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Reuse Engine Bolts?

new 4/08/04

I know a few of you do not believe that you need to replace the "torque to yield" head bolts etc. with new ones.

This article <http://klr6500.tripod.com/tech-torqwrench.htm> provides a bit of insight as to the reasoning behind this and some good general fastener info.

Take care, -- Rob Parker

He has an interesting story but he doesn't explain why not to re-use "torque to yield" head bolts.

Based on engineering principles, I would guess that when you first torque the bolt you take it into the inelastic range, and in effect "use up" part of the inelastic deformation available. If you reuse it when you torque it again you will go that much farther into the inelastic range. Depending on the material it might not have that much inelastic range available. The second time it is torque'd it might reach its limit and fracture. Otherwise there is no engineering reason why you couldn't use it more than once.

I don't believe Ford on everything but V8SHOs don't have head problems, or bottom end issues or head gasket issues.

It's cheap insurance, like oil analysis or frequent chassis lube or ATX or PS flush. When you do a cam weld why not change plugs and check cam shims?

Except for the cam issue, which is preventable, why mess with something that works?

& I agree, the elastic life of the bolts is used up one one use, a 2nd use does not create the same clamping force.

Replace 'em



u stretch the bolt every time it is torqued i forget which vehicle it is but u have to measure the old ones coming out and pitch them if they are XXXX long.

I never reuse old torque to yield fasteners because u have no way of knowing any many people before u cheaped out and did not replace them.

Clare 96 TR V8

They tend to due that on AL engines or bolt surfaces. as some one said allot more critical then iron.

one thing we use to check on routine intervals on the Leopard battle Tanks was the torque on the bolt holding the fold down rearview mirrors. {when up we used to call it vacation mode as it looked like a 78 Impala with those towing mirrors on the fenders} Reason was during live fire close coordination exercises with our Infantry units u did not want the 105mm back blast ripping the mirror off and wacking an RCR, PPLCI, or R22e soldier near the tank. Someone somewhere must have had it happen, see it know in the hospital ward,

"how did who break your arm?"

"flying rearview mirror"

I wonder where he got this part about threads deforming? I have not seen this in automotive fasteners although it might be possible with very high strength rod bolts. In general you don't want the threads to be yielding. They are too small to allow enough deformation to achieve the assured clamping force, whereas deformations of the shank of the bolt will. The only exception to this about threads deforming that I know of are high strength bolts in buildings- A325 high strength bolts are allowed to be reused but A490 high strength bolts are not. With respect to head bolts, you can be sure that the threads there aren't deforming or you will be buying a new block, since there is no way to make a block anywhere close to the strength of a head bolt. (BTW, we studied bolts a lot in engineering school.)

common 4.6 and 4.9 failure we see is bolts pulling out of the block..

cause 1) idiot on wrench, 2) gm design problem 3) using old bolts and doing torque plus extra reading or torque plus x degs of a turn method to tighten.

no one knows 100% for sure. too many variables..

I studied fasteners also.. 1st thing we did in engine class was break stuff.. then figure out why.?

I made the mistake of reusing head bolts on my '96. It was fine until I raced it on a road course. The car ran fine and was really strong all day, but after the race, I had white milky oil and a lot of white milky buildup under the valve covers.

I use new head bolts now.

I have reused rod bolts with no ill effects and probably will again, but not the head bolts. They are too long and stretch too much.

Doug Lewis Ford Performance Specialists Inc.

Didn't Carter have a problem with head gaskets last year when he reused his head bolts?

The rod bolts are so cheap (comparatively) I replace those too...


Not yet, but I am waiting....


As the article states, when torquing, the threads deform on the weaker of the two components of the connection (usually the nut). If reused, the same torque will yield a lower clamping force, which can lead to leaks and fatigue cycles in the connection. That is why reusing fasteners in critical or high cyclic loading applications is not recommended.

While I have reused suspension and steering components fasteners when the manuals have stated to replace them, I would never consider reusing crankshaft or head bolts if the manual states to replace them. The bolts are cheap in comparison to the time and materials to fix the consequences of even one bolt failing. Just my opinion.


Right on u can get away with stuff like ball joint pinch bolts. mine were done about a year ago in the front upon inspection the RF bolt had to be replaced as the threads were starting to deform slightly.

Wheel studs will also changed tons of those because clamped to tight and pulled the threads.

I've got a Ford service training tech video for the V8 (I don't have a gen3 helms, and haven't' really messed around with the V8 cars) but IIRC pretty much all the fasteners are torque to yield and throw away.

Interestingly (unlike the V6) there is even a proper removal sequence of the head bolts.

I think the funniest part is the balance shaft section. "Step 1, remove engine from vehicle" "Step 2, disassembly of the front components..." lol. Never mind step 1 takes a few hrs, they buzz right over like it was an air filter swap <g>


I have both the Helms & the "1996 New Model Training" for the SHO,

From page 6 of the "1996 New Model Training": "Torque-to-yield bolts must be replaced if removed."

Helms 03-01C-74

46: CAUTION: Cylinder head retaining bolts must be replaced with new bolts. They are Torque-to-yield designed and cannot be reused or damage to engine may occur.

Same warning for Connecting Rod bolts,  pp 03-01C-68.

But I can not find the same warning for mains, pp 03-01C-66,67

I'm not 100% sure but I think the only bolts Ford insists you replace are head bolts and Connecting rod bolts, I don't think we have connecting rod nuts?


That's correct they are cheap, but they weren't at one time they used to be at a whole 10 bucks each!!!!!!!

I'm glad that at least you got to read the topic on this a while ago Scott, that me and Hammy discussed the bolts are torque to yield.( use once and throw away). The are made to stretch evenly and apply a certain amount of clamping force across the head but only one time, it's a common mistake made by the V6 guys that buy these cars to reuse the head bolts as they have done this on the V6 forever but it does not work on the V8. The clamping force is different on a AL head to AL block VS the Cast Iron block of the v6, Plus on the V6 the head bolts are closer together than on the V8, and works a bit better.

Tim, you still have the heads that I donated to you and Don for the cross sectioning info, (PICS were in this last issue of the SHO Club Mag) maybe you could take a few pics of the space difference on the bolts between the V6 and V8 heads?

In short if your doing a head replacement you need the following: 10 New Bolts 10 New Washers (they are also TTY) 1 New gasket and while your in there 1 New crank seal 3 in all Timing chain cover gaskets.

F6DZ-6051-DA Left head gasket $ 148.99 (If you need left)
F6DZ-6065-BA Head bolt $ 4.49 ea. Timing chain cover gaskets :
F6DZ-6020-CA center $ 12.99
F6DZ-6020-AA RH $ 11.99
F6DZ-6020-BA LH $ 11.99
F5AZ-6700-A timing chain cover crank seal $ 7.49
F6DZ 6L015-AA Head Bolt washers

It scares me to see stuff like this when there are 100's of people trying to rebuild these cars and cant get the correct info from the website. Just think of all the cam failure cars out there that have been rebuilt re-using the old bolts. One guy contacted me locally that was rebuilding his own, I told him about the items required to do this correct and he said that he heard that all the gaskets were reusable and that I was just trying to sell him more then he needed.. Well needless to say I bought the car from him 10 days later and fixed his leaking head gasket and sold the car and watched it run this year at the convention :)

Kirk J Doucette

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