Have a Look. What Would You Do?

[Peter H.]

Re: Have a Look. What Would You Do?

Don, on a side note clean the threads with a thread chaser ..cleans up the threads with no metal removal..peter ..

[Don L.]

Re: Have a Look. What Would You Do?

Good info/tip on cleaning the block's threads. Thanks for that. Not sure I'd have done that otherwise.

As for OE bolts, I spoke to my local NCRS sponsoring Chevy rep today. He confirms that GM part numbers for these bolts are needed in order to look them up in the parts system. I wonder if anyone here might have GM part numbers for the following head bolts:

• (Quantity needed = 14): 7/16-14 X 3 3/4" long
• (Quantity needed = 4): 7/16-14 X 3" long
• (Quantity needed = 16): 7/16-14 X 1 3/4" long

All class 8 bolts of course.

[Jeffrey S.]

Re: Have a Look. What Would You Do?

Good info/tip on cleaning the block's threads. Thanks for that. Not sure I'd have done that otherwise.

As for OE bolts, I spoke to my local NCRS sponsoring Chevy rep today. He confirms that GM part numbers for these bolts are needed in order to look them up in the parts system. I wonder if anyone here might have GM part numbers for the following head bolts:

• (Quantity needed = 14): 7/16-14 X 3 3/4" long
• (Quantity needed = 4): 7/16-14 X 3" long
• (Quantity needed = 16): 7/16-14 X 1 3/4" long

All class 8 bolts of course.

Don,
According to the GM P & A catalog:
7/16 x 14 x 3 3/4 3734594 (circle on top of head) AR
7/16 x 14 x 3 3767468 " 4
7/16 x 14 x 1 3/4 3704796 16
Jeff

[Joe L.]

Re: Have a Look. What Would You Do?

Don,
According to the GM P & A catalog:
7/16 x 14 x 3 3/4 3734594 (circle on top of head) AR
7/16 x 14 x 3 3767468 " 4
7/16 x 14 x 1 3/4 3704796 16
Jeff

Jeff and Don-----

If he could find those bolts, he'd have original bolts. Unfortunately, those bolts are long-since GM-discontinued having been replaced twice in SERVICE.

The current part numbers are as follows:

3-3/4"------GM #10168526

3"-----------GM #10168525

1-3/4"------GM #10168527

However, the above-referenced bolts are not configured like the originals. These bolts are a flanged (washer) head-type bolt and they have a 9/16" across-the-flats hex head rather than the 5/8" of the originals.

US made bolts of the original configuration are pretty easy to find. Here are some that are probably of acceptable quality:

https://www.ebay.com/itm/OEM-Head-Bolt-Set-fits-GM-1957-99-283-305-327-350-377-383-400-406-Made-in-USA/401148933050?epid=1479660223&hash=item5d6656f3ba:g:gLwAAOSwWktaU-7R&vxp=mtr

For me, though, I do not like to use any used bolts for critical engine fasteners. These include head bolts, main bearing cap bolts, and rod bolts. I don't even like to use OK quality aftermarket bolts although they are probably perfectly fine. For these critical bolts, I use only the best ARP bolts. Period. Overkill for a street engine? Probably. But, I like to sleep soundly.

[Joe L.]

Re: Have a Look. What Would You Do?

Hello all.

I am in the process of completing a complete cylinder head refurb/valve job on my 1972 L48 engine this winter. The machine work is complete and I'm preparing to re-assemble the engine. I've been advised by some to re-use my original head bolts. I'm not so sure.

The back story:
I bought this car in 2005 as a body-off restored car. I've successfully campaigned it as a National Top Flight car. I have receipts showing it had an engine rebuild and valve job in 1999-2000. Based on observation, the bolts look to be re-used originals. I'm now faced with either using these bolts again or buying new bolts. See the attached photo of one of the bolt's threads. This photo is quite indicative of the rest of the set. Considering that they've likely been re-torqued once already, and considering that the threads at the end of each bolt is somewhat compromised, I have considered replacing the bolts this time. What concerns me is that because I am interested in replicating factory appearance as much as I can, I consider reproduction bolts from one of the reproduction parts houses that we all know. Should I trust these replacement bolts as true high quality grade 8 bolts? Should I re-use the original bolts? Should I buy known quality bolts like ARP, realizing/accepting they won't be typical for normal GM production? I prefer the reproduction bolts, however, I worry about their true quality and performance.

Inputs and/or ideas will be most appreciated. Thanks in advance.

Don------


As others have commented, the threads at the bottom were damaged by corrosion and, since they extend into the water jacket, do not compromise the integrity of the bolt. However, note the first few threads below the shank have been galled. I would not re-use this bolt or any bolt like it. Of course, as I mentioned in another response, I do not like to re-use any bolts for critical engine applications.

[Jimmy G.]

Re: Have a Look. What Would You Do?

I have used "used" head bolts on many engines without a problem Should be no issue

[Dick W.]

Re: Have a Look. What Would You Do?

I would run a die over the threads and reuse the bolt. The corrosion on the end does nothing to harm the integrity of the bolt

[Jim D.]

Re: Have a Look. What Would You Do?

I have used "used" head bolts on many engines without a problem Should be no issue

I agree Jimmy. I've built a lot of engines over the past 40+ years and the only time I used new bolts is if I didn't have the old ones. Never had a single issue with any of them.

[Joe L.]

Re: Have a Look. What Would You Do?

I agree Jimmy. I've built a lot of engines over the past 40+ years and the only time I used new bolts is if I didn't have the old ones. Never had a single issue with any of them.

Jim------

Head bolts rarely fail catastrophically. In fact, I've never heard of an instance of it. However, the problems can be a lot more subtle. Failed head gaskets can be the result of bolts rather than the head gasket, itself. Sometimes, one can have a failing head gasket for a long time before the symptoms exacerbate to the point that one realizes it.

I might be more inclined to re-use the bolts if I was certain of their history. In other words, if I had owned an engine since new and had been the only one that ever removed and re-installed head bolts, I might be more inclined to feel comfortable with them. However, in many cases, one does not know the history of the bolts. Did some klutz way over-torque them at some point? Were they ever part of an engine that drastically over-heated? Etc., etc.

[Mark E.]

Re: Have a Look. What Would You Do?

All bolts stretch when torqued. It's a matter of whether the elongation is in the elastic or inelastic range. Vintage small block head bolts stretch within the elastic range, and can be reused if not damaged. Some modern engine head bolts elongate into the inelastic range, but may be reused as long as the elongation does not exceed maximum specification.

Duke

Right, but how do you know if they're damaged? For an engine that matters, at best I would only reuse head bolts originally installed by the factory.

[Mark E.]

Re: Have a Look. What Would You Do?

I agree Jimmy. I've built a lot of engines over the past 40+ years and the only time I used new bolts is if I didn't have the old ones. Never had a single issue with any of them.

I've seen a fair number stripped threads in the block, failed head gaskets, warped heads. Damaged or stretched bolts are a likely cause of these failures, along with improper torquing. The bolt itself doesn't typically "break".

[Jim D.]

Re: Have a Look. What Would You Do?

I've seen a fair number stripped threads in the block, failed head gaskets, warped heads. Damaged or stretched bolts are a likely cause of these failures, along with improper torquing. The bolt itself doesn't typically "break".

Replace them if it makes you feel better. I've never seen any of the failures you listed except for one blown head gasket but that was on a V-6 Toyota and was covered under a factory re-call.
I rebuilt the engine in my 60 over 30 years ago and used the old head bolts. I guess it's a ticking time bomb.

[Gene M.]

Re: Have a Look. What Would You Do?

Be sure when using aftermarket bolts that use a washer, to use the washers. The bolt heads are generally radius under the head and the washer on one side is also to mate with the bolt and not cause a sharp edge contact with the hole in the head.

I generally use the original short bolts that are external so the assembly looks correct. The others are new ARP hardware.

Teflon sealant in water jacket bolts is a must.

[Mark E.]

Re: Have a Look. What Would You Do?

Replace them if it makes you feel better. I've never seen any of the failures you listed except for one blown head gasket but that was on a V-6 Toyota and was covered under a factory re-call.
I rebuilt the engine in my 60 over 30 years ago and used the old head bolts. I guess it's a ticking time bomb.

Jim, I'm sure your engine is well put together. At least two issues with bolts can affect proper torque, which in turn can affect how well the gasket performs: damaged/dirty threads and a stretched bolt. The former you can see; the latter you can't.