Low Compression in Onan

[meby 27]

Hi all, 

  I'm trying to track down the cause of low compression in my Onan BF ms/2929e. I'm checking some things now and noticed the cylinder head on one side (haven't checked the other side yet) has two gaskets. Is this normal? The service manual says two gaskets, but doesn't specify if its two per side or two total.

Thanks

[WH nut 553]

What is your definition of low compression?

[boomers_influence 106]

meby

only one gasket per side.

thank you boomer ( the used onan engine parts guy,

also NOS and new.

[meby 27]

WH nut: 75 lbs on one side and 40 lbs on the other. The engine runs, but starts extremely hard and seems low on power.  Could doubled up gaskets could screw with compression?

[woodchuckfarmer 333]

Id start with 2 new head gaskets . check the heads to make sure there not warped and set the valves. Then check the compression.

[can whlvr 991]

id pull the head and make sure you don't have a bad valve seal,then if you don't go from there as the guys have stated

[Howie 884]

Two head gaskets will change the compression on that cylinder. Pull the head to do it correctly and check the valve seat at the same time.

 

David

[meby 27]

10 minutes ago, Howie said:

Two head gaskets will change the compression on that cylinder. Pull the head to do it correctly and check the valve seat at the same time.

 

David

Thanks. I'll fix the gasket problem and recheck. No valve seat problem on the side I have apart. I'm also going to adjust the valves while I'm at it if I can ever get the exhaust off. 

[WHX?? 46,964]

My question is meby says a manual calls for two gaskets but I'm think that's two per motor...pull the heads....

[boomers_influence 106]

meby

i would have done a leak down test FIRST.

thank you boomer

[meby 27]

Checked the valves on the first side: was .001 off on the intake side and .009 off on the exhaust side. 

[sorekiwi 761]

3 hours ago, meby said:

Checked the valves on the first side: was .001 off on the intake side and .009 off on the exhaust side. 

tight or loose?

 

[meby 27]

Tight on both. I adjusted the other cylinder last night and the intake was about .001 tight as well and the exhaust side had no play at all.

 

And I would rather not admit this, but in the interest of being as accurate as possible...there was only one gasket after all. When I pulled the head off enough material stayed evenly all the way around on the head while the gasket stayed on the cylinder making it appear as if there were two when there was only one.  A little tidbit I discovered when I started cleaning the head. 

[Howie 884]

That's where the leak down test would really helped. Would have helped he to the problem area quicker. I know 

that everyone has the tester though. I do have one and I does help a lot.

 

David

[JackC 616]

"The engine runs, but starts extremely hard....

 

Dirty carburetors will contribute to that also.

My BF/MS ran like it needed to be rebuilt or replaced

I cleaned the carburetor and now it starts and runs like new.

After cleaning a few carburetors and seeing what is inside and the difference in performance, I never feed Ethanol poisoned fuel to my horses.

[meby 27]

On 2/12/2016 at 0:58 PM, Howie said:

That's where the leak down test would really helped. Would have helped he to the problem area quicker. I know 

that everyone has the tester though. I do have one and I does help a lot.

 

David

unfortunately I don't have a setup to do a leak down test.

11 hours ago, JackC said:

"The engine runs, but starts extremely hard....

 

Dirty carburetors will contribute to that also.

My BF/MS ran like it needed to be rebuilt or replaced

I cleaned the carburetor and now it starts and runs like new.

After cleaning a few carburetors and seeing what is inside and the difference in performance, I never feed Ethanol poisoned fuel to my horses.

The carb may be an issue, but I need to track down the compression issue first.

[meby 27]

Update: I lapped and adjusted the valves and put in a new gasket on the 40 lb side and gained a whopping 6 lbs of compression. What would be the next step? Does this mean worn rings or something?

[boomers_influence 106]

meby

as stated a leak down test will

tell you where the is.

thank you boomer

[meby 27]

On 2/26/2016 at 6:09 PM, boomers_influence said:

meby

as stated a leak down test will

tell you where the is.

thank you boomer

 

I don't have the tool to do a leak down test, so I did the next best thing and pressurized the cylinder with air and listened for where the air was escaping. There is definitely air escaping past the rings. 

 

I guess the next question is due to the high cost of doing a complete overhaul and limited availability of parts, is there a pressing reason to keep the Onan aside from it not being a direct bolt on swap. I can get a new Honda with a warranty for about the same price as the overhaul. 

[meby 27]

Also, does anyone know what is the minimum hp just for the hydro system - no mower or anything else?

[boomers_influence 106]

meby

YOU DID in fact do a leak down test.

i only use 50-60 psi.

have the piston at TDC on the compression stroke.

have the choke and throttle open.

remove the dipstick.

then slowly apply the air ( while holding the crank/or flywheel. )

and listen where the air comes out.

thank you. boomer

[meby 27]

I decided to pull this engine and replace it with another one that I already own. I started a new thread for the swap.

 

Edited March 16, 2016 by meby
Accuracy