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I need to replace both upper and lower seals on my 1994 10515 so I started to tear it apart. Got the flywheel off and removed the top seal. Went to work on the bottom got the blade, blade plate, muffler all off and this is where I got confused. There is no bottom seal there was just some crud around the shaft. Am I crazy? Could the seal have totally broken down? The mower would run fine just a hard start when hot and was told that it would most probably be the botton seal.

Yes the seal can break down over time and cause it to start hard. it must be a 2 stroke?
I know I had a snowmobile do that one time I had to hold the throttle wide open to start when it was
hot.

First thing first clean your engine.. Just looking at the picture it looks like a seal in there. My self I buy a bottle of spray engine cleaner, then I spray down the engine with the cleaner and built up dirt I brush or scrap, then spray it down with water. It will be well worth your time in doing so. This also helps to prevents any dirt from entering the engine when you take it apart or remove the seals.

reynoldston said:

First thing first clean your engine.. Just looking at the picture it looks like a seal in there. My self I buy a bottle of spray engine cleaner, then I spray down the engine with the cleaner and built up dirt I brush or scrap, then spray it down with water. It will be well worth your time in doing so. This also helps to prevents any dirt from entering the engine when you take it apart or remove the seals.

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Clean the area X2, Hard to tell, wipe off bore area. I can't tell if there is a seal down in there or if the seal is missing from the bore.

OK I'll clean it and gat a new picture tonight. I really don't think theres a seal in there and if there is I'm not sure how I'll get it out.

if you are going to rebuild the motor just clean the motor and tare it down and replace al the seals so you know it will be right

Not rebuilding just replacing the top and bottom crank seals

so how are you going to replace the top seal with out taking the crank out of the block?

The top seal part #611396 can be replaced by just removing the flywheel. Perhaps we're talking about 2 different things

Nope we are talking about the same thing I do this for a living and I have never done it that way but maybe
it is different with the motor you are dealing with.

Both top and bottom seals can be replaced with out disassembling the short block. Either by using the Lawn Boy seal remover tool or by VERY carefully using a small screw driver and prying them out. Put no pressure or very little on the lip of the seal bore. CAREFULLY side the screw driver between the crankshaft and the rubber lip and under the steel ledge of the seal. Pry upward. You can lay a thin piece of wood flat next to block to pry against to protect the edge of the bore lip. Do not scratch the crank surface.

oh ok I work on 4 stroke engines so I bet that is what is different.

A seal is a seal. If you can get to the seal and the crankcase housing doesn't have a lip over the top of the seal its removable. What I do most of the time when removing this style seal is drill a small hole into the steel part of the seal and install a small sheet metal screw into it. Then you can pull the seal out with that screw. some times it takes two screws.

oh ok most of the time if the seals are gone on the top and bottom it is time to rebuild the motor if not in
a year or to you will be back to tinkering with it all over again and spend more time and money.

Flintmotorsports said:

oh ok most of the time if the seals are gone on the top and bottom it is time to rebuild the motor if not in
a year or to you will be back to tinkering with it all over again and spend more time and money.

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In a four stroke you are dealing with seals meant to hold oil in the crank case...in a two cycle they are to hold in compression as the crank case developes possitive and negitive pressures that opperate the reed valves...two diffrent animals.

Replace both seals and use the mower for another ten years. It may be that the bottom seal fell down and someone removed the pulley and blade collar and seal and never bothered to install a new seal.

oh ok I see I thought that is what the seals did on a 2 stroke.

unclelee said:

In a four stroke you are dealing with seals meant to hold oil in the crank case...in a two cycle they are to hold in compression as the crank case developes possitive and negitive pressures that opperate the reed valves...two diffrent animals.

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I do work on some two cycle engines, but not very often anymore. In my younger years I did a lot of snowmobile engine work which were all 2 cycle. I will still say it again, a seal is a seal. You buy them by number or size and yes there are different styles, but they all do the same job.

reynoldston said:

I do work on some two cycle engines, but not very often anymore. In my younger years I did a lot of snowmobile engine work which were all 2 cycle. I will still say it again, a seal is a seal. You buy them by number or size and yes there are different styles, but they all do the same job.

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The point as that a four stroke runs in a bath of its own dirt and particulates and is far more likely to have bearing and bushing wear causing crankshaft play, and therefore seal damage.
A two cycle runs in fresh oil and is less likely to have bearing or bushing damage, and therefore less likely to have seal damage caused by crankshaft play. Since a two cycle does not have a crankcase full of oil and IS subject to rapid pulsations it is more likely to fail for other reasons, especially dry rot if it has sat for a few years.
Again...they are diffrent animals

New Picture. Does this help? No seal right

Best as I can tell, the the seal is missing. If I were installing a new seal I would remove all traces of oil on the walls of the bore and install the new seal dry on the side of the seal that contacts the bore wall. And prelube the seal lip with either grease or two cycle oil. Install flush with the top of the bore using a seal driver or a piece of PVC thick wall tubing to support the top of the seal going in.

I made a seal-seater from a piece of plastic water pipe cut longer than the length of the exposed crankcase. Put the seal on, slide pipe over crankshaft and tap pipe to get seal seated to correct depth.

unclelee said:

The point as that a four stroke runs in a bath of its own dirt and particulates and is far more likely to have bearing and bushing wear causing crankshaft play, and therefore seal damage.
A two cycle runs in fresh oil and is less likely to have bearing or bushing damage, and therefore less likely to have seal damage caused by crankshaft play. Since a two cycle does not have a crankcase full of oil and IS subject to rapid pulsations it is more likely to fail for other reasons, especially dry rot if it has sat for a few years.
Again...they are diffrent animals

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Yes seeing I have repaired both style engines many times I well know the different in the two engines. So when you go the dealer that sells seals and bearings just what determines if it go's in a 2 cycle engine or a 4 cycle engine. I have personally never seen a different. I have always bought seals and bearings by size, style, and number not what it go's in.

reynoldston said:

Yes seeing I have repaired both style engines many times I well know the different in the two engines. So when you go the dealer that sells seals and bearings just what determines if it go's in a 2 cycle engine or a 4 cycle engine. I have personally never seen a different. I have always bought seals and bearings by size, style, and number not what it go's in.

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Again, the original conversation was...if you replace the seals without rebuilding the engine, you will only have to do it again next year.
This was in reference to a sloppy four stroke, and normally doesn't apply to a two cycle Lawnboy engine as the seals can be replaced without an engine rebuild and still get years if not decades of use from it.
But as it seems you have an incessant need to be right....so yep all seals are the same...be they oil seals, compression seals, dust seals, or what ever....they are all the same.
I stand corrected by your vast knowledge.
That being said....my appologies to everyone else...I will not post here again.
Lee

From the looks of what I can see of the pictures the seal looks missing. There has to be a reason for this. It can't be that big of a job to disassemble the engine to find the reason. Its very hard to know what is what with just a picture. If you don't want a OH it sure has to be worth a few gaskets to look inside the engine.

LB When you say to install the new seal "flush with the top of the bore" are you saying to just drive it in till its flush or to drive it all the way in to what I believe is the bearing

mulligan said:

LB When you say to install the new seal "flush with the top of the bore" are you saying to just drive it in till its flush or to drive it all the way in to what I believe is the bearing

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Drive it in till it's flush, with the opening edge.