Hello, this is my first post to a small engine forum. I have previous experience with car and truck forums with great results.
My Grasshopper 720K has 800 hours on it and at the end of last season it started using oil, getting harder to start and loosing power. This year it would barely start so I checked compression and found the LH cylinder with 35 psi compression with the RH 150. Pulled the head and found the exhaust valve burnt. Replaced the valve and all seals/gaskets, half way kinda lapped the valve seat and put it back together. The motor fired up and ran great to start with. A lot more power is back but after about 5 minutes running it starts to smoke and if run long enough, noticeable oil consumption (still have good power though). I checked the compression again (COLD engine then HOT). After about 4 hours of total operation on the valve job. Since the new valve I have: COLD engine on the bad valve LH side 100 psi and 150 psi on the RH. On the HOT engine I have 125 psi on the LH and 145 on the RH. I also have a considerable amount of air pressure from the oil dipstick tube when I pull the stick. Not sure what it was like before or how much is too much. I'm running 10W-30 4 stroke oil. I don't know what it does but I do have an extra part left over after replacing the burnt valve. There was a cover underneath of the carb and throttle controls that I could not figure out where or how it went back in. I remember sliding it out from under the linkage thinking this will be fun to put back but with waiting for PARTS and the time it took to get back to getting it back together, I totally forgot how it came out. I don't have any oil leaking externally so I don't think it has anything to do with my problem but maybe??? Anyway, the compression check impressed me and also baffled me because it improved while my smoke and consumption got worse. Can anyone explain? I have heard how a good valve job can make older engine rings start to go which is why I didn't go to any length to lap the new valve to the valve seat.
The compression readings on the low cylinder are off compared to the high cylinder. The new exhaust valve not completely sealing could cause that issue. Also could you post a picture of that part you are talking about. A good valve job doesn't make the rings go back, but can make a bad ring show up since more stress is put on them due t the cylinder now being sealed, the extra pressure has to go somewhere.
What does the plugs look like after running. Are you still getting oil fouling of the plugs.
I bought a leak down tester from Harbor Freight today. If the majority of air noise is coming from oil dipstick then the rings are bad? Carb is intake valve and muffler is exhaust valve???
#7
Scrubcadet10
More air out the dipstick, then id say im 99.999% sure its rings.
If you hear air out of the carburetor your intake valve isnt sealing, and air out the exhaust , exhaust valve not sealing.
I have changed the oil to a straight 30 wt Rotella. Ran it for about 30 minutes and did a leak down check. The side with the bad valve is on the line between yellow (moderate) and green to start with and goes more into the yellow by about 7% then as it cool comes back towards the green. I can only hear air from the dipstick tube. Not enough to feel. The other cylinder is really deep into the green like 15% .
If I have to replace rings, what else should I do while I’m there? I have a ring compressor and all common hand tools. Do I need any other special tools? Having just replaced a burnt exhaust valve I’m not very enthused about tearing this thing back down again. What can I expect to pay for the seals, rings and bearings if I should need bearings?
Maybe I’m not seeing the latest responses but the next question is can I keep it full of oil for this summer and tear it down this winter?
#12
Scrubcadet10
You should be able too.
when you tear down, if you have a machine shop, or engine building shop close by, take the block to them and have them mic the cylinder bore. may need an oversize set with oversize piston.
