at the main bearing threads - all are wonderful, solid and and shinny, except one (wouldn't you know it). It has lost one thread off the top and the rest all the way down look dull, ruff and a little worn. There are other clear signs the bottomm of the engine was torn apart before. Is a Helicoil good enough for the mains? What about metal filled Epoxy thread repair to reinforce threads that are only questionable? What if used together, Helicoil with epoxy? Or what are my options with a main thread in such a condition. Buying a main time-sert Kit for just one thread just doesn't sit good.

Thanks guys

BeelzeBob
02-20-05, 04:40 PM
There is rarely a problem with the main bolts. I would assemble it as is.

If the main bolt thread is OK it will take the torque and angle at reassembly. If not, then you will have to deal with it. I would try it first as the mains are not nearly as highly stressed as the head bolts.

In any case, helicoils and epoxy thread repairs are pointless for a main bolt repair in aluminum. You MUST use a solid insert like a timesert for it to hold.

Loose screw
02-20-05, 10:25 PM
Thank you for you continued expert help. :worship: Is there ANYTHING I can do to help strengthen the "as-is" mains threads (not Time-serted) or reduce the assembling wear and tear on them - will anything help?

Also is there anything that should be avoided?

On a nother point - In a previous thread you wrote about rod and main bearings cruch (which was very enlightening) I was wondering why the inside surface of the rod/cap that contacts the back of the bearing and holds a cruch on them are so very smooth - instead of having some engaging texture that might aid in preventing micro bearing movement (after a thermal cycle). Do they do anything different in race engines besides increase the cruch a little to hold bearing better? :hmm:

dkozloski
02-20-05, 11:25 PM
I've used a very thin layer of high strength loctite behind bearing shells. The problem is that if you use too much you will get excessive bearing crush that will result in insufficient bearing clearance and/or spun bearings. I would just make sure that both the bearing saddle and the shell are very clean with no burrs or high spots. Anything you can feel with a fingernail is too much.

BeelzeBob
02-21-05, 12:33 PM
Thank you for you continued expert help. :worship: Is there ANYTHING I can do to help strengthen the "as-is" mains threads (not Time-serted) or reduce the assembling wear and tear on them - will anything help?

Also is there anything that should be avoided?

On a nother point - In a previous thread you wrote about rod and main bearings cruch (which was very enlightening) I was wondering why the inside surface of the rod/cap that contacts the back of the bearing and holds a cruch on them are so very smooth - instead of having some engaging texture that might aid in preventing micro bearing movement (after a thermal cycle). Do they do anything different in race engines besides increase the cruch a little to hold bearing better? :hmm:

You want a smooth surface so as to have as much engagement and support of the bearing as possible.

Basically the crush is what holds the bearing in place. In some extreme cases I have seen bearing pinned with small dowels and such but that is very abnormal. If the loads are correct and the bearing and such are properly designed the crush of the bearing is plenty to hold it in place. I would not consider any additives or loctite or anything like that. The crush of the bearing is so great that it is going to expele any sort of sealant or adhesive anyway.

Don't put anything on the main bolts. There isn't any way to conceivably beef them up. If the threads hold, great. If not, horse pucky is not going to save them.

If you REALLY want to strip the mains out use anti-seize on the threads....LOL...or , better yet, put some of that white, teflon pipe dope on the threads. That will REALLY do them in. Of course, you COULD fill the blind theaded holes with oil or grease. Then when you run the bolt down it will hydrostatically lock on the grease or oil and crack the block...or at least strip the threads out when the bolt can't compress the grease/oil...... LOL LOL LOL

Seriously.......Just make sure the threads are clean and dry and that the bolts are clean. There is a zinc phosphate coating on the bolts that serves as a bit of a high pressure lube to run the bolts down with. That is all that is needed or required.

dkozloski
02-21-05, 05:07 PM
It is my understanding that a lot of bearing inserts have a lead or indium flash plating on the back side to prevent galling and that is all that is needed. If there is any evidence at all at disassembly that the insert has been moving around, you are in a heap'o trouble boy.

BeelzeBob
02-21-05, 09:33 PM
It is my understanding that a lot of bearing inserts have a lead or indium flash plating on the back side to prevent galling and that is all that is needed. If there is any evidence at all at disassembly that the insert has been moving around, you are in a heap'o trouble boy.


Usually the "evidence" of an insert "moving around" is the fact that the connecting rod is a dark blue color, it is in many pieces, the block likely has holes in it from the broken conn rod milling around and the inserts are welded to the crank journal....or spit out into the oil pan in long shards of what looks like black tin foil......LOL LOL LOL

If there is inadequate crush the bearing insert can "squirm around" microscopically and you can see fretting on the backside of the bearing shell that starts out as black areas and escalates into micro-pits as material transfers to the bearing insert from the rod. This is a rare condition that would be unlikely to catch before it escalates into broken parts....but....such evidence lead to the "extra" crush that the Northstar rod bearings work with to this day.

dkozloski
02-21-05, 10:30 PM
I have seen hundreds of connecting rods and main bearing saddles for geared Lycoming engines that the backs of the inserts were polished from squirming around. Sometimes you will even encounter rod bores that have a raised version of the bearing part number where the micro fretting has worn the rod away except for the indentations where the part number was stamped in the insert. The rod can survive some of this and is sometimes even rebuildable. What is not survivable is the micro pitting, especially in the areas that are 45 degrees away from the rod/cap parting surface. Lycoming says that you are about 75 hours away from a catastrophic failure when the pits first appear. It looks to me that in an effort to build a narrow engine for aerodynamic reasons, aircraft powerplant engineers have pushed the limits of short connecting rods with resulting acute angularities. These angularities produce stresses from side loading on cylinder walls and crackcase parting surfaces that results in fretting between the case halves and severe loading of the connecting rods. Loosened main bearing inserts have also been a Lycoming problem for many years. When you pull an oil screen and find it full of finely gound aluminum flakes there is no doubt in your mind where it came from.

Loose screw
02-22-05, 12:04 AM
This is all very interesting, I never knew there was so much critical hidden detail in just holding the bearing. I worked in an Aircraft engine shop for six months 25 years ago doing valve jobs, engine tear downs and cleanings, and magnaflux and dye testing. All under someone else's certificate, I clearly did not know all I needed to do the work I was doing way I would feel confident with today. You say Lycoming had alot of experence with this question of bearings moving. Did their service bulletins describe anything to improve bearing stability?

This engine I am rebuilding spun a rod bearing from what I suspect was oil starvation - I have had the crank welded and repaired I also have replace both rods and have all new bearings and rings. But having lost one bearing all ready I want to make sure that I take all the wise steps I can to see to it can't happen again (as I am sure I drive with a much heavier foot then the previous owner and love those high RPMs).

Thanks

dkozloski
02-22-05, 12:17 AM
Lycoming went through several seiges with this problem over the years. With the mains they went to heavier and heavier shells, more and more crush, and bigger and bigger dowel pins. With the rods they went to heavier and heavier machined all over rods with tongue and groove parting surfaces. They are beautiful examples of the metal workers art and have a price tag to match. Corresponding rods made by Teledyne Continental are much rougher looking with a shot peened surface and go on and on with very litttle trouble. I remember one Continental rod however that had the correct torque on a rod bolt and nut but it was because the nut was seized on the bolt. The nut and bolt could be easily twiddled in the rod but it hadn't failed in 1700 hrs. of operation.

dkozloski
02-22-05, 12:21 AM
According to Bbob, Cadillac went to extraordinary pains while engineering the bottom end of the NorthStar. I don't think you have anything to worry about.

Loose screw
02-23-05, 01:46 AM
Spyder posted today in the other thread:
"I've got a 94 STS engine with a spun rod bearing sitting on the floor in my garage..."

It may be just a coincidence but that was also the failings of this 94 N* engine. I remember reading last year about other owners trying to find the source of an engine knock that sounds like it is coming from the front of the engine (as mine did) but it ended up being a rod bearing problem near the rear of the engine at 7-8 rods which is where mine occured. Are older N* engines more likely to spin a rod bearing, how common is this and what might be the cause - miles or just time? Or what? and does anyone noticed if they are occurring at one location more often than others? Could the speical way these rods a made have anything to do with it. Does an old rod mic out the same as a new and does it stay as rigid and stable as a conventional made rod over the years. Or are rod bearing problems no more like to occure and take out an old high mile N* than any other cause?

dkozloski
02-23-05, 02:39 PM
I spun a rod bearing in a very highly modified Chevy Z28 302 in an El Camino. Under very hard acceleration the oil pickup uncovered for an instant, just long enough for the idiot light to blink. The next instant bllllaaaaaAAAMMMMM!! I have seen several engines with burned rod bearings that had oil passages plugged with silicone sealers that had been applied to excess. I hate that stuff. There are two products that should be taken away from mechanics and never given back; silicone sealers and black electricians tape. The lord only knows where the silicone is going to get squirted and the tape falls off leaving a messy residue as soon as petroleum hits it.

haymaker
02-23-05, 05:55 PM
Loose screw. The oil may have broken down from overheating several times and if it wasnít changed?? When my engine overheated from the blown head gaskets, loss of coolant and went into limp home mode the DIC later displayed the message to change the oil. I think the engine uses the crankcase oil as a coolant even more than usual when in the limp home mode. As to which rod bearing(s) spun, rods #7-8 are the ones the greatest distance from the oil pump and at the lowest oil pressure. On a small block chevy the oil pump is at the rear (next to rods 7-8) so the rod bearing that normally spin are at the other end of the crankshaft at rods #1-2. This of course is if the problem is from low oil pressure.

Loose screw
02-23-05, 09:56 PM
I suspect because the car had a starter that wasn't working well that the car had sat for some time or had been cranked but not fast enough to pick up oil and get it back to 7-8 and when they did get it startered they may of reved it up - dry bearing, high rpms - spun 7-8 bearing Also the engine did have an oil leak because when someone dissassemble the engine and in stalled a new plate (without the molded in steel washers) they didn't get it aligned on the small dowels correctly and crack the plate. (easy to do if you working from under the car) So add oil leak / low oil to the bad starter there is plenty of things that could have led to a dry 7/8 bearing and from what I can tell is it is the most common place on the N* theonly question is how common is it and are they all oil starvation related or do the aging bearing also play some role.

haymaker
02-23-05, 10:42 PM
How much rod bearing debris did you find in the oil pan?

BeelzeBob
02-23-05, 11:10 PM
If the oil distribution plate was misaligned and cracked as you described the oil passages to the bearings were leaking severely internally and hemoraging all the oil pressure.....that is why it spun a bearing. That plate forms the oil passage to the mains....so if it is cracked/mispositioned then the oil pressure will be lost.

Loose screw
02-24-05, 01:10 AM
The mis-alignment was only about 1/32 of an inch, it resulted in a small amount of the lower case to be deformed and pressed down into the dowel hole half way down. The plate was very close to being correctly postion but no doubt it did not lay perfectly flat and experience even contact pressure with the other surfaces. When I did get the engine to start and idle for a few minutes there was no check engine light and surprisingly no noticable oil leakage on the drive way. How much was leaking internally if any I have no way of telling. But the plate did crack clear through at the corner at the front of the engine but the flexible inbeded gasket did not sheer and with there being no engine light there must of been some sealing but certainly the oil pressure could of been just above what would trigger the light.
What exterior oil leaking was evident, appeared to be slow and long term and from many areas - the engine was dry and damp greasy generally and not clean and wet near the crack area or other areas.

I examined the plate to see if it had the molded in steel washers you talked about elsewhere and it does not have them. How can I tell if I already have the right windage tray to prevents cracking the new plate that know I have to buy?

Thank you - you are a wealth of knolwedge - a real treasure.

BeelzeBob
02-24-05, 11:04 AM
No matter...if the plate was misaligned at all and the dowel did not go straight into the hole provided it would cause the plate to not seat and cause an internal oil leak that would hemorage the oil pressure. Likely there would be "some" oil pressure so the light wouldn't come on but not enought to sustain the engine at higher RPM so the rod bearing spins due to low oil pressure. End of story.

Hard to know about the plate without seeing it in person.... Your engine assembles with the main bolts directly thru the plate and the windage tray mounted on top of the main bolts with the stud headed bolts down the center as I recall so make sure it all fits together correctly that way and that no bolts are bottoming or anything.

Sounds like you picked up on a real basket case there......LOL.

Loose screw
02-24-05, 01:36 PM
Thanks for all your help yes it is a basket case - if I only had a clue at the time.

I am still confussed on one point the oil distribution plate - this 94 did not have the 94 plate in it the one with the molded in steel washers. So which plate should I make sure I install? I understand the 96 does not have the steel washers and uses a different windage tray and that the 96 tray goes under the head of the studed bolts instead of on top like the 94 does. Is the 96 tray thicker, than the 94 or otherwise noticably different? The one that was used is only .050 thick so i am thinking it is a 94 windage tray and it was installed on top of the bolt heads on the studs with the nuts (the 94 way) The oil distribution plate (which did not have the steel washers was not cracked at the mains bolt holes. So which oil dist plate should be used on this 94 N*? If the is 96 washer less - it does not require a different 96 bolt correct? Just use the 94s bolts and install in under the bolt heads.

Thanks again

BeelzeBob
02-24-05, 02:35 PM
You really cannot mix the steel windage trays up...the earlier type designed to go on the stud headed main bolts has smaller mounting holes that the main studs will not go thru....and it will not fit to the engine if you tried to put the main bolts thru it. The windage trays are the same thickness steel regardless...they are just shaped differently. The later one that goes under the main bolts themselves has larger mounting holes that clear the main bolts and it is "shallower" to fit the block and rod swing if it is put directly onto the aluminum oil distribution plate before the main bolts are installed.

I think that the earlier model aluminum distribution plate (with the molded in steel washers) was superceded by a plate that is slightly thicker overall that does not have the load bearing steel washers molded into it.....I think. can you post some pictures of the parts you have so that I can be sure what you have.??

Loose screw
02-24-05, 03:19 PM
Sorry no picture avialable but I have look at now with you discription it clearly is the 96 windage tray as the holes are plenty large enough for the bolts to go through and far too loose for a reasonable fit for the smaller studs to work with.

I want to make sure I don't have any leakage where the dowel trouble occured it look good, the damage is very small, with no high spots and does not effect the seal contact area. When appling gasket sealer in the area it should be done as to NOT touch the factory seal right, or does it not matter.

BeelzeBob
02-24-05, 03:48 PM
Sounds like the later version model of the windage tray. Place it on the oil distribution plate and then install the main bolts thru it.

Use the anaerobic sealer or Loctite "gasket eliminator" to the split line surface of the LCC to block. Also, use it on the outer perimeter of the oil distribution plate. Just a thin bead around the perimeter. It will squish into the seal area with no problems. Just use it sparingly as the joint is a zero clerance joint that is highly compressed so most all of the sealer will squeeze out...just a tiny bead will od.

Loose screw
02-27-05, 11:21 AM
One trick one of the mechanic did on an aircraft engine case that had gotten scratch bad on one of the large no gasket mating surfaces and would have cost a fortune to repair was to use non-waxed dental flose and loctite. The dental flose sqiushed very flat and formed a leak proff seal and was held in place by the see thru thin brushed on layer of loctite. The flose would loop around all fastener holes and damaged spots to assure their isolation, though this doubled the thickness where the flose crossed over it's self it seem to sqiush flate just fine. He said it seldom fails to work great, it has to be damaged pretty bad to leak using this technique.

JimD
02-27-05, 11:32 AM
One trick one of the mechanic did on an aircraft engine case that had gotten scratch bad on one of the large no gasket mating surfaces and would have cost a fortune to repair was to use non-waxed dental flose and loctite. The dental flose sqiushed very flat and formed a leak proff seal and was held in place by the see thru thin brushed on layer of loctite. The flose would loop around all fastener holes and damaged spots to assure their isolation, though this doubled the thickness where the flose crossed over it's self it seem to sqiush flate just fine. He said it seldom fails to work great, it has to be damaged pretty bad to leak using this technique.

Now that is clever.

dkozloski
02-27-05, 11:51 AM
Standard factory practice for many years has been to use a sealing compound and a very fine silk thread between aircraft engine parts that fit up metal to metal. ANYTHING thicker betweeen the parts prevents the them from mating tightly enough together to prevent metal frett. Dental floss between crankcase halves is the equivilant of bananas in the transmission and sawdust in the rear end of a used car. It will not last. I managed an aircraft engine overhaul shop for over ten years and I saw it all; everything from polysulfide rubber to grocery twine used to assemble engines. There can be no compromises or gimmicks with an aircraft engine repair. Do it right or get out of the business. The expense of doing it right is not a consideration if you're going to be putting somebody elses neck on the line that doesn't even know what you did. It's one thing to be a daredevil with your own life and quite another to do it to strangers. Who am I to be spouting off? I have been vetted as an expert witness in several trials one of which involved this type of jackleg repair of a damaged crankcase that resulted in an engine failure.

Loose screw
02-27-05, 12:37 PM
I was wondering about the flose Was the silk thread used with a sealer and it that practice still used today? what kind - locitite 510? Thanks

dkozloski
02-27-05, 04:54 PM
The silk thread is sold as a part number by Continental and several sealers are specified. Lycomimg has a spec for the thread and also specifies several different sealers. I will admit that that there may be approval for additional types of sealers that I am not aware of but I'll bet that dental floss is not one of them. The problem with any sealer in this application is that anything that is between the case halves acts as a lubricant and prevents the intimate metal to metal mating of the surfaces. I have had several facory people tell me that the less material you have between the cases the better. Any relative motion in this area produces metal frett and very significant wear. The result is that the halves squirm against one another, leaks develope, and ultimately the crush is relieved on bearing shells and they spin. I have also seen the opposite effect where after the wear developed, the crankcase through bolts were retightened and now the crankshaft was seized by the main bearings and wouldn't turn. There are several machine shops that specialize in repairing aircraft engine crankcases by lapping the mating surfaces until they fit exactly and then align boring the main bearing saddles. I know of one company that had approval for welding up main bearing saddles after they have been spun. I don't know if they are still in business.