docmirror

well, glad we got that cleared up.

Sean???

BC

Thats a great question. I have seen two Early 32V engines with head bolts. An 85 and an 86.5

ROG100

I agree that PET shows these as a replacement for studs on the 85/86 32v heads.

GregBBRD

I, personally, gave up many, many years ago on the ARP hardware. While I've actually never tried a set in a 928, I've tried (and removed) a lot of sets in the 951 application.

My belief is that the head studs were of "too good" a quality and did not stretch as much (if at all) as the factory head bolts or studs. That stretch is really important for clamping the head gaskets down and keeping them clamped as the engine heats and cools.

The other problem was that ARP wanted you to heat the engine up, let it cool down, and re-torque the hardware. While this sucks, on a 951 engine (you have to remove the cam carrier), this sucks in an unimaginable way on a 928.

The result was that it was virtually impossible to keep head gaskets in these engines, when using the ARP hardware, when the stock stuff worked quite nicely.

ARP always recommended using the stock specification for torque and perhaps a higher torque might have stretched their studs and made the difference. I just didn't feel like I wanted to do that research, for them, and simply went back to the stock pieces.

Rob Edwards

Ugh, goddadammeet- Verbus 11.9, not 10.9:

jon928se

[QUOTE=Rob Edwards;10907036]Ugh, goddadammeet- Verbus 11.9, not 10.9:/QUOTE]

I dug out some '87 head bolts this morning (for entirely irrelevant reasons) also Verbus 11.9. They aren't plated like your photo though. If they weren't plated from the factory I wouldn't use them as head bolts.

Observations and thoughts

The '87 head bolts have I would judge a rolled thread and the bolt shank is only around 10mm dia.

Rolled M12 thread to give stronger hold in the block
Narrower shank to reduce the torque required to stretch the bolt (Bear in mind you could lift two or three 928 with just one of these bolts in tension)
I reckon these are not bolts torqued to yield. I think they sit in the elastic region throughout there cold- hot cycle. I'ld have to try and put numbers to it to be surer.

worf928

Well, that should make them easier to find. Not.

Jon, are you saying that the '87 head bolts you have are M10 bolts with a narrower-than-10mm shank? I'm not following.

I am not convinced also. Turn-to-torque does not automatically mean torque-to-yield. However, the math has to be done.

69gaugeman

NONE are torque to yield. Once you yield you lose all elasticity and cannot return to original size. If this was the desired condition (it is not in ANY engine) they would just use larger fasteners that won't stretch.

I have been in the auto industry for 20 years and measuring engines and transmissions is the bread an butter of my living. While I don't engineer engines, I have worked with those engineers daily for the last 20 years.

Once you understand what happens during yield, you would understand that you NEVER want it to yield. You need to be to the point where as the engine heats up the stretch will still NOT be at yield so that when it cools it will return to the original length and not lose the holding force.

jon928se

No - M12 thread but rolled not cut. (Thread proud of the shank) Bolt shank is less than 12mm dia apart from approx 5mm length immediately under the head.

jon928se

The only exception I am aware of to the above statement is the head bolts on Rover K series engines. (Freelander and Rover 25 and 75) nearly 500mm long and also hold the crank cradle on. These were designed to be tensioned beyond the linear elastic part of the stress strain curve into the plateau area and stay in it. Reputed to have caused lots oh Head Gasket problems but it's difficult to be certain as the engine also suffered from a very low coolant quantity which also got blamed for HG failures.

Certainly not my idea of fun.

docmirror

Yes, but does anyone want them?