Mark---Others have written that the Triumph engine is a
"non-interference" engine, which it is. This term became popular when
some of the modern engines came equipped with a timng belt, and usually
overhead cams. When the belt would break, some valves would be in the
opened position and the piston(s) would do damage. This is very unlikely
to happen with the Triumph engine. Not only because they have
chain-driven camshafts, but also because the valves are recessed so far
up into the head, away from the piston tops..
Al bets are off if you lose a keeper, or a stem breaks!
Meanwhile, if you, or anyone is concerned about interference from a high
lift cam and/or higher rocker ratios, along with the head being shaved,
know that this is a measureable set of circumstances. To see just how
close the pistons to the valves are, you can do the following:
1) With the head upsidedown on the workbench, measure the distance from
the closed valve to the surface of the head. (On the later, stock head,
is will be around .625.)
2) Add to this the thickness of a used head gasket. (Approx. .030)
3) Add to the above the distance from the top of the TDC pistons to the
top of the block depth. (Approx. .015)
This adds up to around .670, which is how
much the valves can open without the risk of "interference".
Subtract from this the amount of lift from the camshaft lobes, along
with the rocker ratio. (on a typical stock cam this might total .290)
Add to this .290 the amount that may have been shaved from the head. If,
for example, the head is now at 10,5:1 it would change the .670 number
to about .500. This is now the maximum amount the valves can open
without intererence. This is way above what even the most developed
street engine would have.
Of course there are engines that have larger valve openings and thinner
heads. With these, the trick is to hope the valve drive doesn't break,
or go out of time!
I left out piston rod stretch and pushrod deflection, as they tend to
cancel each other.
Dick
tick-tock
From: mhooper@digiscreen.ca(Mark Hooper)
RE: I may have a serious problem
At 10:1 compression, can the TR engine spin the crankshaft without
hitting the valves? At any compression for that matter?
Mark
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