Excessive bottom end pressure

[440SixPack]

Do these M18 Kohler engines have bottom end vaccum like the book says? If you take the oil fill cap off mine it is like an air compressor. Just got it back together with new pistons rings and a fresh hone job. The bore was 3.126 when I finished honing. Got it together mowed half my lawn and it blew the rear main seal out. Trying to figure out what is going on. Any help would be appreciated.

Dirk.

[West Valley G]

My first thought was maybe something is not right with the
breather. Like it is not put together internally right or a clogged
tube. that would be where I would start.

Ken

[440SixPack]

New breather tube and filter. The umbrella seal is nice and limber and not stuck down. I tink I am going to go buy a leakdown tester to check the piston rings to make sure they are sealed.

[440SixPack]

Got the leak down tester and found quite a difference between cylinders. 12 percent on number 2 cylinder and 23 percent on number one. So I took number one apart and found the rings were only seated on 2/3's of the diameter on the upper two rings.
I did screw up on the stones of my new hone. I used the course stones to finish with. Should I thake the other cylinder apart and re hone with the fine stones? I have done this on number one and am still within tolerance just barely.
I did also measure the rear seal outer diameter. The one from lil red barn does not have a brand on it so I assume it is a chinese import. It measures .012 smaller than the NOK that came with the other gasket set.

[Billy-O]

Did you mic the cylinders before doing hone and rings? Worn cylinders out of round and a hone job doesn't necessarily true the cylinders.

[ol'George]

Did you deglaze the cylinders and go with std. rings
or did you precision hone and go .010 oversize??

if you went oversize with a precision hone,
did the dial bore gauge indicate out of round or tapered cylinder condition before you started?
With a Sunnen precision hone you can feel the tightness at the bottom of the bore and the looseness at the top as you increase the diameter SLOWELY taking
time to check your progress with your bore gauge.
As you approach the desired clearance you will feel and see the bore has cleaned up with no spots remaining.
Within a few tho to desired diameter, you change to fine stones to complete *45 cross hatch pattern.
One has to be careful as in just a few strokes you can go too far and the diameter is over the limit.
Make sure your 5 gallon pail you have the jug submerged in has enough Kerosene to completely submerge the jug so at no time the hone is above the
fluid,
and make sure the hone comes out of the top/bottom of the bore an inch or so insuring that the bore is true throughout its length.
Doing a single cylinder is not a difficult task, but a 8 cylinder engine
will wear a fellow out in a hurry and not recommended.
OH, a SLOW rpm drill is very beneficial so you can control the cross hatch pattern and diameter of the job.

[440SixPack]

I used a rigid hone so the cylinders are round and have less than .001 taper but are out to limits 3.1275 to 3.128. one of the cylinders has discoloration do to water in them. You cannot feel the discoloration but it did not hone out. New standard pistons and rings. Before honing they were 3.126.
What lower end vent valve works the best the umbrella style or the reed valve style? I have both so I could put either in.

Dirk.

[ol'George]

When these engines were new, they offered .003 oversize pistons to correct a problem cylinder and you could use std rings on then.
I snapped up a piston that was on ebay cheap and used it as I had a jug that had some imperfections in it so it was a easy fix, and it worked out well.
So
either live with it and enjoy,-- or go .010 oversize with new pistons/rings.
It is never a good idea to power hone a std size cylinder to "square it up"
Then put in std piston/rings.
Its bad enough to deglaze a cylinder and use std rings/piston, but taking it
it a bit oversize never works out as hoped for.
It usually does not work out well and you will hear the piston slapping in the jug.

I used to build 2 stroke Trail bike engines in the late 1960's with with custom bores to save the guys a few $$ back in the day, because they were constantly
getting dirt/water in the engines or running them to lean on the premix.
So I learned what I could get away with and what didn't work.
Even tried knurling piston skirts like they did in the the model "A" Ford days.
You are learning, and that is a good thing.
Today we have the internet to help, in my day it was conversation and trial & error.
Luck!

[440SixPack]

Does anyone know the dimensions of the original front seal for the M18 52-032-10S I have a NOK BE1177E that came in the rebuild kit. I just want to verify that it is the correct size.
More important if it is the right size how do I get it to stay in the block? I have had 2 blow out now. One was a no name and was .012 smaller than the NOK, the other was a NOK but I had put HighTack on it and maybe that was a problem. Any help would appreciated.

Thanks, Dirk.

[bill682]

When you say "front seal" are you referring to the PTO side or flywheel side?