Green Tractor Talk banner
1 - 20 of 34 Posts

·
Registered
Joined
·
33 Posts
Discussion Starter · #1 ·
Hello Everyone,

Wondering if anyone has some ideas....

I have a 88 John Deere 318 that was rebuilt about 5 years ago. I use it over the winter for snow blowing and last weekend I put the deck and bagger on and did the first pass on the lawn. It seems very underpowered and the blades would slow in long grass to a point where I would have to stop and let the motor catch up. I took the bagger off and it was better but still not great. Today I tried to cut again (without the bagger) and same story. This time the old Deere couldn't finish the job. It stalled in some longer grass (only a weeks worth though). The engine is very warm on the exhaust side and I noticed some gas or oil or possible mixed below the fuel pump. I'm guessing it overheated and needs to cool down.

I also noticed a few month ago a small oil leak on ground on the same the exhaust side after use. Not a lot but some.

Before I start tearing the engine apart searching for the gremlin I thought I would check would you guys to any ideas.

Thanks,

Jeff
 

·
Registered
Joined
·
164 Posts
Sounds like it may be starving for fuel. A quick and free thing to try is to back out the high speed carburetor jet a full turn and see if it runs better and cooler.
 

·
Registered
Joined
·
1,800 Posts
Air cooled engine so it's one of a few possible causes:

-engine cowling is plugged / blocked with grass and dirt
- cooling fins on cylinders and heads are plugged up with crap
- low on oil
- working the engine too hard, cutting grass in the wrong gear, etc
 

·
Registered
Joined
·
33 Posts
Discussion Starter · #4 ·
Thanks for the tips.

The oil seems to be pretty thin... i'm guessing it's mixed with gas. maybe the fuel pump is shot?
 

·
Registered
Joined
·
13,561 Posts
Thanks for the tips.

The oil seems to be pretty thin... i'm guessing it's mixed with gas. maybe the fuel pump is shot?
You would be able to smell it, plus you would be making oil.


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
3,201 Posts
How did the engine perform with the snow blower? Plenty of power then? If it did OK with the blower I'd check the mower deck pulleys and blade spindles to make sure they are turning freely. Check the mule drive to make sure those pulleys are spinning freely.
 

·
Registered
Joined
·
1,800 Posts
Thanks for the tips.

The oil seems to be pretty thin... i'm guessing it's mixed with gas. maybe the fuel pump is shot?
Maybe...or the carb float is leaking and filling it with gas.
 

·
Registered
Joined
·
1,124 Posts
Or the float is sticking open which will also get gas in the oil.
 

·
Registered
Joined
·
33 Posts
Discussion Starter · #9 ·
How did the engine perform with the snow blower? Plenty of power then? If it did OK with the blower I'd check the mower deck pulleys and blade spindles to make sure they are turning freely. Check the mule drive to make sure those pulleys are spinning freely.
It was perfectly fine with the blower. Maybe your on to something with the deck pulley's.... I did take the blades off over the winter for sharpening. Maybe I buggered up a pulley in the process. I will investigate this afternoon.
 

·
Registered
Joined
·
1,717 Posts
Jeff,

An Onan running under powered and overheating is also a sign associated with running on just one cylinder. Have you checked the compression of each side? Look over the plug wires for any signs of cracked insulation where spark can jump to the engine tins.

Most owners are surprised how "well" an Onan can run on one cylinder -- it is not at full strength but it is not totally disabled either...

Chuck
 

·
Registered
Joined
·
33 Posts
Discussion Starter · #11 ·
Jeff,

An Onan running under powered and overheating is also a sign associated with running on just one cylinder. Have you checked the compression of each side? Look over the plug wires for any signs of cracked insulation where spark can jump to the engine tins.

Most owners are surprised how "well" an Onan can run on one cylinder -- it is not at full strength but it is not totally disabled either...

Chuck
Thanks Chuck. Something is certainly wrong... left cylinder only shows 25PSI, right side (exhaust side) marginally better but still only 45PSI. I got 60PSI on one try but the other two were 45PSI. Either way I think the Onan P218 should be 90-100PSI. Time to start pulling things apart! :nunu:
 

·
Registered
Joined
·
1,717 Posts
Before you take anything apart, you need to do a couple more careful measurements. First, ensure you are making the compression measurements the way the manual instructs:

Text Font Organism Line

Then, if still reading low -- verify that the valves are not adjusted too tight:

Major appliance Clothes dryer
Text

If the valve clearances were off, test compression again after the adjustment...

Chuck
 

·
Registered
Joined
·
1,717 Posts
I have reused the valve tappet cover gaskets successfully, and having a set on hand is good insurance that you won't tear one when taking the covers off (but if you do, you have them handy...) You don't have to take the heads off to adjust the valves. Any time you take the heads off, do plan to renew the head gaskets...

Let us know what compression numbers you get when spinning the crank at the correct speed with the choke off and the throttle fully open.

Chuck
 

·
Registered
Joined
·
33 Posts
Discussion Starter · #15 ·
I have reused the valve tappet cover gaskets successfully, and having a set on hand is good insurance that you won't tear one when taking the covers off (but if you do, you have them handy...) You don't have to take the heads off to adjust the valves. Any time you take the heads off, do plan to renew the head gaskets...

Let us know what compression numbers you get when spinning the crank at the correct speed with the choke off and the throttle fully open.

Chuck
Rechecked compression verifying choke open and throttle all the way up. Was getting around 50-60PSI on each side. In checking the value clearances now and there seems like a ton of play! I'm reading 0.95mm on one. See pic. Not sure what position I'm in though. I'm turning the wheel that has the pulley going to the mull drive but the Piston isn't moving. Also found the head gasket was torn and there is alot of carbon.


Sent from my Nexus 6P using Tapatalk
 

·
Registered
Joined
·
1,717 Posts
0.95 mm is well over the specification -- and is in fact a bit more that 0.037 inches. Also, if you can ascertain that you are turning the crankshaft and the piston is not moving there is something seriously wrong. Be sure you are turning the large nut at the center of the PTO pulley and not the pulley itself as it is not directly coupled to the crankshaft.

Chuck
 

·
Registered
Joined
·
33 Posts
Discussion Starter · #17 ·
0.95 mm is well over the specification -- and is in fact a bit more that 0.037 inches. Also, if you can ascertain that you are turning the crankshaft and the piston is not moving there is something seriously wrong. Be sure you are turning the large nut at the center of the PTO pulley and not the pulley itself as it is not directly coupled to the crankshaft.

Chuck
That's it! I knew I was doing something wrong. Now that I'm using a socket on the nut the Piston and values are moving

Sent from my Nexus 6P using Tapatalk
 

·
Registered
Joined
·
2,473 Posts
If the hard gasket was letting that much carbon blow out it might have been bad. And the reason for your low compression.
 
  • Like
Reactions: Drifterbike

·
Registered
Joined
·
571 Posts
once you get everything in check. a bit of engine restore in the silver can will help a worn cylinder and it really does work and it is safe:greentractorride:
 
  • Like
Reactions: Drifterbike

·
Registered
Joined
·
362 Posts
One of the easiest and simplest way to check the engine is connect a small pancake compressor onto each cylinder. Rotate the engine until both intake/exhaust are closed. Open the compressor valve, look at the rate the needle falls. Squirt oil into the cylinder, do again. From there you know if you are dealing with a cylinder problem or valve.

But when I first saw your post I knew it's likely engine problems. My first 318 I got from a craigslist guy, had a bad cylinder.....
 
1 - 20 of 34 Posts
Top