View Full Version : TR2/3/3A Figure of Eight Gasket Compression - Copper vs. Steel

Joel M
01-15-2019, 01:09 AM
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?


01-15-2019, 10:24 AM
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!

01-15-2019, 01:05 PM
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.


01-16-2019, 03:00 AM
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.

01-16-2019, 12:54 PM
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.

01-16-2019, 08:07 PM
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??

01-16-2019, 11:27 PM
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

01-18-2019, 11:36 AM
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.

Joel M
01-21-2019, 07:07 PM
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.