: Main Cap Bolt broken in block, UGHH.



Manic Mechanic
09-30-12, 09:09 PM
I thought I was at the end of my foolish over-heat caused stripped head bolt head gasket seal failure resulting in an overhaul disassembling process. Perhaps that's what happened, I let my guard down being "done" after everything else had gone so smoothly. Since it's commonly recommended to reseal the lower case halves when the engine is out by the guys on here who should know I decided to not chance a future leak. So I'm doing just that this morning and was down to pulling the main bolts. I rigged a 20" long 1/2" ratchet and started giving all the bolts a yank to start loosening them. They seemed pretty stuck but they're sturdy main cap bolts and a quick yank was popping them off, what could go wrong? Well the damn things are about the size of a pencil I now know. So on the second round the studded bolt that holds the oil pick-up just lets go with only about 20 lbs of torque. I pulled it out and saw only a few threads with a pretty clean shear. I had hopes that when the lower half-case was lifted off I would find something to grab onto but there isn't any. Also I noted on inspection that one of the other cap bolts almost broke. When removed it was about 30% twisted just above the threads, which only means it could have been slightly worse and that these are realistically a one time use fastener. I really wish I had read this already but it's something I didn't come across. About three of the bolts pulled a sliver of aluminum threads out of the block but the holes look pretty solid.

So I have the threaded portion of this bolt stuck pretty damn tight in the upper case. Trying to hammer it counter-clockwise with a punch on the only lip gave good traction but no movement. A little heat didn't help and I don't know how much would be too much on the aluminum so I didn't try any more heat. I pulled out my Snap-On reverse Cobalt bits and extractor master set. After much consideration about drilling metal in the crank case with the crank, exposed bearings, and all the rotation assembly still installed I strapped a shop-vac duct to the crank-case so that it was sucking full force just next to the bolt. I was able to get a good centered dimple on the bolt with a punch but due to the proximity and size of the crank position trigger wheel I couldn't get my drill on the bolt straight. I couldn't think of anything else I could do for myself and stopped there. I searched a while under "broken main" and the like in this forum for a while and found a few useful posts but not one where a guy had to remove a bolt. One about replacing the threads and one about replacing the bolts. Both came to the conclusion that if you remove the rods you need to replace the rod bearings but the mains are ok to reuse if still good.

Unless you guys have anything else in Northstar mechanical wisdom to offer me that I haven't found I'm either going to just take it to my machine shop for further extraction efforts or should I just throw in the towel and start pulling the crank-shaft out? If I pull the crank that means rod bearings and rod bolts minimum and at that point what about the rings? It's got 130K on it but was perfect prior to the last over-heat. Also what are the replacement options on the main cap fasteners? Any stud kits or just OEM bolts?

thanks,
Vernon

dkozloski
09-30-12, 10:18 PM
You need a TiG weldor. Use it to build up a weld lump on the exposed end of the broken bolt. Drop an appropriately sized nut over the lump and securley weld that to the lump. Now you can get a good grip on the broken stub with a wrench that fits the nut. The beauty of this procedure is the heat applied to the bolt as well as the fact that if you twist the nut off you can do the procedure over and over. I usually worked the wrench back and forth gradually increasing the force until the stub started to turn or the nut broke off. I managed an aircraft engine overhaul shop for many years and this technique never failed to remove a broken cylinder hold down stud or twisted off exhaust stud with no damage. Dozens of customers from miles around came to me with problems similar to yours and I was always able to accommodate them.

Manic Mechanic
09-30-12, 10:32 PM
Ah yes I know that technique but for some reason hadn't considered it. The bolt end is down about 3mm into the aluminum hole. In your experience is that still doable? I'm not experienced in welding (I pay somebody) so I have to ask.

Vernon

dkozloski
10-01-12, 02:06 AM
That's ducksoup for an experienced TIG welder.

98eldo32v
10-03-12, 06:47 AM
I feel your pain. I hope you get the bolt out..

I had read the stories of the main cap bolts snapping upon removal and sometimes re-insertion. I don't like those kinds of problems. I opted for new lower end oem bolts.

Yes, once you attempt to reseal the midcase, you usually have to replace the rod bearings. I have read that some have had to do mains instead of rods.

When I took my donor 98 sts motor apart, the mains looked brand new. That motor had 154k on the clock. The rods I han't unbolted yet, but going that deep I decided to change rod bearings, main bearings and all the bolts.

I'm not planning on changing the rings unless I see some unusual wear. Yet, with these motors the original hone marks are usually still visisble. If that's the case, those rings are going to stay.

This is a finicky motor. Better be safe than sorry.

maeng9981
10-04-12, 12:28 AM
My Deville engine has been severely overheated (we're talking about possibly more than 300 degrees here), it has 110,000 miles on it, and the internals still look pretty nice. No visual cracks. It will be checked for warping though, but nothing so far seems out of ordinary. It still has the factory honing pattern and it looks nice. I'm planning to reseal the bottom half and replace all the bearings as well as repairing the top half.

Manic Mechanic
10-04-12, 02:40 PM
Then just take a lesson from me and break the bottom end bolts loose with steady pressure and a lot of patience, they are weaker than the grip the block develops on them and will take some time to come out without twisting.

I'm busy with customer cars and haven't had any work week spare time to address mine yet.

Vernon

CadillacLuke24
10-04-12, 04:05 PM
My Deville engine has been severely overheated (we're talking about possibly more than 300 degrees here), it has 110,000 miles on it, and the internals still look pretty nice. No visual cracks. It will be checked for warping though, but nothing so far seems out of ordinary. It still has the factory honing pattern and it looks nice. I'm planning to reseal the bottom half and replace all the bearings as well as repairing the top half.

I just GOTTA say it.....

Woman driver?

SC2150
10-04-12, 04:39 PM
Kent Moore has a complete time-cert kit for just this. It includes the jig, drill, tap and threadcert to repair it. This is not a rare occurance.

Let me know if you need the part#.

:thumbsup:

Manic Mechanic
10-14-12, 12:41 AM
Well it worked just as dkozloski said it would. I picked the block up from a local welder I found today with the broken bolt out clean. He was able to build up several successive beads and once he had about a centimeter on it twist it right out with the threads intact. Thank you dkozloski for the tip, I don't know if I would have thought of that on my own. But it's good to know and also good that I found a gas shielding welder local. He owns a shop in Houston but keeps some special equipment at his house out here for hobbies and small side jobs like mine that require finesse or special materials like Magnesium.

Now I get to start on engine reassembly and transmission repairs etc.

Vernon