> What is the collective wisdom on using silicone instead of shellac
> soaked felt for the rear sealing block on the TR4A engine? My local
> machine shop turned the scroll and drilled the rear main cap on my crank
> for the modern seal (from BPNW). The suggested (and used silicone)
> instead of the felt that I provided on the rear sealing block; they said
> the silicone that they shot in would seal without leak and would be
> superior to pounding in the felt pieces. At this point the only thing in
> the engine is the crank but before I complete assembling the rest of the
> pieces, I though that I would ask for a second opinion. So should I take
> it apart or leave it and continue?
Just be certain that there is no silicone hanging out inside the block,
where it can potentially break off and plug things up.
The felt and shellac works just fine, but I don't see any reason that "form
a gasket" wouldn't work just as well, IF you're certain it was forced
thoroughly into the channel and completely fills the channel, without
hanging out as I mentioned above. A tall order methinks.
BTW, Racetorations and BFE have changed their recommendation for what size
to grind the scroll to. Apparently the instructions packaged with some kits
said 63mm (2.480"), but BFE recommended first 63.5mm (2.500") and they've
now upped that to 2.520" (64mm) (-.000/ +.010). The smaller dimensions were
apparently not getting enough pressure on the seal, and serious leaks were
the result in some cases.
Randall
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