• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

General Tech ARP Head Studs/Liner Protrusion

Share this page

KVH

KVH

Darth Vader
Silver
Country flag
Offline
I have two issues: First, my ARP stud lengths do not match the Shop Manual specs. Nine of ten match, but there is no 5 5/8" stud for the front passenger position. It's 5 1/2 inches. Any big deal?

Second, two of my new liners (County Brand) are proud of the block by .007, and spec is .003 to .005. I'm inclined to believe a good sandwich head gasket will address the issue. I'm not inclined to pound them out and go through some kind of return routine. I once actually measured the thickness of the "figure 8" gaskets and found the copper ones .001 thicker than the aluminum ones. I probably should've used the aluminum ones--since they were in the kit. But I remember seeing aluminum ones all chewed up and corroded on a rebuild years ago and opted for copper.

I'm curious if others have addressed a similar issue and whether I'm likely right about the gasket forgiveness. And what's with ARP? Is that a mistake or do they figure an "eighth" of an inch doesn't matter?

Postscript: I just "mic'd" the aluminum figure eights. And then rechecked and corrected my readings. They measure .0157. The copper measure .0189. That's right about .003 difference. I guess I messed up using the copper ones but I'm surprised despite my last experience that there's some deliberate sizing going on there. It "sort of" tells me that a .003 variance isn't a problem so long as the variance is proud. It's as if the gasket set makers must make assumptions, and they assume thicker--safer for a fit. I'm actually puzzled.

Any thoughts?
 
Last edited:
I’ll let smarter folks answer the Fo8 gasket questions…

Yes, the ARP stud lengths do not match the manual. The difference is small enough not to be an issue.
 
I chickened out. I pulled the sleeves and replaced the figure 8s. I had two measurements at almost .008 proud with copper and couldn’t sleep.

Now I have another question. Am I supposed to have the pistons face a certain direction? I ask because each of my new pistons has a blue dot on one side of the wrist pin. Is this telling me that the blue dot faces forward or backward? I guess I should ask the same question with regard to the number “stampings” on the top of each piston. Is there some logic there, meaning that the stamping faces toward the camshaft or away from the camshaft?
 
Are you confident there is no gasket or scale left in the block that is giving you a high sleeve height reading?

Graham
 
That is common with F08's. In the "old days", I am sure you had enough options to find the perfect thickness f08's to get the perfect liner height. Now we are stuck with one copper and one steel option...unless someone overseas has more options. By all means, use the one that gives you the best liner height. If the height is too high with the steel, then you have to have the top of the liners shaved into range. I am sure the head gasket would allow a few thousandths extra protrusion, it's just too easy to correct when the engine is apart. I have been using Wellseal on the F08's and the head gasket. If Rolls used it on the Merlins, that's reason enough for me!?!
 
What’s surprised me were the measurements I took late yesterday. If the copper gaskets automatically guarantee .003 greater protrusion, anyone would be quickly out of spec with gaskets and liners already perfectly measured to be within spec— particularly at the high end.

In my case, it appeared I was .003 above spec and I wasn’t confident that was acceptable even with the extra protection of a head gasket. In the end, as you’ve said, it’s easier to fix when everything is apart. No one would ever know in a case like this, but my “guess“ is that it would never have been a problem.
 
KVH said:
What’s surprised me were the measurements I took late yesterday. If the copper gaskets automatically guarantee .003 greater protrusion, anyone would be quickly out of spec with gaskets and liners already perfectly measured to be within spec— particularly at the high end.

In my case, it appeared I was .003 above spec and I wasn’t confident that was acceptable even with the extra protection of a head gasket. In the end, as you’ve said, it’s easier to fix when everything is apart. No one would ever know in a case like this, but my “guess“ is that it would never have been a problem.
Click to expand...
Your initial comments stated one set of Fo8 were aluminum. I do believe they are steel. So the difference between the compression of steel and copper is what is at hand. I would suggest that they should both end up with the same compressed values. I have used both types without a problem.
Charley
 
I think copper might compress a bit, but that’s a bit of an exercise to prove, and I was way high. in retrospect, I probably could’ve just left the copper in and relied on the head gasket and compression to solve the problem. I just re-measured the steel ones, however, and they really are about perfect now. Every liner seems to be about .005 protrusion. My concern with what I ultimately did, using the steel F 8s, would be if the steel might rust and leak over time.
 
Yes, I've been through all this:



One thing I found: there are irregularities in the gaskets, caused by variable thickness, burrs on the edges, and lack of perfect flatness. You will get the calculated protrusion ONLY if the gaskets are perfectly flat, which is difficult to achieve. In the second of the above links, you can see what I did to flatten the gaskets--it wasn't difficult and helped a lot. In that case, the block had been shaved, so the numbers worked out better. I found that the sealer added no more than a mil or so to the protrusion, as long as the cylinders were well seated.

The gaskets will not compress to any measurable degree, but they will flatten out. Use plenty of sealer and tap the cylinders well into place with a hammer and wood block. Then, use bolts and large washers in the stud holes to prevent them from working their way out.

Like John, I question how critical this really is. A mil or two extra probably won't matter--but I'd err on the high side, not the low.
 
If you use wellseal or other sealant, only the edge of the steel will be exposed to coolant. It would take several engine lifetimes for the gasket to rust through. In other words...it won't be a problem using the steel. Plus, steel was the original and only option for the first many years of production.
 
Back
Top