Re: starting run issue

Sun Oct 21, 2012 6:51 pm

Bakers51 wrote:the compression is off. #1 = 87lbs, #3 = 65lbs, #4 = 85lbs, #2 = 96lbs.
Something is off for a rebuild 8 to 10 months ago. Certainly not right. Readings are uneven for a new rebuild. Something you would expect to see on a 10 or 15 year old work tractor engine. Could be a faulty compression tester. Not seated properly in spark plug hole. Lack of engine rotations.
Bakers51 wrote:I assume a dry compression test amounts to putting 10 to 20 lbs of air into each cylinder and listening and watching the bleed off noise and time? Wet test similar?
Dry compression test. Remove spark plugs. Take and record compression readings. Need at least 5 compression strokes per cylinder to achieve the highest reading. Record all readings.

Wet test. Add table spoon of engine oil to each cylinder. Rotate engine several revolutions to distribute oil. Take compression readings again.

Re: starting run issue

Sun Oct 21, 2012 7:19 pm

Putting air into the cylinders is a leakdown test. You have done the dry compression test. Now squirt a little oil into each cylinder and retest the compression. If the compression rises significantly, the rings are leaking (the oil seals the rings). If little to no change in compression, you're leaking somewhere else, like the valves or head gasket.

(sorry, I missed Eugene's post)

Re: starting run issue

Mon Oct 22, 2012 8:04 am

Thanks for the help guys. I will get back to you with my progress in a week or so. The compression issue may be my cheap self. I had a trained mechanic mike the cylinders and they are with in tolerance and very close to each other; so the original pistons were used with new rings and wrist pins.

Re: starting run issue

Mon Oct 22, 2012 1:03 pm

You should have well over 100PSI per cylinder, all even.

Did you hone the cylinders and put a nice cross-hatch pattern on them before installing the new rings?

The cross-hatch is what seats the new rings into the cylinders. It acts like a file and rakes material off the "high spots" in the rings.

Also, ring end gap, and gap alignment.

Re: starting run issue

Thu Oct 25, 2012 7:04 am

Yes they were crosschecked honed and I did a dry test making sure to really tighten down on the fitting in the plug holes. 1=91lbs, 3=70lbs, 4=91, and 2=96. I also tested the coil and it lights up my test light. I will do the wet test today sometime I HOPE. Thank you again for all your help.

Re: starting run issue

Thu Oct 25, 2012 8:25 am

While those compression figures are not as good as expected, an engine with such compression should start easily. So the immediate problem is elsewhere.

Re: starting run issue

Thu Oct 25, 2012 9:00 am

When the engine dies does it slow down like it is under load and then die? did you gap the rings when you installed them? Also have you tried new spark plugs since you started having problems? I have been seeing a lot of problems with new plugs lately.

Re: starting run issue

Sat Nov 03, 2012 7:48 pm

Hello everybody
I changed the Coil after I started 1 more time and died and immediately checked spark. Now my Cub is running again and I' trying to adjust the governor using the IT shop manual because the original maintenance manual is lacking. My low throttle is good but my high idle (is "hunting" - fast to slow and) wont even out unless you idle down. I know that these were set from the factory but when I was cleaning 61 years of gunk off I found the wire missing to the high Idle speed adjuster screw and I moved the bumper spring adjusting screw in order to spray brake cleaner inside when I disassembled to clean. This was a bad idea I know. So now I'm adjusting by book and ear and trial and error.
In addition I did a dry test and a wet test (compression)
Dry 1=95, 3=75, 4=91, 2=97
Wet 1=110, 3=91, 4=109, 2=111
I don't think I will tear down the motor again right away especially since the new coil did the trick.
I would appreciate any comments you have especially on the governor.

Re: starting run issue

Sat Nov 03, 2012 8:56 pm

Adjust the linkage from the governor arm to the carburetor. That will probably solve your surging problem.

Re: starting run issue

Sat Nov 03, 2012 9:11 pm

I would still clean the high speed jet again. It can clog in seconds, even after complete rebuild. 3/8 wrench on the brass "nut" on the side of the carburetor. The tiny axial hole is the metering portion. Debris in it is pushed into the opening(s) nearer the hex end. If not blown out, that debris will get right back in the metering hole again. Clean with soft wire AND compressed air.

Re: starting run issue

Mon Nov 05, 2012 10:08 am

Have you adjusted the valves? The low compression readings on #3 could be a valve not closing all the way.

Re: starting run issue

Tue Nov 06, 2012 9:29 am

Hello everybody:
Thanks for your help. The High speed jet is clear and a non issue. I have blown it out and run a wire through it and used card cleaner. I checked the valve adjustment per the manual and all are set correctly according to specs and my basic knowledge. I can adjust the gov linkage rod to the carb to stop the "hunting" but then I have medium throttle and high throttle only; and cannot achieve low idle. I will be rebuilding my governor and or inspecting. I noticed parts for the governor internals are only found @ Case IH dealers. I'm unable to find after market parts for the internals of the 1951 Farmall Cub Governors. I down loaded some info from this site on governor repair. Once again; thanks for your suggestions with my problems.

Re: starting run issue

Tue Nov 06, 2012 9:37 am

I have one more comment about my #3 cylinder pressure. I was talking with my friend and when we 1st started to try to start my rebuilt engine' I had the timing 180 out by mistake. By the time we figured this out we had been cranking the motor for a while without oil getting to the top. This is DUMB in hind sight but maybe this caused my issue. Who Knows? I don't care as long as it runs. Maybe in the future I will punch it out for larger pistons with higher compression.

Re: starting run issue

Sun Dec 02, 2012 7:28 am

Just giving an update on my 51Cub.
Rebuilt the Gov and still have hunting. Everything is tight. I will be checking the gas level in the carb to determine if I have an issue. I cannot adjust my gov or gov rod to the carb to correct hunting; although the rebuild helped. I can run my tractor @ idle with no issues but when running mid throttle the gov starts to hunt. I have been able to sometimes achieve high idle but loose it quickly. I will let you know how I make out in a few days.

Re: starting run issue

Thu Dec 13, 2012 4:34 pm


Ive got a new to me 48 cub that i just got running and it also would hunt. I found that i had an air leek on the intake between the carb and manifold. I made a new gasket and tightened it up and the hunting from the govenor went away. Just some thing to check. Also I checked my oil bowl on the intake and it had water in it raising the oil up into the screen. this was on a super C that was trailered through a rain storm. Just seems like it is simaler to the cubs air intake. Once I corrected this it would start.