1949 Farmall Cub Compression Test

M

moose34

Member
Hello Gentlemen,

Just coming back from a much needed vacation and yes dove right back into the old cub with my son. Life is good!!! I finally got the compression tester from my buddy and the results are as follows. Dry Test on cylinder #1 90psi #2 0psi 3# 100 #4 0psi. Wet Test on cylinder #1 100psi #2 0psi #3 110psi #4 0psi. After all the headaches and some stupid questions to you guys it was the compression from keeping the old girl from starting all along. I have learned a lot from you guys over the last couple weeks but now seek advice even more because I am not sure what to do next? Any advice would be greatly appreciated.

Thank you,

Moose
 
Valve or valves stuck open in #4 cylinder. And yes, this will severly limit the engine's ability to start and run.

Use the search function and check for stuck valve. There are several possibilities on how to free up the valve or valves.
 
With #2 and #4 both showing 0 compression you have at least 2 valves stuck. You can remove the valve cover and try to free them from the side or bite the bullet and remove the head and attack from above. With the possibility of carbon buildup being a contributing cause I think it would be worth the effort to remove the head, clean things up and find the root cause.
 
Open up the side cover and check the valves and clean and lubricate them. Mine were a little bad....not a hard job at all, and after you get it running....run it hard and things loosen up...
normal_valves1.jpg

normal_valves2.jpg

Robert (been there done that) Miller
 
Will take the valve cover off an attack from the side. Thanks a lot guys for the advice guys. I will let you know tomorrow afternoon what I find out. Thanks again!!

Moose
 
Gentlemen,

I was able to get those two valves loosened up and wow got good compression now. Here are the new results. Dry test cylinder #1 95psi, # 2 100psi, #3 100psi, #4 100psi. Wet test cylinder #1 105psi, #2 110psi, #3 110psi, #4 110psi. Are these decent enough psi readings? Ok now we got everything hooked back up and tried to fire the old girl up and again nothing. After doing some thinking I pulled the plugs to check for spark and guess what no spark. Not sure how this could be now. I had great spark, fuel but no compression first go around. Now I have fuel, good compression and no spark. The only thing I changed on magneto was rotor, condensor and points. Are the point gaps not set right causing no spark? Any help again guys would be great!! I know I am closing in on getting her to run.

Thank you,

Moose
 
Point gap will affect spark quality. Check to make sure your mag is in time and that the rotor is also in time. There are marks on the rotor and the pinion gear to assure correct timing of the rotor. Your mag may be firing while the rotor is between towers.
 
Clean the points first. Check gap and do what the BD said. I try to run the engine before I change points, condenser etc and then immediately after. It keeps me in tune. Hate to do many changes at once. If you have the same damp weather now we have carbon tracks on the cap can do the no spark too. Oh check you put the plug wires in right after the changes too. Guess why i ask that??
 
Gentlemen,

I checked the gap for the points which are new and yes I did not set them properly. I adjusted point gap and figured I better make sure timing was set so timing was set again at TDC #1. I pulled spark plugs and made sure I had spark and yes I had spark. Now we have spark, fuel and compression she should run?? Well she sputtered and blew some white smoke but would not start. It seems that my battery which was new has lost its juice. I have tried several times to recharge but she just wont take a charge and when cranking over the DC drops to 5.3 volts and just doesn't seem to be enough to get her to fire. It seems that a weak 6volt battery might be my problem now any advice? On the carb there is an air/fuel mixture set screw, how many turns out should this be set at? This could be my other issue. Guys I know I am almost there so any help on these questions would be of great help. And yes thanks a lot for all the help me and my son are having a blast with geting this old girl to run!!!!

Moose
 
Bottom out the carb screw and then back it out 1 1/2 turns, that should get you pretty close for starting.
Sounds like the little tractor may need a pull start to get her going.
Good Luck !
 
Reading this thread reminds me of when I tried to get my Cub running last year, and I'm just wondering ...

If this tractor sat long enough for a couple of valves to stick, you probably ought to check PDQ that your oil pump hasn't lost it's prime also.

If it has lost prime, it will not pick up oil from cranking it over.

I may have mentioned this already??? I guess I'm just paranoid after toasting my engine last year !! HAHAHA
 
moose34":qzs85fat said:
I have tried several times to recharge but she just wont take a charge and when cranking over the DC drops to 5.3 volts and just doesn't seem to be enough to get her to fire.
Click to expand...
The voltage drop is within the ball park for a fully charged battery in good condition.

There is a video on this board on how to time an engine with a magneto. I think you ignition timing is - not correct.

Edit: viewtopic.php?f=1&t=44756&hilit=+magneto
Video on how to time a magneto to engine.
 
Ditto to Marion's suggestion to check the oil pump prime.

If it's a mag, then battery voltage will not affect the spark. If you are just concerned that she is not spinning fast enough, pull starting may be the answer.
 
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