Graham Stretch wrote:
> This is a brilliant test, though I believe it has a draw back, won't the
> same thing happen with a long duration camshaft, as they tend to have longer
> valve overlap?
Yes, to a degree. The bill test is general and not very
quantitative--it's mostly a used car dealer/buyer trick to determine the
general health of a stock engine. It's not a substitute for more precise
diagnostic testing.
> I ask this as you started me thinking, I have a 150 bhp TR5 cam in my PI
> saloon and I get the suck back effect, but I also have a cylinder that only
> reads 160 psi on the compression test, and although this doesn't seem too
> low the rest read 200 psi, I never connected the two things before though I
> was concerned about a burnt valve. Can you or any one else shed any light on
> the cam duration aspect?
If you want to discount the effect of the cam in determining the
likelihood of a burnt valve, the best means is to buy, borrow, rent or
steal a leakdown tester. With that, and a source of compressed air, you
can determine exactly the nature of the compression loss in the cylinder
in question. The leakdown tester supplies compressed air to the cylinder
and measures the rate supplied against the leakage rate, and with a
stethoscope, you can readily determine where the air is leaking--through
the exhaust valve, the intake valve, past the rings, etc. It's the
surest way to determine the fault before opening up the engine.
Cheers, Graham.
--
Michael D. Porter
Roswell, NM
[mailto: mporter@zianet.com]
`70 GT6+ (being refurbished, slowly)
`71 GT6 Mk. III (organ donor)
`72 GT6 Mk. III (daily driver)
`64 TR4 (awaiting intensive care)
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