LT5 Head Gaskets

[LGAFF]

I have heard of these being reused multiple times(3 or more)

[QB93Z]

Originally Posted by A26B

..... Wish I knew who is going to take over this little LT5 biddness in a few years when I retire again!!

Jerry,

The LT5 Business IS your retirement. Everyone needs a project, or retirement would be boring.

Thank you Sir for everything you do for the ZR-1 Comunity.

If you will be the Technical Advisor, I'll take over the business any time you want.

Jim

[-=Jeff=-]

Originally Posted by QB93Z

Jerry,

The LT5 Business IS your retirement. Everyone needs a project, or retirement would be boring.

Thank you Sir for everything you do for the ZR-1 Comunity.

If you will be the Technical Advisor, I'll take over the business any time you want.

Jim

I would possibly be interested in that business when you both retire!!

[Pete]

Originally Posted by HAWAIIZR-1

Speaking of head bolts, I was told by someone that got the info from Graham Behan that even though torque to yield bolts are supposed to be used only once, it is safe to reuse another time. How many times can they safely be reused for heads?

If we are talking about head bolts they are not torque to yield bolts you torque them to 118 ftlbs.

I have reused my head bolts i would say about 5-6 times with no issues.

Pete

[A26B]

Originally Posted by HAWAIIZR-1

Speaking of head bolts, I was told by someone that got the info from Graham Behan that even though torque to yield bolts are supposed to be used only once, it is safe to reuse another time. How many times can they safely be reused for heads?

There is no way to quantify how many times a bolt can be reused, whether torque only or torque to yield.

Think of a bolt as being elastic, because it does have those properties. The elastic range of the bolt occurs prior to exceeding the yield strength of the bolt, once a certain amount of axial force has been applied. Once a bolt has exceeded its yield strength and "yielded" then it will have streched permenantly i.e. permenant deformation has occurred.

Permenant deformation can happen in one use or several uses. The only way to know would be to serialize each bolt, have accurate flats machined/ground on both ends of the bolt and an accurate measurement of each bolt taken & recorded. Then when the bolt is removed, it can be measured again & compared to the original measurement. If it is longer, then yield strength has been exceeded and permenant deformation has occurred. The bolt is no longer reliable for its intended purpose.

Now, regarding the elastic range. The idea behind torque to yield bolts is to tighten them very accurately (hence torque-angle procedure) so the bolt will be in the elastic range. When in the elastic range, the bolt act like a bungee cord, maintaining the same clamping force when pressure or temperature changes create additional forces on the parts being clamped/bolted. Constant clamping force prevents damage to certain types of seals, bearing & mating surfaces.

Think of it this way. The upper & lower crankcase parts of the LT5 engine are aluminum. The bolts are steel. You assemble the engine at ambient temperature, but it operates maybe 200F higher than that. Aluminum expands at roughly 2-times the rate as steel with an increase in heat, i.e. coefficient of thermal expansion. As such, the clamping force applied to the lower crankcase at ambient temperature would be higher at operating temperature because the thickness of the lower crankcase increased more than the bolt grew longer.

However, because the bolt was in its elastic range, it stretched (below the yield point), maintaining the same clamping force. Now, you can see that bigger bolts are not the answer to all problems. They can actually cause problems. Bigger is not always better.

I developed a concept to test used head bolts and discussed it with a bolt engineering firm. In short, bolts do not always behave exactly the same way (longer story) so there is no way to definitively determine if a used bolt can still be used, by testing. This particular engineer tried many procedures and came up with varying results, noe of which gave a predictable answer. Measurement is the only accurate way.

So, in summary, every time you reuse a bolt that has been installed as a torque to yield application, it's a gamble. The degree of risk is essentially unknown, but has been somewhat established by practice. I say somewhat because cam sprocket bolts have broken in service.

To the best of my knowledge, there have been no head bolt failures from re-use.

[Polo-1]

Originally Posted by A26B

Ain't it the truth!!

I've been working on new head bolts. Original manufacturer told me it would be about $7,000 for tooling and would need to do a min run of 5,000 bolts. I said can't we run less? He said "sure, but it'll cost you the same as 5,000 bolts." I never had the guts to ask him how much 5,000 bolts would cost. Imagine what that would make a set of head bolts cost if you were trying to just get even in 3 or 4 years.

ARP told me after I gave them my spec's $171 per stud ( not including nut and washer)... This was for the mains.

[HAWAIIZR-1]

Thanks for all the information and as always I appreciate the input by all as I am trying to be a sponge for information and learn as I go. I understand that a lot of information is available on the internet and in books but nothing beats real, first hand information from folks with the exact application and experience. I am going to reuse my head bolts because I can't afford to buy new ones at this point and I surely don't want to be the first to break head bolts but it sound like they have been reused way more times than I plan to.

I know one thing, I am not going to get crazy with higher than recommended redline or disregard recommendations about oil, or attempt any forced induction or nitrous applications to my LT5.

[BOB HDZ]

i use a cotton polishing wheel on my bolts works the same and doesn't take any metal off the bolts!

[Pete]

Hi Jerry
Can you give us an idea on the price for a set.

Thanks
Pete

[A26B]

Pete, I will be better able to do that once all the testing & verification is done.