engine and drivetrain Re-asking my question on main cap bolts

[nbristow01]

In my last post i asked about MAIN CAP BOLTS, everyone started telling me about head bolts. I did a lot of research on the head bolts before I put the head back on my car. I ordered new ones because mine had various shoulder lengths and they should all be he same..BUT Several very qualified M10 builders as well as every machine shop I called told me the same thing...I=Unless you see some sort of physical damage to the bead bolts they can be reused over and over. But they also stated if it is a racing moor that wil see 6000 plus rpm often then either buy new ones for each build or better yet use studs.

Now back to the MAIN CAP BOLTS. These bolts are so cheap I will be going ahead and ordernig new ones BUTTTT same story as above, machine shops, engine builders etc told me the main cap bolts can be reused over and over since they are not stretch bolts. UNLESS you race and then it is advised to replace them or use studs.

I will be replacing mine with new ones out of choice...not necessity

But I do think it is pretty dumb to use analogies such as comparing used tolet paper and used condoms to used head and main bolts. Lets keep it apples to apples

[bluedevils]

How expensive are the head bolts? You said main cap bolts are cheap, I assume so are the head bolts. Isn't a safe bet to use new bolts all around, head or main, especially since you are rebuilding your motor and spending a considerable amount of cash? Just my five cents.

[pkbinplano]

Buy NEW head bolts and cap bolts. Cheap. End of discussion. Gather up all your change from your change buckets. How much you putting in to your new engine ? And skimp on critical hardware ? Cheap insurance and piece of mind. You'll sleep better. It's like when I cracked one rocker. replace one ? Hell no. Replaced them all.

[Napes]

On head bolts I'm not suggesting one way or the other, but I'd be interested to know from the metalurgists if repeated heat-cycling in fact strengthens the metal in the head bolts. This was the case when BMW went out and got M10 blocks with 60-70K miles on them to use in their 1150 HP turbo F1 engines in the early 80s. I don't know if it is applacable

to the metal in M10 head bolts or not.

Bob Napier

[nbristow01]

I am buying new cap bolts, not new head bolts. These head bolts have only 15k on them. The machinists and engine guys i talked to said it takes extremes to alter these bolts at all. They were designed to last longer than the engine. I have friends that build motors, regular and race, for a living. they have told me they have never bought new head and main botls for any motor unless one was damaged. Ands in 20 plus years of doing so have never had an issue.

i just think it is worong thinking to believe that everything has to be replaced or it's no good. Heck they even use the same head bolts on ferraris when they do head sevice on them.

[john_a]

I am buying new cap bolts, not new head bolts. These head bolts have only 15k on them. The machinists and engine guys i talked to said it takes extremes to alter these bolts at all.

But you said *your* head bolts did not all have the same shoulder length, so I'd say you were given bad advice.

For the head gasket to seal, you need to have very even clamp load applied across the joint, and the differences in your bolt shanks can produce different tensions.

Head bolts are $2 each which is way cheaper than a new head gasket.

Reuse head bolts? Maybe OK if you know they are all in "new" condition.

But to reinstall bolts that are not all the same design? Not very smart.

You can try it, and there is a good chance you'd never notice any problem & the engine could hold together. Same could be said for eating a smallish amount of rat shit, you might not get sick or even notice a problem, but to knowingly take the risk & choose the crap that science tells us is wrong, that's not something to consider OK based on anecdotal evidence alone.

[nbristow01]

John, I did the head myself and when I pulled it apart it was obvious a variety of headbolts were used. I chose to go ahead and use new head bolts, no machine shop was involved in that decision. I may have not explained that well enough

[nbristow01]

If you knew the answer, why waste our time?

Dude you seem to have a chip on your shoulder. The reason I asked is the more feedback i get from experiences people the more knowledge I gain, thus have the ability to make better decisions.

I am not sure what your beef is with the guys on the post but if your attitude is that way then just please don't respond to my posts

[jerry]

On head bolts I'm not suggesting one way or the other, but I'd be interested to know from the metalurgists if repeated heat-cycling in fact strengthens the metal in the head bolts.

under normal engine temperature cycles, whether the bolt would soften during repeated heating cycles depends on the alloy content of the bolt. to harden the bolt initially, it would likely be heated up to a red-hot temperature (about 1200F) then quickly cooled to at least 400-600F either in oil, forced air or water. for low alloy hardenable steels the RATE of cooling would affect the microstructure and the hardness. tempering is a subsequent heating to an intermediate temperature between 300-700F (depending on desired strength and hardness) whereby internal stresses are partially relieved by diffusion of carbon and realignment of dislocations (imperfections in metal lattice structure). the ease with which diffusion occurs impacts the effective tempering temperature of the alloy.

i would expect that the head bolts are of such an alloy as to withstand normal heat cycles. i would not expect them to increase in strength under normal operating conditions.

other than quench and temper described above the only other way to harden metals is by work-hardening whereby the hardening mechanism results from increasing the dislocation density. (edit: other methods include solid solution strengthening, and precipitation hardening)

i can add that in the aeroengine repair business, most parts are inspected for serviceability before discarding. there are some items, such as turbine blades and nozzles which are exposed to extreme heat cycles which are life limited by time (or cycles) regardless of appearance.

[TobyB]

I'd be interested to know from the metalurgists if repeated heat-cycling in fact strengthens the metal in the head bolts.

no.

They're so fuc*ing, pardon my language, overbuilt that you could

hang 2 cars off of ONE and it wouldn't stretch past its elastic limit.

Neither the cap bolts. Well, one car off those.

In fact, I'd recommend NOT changing the original head and main bolts

because there is now a significant chance that the new hardware isn't

'real' but made in a country without adequate quality controls.

The only fasteners I replace religiously when I rebuild a RACE motor

are the rod bolts... and anything I don't like the look or feel of.

If it's rusty, throw it out. If it's bent, throw it out.

If it doesn't have the normal head markings for manufacturer and

strength, throw it out. If it's galled, toss it. Blah, blah, blah.

But in a normal rebuild, rod bolts only.

You can change the flywheel bolts if you're fond of your toes...

I don't.

heh

everything you read on the internet is true.

t

[nbristow01]

Toby thank fo rthe input. That is what i was looking for. I talked to one of my racing buddies last night and he told me the only botls he every replaces are rod bolts and only if they look wrong. Thanks for the 02 input and thanks for saving me a few bucks. I will stick with these original main cap bolts. He also pointed out that the old metal in these cars, botlts etc, is a much beter metal and more durable than the new crap they make overseas