1450....no spark

[metalrain]

Gentlemen:

Got a chance to look at the motor. The little bit of history i have on it is vague. The guy parked it because it was smoking quite a bit and bought a new craftsman....(go figure). He said what he could recall was, it never burned oil, then one day, it just started smoking, he used it a few other times after that, then just parked it.

I did get it running, and it did smoke, but no knocks or noises....seemed to run good...started easily...i"m hoping to get by with the minimum and not a whole lot of machine work. Heres what the insides look like...hope somebody can take a guess as to what this thing needs.

The one valve is black and looks like its covered in oil




The head



Cylinder walls look good...no scoring, or scratches, if you look hard, you can almost see some cross hatching, but the piston has a major oil depsoit on top of it.





i'll tear the bottom off today and see what the crank/rod look like today....anybody know whats going on with the valves and all the oil?
Thanks again for the help

Metalrain

[Matt G.]

The valve guides might be loose...after you remove the valvesprings, stick the valves back in and try to wiggle them side to side. If there's play, that could be part of the problem.

[MBounds]

Metalrain, MattG:

Take a good look at the top of the block...it's obvious that it had a blown headgasket - the likely culprit of it all....Blow a head gasket and the engine wil smoke for sure...and the likely cause of "it just started smoking all of a sudden" but still runs ...hmmmm

Myron B

[metalrain]

Gentlemen;

Well....strange things...got the piston out...crank looks excellent, along with the rod



But...the top side of the piston is chewed up down to the top ring...wasn't noticeable untill the piston was out....





So what do you thing caused all that???? The cylinder wall is fine....i can detect one small scratch, but cant pick it up with a fingernail....also, there might have been something going on with the head gasket...on the block and head if you look close, one side is brown, the other side is clear...i will check the valves for side to side movement, but real curious as to what would have caused the piston damage.
Thanks guys

Metalrain

[Matt G.]

Does the damage to the piston coincide with the carbon deposits on top and the side that faces the blown part of the head gasket?

[metalrain]

Matt:

The bad side of the piston is facing the valves...as for a "blown head gasket" I've never seen one, so i don't quite know what i'm looking for there...the gasket is intact, its just dis-colored on the left side...and clear on the other side, like something maybe blowing thru the dis-colored side. There was lots of oil/grease buildup on the left side of the block/head....pretty clean on the right side...





Metalrain

[Matt G.]

A blown head gasket means a leaking head gasket. Rarely do they ever blow pieces of it out. I've seen it once...see that oily mess on the gasket surface that faces the PTO end of the engine? It was blowing oil out through there.

I think that piston damage may have been caused by all that carbon buildup, which was probably caused by the blown head gasket. Every time the engine was run, the expanding gases on the compression stroke probably pushed some of the carbon debris down between the piston and bore in that area. I took apart a twin cylinder engine that had pistons that looked like that all the way around. That thing had 2 blown head gaskets, and finally threw a rod before I got it.

[Merk]

Most Kohlers I've rebuilt have the piston burnt in the same area. The white on top of the exhaust valve tells me that the motor was on the lean side when it was running. The hottest area in the combustion chamber is the area between the exhaust valve and the top side of the piston that was burnt. The piston is made from alunimun and block is made from cast iron. Cast iron can take more heat before it starts to melt.

There should be a number or letters stamp on top of the piston. Odds are you find the letters "std" which stands for standard. If the piston has "std" it could be the orginal one.

[Merk]

by metalrain
No, it wont be a complete restoration. I'll check the motor out and see what that needs, hopefully maybe just a set of rings.

Your burnt piston is a good reason not just replace the rings. Read sections 10 thru 12 in a Kohler manual. Pay close attention to how to measure a block. If you measure before you hone a cylinder and measure after you hone a cylinder you will be close to being out of tolerance. A cylinder bore that is close to being oversize can lead to rings not setting and piston slap/knocking noise.

Do your Cub a favor.....rebuild it's motor the right way. I replace the following things when I rebuild one:
piston/rings
connecting rod
governor gear (plastic version)
comeplete gasket set
head bolts

[metalrain]

Yup Merk...i'll replace all the parts mentioned. The piston had a number stamped on it...something like 436702....but i didn't see the "std" on it anywhere, so i'm assuming its standard. Appreciate the help on this project.

Metalrain