K301S compression testing

[sbvandepol]

Hello---- I have a circa 1985 Gravely with a Kohler K301S 12 HP that blows some clouds of blue smoke when starting (and a constant bit while running) and has had power decline over the last 2 years. The tractor came with the house we bought 10 years ago, and I like its rugged frame and bulldog performance. I have a a pdf of the Gravely owner's manual and the Kohler engine owner's manual (but not a detailed shop manual). I tuned it up the best I could according to the manuals without much improvement. Then had a local repair shop also "tune it up" ---power not restored. Then ran engine until hot and tested compression myself: 95 psi. I cant find in the manual what compression should be.

I have seen some discussions that the K301S engine has a pressure relief valve (not sure how that works) requiring a vacuum leak test instead of a compression test, but 95 psi seems high if such a valve is active.

So is 95 psi compression good, or does it explain the progressive loss of performance? BTW it also has other problems: it needs new rear tires, and does not stay in the low range of gearing (pops out) but I dont use the low range of gears. In the plus department, I had the clutch rebuilt three years ago. So I would like to keep it going but I am worried about having a major rebuild expenses followed by it being a long-term unreliable money pit. I am not a tractor hobby person, but I like it, and would like to keep it going...

Recommended next step?

 

[don45640]

95 psi is considered pretty low on most engines. I would guess it should have between 120 and 150 psi, but could even be a little higher.
Smoking is probably indicating stuck or bad rings.Hmmmmmm....just a single-cylinder ....I'd re-ring it after checking the bore and piston for` out of roundness'. Deglaze the bore unless it has that special chrome bore.
Probably just an iron bore. Should be able to get specs on it. Might wanna replace valve springs while you're at it.I would.
Of COURSE, you gotta check the rod and wrist pin for play, and the play in the crankshaft and end thrust play of the crankshaft.don-ohio ^)

 

[Don87]

Read this thread: http://www.tractorbynet.com/forums/general-lawn-garden/14805-rebuilding-kohler.html

 

[ThomasH]

Compression is typically in the 120 PSI or so for an engine of that size. What I have read is that 95 or below PSI it's rebuild or replace time. If it were me, I would have the engine checked out to see if the bore can be honed, or whether it has to be bored or not. If it needs to be bored, then you have to determine if it can be replaced for about the same, and if so I would replace it. There are lots of worn parts on an engine of that age.

Good luck!

 

[don45640]

Yes,that is good info.,Don! I don't think I'd go for the 14HP deal,unless it could be done with a minimum of adjustments.Depends on how much he wants to spend,I guess. don-ohio ^)

 

[sbvandepol]

Thank you to everyone who replied to my posted questions! I appreciate the time you have taken to help out a stranger with an old tractor. The Kohler rebuild thread that Don supplied is a rich source of information and I am working my way through it. The thing I like about my Gravely is that the motor is right over the back wheels so it has a low center of gravity, has great traction, and it is built like a tank, so I can mow a steep slope into the woods behind my house with the deck up to about 6-8" and the Gravely just chews all the sticks and knee-high weeds and debris up. Its great, even though the brakes totally suck.
I found the Kohler engine manual online. I do not know if the engine on this tractor has ever been refreshed or rebuilt, but if I were to pull the cylinder head and measure the cylinder, what measurements would I expect for:

a "refreshable" engine that could be reamed, honed and get a new set of rings and valves
a "needs to get rebored cylinder"
a "already has been rebored" cylinder (I presume measured at the top above the ridge?)

If an engine has already been rebored once and the cylinder ridge is out of range, it that THE END or are there oversized cylinders beyond the first series of oversized?

Online K301 remanufactured are about $800-1000, but I worry that there will be some small but aggravating incompatibility in how it mounts to the frame or mates with the transmission, etc. Is that a reasonable worry?

Once again, thank all of you for your thoughts, experience.

 

[Don87]

Thank you to everyone who replied to my posted questions! I appreciate the time you have taken to help out a stranger with an old tractor. The Kohler rebuild thread that Don supplied is a rich source of information and I am working my way through it. The thing I like about my Gravely is that the motor is right over the back wheels so it has a low center of gravity, has great traction, and it is built like a tank, so I can mow a steep slope into the woods behind my house with the deck up to about 6-8" and the Gravely just chews all the sticks and knee-high weeds and debris up. Its great, even though the brakes totally suck.
I found the Kohler engine manual online. I do not know if the engine on this tractor has ever been refreshed or rebuilt, but if I were to pull the cylinder head and measure the cylinder, what measurements would I expect for:

a "refreshable" engine that could be reamed, honed and get a new set of rings and valves
a "needs to get rebored cylinder"
a "already has been rebored" cylinder (I presume measured at the top above the ridge?)

If an engine has already been rebored once and the cylinder ridge is out of range, it that THE END or are there oversized cylinders beyond the first series of oversized?

Online K301 remanufactured are about $800-1000, but I worry that there will be some small but aggravating incompatibility in how it mounts to the frame or mates with the transmission, etc. Is that a reasonable worry?

Once again, thank all of you for your thoughts, experience.

All the information you just asked for is in the thread that I linked to. Except you can't measure 'above' the ridge, because the ridge is at the very top of the cylinder.

EDIt: Yes, there should be rebuild kits available for .10, .20 and .30 over(that's the piston and ring size).

 

[Don87]

I'm hoping you ordered the 'repair' manual and not just operators manual.

 

[sbvandepol]

I downloaded the service manual from Kohler web site:

http://www.kohlerengines.com/onlinecatalog/pdf/tp_2379.pdf

 

[Don87]

I downloaded the service manual from Kohler web site:

http://www.kohlerengines.com/onlinecatalog/pdf/tp_2379.pdf

That's great, it should have all the info to rebuild the engine yourself, if you decide to do so.

As you could see by the thread I linked to, It's actually easy to do. Now you need to decide if the machine is worth putting 120 dollars into.

If you need parts, the 'Jacks Small Enigines' is a good link, and a lot of TBN members order from there.