Recent valve overhaul

Brian R

New member
I recently replaced the valves in my 53. It would start fine before this but had no power and low compression. The problem is I can't get it to start, not a sputter. I cleaned the carburetor and repolarized hoping that it would help. I'm concerned it might be something more serious. I'm not sure what to try next.
 
I'd suggest doing a dry/wet compression test before you do anything else. That would be the best place to start. If compression is to low, it will never start.
Were the valve seats cut to spec? Were the valves lapped in? What is the condition of the cylinders and rings?
 
I'd suggest doing a dry/wet compression test before you do anything else. That would be the best place to start. If compression is to low, it will never start.
Were the valve seats cut to spec? Were the valves lapped in? What is the condition of the cylinders and rings?
I did a compression test and the results were more than disappointing. 1,3 and 4 were all the same at 75- 77 and no. 3 was only 50. The old results ranged from 75 to 95. I carefully cut the valve seats and spent a lot of time lapping the valves. I did put new rings, honing cylinders in 2018 but didn't touch the valves until this past summer.
I have all the valves at.013 like the manual says.
I have a feeling I'm going to have start over.
 
I did a compression test and the results were more than disappointing. 1,3 and 4 were all the same at 75- 77 and no. 3 was only 50. The old results ranged from 75 to 95. I carefully cut the valve seats and spent a lot of time lapping the valves. I did put new rings, honing cylinders in 2018 but didn't touch the valves until this past summer.
I have all the valves at.013 like the manual says.
I have a feeling I'm going to have start over.
It sounds like you've done the valves correctly so that's likely not the problem.
New rings in worn cylinders, though it may temporarily somewhat improve performance, but is usually just throwing money away.
Did you measure the bores when you had the head off? Remember, this is a 70 year old tractor you're working on. I've rebuilt some that still had standard pistons in them.
 
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I did a compression test and the results were more than disappointing.
Hi,
Here is some info for doing a compression test, if you need it.
Open the throttle fully when doing the compression test, so the engine can get air for the test.
The results of the test may be lower if the throttle was closed.
Have all 4 spark plugs out of the engine at the same time.
Use the starter for the test.
Charge the battery fully before the test, if needed.
The Cub service manual says a Cub before serial number 192113 had 107 lbs of compression turning at 240 RPM. After that serial number they had more compression, 120 lbs.
Those numbers are probably for new engines. They can have some less and run, I think they have said on here 90 lbs or above. :)
 
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