B&S 20.5 overhaul

[jlsanborn]

So we've got a very nice rider but it smokes like a steam engine! It runs pretty well but not that well. I'm thinking of doing an overhaul, or at least tearing it apart for inspection. What's the story on these B&S twins? Is it worthwhile or should I look for a not-so-smokey donor motor on Craigslist? What do you suppose I should measure on a compression tester? Are new valves gonna help if all I can do is spin them with a little grinding compound? Are there guides / stem seals? I've torn down a few singles and swapped parts around as a kid but never actually bought new parts to try and revive one for reals. Am I wasting our time?

 

[Baby Grand]

I re-engined our 21 HP Intek Craftsman after it kept shearing Woodruf keys on the flywheel. The 2nd to last one sheared the flywheel, not the key, so I replaced the flywheel. Then it sheared the flywheel again. Flywheel is expensive. Bought a different model B&S of similar HP figuring the one in our lawn tractor has a design defect. Cost of entire new engine was equal to about 4 flywheels. Price out the parts you're thinking about replacing, then see what a whole new engine costs before you buy. Keeping fingers crossed and looking for a baby 'Bota, Deere, Ford, etc, to replace it.

Your problem may stem from a different root cause than mine. Before the key shearing nonsense started the engine blew a head gasket. This was at maybe 40 to 50 hours of time on the engine. Had it fixed under waranty. It was smoking like a cold chimney.

Head gasket repair is simple and reasonable cost. Need to retorque the head after it has run a bit and adjust valve clearance when you do.

Diagnosing head gasket failure is complicated by the diffculty in getting a compression check, due to the compression release timing of the cam. Or so I have been told. Maybe there's an IC guru who can step up and dish with better intel than I am spewing.

-Jim, who is not a big fan of the Intek motor.

 

[football19887]

I have a 20.5 HP and for some reason when I run it for awhile and or cut the lawn. I turn it off and try starting it again. It sounds like its about to but it won't until its cooled down. What causes that and what should I do? I know its not in the right section but I just started. Thanks.

 

[bindian]

So we've got a very nice rider but it smokes like a steam engine! It runs pretty well but not that well. I'm thinking of doing an overhaul, or at least tearing it apart for inspection. What's the story on these B&S twins? Is it worthwhile or should I look for a not-so-smokey donor motor on Craigslist? What do you suppose I should measure on a compression tester? Are new valves gonna help if all I can do is spin them with a little grinding compound? Are there guides / stem seals? I've torn down a few singles and swapped parts around as a kid but never actually bought new parts to try and revive one for reals. Am I wasting our time?

I overhauled my Dad's 18 hp B&S twin about 15 years ago. It was worth it then. You can attach a short length of rubber gas hose to the valve and spin it with a drill, but you need to finish lapping it by hand and rotating back and forth, then lifting and rotating 90 degrees and start again back and forth. Buy a B&S overhaul book. All the specs are in there. You can always look for another used engine, but air cooled engines tend to smoke faster as they put on hours. Your only wasting your time if you don't like working with your hands and have the cash to buy new.
hugs, Brandi

 

[bindian]

I have a 20.5 HP and for some reason when I run it for awhile and or cut the lawn. I turn it off and try starting it again. It sounds like its about to but it won't until its cooled down. What causes that and what should I do? I know its not in the right section but I just started. Thanks.

This is a common problem on this design, as it is tightly cowled for cooling air flow. The fuel line develops a vapor lock after shut down from engine heat just sitting there. As I remember, this engine has a vacuum fuel pump. It might need new seals. I don't remember what we did on Dad's engine on his Gilson tractor, but I am thinking we choked it a lot and sometimes ran down the battery. Check into putting an electric fuel pump on it..............or don't shut it down until you are finished for the day or a few hours.
hugs, Brandi