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After installing new pistons, rings, valve job and seals she’s burning quite a bit of oil. I had the honing and valve job done at the machine shop. The piston clearance was in spec. Ring gap was checked but now she burns oil. I broke in in carefully with 30w conventional oil and heat cycled it several times before light short mowing sessions and after that switched to my ams oil small engine synthetic. I pulled the air cleaner and see some oil coming up from crank vent but not much. I’ve seen much worse. I plan on doing a leak down test as soon as I can. I fear another tear down though it runs very well. Is there any trouble shooting tricks to narrow it down or am I going to have to take it apart again
It is a Kohler m18

Was the engine burning-using when you used conventional oil?
How was the cylinder bore check?
Was the cylinder bore per Kohler manual (top-middle-bottom-in line with crank-90 degrees of the crank) ? you should have 6 measurements.
Do you have a copy of before and after cylinder bore measurements?
Kohler replacement parts or aftermarket parts?
How did you break in the engine?
New parts in crank case breather?

Reading through there it seems you only ran it lightly not really worked it. Take it out and work in hard, get it up on the governor and keep it there for a while. See if the rings seat in and the oil stops burning. Also keep in mind that air cooled engines will burn synthetic oil more than conventional, in some of the books they even warn against using synthetic in them for that reason.

Ok well the shop did work from the manual I provided. I did watch him measure each cyl in three locations. Not sure he did in-line or perpendicular to crank and no I don’t have finish measurements but he said it was within the specs from manual. I used Red barn pistons and rings and installed per manual. I mowed with it several times for more than an hour each time after I had heat cycled it several times at various rpms I have only mowed twice after changing to synthetic oil. It actually smoked less after changing to synthetic which I have used for years in my other Cubs
At steady rpm smoke is barley noticeable however if you idle it down then rev it back up it huffs blue pretty good
I would say it’s consuming 1/4 quart in a couple hours. It starts instantly and runs great. I plan on getting an oil breather kit for it just to eliminate that possibility. And no it wasn’t burning anywhere near that much oil prior to engine work

How many hours since freshened?

Sorry to hear. Man that's a kick in the shorts! Yes new breather is a must. I don't think I read anything about valve guides but maybe that was lumped in with valve work. How about the valve seals as well. These are installed? Just wondering if something got innocently overlooked. Good luck

Maybe ten hours since work was done. I think he replaced both exhaust valves/guides and did install new valve seals.
If a new breather kit doesn’t help I guess I know what I’ll be doing for a winter project

After checking/changing the breather I would find a wooden skid and load it as heavy as possible. I would put conventional oil back in it. Chain it up and load the engine as much as is safely possible and work the engine hard. Working it hard will build cylinder pressure and put pressure on the rings to see if you can get them to seat.

What BM said, +1. Do this before using the tractor any more, you need to get the rings seated before the cylinder walls glaze over. Full throttle only, drag the heavy skid, up a hill if you have one. Also +1 on conventional oil ASAP. Everyone has their brand, and I don't want to start an oil thread, but I use Valvoline Racing VR1 SAE 30 in all the tractors and other outdoor equipment. High zinc, proven oil.

I like to vary the RPMs during break in. It puts different loads on cylinder wall(s).

Ok then thanks for the input. I’ll give it a go. I got the 1864 back up and running so the pressure is off the 1872 for now

Merk wrote: ↑

Sun Sep 05, 2021 3:58 pm

I like to vary the RPMs during break in. It puts different loads on cylinder wall(s).

Dale does have a point, so I'll modify my response to "concentrate in the upper rpm range". I was just trying to keep you from lugging the engine too badly. You want to load it down without lugging it unmercifully.

This is how I break in a newly rebuilt engine:
1. Vary the rpms from 1500 to 3600 rpm for 30 to 45 minutes
2. Change oil and filter (if engine has a filter).
3. Run the engine with a light to medium load on it. My lite load is driving tractor around my property. My medium load is a sled that I will put 200 pounds on it to start. I will add up to 500 pounds weight as times goes by. Vary the rpms from 1500 to 3600 rpm for 2 to 3 hours.
4. Change oil and filter (if engine has a filter).
5. Run the motor hard for short bursts ( Run it like you stole it).
6. Motor should be broke in when it has 5 hours total run time on it. Changing oil and filter (if engine has a filter) up to the owner.

Some may say I'm wasting oil. The reason I change oil that often is to make sure all the fine pieces of metal are out of the engine. I have seen what happens when fine pieces of metal floating around inside an engine.