Help with warm starting difficulties

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Re: Help with warm starting difficulties

Postby Ironlegs » Fri Apr 12, 2013 8:27 am

PROBLEM FOUND!
First of all, a big THANKS to those providing ideas and guidance. I hope I can help others here in the future by giving you all a post-mortem on what the problem was and how it was fixed.

After the checks I mentioned previously, I removed, cleaned and inspected the carburetor. I found some varnish and applied some minor adjustments to the float (1-5/32 offset) but did not see any causes for my problems. With the carb removed, I next took off the side panel to the valve tappet gallery and checked the tappet clearances. The tightest one measured about 0.009 and the loosest one measured about 0.012. Apparantly, I did not get the valves fully seated when I had the head off for piston ring replacements. The valves and seats appeared to have been serviced and were in good condition so I only cleaned away the minor carbon buid-ups. I returned each valve to its previous location but neglected to seat them completely. Clark (see above) was right on the target.

When the engine would heat up, the valves (especially the exhaust valves) warm more than the head and, therefore, grow in length more than the cylinder casting grows in depth. This expansion closes (some of) the valve tappet clearance which results in the valves being open too long.

I reset the valve tappet clearances to 0.015, cold condition. I'm aware that the literature gives several setting from 0.013 to 0.015. The engine was run about 20 to 30 hours after the piston ring/head work, which was enough to re-seat the valves (lower) and cause the lack of compression and subsequest hot start problems.

I checked the spark and found it to be hot and blue...no condenser or coil problems (this time). You can find a photo of my (Daniel's) cub on my post "1958 FCub Engine Cylinder and Head Restoration". What a great bunch of guys...give yourselfs a gold star.
Ironlegs John
Ironlegs
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Tractors Owned: 1951 Farmall Super A
1958 Farmall Cub
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