• 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

TR2/3/3A Figure of Eight Gasket Compression - Copper vs. Steel

Share this page

J

Joel M

Senior Member
Country flag
Offline
I am currently making preparations for engine assembly within the next 3-4 weeks, and am trying to decide between steel and copper Fo8 gaskets. I understand the corrosion aspect, but the copper gaskets I have are 0.003" thicker than the steel ones (0.018" compared to 0.015"). Are these equivalent thicknesses due to copper being a softer metal that will compress more once the head is properly torqued? If not, I believe the extra 3-mils will force me to take down the liners some, and I'm not sure going with copper is worth the extra step. Also, I assume that two sets of Fo8 gaskets are required - one for checking protrusion after torquing and removing the head, and the second for final assembly. Is this correct?

Joel
 
It's generally accepted that the copper are better. That said, I do not think they are enough better to warrant skimming your liners. If you would need to skim, and you cannot obtain the proper size copper, then use the steel with Wellseal (or other favorite sealant) and never look back!
 
You should only need one set unless you find the liners either protrude too much or there is not enough protrusion. Then you would have to remove the liners to rectify the problem possible damaging the Fo8 gaskets.

Remember to check the protrusion on both left and right sides of the cylinder. The protrusion may be different.

David
 
I think the copper will compress more, that is just an amateur seat of the pants guess. Then again I rebuilt my first TR engine without the aid of any precise measuring tools. The liners portruded "a tiny bit" over the plane of the block, pretty sure the gaskets were copper. No problem with the liner seals or head gasket many many years on.
 
Last edited:
I pretty much agree with glemon although I think the book says .003 to .005. I measure with a straight edge and a feeler gauge and have had no issues even with a bit less. I've also had several where the little bit went to nothing but never had one that was too high. The low ones were fixed with thicker FO8s but I don't know if those are still easily available.
For what it's worth, I've also checked them with copper FO8s before and after I torqued the head, just to see if they did indeed compress. I could not discern any change albeit with the feeler gauge and straight edge.
The steel ones started to come with the liner kits at some point but I never used them.
Tom
Tom
 
I know I tend to be a bit anal...but some anal tips:

Due to irregularities on the block and liners, I don't feel the first install tells you anything. I always buy 2 sets of gaskets, and do a mock build using the first set. After torqueing the head and later removing, I can see if/or how much the F08 will compress. I then take the liner measurements and adjust the F08 thickness if I need to.

Wellseal was designed to keep the liners sealed in Mustang Merlins with 40# of boost...so I figure it'll work on my Triumph. That's what I use for the final build. Once again, if you goop the F08's before you measure the liners, it'll affect your measurement too.

Anal enough??
 
Neither the copper nor the steel gaskets actually compress to any measurable degree, if you mean in the standard sense, i.e., elastically. If they seem to compress, it's probably because of the sealer getting squooshed out from under them, burrs along the edges getting flattened, or irregularities getting flattened. It's a good idea, I think, to deburr the gaskets and make sure they are flat. Also make sure that NO debris gets under them.

In the engine I'm currently working on, I first trial-fit the gaskets, got the protrusions right, and marked the cylinders' and gaskets' positions. I then disassembled them, added sealer, and reinstalled them. I found it necessary to tap the cylinders into place with a hammer and wood block, to squeeze all the sealer out and to have the same protrusions as when I trial-fit the cylinders. You want to end up with mostly metal-to-metal contact, and sealer just filling irregularities. You don't want the cylinder floating on a layer of sealer. If you obtain the same protrusions with sealer as in the trial fit, I think you can be confident that you have metal-to-metal contact and the protrusions will not change when you torque the head.

Here is a detailed description: https://www.nonlintec.com/tr4a/engine2/#cylinders
 
I had a set leak once at least I think it was F8 gasket, but cannot be sure exactly where the leak happened. I fixed it with block sealer. I also seem to remember on the older gasket kits the figure 8s were maybe iron steel alloy gasket with this white coating over them, like a plastic or something. My concern after I had this leak was that the down time from taking the temporary hold downs off the block and putting the head on and torquing the head down something happened. Perhaps the sleeves separated from the F8 or perhaps the permatex non- hardening gasket material I used never bonded correctly.


Anyways, I took this story to a machinist whom I thought was the best. His suggestion was to take the gaskets and put about 3 to 4 heavy coats of silver spray paint on the figure 8s and put them in that way because the paint never really dries well and lays flat and would give me time to work. I did that, but I have not run this engine for more than half hour, but so far so good. Moreover, I am always surprised how tight the sleeves go in and how small the area for sealing is, so whatever is used on the gaskets should be thought out. In addition, I figured when the engines were first built, they put the head on within an hour or so, so if that is the case that would eliminate what I was concerned about with a gasket sealer not bonding, plus it is my understanding they used the weelseal product.
 
Thank you all for the advice. I think I will first try the copper gaskets and gauge the protrusion. If out of spec, I will try the steel. Not sure where to source 15-mil copper gaskets. The only ones I've seen are 18.

Joel
 
Joel M said:
Thank you all for the advice. I think I will first try the copper gaskets and gauge the protrusion. If out of spec, I will try the steel. Not sure where to source 15-mil copper gaskets. The only ones I've seen are 18.

Joel
Click to expand...
I just posted on this identical subject. Years later, of course. I'm inclined to use the copper ones, and yes they mic at about .018 compared to steel at .015. I can knock my liners out and start over with steel, but the manufacturers of copper must have something in mind. I measured after gooping up everything, all sides, with Wellseal, and I come up .002 to .003 too high. But I'm thinking the head gasket should take up imperfections in protrusion, and I'd rather a little extra protrusion than too little. Any further thoughts?
 
KVH, Did you torque the head before you measured the protrusion (I save an old head gasket to do that). I've never had one too high, at least not with the FO8's that come in the gasket set. It's also important to have the protrusion on all cylinders the same or very close.
(See Sarastro's post above)


Tom
 
No I didn’t torque the head on, but I measured again and I found two areas as high as .007—so I just yanked the liners out and used the gaskets that came with the liners, driving home another later-in-life lesson in the process: I should resist the habit of always overthinking. “County” put those figure 8s in the box for a reason. I’m now all .005 with one right about.006. I figure I’ll be in my 90s before anything is an issue. Thx Tom
 
I agree and hope we are both driving TRs in our 90s.
I think the racing community might have more trouble with the liners than we do with their high speed, high compression and heat. I've never had an issue.
Tom
 
I've always been a bit annul on engines. I always buy 2 sets of gaskets I plan to use. With one I do a full "mock up" build and take all measurements. I then toss those gaskets for the final build. If you use a sealant on the F08's, then they will measure a bit high initially, but it will compress down a couple thousandths on torqueing the head.
 
I go with the copper and paint them with 3 coats of silver spray paint, my old machinist buddy’s idea. I like the idea of 2 gaskets and the gathering of data. I once put a tr3 engine together with a metal figure 8 gasket that stood too high and the head was up a fuzz. The engine leaked oil on that little strip off cast iron where the lifters go.

A different buddy gave me a fix for it with some kind of form a gasket that came in an aerosol can and i laid down about 1/8 bead. I basically cleaned everything up nice and tapped the area off and chalked it place. He was a machinist also, and said he hates cluing some of these old engines together, but what the heck. I guess the oil pressure in that spot is not too high because it worked; the moral to the story is the protrusion can be too much.
 
It’s hard to know at times. Pulling my copper Figure 8s out and swapping in the steel ones over .003 seemed excessive. The open question is the logic behind a thicker copper replacement. My hunch is that there’s more consistent sealing and greater likelihood of reaching spec across a broad sampling of piston/liner sets—an assumption not so applicable to a new set of pistons/liners off the shelf, one packaged with its own steel Figure 8s. I hope I can report “A-Okay” in a few weeks.
 
If somebody wanted to reduce the thickness of their Fo8 gaskets, how would one go about that?
Is that a practical thing to do?
 
I certailly can't think of a way to do that although some racers have made them from metal sheet. I don't know how they cut the circles. Creative milling I suppose. They may not have been joined in pairs like the originals.
FO8s were and perhaps still are available in several thicknesses.
Too thick seems unusual, more likely too thin. Make sure the lands on the block are scrupulously clean.
Tom
 
There was an article somewhere on the interwebs about how to make Fo8 gasket. Of course I can’t find it now, but basically entails cutting copper sheets of differing thickness into circles.

Being a soft material, I suspect a craft-store circle cutter would work well on copper.
 
Back
Top