My Tractor Forum banner

Kohler engine ring gap problem

23K views 33 replies 11 participants last post by  RED-85-Z51 
#1 ·
Hi.

I have a 16hp k341 Kohler I am rebuilding. It was freshly bored .020 over. I have a new .020 piston and rings, these are PrimeLine aftermarket parts. I have had them for quite a while (couple years) and am not sure I could send anything back. I checked the ring end gap on the top compression rings and found that the very top ring has 25 thousandths gap. The kohler manual states that it should be no more than 20 for a new ring, but that 30 is acceptable for a used ring. The lower compression ring is just fine at about 15 thousandths. Do I need to get a different ring or can I still use this.

Thank You.


-Chris
 
#2 ·
It'll work, but . . . .
Was the cylinder bored for the piston you have?
If so, I would worry that the cylinder clearance is too large.
The rings came with the piston, both specified for .020" overbore.
If the piston/ring manufacturer is working to the Kohler specification of .015" for ring end-gap, then the cylinder bore diameter must be larger than desired. It is more common to have to file the ends of a ring to attain minimum gap than to have to worry about being too close to maximum.
 
#3 ·
I'm inclined to agree with Steevo. Think I'd take that block somewhere besides where it was bored and have the bore checked. Could be they cut it out oversize. Probably not but I'd sure check it.

Take the piston with you and see if the bore is proper for the piston, remote chance you have a ring that is just a tad loose.

Mike
 
#5 ·
With heat and expansion....005" is a big deal.
On the race engines I used to build (BB chevies), we always ran .012" file fit.
Too tight, you'll score the cylinder from expansion, too big, you psh oil, and lose comp.
There's a reason for factory recommended gaps.
 
#9 ·
I tend to think it has to be my rings, not the block. Reason being is that the rings were placed at approximately the same location in the cylinder when each was measured, and still there was one that was perfectly fine and the other was .005 out of new spec, but its still in spec for a used ring so I guess it will have to work. I'd buy the OEM piston and rings but they'd cost a minimum of $130, and I paid $60 for the prime line so I'd just be out too much money. The cylinder was bored to Kohler .020 specs, not to the aftermarket piston size nor was it just bored .020 beyond what it was previously. The piston and rings were designed to fit the .020 Kohler spec.
 
#10 · (Edited)
The newer Kohler engines have .025 ring end gap.
Having the top ring end gap a little wide, is better to than too narrow. With too tight of a gap on the top ring especially, since it receives more heat than the other rings, it will expand, butt up and break, then you'll have real problems.
If you want it dead nuts, buy another .020 over ring set. If it were me, I'd put it together with what you have, being the second ring is at the correct gap, the compression lose would be minuscule.
 
#12 ·
AC
Are the top and second ring the same thickness and style?

The reason I ask, after reading this, if you swapped the rings they would go along with this quote from Speed- Pro.

" Recent testing has proven that a
larger second gap increases the top ring's ability to seal combustion. This larger "escape" path prevents inter-ring
pressure from building up and lifting the top ring off the piston allowing combustion to get by. Many engine builders
have reported lower blow-by and horsepower gains at the upper RPM ranges with wider second ring gaps. Also,
almost every new car made is using this inter-ring pressure reduction method to lower blow-by and emissions and to
increase engine output".
 
#14 ·
You have hit the nail on the head yourself. Anytime an overbore is needed, the machine shop should require you to supply the piston that is going into the engine, not just to bore to a "spec.". Since this has already happened, as long as the top two rings are the same (as they may be) use the second ring as your top ring (properly gaped) as this will affect your compression directly, then use to "larger gaped" ring in the second position, which isn't as critical.

Good luck with your rebuild
Roosamaster:goodl:
 
#15 ·
I quit using a custom machine shop years ago because, even after repeated complaints, they were boring the cylinder too large. They do this to CYA, ensure rings don't seize.

Now there has been a bunch of posts here about end gaps, saying .025" end gap is OK. I disagree. B&S engines of similar bore size specify .008" min. end gap. I have used this for years, hand fitting, and absolutely no problems. I don't think there is that much difference between a Kohler and a B&S, actually I have been doing that also on the few Kohlers I have done. Heck, .025" is pretty nearly worn out with .035" being replace. By the time .025" end gap rings are seated, the end gap will be .030" or close to it.

I now oversize cylinder bores myself to suit and use .010" oversize rings when installing new rings in a bore that does not need oversizing, hand fintting to as near .008" end gap min. as I can.

Walt Conner
 
#17 ·
How do you bore to match a piston if you don't know which overbore the block will clean up at? Should a person have it bored till clean, then order the piston and have it finished bored when the piston is in hand? I should also note that the top two rings are each made of a differnt material or process, one is black and one is silver. The top 2 ring grooves on the piston check out at identical sizes.
 
#18 ·
"Do you use .008" on every size engine, you rebuild?"

As it happens, I specialize in 12 - 20 hp B&S engines. The bore of these engines are the same except 31 series which is just a little larger. The old 10 & 11 hp B&Ss also used this size bore. The spec. I gave are for roughly 3.5" bore. The Kohler mentioned above also fits in this category with 3.43" std bore. Note that I say .008" is the min., I generally am just over that.

"How do you bore to match a piston if you don't know which overbore the block will clean up at? "

Right, +.020" will catch most, I hate going +.030" but occasionally do, +.010" rarely does it.

"note that the top two rings are each made of a different material or process, one is black and one is silver."

The "silver" one is chrome plated top ring, same material underneath.

Walt Conner
 
#20 · (Edited)
"

I made the mistake of not going back to check the engine and was thinking it was a CV12.5s which I guess was in another thread somewhere. .025" is still way too much end gap, I would probably shoot for .010". I would point out here that I test block run my engines for a min. of 1 hour then tell people to not load them heavily for at least 10 hours running time, drain the oil while hot and refill then.

"I'd buy the OEM piston and rings but they'd cost a minimum of $130, and I paid $60 for the prime line so I'd just be out too much money."

"I tend to think it has to be my rings, not the block."

My guess also, probably Chinese made.

Walt Conner
 
#21 ·
Walt:

Maybe should do this PM but think it's sort of "on topic".

The local small engine guy in our small town is a bit of a character. I don't want to imply that he's hard headed or set in his ways but if you want something he doesn't agree with you can take it elsewhere.

He's rebuilt a number of small engines for us over the years and follows pretty much what you do. One step he takes that I have never seen done elsewhere is when the long block is done, and prior to putting the head on, he will put the engine on his test stand and run it at about seven or eight hundred RPM by driving it with an electric motor. He has of course filled it with oil and all that.

What's your opinion? What he does seems to work as we have had good luck with his rebuilds. Way better I must confess than the ones we have done in our own shop. Course we only do the ones we don't have to bore.

Mike
 
#22 ·
He does that to break in the crank and cam bearings with out putting the compression strain on them.
The rings will only seat when once the block/head have been brought up to full operating temp, and run under load, then at freewheeling high rpm for awhile.
That's areal good idea...using the electric motor. But, it must be pretty big.....like a 3 hp,220v ,motor.
 
#23 ·
Walt
Granted someone goofed when they put the top ring in that set and it's a bit wide, but .010" is too tight for a 3.77" bore size, that Ac's block should be.

The rule that most engine builders and Ring manufacturers use is

Ring end gap = Bore X .004, So the spec. of .015" is right on the money.

From SPEED-PRO PISTON RINGS

Comparative tests using a 350 cubic inch small block Chevrolet engine, reveal definite improvements in blowby
control and horsepower as top ring end gaps were decreased. Blowby was reduced by approximately 50 percent, and
horsepower increases ranged from 5 to 13 percent. The baseline test was run with top ring gaps set at .024". In the second test, top ring gaps were reduced to .016". An additional test was made with the top ring gaps set to 010”. In this final test, the results again showed a reduction in blowby; but a noticeable loss of horsepower was observed at
higher speeds. Examination of the rings indicated that the top rings were butting. Running with ring gaps butted will
result in scuffing of cylinder walls and/or flaking of moly from the ring face.
A 350ci Chevy has a 4" bore.

eastonct

If it takes a 3hp 220v motor to spin a small engine long block at 700rpm, that engine is junk. Electric motors run at 2200rpm. So a 3-1 reduction would bring it down to 700rpm or so. A small electric motor would work and it's a good idea.
All of Henry Ford's complete Flat head engines were spun up by a big electric motor before they were installed in a car or truck. The operator would spin the engine up and if it pulled too many amps on the electric motor, something was wrong and the engine was sent back to the engine shop to be torn down. If it passed the test, the engine was stamped with its serial number and sent on down the line.
 
#24 ·
I have very little exprience with how much hp an electric motor needs to run something. My thought of "He must be using" was based on acouple of motors I've hooked up to various things....those things usually old and rusty.
So, with actually thinking about it...you're right. It probably takes very little to spin a small engine with no head.
 
#25 ·
The electric motor in question was something around a half horse just judging from the size. Since electric motors come in a range of RPMs it's hard to say what the speed of the motor was for sure, just kind of a guess watching it spin. The electric motor looked to be similar to what we use on various augers, fans and the like and they are usually the normal 1750 RPM with a few being the 3400 RPM type.

Didn't know the rings would not seat while running a motor that way. It's interesting Ford did that with the flatheads, never had heard that before and I used to use those for drag racing. Kind of dates me a bit.

Mike
 
#26 ·
Mike
Your right, most electric motors run at 1750rpms. I don't know where the 2200 came from.

I've got a 34 Ford BB Truck that had the original V-8 in it. My brother-in-law is a car history nut. He gave me the article on the Ford Flat Head engines, with even a picture of a V-8 on that test stand. When they put the engine in the frame, the frame was then stamped with the same number as the engine, both the numbers on my truck matched.

The rings would ware in some with the ring tension alone, but near as much as with the pressure of combustion.
 
#27 ·
Yeah, the old saying of "Driving it like an old lady while you break it in", is 100% wrong.
The first 1/2 hour at idle just lets the cam an crank/rod bearings find their place. For the rings to seat, they need to see a variety of rpm's and load like it'll see when abused.
I used to pull my 427 on a friday night, tear it down, run a ball hone through it, put it back together with a rering kit, have it running that night, then take it out for a couple hours and beat the crap out of it.
The next morning we'd be at West Hampton Dragway.
It ran 9.80's @142mph without a problem....except the time before the rev limiter, when I was driving it with street tires....and bent a few exhaust valves.
Seems 8,500r is fine with slicks....but the valve springs don't appreciate it when the tires can break loose at will. :duh:
 
#28 ·
"prior to putting the head on, he will put the engine on his test stand and run it at about seven or eight hundred RPM by driving it with an electric motor. He has of course filled it with oil and all that."

"What's your opinion? "

I have no opinion other than I guess it wouldn't hurt but I am not going to do it.

"but .010" is too tight for a 3.77" bore size, that Ac's block should be."

I disagree but am not going to argue the subject. I would note that I have been working on small engines for over 65 years, as I said before, part of that time I specialized on just rebuilding engines. I don't think V8 Chevy or any other auto engine has much bearing on what we are doing.

If you will put "Kohler Ring End Gap" in your browser, it brings up a technical sheet that says End Gap for Kohler K341 is .010" - .020".

Walt Conner
 
#29 ·
I always file fit to .012" for a V8. If kohler recommends .015"....then that's what it should be.
We're not arguing, just debating personal preference.

I've always believed there is a reason for factory specs....and I adhere to them, unless I find out something alittle out of the ordinary works better...but I don't offer advice that's not proven fact to me.

I'd stick with factory in this instance...even if he needs to buy new rings.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top