Rebuilding Kohler

[justractors]

I did not mean to ruffle anyone's feathers but like most things in life there is a right way and a wrong way and it is better to learn the right way from a young age than to go through life figuring that you know everything.
I know many folks in the small engine repair business who also are told by their customers that they overcharge for rebuilding an engine because the owner figures all you have to do is throw some new parts into it and you have a rebuilt engine. It ain't so.

Bill

 

[qwerty15]

I guess it is better i learn now. should i see how it runs before i take it apart or just start over? I read everything in the service manual twice and checked to be sure i was doing it right. Maybe i should have researched this a little more before i started it.

 

[kubmech]

Depends on why you were rebuilding. Was it smoking? Low on power? Sometimes rebuilding is pretty close to the price of a new short block. By the time you pay for the machine work and parts. Like Bill said as a minimum, considering the condition of the engine, did you you hone the cylinder? How do the valves and seats look as well as the guides. What was the condition of the crankshaft journal? Is the throttle shaft on the carberator worn (if it is this will allow fine dirt particles to get in the engine and cause premature wear of the intake valve as well as the cylinder and rings). Most of the cast iron kohlers I have rebuilt had to be bored oversize, valve seats and faces cut, valve guides replaced, and crank turned to undersize. There is the possibility it just needed to be refreshed which would consist of a light honing with new rings, cleaning the valves and lapping, removing carbon from the head, a new set of rod bearings and a carb rebuild. If that is the case you would be fine. But you really need to check the bore size, crank journal, valve seats and guides to make that decision. If they are all in spec. then a refresh will give you good results. As a side note, kohler now has walbro carberators to replace the original carb which is a big improvement to the way the engine runs compared to the original carb.

 

[s1120]

<font color=red>Is the throttle shaft on the carberator worn </font color=red>

Is there a fix for this? One of mine is REALY sloppy. Also I have the Walbro carb on mine now. Is the new one a better desine?

 

[qwerty15]

I was rebuilding because it was burning oil. And its been running since 67. I didnt hone the cylinder. The seat on the exhaust valve had carbon on it and didnt look like it was closing so i cleaned it up. the new valve appears to close properly. The intake side was fine. I just replace the valve. Whats a crank journal? Throttle shaft isnt worn. Would you know the price on the Walbro replacement carb? Thank you for trying to help me out.

 

[kubmech]

Usualy what causes the throttle shaft to wear is running a dirty air filter. The engine trys to pull in air through the filter. Because the filter is restricted it ends up entering around the throttle shaft and pulls dirt along with it causing the premature wear. Yes the walbro is a better design. The original carbs had a problem with the float bouncing which they tried to correct with a spring that helped stabilize it. Even with that "mod" the carb was always difficult to get just right. I have found that with the new carb they run alot better and are easier to adjust. The fix for that is generally a new carb. I have had luck with rebushing some of the older briggs carbs but never really looked into it on the walbros.

 

[kubmech]

You really should do the measurements in the book. That engine most likely has a ton of hours on it. Measure the bore and check the valve guides. The crank journal is the part where the connecting rod bolts to, that too should be checked to ensure proper clearance. The manual should describe these operations. Your local auto parts store may have the tools you need to do the measurements for rent. I can generally "eyeball" the valve guides and be able to tell how worn they are/remove the valve spring and pull the valve up off the seat, wiggle it around in the guide, there should be very little play. Check the valve stem as well. Does the valve you did'nt replace have a groove on the face (where it seats)? The valve seats should also be re-cut and the valves lapped in to them. Again your manual should describe this operation as well. An alternate way to check the cylinder bore is to remove the piston and rod, remove one of the new rings and place in the top of the cylinder, use the piston upside down to push the ring in squarely (by the way do you have much of a ridge at the top of the cylinder?) check the ring gap, if it's in spec then the cylinder is not terribly worn, push it down to middle and ceck the gap again this will give you an idea of the taper if the gap opens up more as you go down the cylinder. If your not confident with doing the measurements yourself, your local machine shop can help you out. But, by all means if you decide to give it a shot without doing the measurements, you have to hone the cylinder in order for the rings to seat properly. Two of the most common reasons for using oil is worn rings and worn valve guides. I'm not sure what the new carb runs, take the numbers off of the mounting flange of the carb and your parts dealer should be able to cross reference to the walbro number.

 

[qwerty15]

I did replace both valves. I didnt notice a ridge near the top of the cylinder. I take it apart tomorrow to check these things.

 

[qwerty15]

In the manual it talks about using a hand held drill with a honing tool. If the cylinder is tapered or oval shaped just a little bit could i hone it or send it to the machine shop?

 

[StoneHeartFarm]

If it's out of round you probably should think about a machine shop. Honing is basically just to break the glaze on the inside of the cylinder. When the piston is hot and is pushing the rings back and forth over the cylinder wall, it causes the wall to "glaze", (get real smooth.) Honing with one of several tools will leave very fine scratches over the cylinder wall, thereby breaking the glaze.

There are a couple of tools that I've seen used. One is a plain old cylinder hone with 3 stones on springs that rub aginast the cylinder wall. The other tool that I've seen pictures of but never owned looks like a giant bottle brush with a little ball at the end of every bristle. The balls rub against the cylinder wall and break the glaze. I'm told this type is somewhat easier to use than the other.

You also need to look hard at the cylinder wall for scoring. These are deep scratches on the cylinder wall, and honing will not remove them. I've had engines with a ridge around the top and some without out. There is a tool for removing the risge called a Ridge Reamer.

SHF

 

[qwerty15]

SHF
So your saying if its out of round take it to the machine shop but if its tapered i could do it myself? When the engine was apart i didnt see any scoring. the walls were every smooth and shiny. Ill look over it again. I will let you know what i find later.
FRank

 

[qwerty15]

Kubmech
I took the new ring and put it in the cylinder. the gap at the top was .03, Middle .035, and bottom was .023. I thought the bottom was supposed to wear more than the top. I guess that was why the crank was easier to turn in the middle of the stroke. There was a very little ridge at the top of the cylinder. No scoring was on the walls. The ring sealed the cylinder perfectly so i dont think its oval shaped. The manual says the maximum taper is .002 and the maximum wear limit is to 3.378 from 3.3755. Could i have measured to far down in the cylinder since the stroke is only 3.25? Should i have measured above the ridge or right below it?

 

[StoneHeartFarm]

I would say if it is tapered or out of round, you should consider a machine shop. Remember, the machine shop will bore the cylinder out, which will require a larger piston and/or rings. The cylinder walls were shiny? That's the glaze we've talked about. The reason for honing is to break that glaze up so that the new rings can grab onto the cylinder walls and seat themselves (shape to fit).

If the only reason that the engine is being rebuilt is oil control, then you need to work hard on the areas where oil can be lost/used. These would be the rings, gaskets, seals, and valve guides. If you decide to take the cylinder for boring, consider having the machine shop grind your new valves and seats. It probably won't cost that much and you'll know the job is professionally done. Also, don't be afraid to shop around for the machine work, and talk to people to find out how the shop works. I've got several within 30 minutes of me and there is only 1 that I wouldn't hesitate to recommend. The others all have varying levels of "issues".

SHF

 

[kubmech]

The ridge at the top will be about 1/4 to 3/8 of an inch down. Measure just below it. The cylinder at the bottom should show no signs of wear due to the piston not riding all the way down the cylinder. You should be able to see where it stops due to the wear pattern. If you have a very slight, to no ridge at the top, from what you just said it sounds like you may be able to get away with just breaking the glaze. Use a ball hone and clean up the cylinder walls. Use automatic transmission fluid, low rpm on the drill with quick up and down srokes till you have a good cross hatch pattern in the cylinder. Don't spend too much time with the hone, just enough to eliminate all the shiny spots. The reason you have less tension at the bottom or top is that is the point where the rod rocks back and forth on the crank. You will have steady tension with the piston installed due to the friction of the rings against the cylinder wall. With the rod and piston removed, the crank should turn freely all the way around. If the crank is free you should be in good shape. The book probably mentions using plastigauge for checking the connecting rod to crank journal clearance. Do that as well. After honing, clean the cylinder real well with soap and water (tide works good). Get it so if you wipe the cylinder wall with a white towel you don't get any dirt on the towel. If the valve guides are not too bad, go ahead and put it all back together and see how it goes. Run it half throttle for about ten minutes, check for leaks as it runs and don't worry about the smoke at initial start up. Use engine oil to pre-lube all the parts and wipe a thin coat of ATF on the piston and cylinder prior to assembly. If the valve seats look O.K., lap the valves in. Make sure you clean off all the lapping compound. Keep in mind the best option is to bore oversize, cut the crank and replace the rod with an undersize, replace the guides and have the valve seats recut. Don't get me wrong, I have had good results just "refreshing" an engine, which seems to be the direction you want to take.

 

[qwerty15]

Re: Refreshing Kohler

Kubmech
The crank is free when the piston and connecting rod are not attached. Is this honing tool expensive and can i get one at an auto parts store? Whats ATF? How long will the smoke last when its started up?

 

[qwerty15]

Re: Refreshing Kohler

SHF
Is it necessary to break the glaze because the rings are really grabbing the walls now? I had a very difficult time turning the crank with the piston installed. I dont think the starter/generator would be able turn the engine over. Is this normal when refreshing an engine?
Frank

 

[s1120]

Re: Refreshing Kohler

The hone is not that pricy. Last one I got was about $35.00. Also a new motor will be a little tight, but the starter should turn it. Try pulling the pisten and see if the crank turns.

 

[qwerty15]

Re: Refreshing Kohler

The crank does turn without the piston.

 

[s1120]

Re: Refreshing Kohler

Good, next, after you give a little hone, check ALL the rings in the bore. I have seen some made to big.

 

[qwerty15]

Re: Refreshing Kohler

Note: if new rings are installed, you should deglaze the cylinder wall with fine emery cloth in a cross-hatch pattern (diagonal strokes). This is needed break in the new rings. Then very thoroughly clean the cylinder to remove all traces of abrasive residue.

Found this on a web site. Would the emery cloth work to deglaze or just buy a hone for 30$?