OCD Solutions
Original, Clean and Dependable Solutions
- Location
- Rentz, GA
I have been trying to sell a GP800 66E engine for over a month now. One of the problems with the motor is that, even though it runs, one cylinder has low compression, (90/135). A visual on the piston showed minor scuffing but the cylinder was unmarked. The only thing I really found was that the ring wear was way overspec at +.045".
I purchased a new OEM Yamaha ring set, honed the cylinder and reassembled. Ring gap was now at .016" but Compression only came up from 90 to 100, not quite what I was hoping for.
**All testing on this engine has been with it sitting on my shop bench with no intake or exhaust, connected up to a battery, solenoid and starter.
I questioned proper ring seating on the hardened Nikacil Cylinders so I added some oil to each cylinder, swished it around as best I could and then turned the engine over by hand to remove as much of the oil as I could so the volume didn't affect my readings and took them again. This time I got 135/153, still not quite what i was looking for. If i let it sit overnight and come back to it without adding any more oil since, i now get consistant 125/150 readings.
I have been using the starter to turn the engine over for a minute at a time to see if it will seat but am unsure if it will without the heat of actually running. A minute at at time is all I dare try for fear of burning up the starter. The starter draws 28 amps and the outside housing gets warm to the touch at 1 minute. I have been leaving it several hours between sessions to cool down. (As I type this I realize I have been using synthetic rather than mineral oil for this seating process but i doubt that it has that much of an effect.?.?.?).
I believe i have another isssue, I just can't see what it is right now. What else is left? Rave Valves? I inspected them and found them to be in good working order except that the clearance in one is much more than the other. The cylinder with good compression has 0.045" clearance and the other is almost .075". Closing, (Lowering) the rave while cranking, increases the recorded pressure in the good cylinder but has no affect on the bad one.
When I finally spoke to the old owner about the problems he said that he had ruined a cylinder and had bought a used one to replace it with. It seemed to run fine for him other than hard starting so he never looked any deeper. Is there a chance he mixed up some of the components during the swap? Is there a difference between 800 and 800R parts? Port height? Piston Dimension?
So what do you guys think? What should I do next?
P.S. Am I sick for actually enjoying this little project. :biggrin:
I purchased a new OEM Yamaha ring set, honed the cylinder and reassembled. Ring gap was now at .016" but Compression only came up from 90 to 100, not quite what I was hoping for.
**All testing on this engine has been with it sitting on my shop bench with no intake or exhaust, connected up to a battery, solenoid and starter.
I questioned proper ring seating on the hardened Nikacil Cylinders so I added some oil to each cylinder, swished it around as best I could and then turned the engine over by hand to remove as much of the oil as I could so the volume didn't affect my readings and took them again. This time I got 135/153, still not quite what i was looking for. If i let it sit overnight and come back to it without adding any more oil since, i now get consistant 125/150 readings.
I have been using the starter to turn the engine over for a minute at a time to see if it will seat but am unsure if it will without the heat of actually running. A minute at at time is all I dare try for fear of burning up the starter. The starter draws 28 amps and the outside housing gets warm to the touch at 1 minute. I have been leaving it several hours between sessions to cool down. (As I type this I realize I have been using synthetic rather than mineral oil for this seating process but i doubt that it has that much of an effect.?.?.?).
I believe i have another isssue, I just can't see what it is right now. What else is left? Rave Valves? I inspected them and found them to be in good working order except that the clearance in one is much more than the other. The cylinder with good compression has 0.045" clearance and the other is almost .075". Closing, (Lowering) the rave while cranking, increases the recorded pressure in the good cylinder but has no affect on the bad one.
When I finally spoke to the old owner about the problems he said that he had ruined a cylinder and had bought a used one to replace it with. It seemed to run fine for him other than hard starting so he never looked any deeper. Is there a chance he mixed up some of the components during the swap? Is there a difference between 800 and 800R parts? Port height? Piston Dimension?
So what do you guys think? What should I do next?
P.S. Am I sick for actually enjoying this little project. :biggrin:
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