[Fot] Figure 8 gasket thickness

[Jack Wheeler]

Hi Tim.  I rebuilt the engine in my street TR-3 (10:1 compression, mild cam, etc.) a couple of years ago.  I used the steel figure 8 gaskets, and the liners were a new set of 87MM from Moss (so were the gaskets).  After break in, I noticed it still using a small amount of oil.  I couldn't see any leaks, and with new pistons/liners I can't imagine I was getting blow-by past the rings.  I ran a test on the coolant and found a small amount of combustion gas in the coolant.  At the time of assembly, I checked the amount that the liners were "standing proud" of the block, and it was marginally within spec, maybe a little below.  I would have liked to see it up around .004 - .005.  Instead, I was getting .002 - .003, which I concluded accounted for the missing oil (i.e. oil leaking past the head gasket and into the combustion chamber).
So, I did an 'in chassis' rebuild and replaced the figure 8 gaskets with some old copper ones that I happened to have around.  I have a lot of figure 8 gaskets (left over from my racing days), and I checked all of them (steel and copper).  On average, I was finding the same thicknesses being reported in these messages, with the copper ones measuring about .002 thicker than the steel ones.  I put it back together with copper gaskets, and that solved the problem.  It passed the coolant test, and hasn't used a drop of oil since I changed to them 2 years ago.
Hope this is helpful.  Good luck.
Jack Wheeler



On Tuesday, August 1, 2017, 12:57:37 PM EDT, timmmurphh--- via Fot <fot at autox.team.net> wrote:


Thanks for the responses to my recent post regarding the thickness of the figure 8 gaskets.  I’ve done a little more “digging” and these are my results.

All of the steel ones I have of have gotten measure 0.015+.  I recently ordered some non-copper ones from British Parts Northwest and they are aluminum and also measure 0.015+.  These are the first aluminum ones I’ve seen.

All the copper ones I have, including some used ones, measure 0.020+.

I contacted Moss US and asked about their copper ones and any problems.  They only had one report of water leaking, back in 2014.  I was told that maybe the copper 0.020 ones were supposed to compress.  I hammered some copper ones to 0.015 and they are twice as wide as the original and would not fit between the liner and the block bore.  Additionally, I don’t think there is enough force to compress them.

The Moss ones are from Moss UK and are now specified at 0.018 by BPNW.  The BPNW part number is the same as the Moss UK part number.  I contacted Moss UK by email but never got a response.

I also recently ordered a Payen lower engine gasket set and the figure 8 gaskets in it are steel and measure the 0.015+, as all of the other steel ones.

The one engine builder that I know who uses the 0.020 copper gaskets typically uses them on blocks that are decked with the liner seats cut to allow the 0.003 to 0.005 stick out as specified by the Triumph TR4 Workshop Manual, Pg. 1·121.

I am interested in anybody who is using the copper gaskets.  Please post how you are getting the proper stick out.

For myself, I will continue to use the steel figure 8 gaskets.  I would also be interested in anyone using the aluminum figure 8’s.  Any problems?  What did you get for stick out when assembled and the liners clamped in place?  Personally, I don’t think I want to experiment with these.

Tim Murphy

1961 TR4 #317 (It really is a 1961 with an early Commission Number CT511)

  
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