Compression on TO20

Todd from NC

New User
Have a TO20 that has a miss. The miss does not seem to be one cylinder or another. Spark plugs look like they carbon and oil deposits. Suspect oil fouling.

Did a compression test; all the cylinders were 95 to 105 dry and 110 to 118 wet (all numbers PSI).

What does a new Z120 engine run on a compression test?
 
There is no specific compression for the engine. Too many variables, like cranking speed, valve adjustment, and throttle position can effect the reading. The numbers you listed look good, the engine compression is healthy.

It's possible the oil rings could be leaking, but not likely with the compression that good. Bad oil rings show as blue smoke under load.

Black plugs can also be caused by rich mixture, poor spark, wrong plugs, or running without a thermostat.
 
It should be around 120psi
Check the ignition side of things as the pressures seem OK.. could even be duff plugs..
Make sure that there is no side play in the Distributor Shaft or it will be varying the points gap when the engine is running, that could cause erratic running. Check the Distributor Cap and the Rotor for any cracks or thin black lines which would denote HT leakage to ground. Set points to .022 and the AC86 plugs to .025". Use correct plugs, not some that look similar. Check points, if there is a hole or a spike on the contact faces, replace the Condenser as it is on its way out. Are you getting blue smoke from exhaust, that is oil, black smoke is too much fuel John(UK).. [email protected]
 
Thanks John.

The tractor was converted to 12 volt.

I have autolite 3116 spark plugs gap set at .28 today (second set). New cap, rotor, condenser, and points (no hole or spike). Points are set to .24 gap.

Will try tightening up the points and the AC86 plugs at .25 gap.

I was thinking timing as well. Have a timing light coming on Tuesday or Wednesday.

Blue smoke at start up. Once it is running, seems to be clear.
 
How do I check for side-to-side play on the distributor shaft? I have tried taken the rotor off and the dust cover and tried wiggling the shaft with no success.

Thanks
 
Don't forget we are only talking about very small amounts of movement. If you turn the Engine until the Heel of the Points is just on the lobe of the cam on the shaft but not started to open. Now press the shaft sideways towards the Heel of the points, watch the contacts and see if they do open a little. There is almost certain to be some wear but maybe not enough to really be troubled by. How often do you check the oil in the bottom of the Distributor as it is this that lubes the Bearings and Bush on the Drive.. John(UK) [email protected]
a162977.jpg
 
Blue Smoke as you start up is usually oil that has run down the valve guides. You could replace the Guide Seals if the Guides aren't too badly worn. If the timing is slightly retarded you could get this problem. Ignition Timing should be 7 deg BTDC. What type of ignition leads are you using, they should be copper wire type. Check ends for green corrosion. Check that the low tension feed from ignition switch is attached to the opposite polarity of the tractor. (If the tractor is Positive to Ground, then attach to negative terminal on Coil) If you don't know which is which, try the low tension leads both ways on the coil and use the way that gives the best spark at the Plugs. You could also check that the Breather pipe on the Valve Cover is clear and isn't blocked, if it is it will pressurise the Crankcase and it will escape wherever it can, like down the guides.. John(UK).. [email protected]
 
Yeah thought about the valve guide seals.

Yes copper wires - replaced them. Not sure about the ground question, will need to check.

Breather pipe is clear, get smoke out of it.

Thanks again!
 
Worked on the tractor some tonight. The distributor does have some wiggle. In addition, the timing was pretty far out, like maybe 15 degrees.

Tried putting oil in the distributor, through the little hole. Did not seem to take much.
 
Good thing about the oil then.. Providing the movement isn't too much, then it will still work for a little longer yet before you need to give it more attention. Timing out as much as that would could cause you those problems...only thing to do now is run it and see what happens. If you want more info about your tractor generally, email me direct at the address below and I will send you some. Then you can re-set most things as to how they should be..John(UK).. [email protected]
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top