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20 hp onan

Weekend Freedom Machines » The WFM Archives » Restoration Forum - Hydrostatic Tractors Archive » 20 hp onan « Previous Next »

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Matt Bennett
Member
Username: Mpb
NY
Registered: 8-2010
Post Number: 2
Posted on Saturday, August 21, 2010 - 11:09 am:   Edit Post Delete Post View Post/Check IP    Move Post (Moderator/Admin Only)

Does anybody no what the compression should be on the 20hp onan engines.I have one in my F910, after it warms up it starts skipping and loses power. any help would be appreciated.
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M. Drew
Member
Username: Drew
WI
Registered: 4-2007
Post Number: 760
Posted on Saturday, August 21, 2010 - 12:09 pm:   Edit Post Delete Post View Post/Check IP    Move Post (Moderator/Admin Only)

Matt,

The manual says a minimum of 75 psi and a difference of less than 10 psi between the 2 cylinders.
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Jim Briney
Member
Username: Lodogg2221
IN
Registered: 1-2006
Post Number: 4614
Posted on Saturday, August 21, 2010 - 12:22 pm:   Edit Post Delete Post View Post/Check IP    Move Post (Moderator/Admin Only)

Depends if its the P220 or B48G...75 for the P220, 100 for the B48G.
Looks like the F910 had both engines, so you will need to know which one you have before going much further.
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Matt Bennett
Member
Username: Mpb
NY
Registered: 8-2010
Post Number: 3
Posted on Sunday, August 22, 2010 - 7:02 am:   Edit Post Delete Post View Post/Check IP    Move Post (Moderator/Admin Only)

Thanks for the info.one side has 95 the other has 75 but it doesnt seem to smoke. But after a half hour of mowing it can hardly get out of its own way. do you think it could be a valve?
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Jim Briney
Member
Username: Lodogg2221
IN
Registered: 1-2006
Post Number: 4616
Posted on Sunday, August 22, 2010 - 10:27 am:   Edit Post Delete Post View Post/Check IP    Move Post (Moderator/Admin Only)

Matt, which engine is it? That doesnt meet the spec for the P series, and neither because of the difference in readings between the two.

Again, you need to know which engine you have FIRST!

More likely rings, but you could check the valve clearances first. And to get to the rings, you will need to pull the head, so you could also check that as well.
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Matt Bennett
Member
Username: Mpb
NY
Registered: 8-2010
Post Number: 4
Posted on Sunday, August 22, 2010 - 11:11 am:   Edit Post Delete Post View Post/Check IP    Move Post (Moderator/Admin Only)

I will find out and let you no thanks jim.
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Jim Briney
Member
Username: Lodogg2221
IN
Registered: 1-2006
Post Number: 4617
Posted on Sunday, August 22, 2010 - 11:15 am:   Edit Post Delete Post View Post/Check IP    Move Post (Moderator/Admin Only)

Should be right on the engine label on top of the heat shields...will either start with P220 or B48.
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Matt Bennett
Member
Username: Mpb
NY
Registered: 8-2010
Post Number: 5
Posted on Sunday, August 22, 2010 - 4:17 pm:   Edit Post Delete Post View Post/Check IP    Move Post (Moderator/Admin Only)

Its a B48G. I checked the compression cold, it was 115 and 90. I let it warm up for a half hour and checked again and the right side was down to 75. looks like im going to have to pull the engine and see what i find.
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Ken Combs
Member
Username: Kencombs
ok
Registered: 2-2008
Post Number: 67
Posted on Monday, August 23, 2010 - 8:04 am:   Edit Post Delete Post View Post/Check IP    Move Post (Moderator/Admin Only)

Dropping compression when going from cold to hot could be as simple as a valve adjustment. Costs nothing and doesn't take long. Worth a shot before pulling the engine.
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Jim Briney
Member
Username: Lodogg2221
IN
Registered: 1-2006
Post Number: 4618
Posted on Monday, August 23, 2010 - 9:42 am:   Edit Post Delete Post View Post/Check IP    Move Post (Moderator/Admin Only)

Matt do you have the CTM2 for the Onan engines?
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Matt Bennett
Member
Username: Mpb
NY
Registered: 8-2010
Post Number: 6
Posted on Tuesday, August 24, 2010 - 8:08 pm:   Edit Post Delete Post View Post/Check IP    Move Post (Moderator/Admin Only)

I took the valve covers off last night and there was no clearance between the valve and tapit. the valves were open slightly. I adjusted them but i have to order new gaskets. I will let you know how it works out. Jim i am not sure what the CTM2 is you will have to fill me in. thanks for all the help guys.
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Chuck Van Dusen
Member
Username: Chuckv
OR
Registered: 1-2007
Post Number: 3950
Posted on Tuesday, August 24, 2010 - 9:00 pm:   Edit Post Delete Post View Post/Check IP    Move Post (Moderator/Admin Only)

Matt,

The CTM2 is the engine manual for the Onan engine. CTM stands for Component Technical Manual...


Chuck
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Jim Briney
Member
Username: Lodogg2221
IN
Registered: 1-2006
Post Number: 4620
Posted on Wednesday, August 25, 2010 - 11:56 am:   Edit Post Delete Post View Post/Check IP    Move Post (Moderator/Admin Only)

Matt, do you have the correct specs for the valves?
If they arent properly adjusted, it can do more harm than good.

BTW, you have mail...
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Matt Bennett
Member
Username: Mpb
NY
Registered: 8-2010
Post Number: 7
Posted on Wednesday, August 25, 2010 - 8:45 pm:   Edit Post Delete Post View Post/Check IP    Move Post (Moderator/Admin Only)

talked to the local jd service manager he gave me the numbers. Thanks Jim and Chuck.

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