560 LP Piston to Valve Clearance

ecaudell · Apr 25, 2019

My 1960 560 LP broke an upper pushrod cup after 20 years of faithful service. While replacing the pushrod, I noticed that valve tip/spring retainer is .150 lower than the 4 valves next to it. That makes me think bent valve. I am familiar with engine building, but not tractor engines. Questions:

1. What is stock piston to valve clearance on these propane engines? (To determine if I can reassemble and crank engine for compression test.)
2. Do the valves tips ever have that much variance in height?
3. Are 1960 valves soft, two piece construction, or prone to breaking if they kiss the pistons and are run.
4. Anyone seen similar, how risky is it to start engine if I cant find any damage or debris?

Thanks.

Bob · Apr 25, 2019

Do a cylinder leakdown test or simply put compressed air to the cylinder involved (with the valves closed).

If not leaking past the valve in question, the valve is not bent.

Janicholson · Apr 25, 2019

If the seat has come loose it can block the valve part way open. I agree with Bob, a leakdown test is needed. With the piston at the bottom, and the rocker removed from both valves, pressurize the cylinder through the spark plug hole, and listen in the exhaust and intake for a tornado. Turning the engine by hand feeling for interference is OK. Jim

the tractor vet · Apr 26, 2019

As to the piston to valve clearance i am not sure on this but there is a lot on the gas engine . The only one that will give you a problem is the L P head for a 450 when usen the above 8500 ft. pistons in a 400 -450 engine . IT is not common for a valve seat to come out but can happen . Now as what has been done to that engine since new is any bodys guess , or how many times it has had valve work and the head refaced as they do warp . And for the cost of a head set pull it and look.

ecaudell · Apr 26, 2019

I can do tests on the cylinder but I was more interested on the characteristics of the engine. We are 1200 ft above sea level. I agree on the "anybodys guess" but I have run it for 20 years and I dont think the previous owner was inside the engine for the 10 years before that. I suspect this is all original. I know it hasnt been hot and I was doing light dirt leveling at low RPM when it started missing. If they have more than .250 clearance, then there is no way the valve kissed the piston and something is holding it open (like a seat). The spring is not broke. I can move the valve up and down with a prybar so its not galled and stuck.

Janicholson · Apr 27, 2019

Use a bore scope or fiber optic viewer to look inside. A screw from the intake side could be wedged in the valve seat. Jim

560 LP Piston to Valve Clearance

ecaudell

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Bob

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Janicholson

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the tractor vet

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ecaudell

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Janicholson

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