[Fot] Valve overlap and compression test

[tr4racing at googlemail.com]

Hello Marcel,

 

Your engine has leaking valves.

It won’t get better from changing measurement procedures.

Maybe the seat is rough, or the valves bent, or offset .

Something to make sure about.

 

Enlarging the valve leash could result in hammering everything dead in the valve train.

 

Cheers

Chris

 

Von: Fot <fot-bounces at autox.team.net> Im Auftrag von van.mulders.marcel--- via Fot
Gesendet: Samstag, 2. Mai 2020 14:43
An: fot <fot at autox.team.net>
Betreff: [Fot] Valve overlap and compression test

 

A leaking test on my TR6 engine is showing a leaking exhaust valve on cyl no 1 (48% on the gauge of the device) and a leaking inlet valve on cyl no 2 (75%). Compression on cyl no1 is 9.5 bar and on cyl 2 it is 8 bar. The compression on the other cylinders is between 12 and 13.5 bar. This is with a race cam with a valve overlap of 110° (320-F grind). Because of the high overlap, the piston has risen a lot before the inlet valve is closed, so I did the compression test again, but with a valve lash of 2.5mm/0.1" : compression went from 9.5 bar to 14.5 on cyl no 1 and from 8 bar to 15 on cyl no 2. With this valve lash, the compression on the other cylinders went up to 16 - 18.5 bar. Of course, when the engine is running at high rpm, a lot of valve overlap is necessary for best cylinder filling, but I wonder if 110° isn't too much?? The recommended valve lash is 0.40mm/0.016" when the rocker ratio is 1.45(0.43mm/ with my 1.55 roller rockers). Would it be risky to set the valve lash at some 0.05mm/0.002" higher?

PS : is it common practice to set the valve lash at a couple of mm to perform a compression test, because it seems that the valve lash has a lot of influence on the result when testing a race camshaft?

Marcel

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