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Hi, I have a Husky lawn tractor with a 23HP B&S Intek engine that's about 6 years old. Been running fine until end of last season when it started blowing blue smoke out of the muffler.

I pulled the carburetor and cleaned it, it had oil in the intake manifold (guessing from the breather tube?). I tried starting up again (without breather attached) and it started smoking after about ten or twenty seconds.

I've pulled the heads now and don't see any gasket damage. This is what things looks like. Any ideas on where to look next for the problem?

Thanks!

shp, Can you move the piston around in the bore? Try a .001" feeler strip between the piston and bore, then a larger one, then a larger one and judge the withdrawal force as none, some, heavy. Let's say the withdrawal force for .001" should be be heavy. Pic five shows cross hatch hone marks. Don't think they should be there after 6 years. Has someone honed and refitted the same piston/rings? Bores and pistons are very fussy. Does look like some oil is entering chamber. IMO

Thanks for the input, I'll try the feeler gauge tomorrow. Definitely no piston work done on in before, I've had it since new. Mower has about 150 hours on it total.

Can't see anything wrong there.
Try a vew gasket and a new valve stem oil seal.
Inlet valve sucks oil down the valve stem.
Plug looks a little lean so give the carb a once over while it is off.

I suspect a blown head gasket, but can't tell from your photos. Do you still have both head gaskets and can you post pics of both sides of each gasket?

The second picture of the head with the head gasket. It looks like some discoloration around the center top near the push rod cavity divider. I would like to see the other side of that gasket. Just looks like evidence of blown head gasket in that area.

motoman said:

shp, Can you move the piston around in the bore? Try a .001" feeler strip between the piston and bore, then a larger one, then a larger one and judge the withdrawal force as none, some, heavy. Let's say the withdrawal force for .001" should be be heavy. Pic five shows cross hatch hone marks. Don't think they should be there after 6 years. Has someone honed and refitted the same piston/rings? Bores and pistons are very fussy. Does look like some oil is entering chamber. IMO

Click to expand...

Turns out my smallest feeler strip is .003" and that one won't slide past the rings at all. Not sure if I can find .001" and .002" gauges locally to buy or borrow, if so I'll try those too.

shp, The feeler test is ONLY for piston fit. Do not try to force past rings, Your (relative) low hours, sole ownership, suggest the cross hatch is the factory machining. Don't bother with the .001 " strip. Wait to reassemble and do compression test. The pros are suggesting oil up pushrod galleys and accross gasket into chamber, I guess.

Blown head gasket is almost always between the cylinder bore and push rod gallery, often on the engine block side and may only look like a pencil mark. Sounds like blown gasket to me.

Walt Conner

motoman said:

shp, The feeler test is ONLY for piston fit. Do not try to force past rings, Your (relative) low hours, sole ownership, suggest the cross hatch is the factory machining. Don't bother with the .001 " strip. Wait to reassemble and do compression test. The pros are suggesting oil up pushrod galleys and accross gasket into chamber, I guess.

Click to expand...

Ah, ok, well the .003" definitely fit between the piston and bore on both cylinders if that indicates anything. I'll be getting some better gasket pics up too in a few.

Here are some (hopefully) better pics of both sides of the gaskets. Please let me know if anything looks out of the ordinary.

It sounds like my next step should be new gaskets and valve stem oil seals. Gaskets are straight forward but I'm not sure the process to change the stem seals - is there a decent howto out there (ideally with pictures) that I can follow?

Also, I want to thank everyone for jumping in with advice and opinions. It's much appreciated.

This manual should help you out. I hope you kept the heads separate, as there is a #1 and #2.

https://doc-0o-5o-docs.googleuserco...253/*/0B6NaqjIxWV1ySkZjTTA5TGltZEE?e=download

"Pic five shows cross hatch hone marks."

That same picture also shows score marks.

Walt Conner

Gonna be pretty hard to confuse #1 & #2 heads.

Rivets said:

This manual should help you out. I hope you kept the heads separate, as there is a #1 and #2.

https://doc-0o-5o-docs.googleuserco...253/*/0B6NaqjIxWV1ySkZjTTA5TGltZEE?e=download

Click to expand...

Thanks, that looks like just what I need.

I have just flipped through the Intek repair manual looking for a piston/bore clearance and could not find it. Anyway the feeler strip is not suggested and was only an idea among others. The strip test should be specified with a thickness and a withdrawal force (like a fish deliar) and it is not used anymore. Also the placement is important . If I remember piston crowns are usually different dia than the skirts where the measurement is taken. Without further disassembly you cannot get the skirt dia. You could use a 3 position bore gauge, but the reading would not have much meaning without the piston dia. Intek does call out only .0015" out of round allowance in the specs. A dia bore gauge is a pretty specialized piece. I have used the cheaper telescoping gauges and IMO they are difficult to read accurately, especially if first usage.

Update on this problem. I got the head gaskets and valve stem seals in the mail and put the engine back together today, after cleaning everything up best I could.

After reassembly I tried to do a compression test on each cylinder with a gauge I borrowed from the local auto parts store, but it did not register anything at all - a big fat zero. However I could feel resistance on the compression stroke, and if I pushed a valve in under compression I could hear the pressure release with a hiss. So, guessing maybe the gauge wasn't working properly I finished buttoning it up and did a test run.

Engine started right up, and runs strong and sure. The rough idle that it had all last season is gone; it now purrs along at idle and wide open. And, no smoke.

Seems like the engine should not be running well if it really had 0 compression on both cylinders? If so is it reasonable to conclude that the compression tester was not working properly? There's no other place nearby that I can borrow a tester from, or else I would just test it again to be sure.

A better test is to start it up and see how it runs. As you see you passed that test with flying colors. I think you solved your problem.

Thanks to you and everyone else for the help!