Low hr M20 issue
 

After "swapping" this low hr M20 in my 1872 (Now 2072), I found out really quick, it's not going be a turn key swap. The carburetor got issues, some sludge where hiding behind those shield but no oil leak from both crank oil seal and head gasket. I clean the engine put it back together and in the 1972 he goes.

I decided to do some tuning and testing, I manage to make it run smoother but the carb still need to be restore. no big deal since the M18 got one running well I swap that later if need. Things get wear when I did a compression test here the result after 10 minutes warm up.

First test cylinder one 105psi
https://scontent-yyz1-1.xx.fbcdn.net...f5&oe=5A73A389
First test cylinder two 75psi
https://scontent-yyz1-1.xx.fbcdn.net...28&oe=5A75D962

I warm up the engine again and give it another try:

Second test cylinder one 95psi (sorry this one is out of focus)
https://scontent-yyz1-1.xx.fbcdn.net...91&oe=5A79B46F
Second test cylinder two 89psi
https://scontent-yyz1-1.xx.fbcdn.net...3a&oe=5A3F07FD

I think it's a bit low for a 200hr engine, I suspect a valves leak so as soon I found out how to find the dead center position on this engine I will do a leak test. If my suspicion are right I need to remove that engine from the cub and open it, This need to wait a bit... story to followed soon...:beerchug:

Head gaskets are another good thing to check, if the engine has a blown gasket it can cause bad readings on a compression test. Just something else to check out.

Good thinking Ryan!:beerchug: Having variable result like that make me think "Sticky valves", since that engine was sitting in a corner for few years it make sense but I'm not ready to remove the engine from that cub, my expensive Canadian made cherry picker hydraulic cylinder crap out! Kapout! I will pick a cheap Harbor freight air/hydraulic Friday ($72 with a 20% coupon), no way I spend $500 on a new OEM cylinder or lost my time rebuilding the old one .....To be continue :beerchug:

It may or may not be it, but something to check since you're taring it down anyway. You'll know right away once you remove the cylinder heads. :beerchug:

ol Skull,
Been my findings that the M-18's run in the #90 range.
I have 4 engines that reflect that.
One engine has new .010 overbore, pistons & rings and about 50 hrs running time and both cyl read #92
The M-20 is stroked a bit, so it could run higher, they say + or - 10%
and with carb butterfly wide open

You can check valve clearance, but I say run it a bit and get a "feel" for it.
:beerchug:

Now I'm confused! John Hall did a partial rebuild lately (tittle M-18 running rough/missing) and he report 130psi on cylinder 1 and 120psi on cylinder 2 and this is before he open this engine! Check post number one of this thread:
http://www.onlycubcadets.net/forum/s...ghlight=Magnum

Now you tell me you got four M-18 in the 90psi and among them one partially rebuild with 50hr on the counter! :bigeyes:

G...I think I have a brain fart.....Cricket.....cricket :Help:

George has posted before that these engines don't have really high compression. If I had to guess, mine or his compression tester is out of calibration. The one thing is certain though is that you have a noteable difference between the 2 sides. FWIW, mine was about the same before and after the "rebuild". I'm not near my service manual to see what Kohler has to say is a normal range. Know anyone that will loan you their compression tester to see how the readings compare to yours?

I want to say that the manual states less than 90psi requires servicing. I'm 99% sure that's what the manual says.

Edit: Found it; if the difference between cylinders is greater than 15% or the pressure is less than 90psi, service is basically required.

I'd run it a while and see if it comes out of it. Make sure it's tuned up right, fuel system clean.... then run it. Work it hard. It may just surprise you.

Ryan is right about the manual saying 15% or under 90 psi engine need services, that why George statement surprise me a bit but he is not a young spring chicken and have done a few before and even if his tools are old as he is, they are like him build from a era of quality and perfection...( I'm such a..hole licker, you can pay me later George:biggrin2:)

Joke aside I really don't know what to think, for me 90psi is way lower then anything I work on before, these are very low compression engine so I walk in darkness territory here and I try to avoid stumbling on the carpet flowers...

For now my cranium Hamster need to be feed before he spin the wheel on high gear so i'll be back in a jiffy! :biggrin2:

I would do the leak down test to see where the compression is escaping. If it is a head gasket than that is a easy fix. if ring leakage do as Jon said and take it out and work it hard for some time and see if it gets better with use. Depending on how long it has sat the rings might be sticking. Put some Marvel Mystery oil in the Gas and crank case and just run it. Good luck.
Tom

Never try that Mystery oil before but they have that at the local Canadian tire store so I give it a shot for fun :beerchug:

Today I change the gas filter, change the air filter and swap the carburetor for the one I have on the M18 but before I can start that engine again a leak need to be repair, the oil filter cover gasket (KH-52-41-16) need to be replaced. I call all local source but few are open because of the Canada Birthday and those who are open have none, one of them tell me they are B/O at the distribution center....Gosh! Got no choice, I need to make one! Using the old one to make a template over a single side adhesive gasket sheet, I then use my template to cut one out of a 1/16" thick oil resistant gasket sheet.
https://scontent-yyz1-1.xx.fbcdn.net...77&oe=5A429526

I just add Brad Penn 10-30W high zinc content oil in the engine and crank the puppy up, he run better and my home made gasket hold on apparently. I take care of most of the gremlin's .... Put a new battery (11LU1), a new solenoid, change the starter cable (M20 need longer one), put a new seat and...More later :biggrin2:

One thing at a time will get it fixed. :beerchug:


Now go run the dog sheet out of it and see if it runs better. :biggrin2:

Well I'm not sure anymore, he now back fire and smoke, G.... I need to take care of that carburetor, I try again tomorrow and if nothing change, I check the valves clearance, do a leak test and remove both head.

I'm already looking for spare parts just in case.... Finding pistons and rings for a M20 is pretty expensive, I found piston and rings 52 874 17-S (+.003 rings) for $126.63 each (I need 2) and 52 874 18-S (+.010) for $126.40 each, Can't find intake valves nowhere. If anyone have a better deal let me know, I'm not having fun working on this one at all but I have too, and I want to!

PS: breather is all ok..

try this guy for a gasket set, I am pleased with mine. Know your part # first!!
http://tewarehouse.com/7-02654

Got a fuel pump from here, appears a lot of folks selling them on Ebay
This is the guy I think Jmech gets a lot of parts from
419-337-1548 (9A.M-12N EASTER TIME M-F).
Ebay seller name is bakt4kids
He had pistons for my M18, but doesn't list them for a M20. He said he didn't have anything for the m18 engine, but I told them he had a listing for them. So far they are working great--word of warning--I learned the hard way about checking ring gap and filing it. I would ask him to check to see if he can get them for the m20

How bad are your valves? Maybe let the machine shop inspect them before you go any further. Mine were a little loose it seems, but engine is running fine. I think I miked the stems, but I don't remember for sure.

Have you tried IHCCW? He comes across a lot of stuff, it will be OEM and pricey, but if you really need it....

Thanks for the link John.:beerchug:

Just take this as a notice John:
Rule of thumb for ring gap is .004 per inch of piston.

Today I disassembled the carburetor, give him a good bath and try to adjust again this POS (2 screws model) Well I manage to adjust the idle to 1200 rpm and he purr like a kitten, compression is now 105psi on both cylinders but he puff black smoke during first startups, a bit less on all next one so is it valves seal or piston rings? Leak test need to be done but I think I run the $hit out of it next winter with the 45" 364 snow blower and we will see!
In the mid time I can focus on finding spare parts for the M18 and M20 for a partial rebuild.

Please post if you find a supplier for valves, not just some guy clearing out old dealer stock. I don't need any but did notice I wasn't having luck finding them or pistons for the M20. Sometimes it seems a good automotive machine shop can do wonders coming up with components that can be modified to work. It might be worth a call to your local shop to see if they can supply them. If it is just stem wear, maybe new guides honed to fit wold be the answer.