: which timeserts to replace with Bigserts?

11-12-04, 09:05 PM
I'm REALLY Bummed out......
.... My Timesert repair failed. To be more precise, the engine block stripped again where the timesert threads in. I bought the 2nd Timesert Repair kit (Bigsert) and fixed the problem. When I started to torque the head back on, a second timesert pulled out of the block before the initial 30 ft lbs. Now I'm starting to worry about the rest of my timeserts holding. I hate to pull out the timeserts if they're in good condition because there's no such thing as a 3rd repair. Once the 2nd repair fails, the engine block is junk.

Additional info:
I checked the head for warpage - it was okay.
I suspect that a previous owner overheated the engine because I found a receipt for a new radiator under the seat.
I bought a new thermostat as a cheap safemeasure for the 2nd repair although I don't think the engine overheated after the 1st repair.
I also bought a new fuel injector for the blown cylinder which I believe had a intermittent leakdown problem - just in case my injector cleaner didn't fix the original problem. I think there's a chance the engine has been trying to compress liquid fuel in the cylinder putting an extra load on the headbolts & threads.

My questions:
How can "test" the integrity of my remaining 1st repair timeserts?
Can I assume good timeserts if I can place a 30 ft lb + 200 degree static load with a used head bolt?
Should I replace all of my timeserts with bigserts?
What do the pros do in a situation like this?

11-12-04, 09:10 PM
Also -
forgot to ask.
What is the preferred method for removing 1st repair timeserts? Is it a wise idea to just torque it down until they strip the block?

11-13-04, 01:00 AM
I am not an expert in N* repair but I like you have time-serted my N*. I am willing to give you my opinion as to what I probably would do if faced with this problem.

First given the fact that you have already completed the time-sert repair and used the new increased (higher) torque specs that in its self was a test. You stated that two of the inserts failed so Im not sure that testing the remaining inserts at an increase of 10 degrees torque angle would prove they may or may not fail in the future. Were the inserts that failed next to each other especially on the corners?

Think about it if the inserts were installed correctly and still failed the material they were threaded into could not have been good solid material (be it damage from the original block-thread failure pre time-sert, a problem with the block-casting or just from overheating). If mine fail as yours have I would big-sert all ten holes on the side that failed. Fact is I would big-sert all twenty. You already have the big-sert kit and the inserts themselves are not that expensive. You have already big-serted one hole and if that one fails the block is toast anyway. Drilling the holes to the (big-sert) larger diameter gives you the last best chance to repair your engine. Maybe you will find good solid material for the big-sert threads. Then when installing the head bolts I would use the original torque specs 22 lb/ft 60 degrees+60degrees+60degrees for a total 180 degrees torque angle. Millions of N*s are running just fine using those torque specs. To me if your block threads have failed for any reason I dont think it is a good idea to increase the stress in the area of the original failure by using the higher torque specs (30 lb/ft,70+60+60 degrees, 190 degrees total torque angle. The engineers on the forum may totally disagree but this is my opinion..

As to the removal of the existing time-serts below is an exert from their instructions.


Good Luck.

11-13-04, 11:38 AM
The first threaded hole to fail was on the firewall side of the block,
on the cylinder closest to the driver's side (yes a corner cylinder) but wasn't the corner bolt. It was one of the middle bolts on the bottom row (closest to exhaust manifold).

It also happens to belong to the cylinder I had been having fuel injector leakdown problems with.

After the bigsert repair, I started torquing down the head and the corner headbolt failed at about 25 ft. lbs. (dial torque wrench)

I will take your advice on the torque specs. I had been using the specs on the Alldata.com website: 30 ft. lbs. +70 +70 +60 (200 total)
and I have to say, of the four Northstar Headgaskets I've repaired, it didn't look like the gasket had "blown" like a traditional engine. In all cases, the gaskets looked normal (undamaged fire-rings, etc) but the tension on the bolts had relieved due to engine block thread failure. If I had to choose, I'd much rather have a future gasket failure from loose bolts than a engine block thread failure, so I'm going to start using the lowered torque specs. Where are these specs published by the way?

Thanks so much for your comments. I'm probably too frustrated to be thinking rationally about my repair :)

11-13-04, 12:36 PM
Brad, maybe i missed it but I'm not clear on the failure...Did the timesert pull the threads out of the block? The threads should be stuck to the timesert then. If so the block itself must be bad.

If the timesert rotated out the loctite either failed, you didn't give the loctite time to setup, or you didn't clean the block well enough.

Please clarify the exact failure. It would be great if you could get a couple of pics.

11-13-04, 12:52 PM
Yes, the threads pulled out of the block - they were stuck to the timesert.

11-14-04, 11:50 AM
Then I think you'll need a new block or attempt to fill the existing hole (at least partially) with a weld, then retap. It sure sounds like a soft spot in the metal itself.

The metal stayed on the timesert so you sure did that part right!

11-14-04, 11:55 AM
Yeah, I bet I could have unscrewed the helicoil shaped threads off of the timesert in one piece. I'm much happier to see this than to see the threads crumble into a zillion pieces, so I'm sure there's at least some strength left in the block. To be on the safe side, this time I'm going with the lower torquing specs and going with a lower thermostat too.

11-14-04, 05:06 PM
I just went back and reviewed your first post. I am trying to understand the sequence of events. Why was it timeserted the first time? Did you buy it and at a later date it overheated or did you just have it tested and found a problem with the head gasket? Which torque and torque angle setting were used on the first time-sert installation?

You said in your first post I don't think the engine overheated after the 1st repair. Why did you tear it down after the first head gasket repair? Was it just forcing coolant out of the coolant recovery tank but never overheated all the way into limp-home mode? Was someone else driving the car after the first time-sert repair.

Could you explain in more detail how the head gasket problem was first diagnosed and on to the need for the second repair.

After my head gaskets failed just a few minutes on the expressway at speed and the engine would overheat. The coolant was forced out of the coolant recovery tank on to the roadway.

What year is your N*? Over the period of the two head gasket problems have you used a lot of stop leak?

11-14-04, 06:11 PM
I bought the car knowing that it had a blown headgasket.
I discovered the damaged engine block threads and installed the 1st repair timeserts using the specs from Alldata.com: 30 ft. lbs. +70 +70 +60 (200 total)

Not long after the headgasket repair, I discovered a receipt under the seat for a new radiator, so it is my belief that this vehicle was overheated in the past.

My first clue about the repeated headgasket failure was the "low coolant" displayed on the message center. I never had a message mentioning an overheating condition, although I admit I don't know if such a message exists.

I followed up with a chemical test for C02 in the coolant with a block tester which almost immediately confirmed my fears.
As a last resort to another headgasket repair, I removed the valve cover to attempt to add a little tension to the headbolts, but soon discovered the headbolt that wouldn't tighten and knew there was another problem with the engine block threads.

This Northstar belongs to a 1998 Deville. I've never been a believer in stopleak in the past, so I've never used it on anything. However, there are enough convincing arguments on this website to convince me to spend the extra $2.50 in this case.

11-14-04, 10:26 PM
Something that I don't understand is how the timesert repair could pull out with only 30 ftlb of torque when the head bolts were being brought up to torque.... I don't doubt that it happened like you described but something doesn't make sense. Especially as you describe the threads being pulled completely from the block intact on the timesert. It takes a LOT of force to pull that timesert out...it should be stronger than the original threads since the timesert is engaging more material on the OD than the original head bolts did.

Did you check that the holes for the head bolts are to the correct depth and that the replacement head bolts are the same/correct length?? Any change to the block deck height or to the head deck..i.e..was anything decked for flatness which would have shortened the grip length of the head bolts and possibly caused them to bottom out. Any change to the head such as remachining the head bolt spot faces where the head bolts bear against the head to get more thread engagement??

If the bolts are too long or the grip length was changed so that the head bolts are bottoming in the head bolt holes then 30 ftlbs could force the timesert out as that would exert tremendous load on the threads and explain how the timesert could pull out.

I bring all this up because until you can figure out how timeserts that were correctly installed pulled out it is liable to happen again with the bigserts. They will seccumb to the same problem if it repeats itself.....

Are you adding some sort of lube to the head bolts?? I have seen cases where oil/grease on head bolts caused the head bolt to hydrostatically lock on the grease in the head bolt hole and strip and in some cases crack the block in that area. The grease or other debris in the hole cannot escape as the bolt is run down the incompressable materal acts like a too long head bolt that is bottoming in the hole.

I admire your perserverence on this....too easy to give up after one failure and call it a day. The big serts are very very strong in the block and will hold tremendous load if they are installed correctly and the bolts are correct,new and not oiled or lubed. Just make sure they are not bottoming for some reason.

11-14-04, 11:11 PM
When I first started having the problem of lost coolant I tried everything I could think of to fix the leak without removing the engine. I tried the GM pellets many types of Bars stop leak including four tubes of the golden seal. Nothing even slowed it down. Then I tried the Bars block and head gasket sealer, still had the problem. I had to add one to two gallons of mixed Dex-cool every time I wanted to drive it. When in the process of installing the time-serts I was blowing out the chips and the nozzle passed over the area around the cylinders (water jacket) and some debris came flying out. After completing the installation of the time-serts I decided to clean the water jacket. At the bottom of the water jacket on the exhaust side of cylinders one, seven, two and eight stop leak had built-up to a depth of about 1 . The area between these cylinders had a build-up of only about a of stop leak that had the consistency of firm mud. The stop leak at the other cylinders (1,7,2 and 4) was set about twice as firm, very firm. I flattened a piece of tube and attached it to the shop-vac. That and a piece of rod helped in removing the built-up stop leak. After cleaning the area I saw what looked to be small casting brace maybe 1 1/2 tall and 1/8 thick at the bottom between the cylinders and the outer portion of the block that was acting like a dam for the stop leak. Im not sure how well the hardened stop leak would transfer the heat from cylinders to block or how the casting would react to a semi-solid between the cylinders and the block as they both expanded. All I really know is the area was designed for coolant to flow around the cylinders from top to bottom.

Just in case the previous owner used a lot of stop leak you may want to check those areas. The engine would at least have had the GM pellets that were installed when it was first built. It just seams reasonable that if a fair sized piece of the hardened stop leak in my engine had dislodged and moved elsewhere it could cause a blockage in the cooling system. Then another overheating problem.

Did you notice any difference in the drill shavings when drilling the holes for the time-serts? Did some of the shavings come out like small granular bits instead of nice long sharp shavings?

11-15-04, 11:15 AM
Hi BBob - it's great to hear from you - although I admit I'd rather be reading about somebody elses headache! LOL

yeah - I agree it sounds odd for the 2nd headbolt to pull out so easily, but it's obvious that it was about to fail very soon. I should also mention that it was also located on the bottom row of the same corner cylinder. My best guess is that my leaky fuel injector (on that same cylinder) made a small puddle inside the cylinder after shutdown that caused an extreme load on the headbolts when the cylinder came up on the compression stroke. I blame myself for being such a cheapskate and trying to clean instead of replacing that $130 injector when I knew there was a problem.

As far as the thread depth goes, I believe the depth was correct because the timesert kit has a depth mark on the insert tool to make it idiotproof. I also cleaned out my threads with a squirt of brakeclean and a long nosed nozzle of shop air. I did not have my heads decked, add anything on the threads of the headbolts, see any evidence of machinework or a previous entine teardown, so I doubt that's the problem although I'm impressed you thought to look at that because it would make total sense.

I also didn't add anything on the threads of the headbolts. only the original thread sealant that comes on the bolts from the dealership.

I like Haymaker's theory about making sure there are no deposits in the water jacket. This is a corner cylinder, so I'll definitely be checking that out.

What do you think about my leaky injector theory? On a traditional engine I'd expect to find a bent connecting rod after hydrostatic shock, but maybe it's possible the engine block threads were the weak link?

Also, what is the preferred torque spec for this engine? I think I'm going to go with the lowest spec I can find this time just in case.

11-15-04, 06:48 PM
My theory on the head gasket problem hasnt anything to do with the stop leak build-up. I didnt mean to mislead you. The stop leak was added to my system after the head gasket had started to leak so I cant place any blame on the stop leak. I simply wanted to indicate a potential problem before it occurred. It is difficult to view the bottom of the water jacket around the cylinders and if a lot of stop leak had been used in the past build-up may occur thus a potential overheating problem.

11-15-04, 09:17 PM
I would screw the head bolts into the holes until they lightly bottom without the head or the gasket in place. Measure the distance between the deck and the bolt head/washer. Compare this to the thickness of the cylinder head bolt bosses and the head gasket (usually about 0.75-1.0 mm compressed) to be positively sure that none of the bolts that you got are bottoming. And/or compare the old bolts to the new ones also to compare the lengths. Something is wrong if you pulled out the timesert with the initial torque and no angles.

Forget the idea of the lesser head bolt torque. If the threads won't take the intial bolt tightening then they are doomed as the stress during thermocycling is much greater then the load tightening them the first time. The threads are burnished at the factory by "overtorquing" the headbolts slightly before loosening and then retightening according to the spec. The bolt holes never fail during that pre-working of the threads so they should take more torque/tension than the original tightening specs easily....ESPECIALLY if a timesert is in the hole.