Engine Compression

Sat Jan 24, 2004 5:32 pm

Hi All,

I just ran a compression check on the Cub that I bought last week.
As I supected, the engine was not rebuilt durning an earlier restoration.

I noticed that it has a good bit of blow by out of the dip stick tube.

The compression numbers I got were, 60,60,58,55. :?: :?:
I'm just curious as to what is a normal reading for a Cub.



Sat Jan 24, 2004 7:40 pm

A recently overhauled engine will normally run about 115 to 125. 85 is useable, but will burn a little oil and be low on power. 65 is hurting. If the cub has been setting for an extended period, try putting some Sea Foam (available at many auto parts stores) through it to help free up the rings. Another test is to squirt a littl oil in the cylinders and take readings again. If pressure goes up, the rings are probably sticking or worn. With as low a readings as you have given, more than likely the block will need bored and new pistons installed, rather than just installing rings.

Sun Jan 25, 2004 9:12 am

John *.?-!.* cub owner

had to respond to this one :!: Perfect avatar :!: :lol: :lol:

Ron: sounds just about the compression readings i got on my '49 cub. in my case, i got lucky. the previous mechanic in the engine installed standard rings on .030 pistons, zero wear after the .030 bore job so i just replaced rings, verified that there were new, correct bearings, did the valves and seats, etc. there was soo much blow-by, the oil was collecting in the dipstick cap and dripping out.
So, have fun! Motor job ! Grease time !
Might be more enjoyable than seat time :)

Sun Jan 25, 2004 10:33 am

Yeah, great av, John.

Ron, I agree with artc, you may have what was only a poor mech. job. You most certainly will have to "go in" now. I did mine last year and it was not that bad of a job. The worst part I found was getting motivated. Get a good service manual, measure you clearances, measure your bores etc..

I started by dropping the pan, (that's fun!), pull the head, and removed one piston, #2, it was the worst. I found the cylinder wall scored, from then on I learned alot of stuff about these great little engines.

Oh yeah, while in there I lapped the valves and this also improved things greatly.

Cub Comperssion

Sun Jan 25, 2004 4:18 pm

Thanks for the replies!

I kind of like engine work so this will be interesting.
I'm hoping that I don't have to bore it. It would be much less work to just hone it and install new rings and bearings. But, considering the age it will probably have to be bored.
All my mx experience has been with automobiles. What is involved in bracing up the tractor when you remove the block?
Any tips would be appreciated!!


Sun Jan 25, 2004 4:23 pm


The service manual describes it quite well. I am hoping that George, BD, Ralph or some of the other pro's on the board will write an article on it with pics so I can post it. That would be a very useful article - step by step with photo's would surely help those of us who have never done this before.

Any takers :?: :wink:

Sun Jan 25, 2004 5:06 pm

Rudi i'll send you a pic of the splitting stand i made quick one night when i needed it. post it to this thread, if you would.


i intend to weld another piece on the uprights to catch both holes and add more forward/backward stability. i intend it for use on my 'A' also, with higher holes. the holes for the cub are set 1 inch higher than the cub normally sits on the ground, so you can easily remove the front end.

i'm sure there's a few out there.

Sun Jan 25, 2004 11:38 pm


That picture of yours has inspired me. I will be doing alot of work on my '67 Loboy soon. I want to tear it down, strip and repaint. I also will be swapping out the timing cover as the one on it has been "bubble-gummed". The ears that hold the fan assembly had broken, lots of big gobs of brazing, and the fan is sitting very crooked. I think this one will take awhile. I also did a '44 A 2 years ago. I miss that one, I sold it to fund my new passion for the Cub and Loboy.

Ron, as you know, doing mech and body work etc....patience is the key. You can see the end product in your mind, it just takes awhile getting there. Especially when you have a family and lots of commitments. 12 more years 'til retirement for me.

Mon Jan 26, 2004 6:22 pm

Art, I like the splitting stand,simple and effective, good show!!

This will probably make you all laugh, but we just use large 10x12 blocks, with some bottle jacks. We don't have an engine stand yet either! That is one investment I do plan to make as rolling 40-50 engines around the floor each year to dismantle them gets OLD real quick!! :roll:

Mon Jan 26, 2004 9:50 pm

parts man,

I can't laugh, that's how I held up my A when I redid it, 10 X 12 blocks and bottle jacks, 2 X 4 frames to block the rear wheels from rolling. You gotta do what you gotta do!

Would be nice to have the real deal though.

Tue Jan 27, 2004 10:25 am

I guess splitting stands aren't a big deal to us, because for the most part we are just stripping the tractors. If we did a lot of rebuilding that would become a lot more important.
We do have a very nice self propelled engine hoist though! :lol: