Temp range for an exhaust valve? 3

[Torquey]

I'm hot-rodding a Toyota 4AGZE, which is a 1600cc 4-valve supercharged motor. I would like to test the exhaust sealing ability of the valves by heating a closed valve with a propane torch (and then pressurizing the valve from the back side). Can someone give me a ball-park figure for the normal operating temperature range for an exhaust valve in such a motor? Probably the operating range of an exhaust valve for a generic IC gasoline engine would be close enough for what I am doing. Thank you.

 

[BrianGar]

750 c - 850c extremely roughly and as always, it depends.

 

[Torquey]

Thank you for the reply. How much cooler do the intake valves operate?

 

[evelrod]

It seems to me what you are trying to do is a bit counter intuitive. To start, I doubt you will be able to get an exhaust valve, assembled in a cylinder head, anywhere near hot enough with a "propane torch"...An oxy-acetylene torch, perhaps. Second, you are "pressurizing" the ex valve from the wrong side. My question is WHY? There are several other, more conventional testing methods to check the valve seal...comp ck, leak down and, even just sticking a vacuum cleaner hose in the ex port and using a stethoscope to listen for leaks. As primitive as that sounds, I find it more reliable than "pressurizing the valve from the back side".

Rod

 

[BrianGar]

@ Torguey, Im guessing you have rockers, and are trying to find the minimal clearance needed when cold but ensuring you have a gas tight seal at operating temperature? If you are trying this on a bench then you'll need to pump water and oil through head also and make sure guides are in tip top shape and it would get crazy.
You could figure this out on the run of course, the old way with a spanner and a screwdriver...
What are you hoping to do, Im intrigued

 

[BrianPetersen]

I have never heard of attempting to check valve seal when hot. If it doesn't seal when it's cold, it won't seal when it's hot. For valve clearances, what's wrong with original manufacturer's specifications?

 

[patprimmer]

The problem with trying to calculate tappet setting changes in a running engine is that it is very dynamic with everything constantly changing and everything with a different rate of change and different end to end temperature profiles.

The normal method if you need them really tight is to close them down under various full load conditions then when power suddenly drops off, open them up a bit so they end up slightly wider than the widest setting that never lost power under any circumstances.

Unless for some reason they need to be really tight, the tight end of the manufacturers recommendation is OK.

Regards
Pat
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[Torquey]

This has nothing to do with valve clearances. I'm just trying to double check that the valves are seating.

Rod, thanks for the tip. I never considered a vacuum cleaner and stethoscope.

 

[tbuelna]

Torquey,

The primary path for heat transfer in an exhaust valve is through its contact with the valve seat. And since your exhaust valve is an axisymmetric part with a relatively uniform input of heat flux, it should not experience much distortion with temperature. The heat input into the valve varies during an engine cycle, due to things like exhaust gas pressure and temperature, intake/exhaust flow overlap, A/F ratios, and engine load.

The leakage rate of your seated exhaust valve will be more affected by the heat transfer rate between the seat and head than anything else. With a small valve head diameter, overheating should not be a problem. Your exhaust valves should not see temps higher than about 1300degF, even with high levels of supercharge. But if you want to check exhaust valve leakage at operating temps, you will need to make sure that the valve, seat, head, etc. are all at the correct temperature, not just the exhaust valve.

Additionally, pressure leakage past the piston rings is likely much more detrimental than any leakage past the exhaust valve seats. So maybe you're efforts might be misplaced.

Regards,
Terry

 

[mattsooty]

Disagree with the numbers a bit for modern valve materials - the forced induction applications I have the greatests experience with are closed loop controlled to 950degC.


MS

 

[evelrod]

Torquey

Old school stuff. It even works with a fully assembled engine to ck if you have a valve seal problem, ring blowby problem or blown head gasket. A shop towel and vacuum, a stethoscope (even a piece of fuel line hose stuck in you ear) can do all sort of diagnostics. A stethoscope can also aid in tune up jobs, e.g., balancing a set of Webers or SU's.

Sometimes the old way is still the best way, at least for some of us.

Rod

 

[patprimmer]

Rod

Sometimes the old way is the only way, at least for some of us. ;-)

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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for site rules