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I have a 1998 Craftsman lawn tractor with a Briggs & Stratton 20.5 HP twin cylinder engine that seems to be losing power as my 42" cutting deck is really lugging. The deck is fine. the tractor we got with the farm last year. It smokes when engaging the mower. I put oil in in every time I cut the grass all 2 acres. Up until now its been fine. Today more smoke than ever. I did a compression test & both cylinders are at 90lbs & holding. I'm thinking the motor needs a little freshening up. What should the minimum compression be? The tractor had probably sat a couple years before we bought the place.

90 psi isn't bad, what is the model, type and code of the engine so we can see what engine you have.

I squirted a little oil in the cylinders & had the compression jump to 150psi. The engine is YBSXS.7842VE 274567

The number you posted is the EPA emissions certification number. the number I need is stamped in to the valve cover or the blower housing. While actually say Model, type, code.

If its holding that pressure for a 98' machine it cant be to serious...how long is it holding??....head gasket, valves, drive pulley id look at for that year..:2cents:

Michael72 said:

If its holding that pressure for a 98' machine it cant be to serious...how long is it holding??....head gasket, valves, drive pulley id look at for that year..:2cents:

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It held the pressure all night. But still smokes when I put the mower blades on. I know it can't be the rings.

Can you do a leak-down test on it ? That will determine if it's top end or the rings..

Although for the compression reading to jump 60 lbs to 150 after adding oil & re-testing, does indicate the rings seal is not ideal.( that is the purpose of that old school test).

Any viratin more than 20% on a wet & dry compression test = worn out rings.
Replace them ow & it will just be new rings & a hone.
leve it or much longer & it will be a new piston & rebore.

I use a digital leak down tester and have had different readings depending on position of piston in cylinder on older machines...as mentioned above its def a leak up..that extra ask when blades are engaged is a good test for rings....good luck :smile:

Here what I know for sure. Model 61707 Type 0145 E3 Code 9912205A I definitely leaking from the crank shaft seal underneath. Smoked for a while this morning blades weren't spiinning too fast just kind of died in the grass. Motor kept running though. Last year all was well it just was using a lot of oil. This year I have had it out for about a month now I its getting weaker. I also know its using almost twice the fuel. All I have is a standard compression gauge. I'm tempted to take it apart. Its not in the cards for a new tractor this year. Right now I'm all ears.:smile:

b1mmuo27 said:

Here what I know for sure. Model 61707 Type 0145 E3 Code 9912205A I definitely leaking from the crank shaft seal underneath. Smoked for a while this morning blades weren't spiinning too fast just kind of died in the grass. Motor kept running though. Last year all was well it just was using a lot of oil. This year I have had it out for about a month now I its getting weaker. I also know its using almost twice the fuel. All I have is a standard compression gauge. I'm tempted to take it apart. Its not in the cards for a new tractor this year. Right now I'm all ears.:smile:

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Hows those head gaskets??...you will lose power there too if gaskets are bye bye...it smoking all the time but stronger on start up?...

I'm going to pull the top off & see what's going on.

The briggs opposed engines where decent engines for their time, their was a habit of oval wearing the cylinders and cause loose of power. Having the valve seats get loose and come out allowing the engine to run on one cylinder. Since it is an 98 possibly could be floating the valves somewhat, some reseating the valves may improve things.

Thanks. It does start right up & runs fine but is lacking power & smokes plus leaking from the bottom which I believe is the crank seal. I'm going to open it up later today. I'm a little slow because I have a cracked bone in my wrist.

like ilengine said....its a good option for now...quick a cheap fix...if gaskets and valve seats dont cure it then its dollar time

This is a picture of both sides.

Weak point on gasket is just at exhaust vale to cylinder...id bet anything they were fried there...if you bring the piston to TDC and see how those valves are sitting....bet they lose

I was impressed with the size of the valves & piston. Yes both sides were loose at the bottom. I cleaned what I could. Spun the valves. The pistons aren"t sloppy. Last engine I had apart was my 05 Sprinter with a 3.0ltr diesel. Those pistons were sloppy. Bolted them back on torqued them all round & started it. Sounded like it use to. Strong. no smoke. Took it around the field put on the mower no smoke. Seems like the power is back. I'll wait & see. Thanks for everyones help.

Happy days...nice job!!... :thumbsup:

It's like a new machine today. Went out with the trailer to pick up wood I cut down. No smoke on start up or any start ups today. I'll get a new mower belt tomorrow as today is a holiday here.

Did you put fresh gaskets in????

No they were the thick ones. Cleaned everything up. Torqued them even all around which it obviously was not.

:thumbsup:

Michael72 said:

:thumbsup:

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I sold the tractor today. Got a good deal on a Cub Cadet. I has the the twin cylinder OHV engine with an oil filter. 2001 only 500 hours on it. Cost me $200 selling mine to getting this one. The guy seemed to be happy it was running good. A little bit of smoke. I'm happy, he's happy. Win win.