Question about cylinder bore wear

[tntatro 181]

Hello, I have a K241 that I got a while back. The seller said this one smoked and knocked. I finally got around to taking it apart and the specs do not look real bad but the top of the bore has more wear than the rest. At the top about 1/4" down where the top ring would be at top dead center the bore measures .006" over, about 1/2" down where second ring would be it measures .004" over, at the oil ring it's .003" over. Just below where the rings would be at top dead center of bore it's .002" over. At the middle of the bore it's .0015" over at the very bottom there is not much wear. Worn cylinders I've done in the past were worn more in the middle than the top. 

 

Does this cylinder need to be re bored? I know that by the book it does based on the wear limit and out of taper but the wear is different than I've seen from the few other engines that I have done. This engine has a standard bore and the crank pin is standard but a little out of the wear limit. The camshaft and crankshaft end play are in spec so not sure where the knock was coming from. There is no scoring on the crank pin and the valves do not look very worn. I'm guessing someone did the valves and replaced the piston at some point because the piston is just out of spec and well within the wear limits. If the rod looks good with a plasti gauge test then I was hoping to check the rings and put it back together, I'm not sure about the wear on the bore though. 

 

Edit: I had to edit the post. Originally I wrote .015" for the measurement in the middle of the bore which was a typing error. I changed it to .0015". Sorry for the confusion. My concern about the bore is the top 3/4" and how it tapers from .003" to .006" in that short section and if that indicates that it really needs to be re bored. The rest of the bore is within the wear limits. 

Edited November 1, 2020 by tntatro

[squonk 42,524]

Bore it. I haven seen a Kohler yet with any run time that didn't need a rebore. Did you check out of round? 

[Ed Kennell 40,472]

2 hours ago, tntatro said:

 Just below where the rings would be at top dead center of bore it's .002" over. At the middle of the bore it's .015" over at the very bottom there is not much wear. Worn cylinders I've done in the past were worn more in the middle than the top. 

 

I think you answered your own question.         

Your measurements  over spec

.002 at the top

.015  at the middle

.000 at the bottom

[953 nut 57,899]

 

[tntatro 181]

1 hour ago, squonk said:

Bore it. I haven seen a Kohler yet with any run time that didn't need a rebore. Did you check out of round? 

It's not out of round by much.

[tntatro 181]

58 minutes ago, Ed Kennell said:

I think you answered your own question.         

Your measurements  over spec

.002 at the top

.015  at the middle

.000 at the bottom

The wear limit for out of taper is .002", according to the repair manual those numbers are still okay, it's the top that is way out and it seems odd that it is worn out at the top but maybe that is not uncommon.

[squonk 42,524]

With most engines, the maximum wear occurs right below the ridge line with the most amount of material removed in the downward thrust side.

[tntatro 181]

3 minutes ago, squonk said:

With most engines, the maximum wear occurs right below the ridge line with the most amount of material removed in the downward thrust side.

So that is normal wear? I've only done between five to ten K series single cylinder rebuilds and most of them were worn in the middle of the cylinder from front to back.The odd thing about this one is that it gets a tiny bit wider above where the piston ring reaches at the very top 1/4".

[squonk 42,524]

The areas 90degrees from the wrist pin wear the most. These are where the piston thrust surfaces contact the cylinder walks

[lynnmor 7,559]

Yep, your cylinder is wore out.  Make sure that you have a good air filter and change the oil often to prevent this kind of wear.

[tntatro 181]

I just checked my notes and the ones with the most wear in the middle of the bore were only the ones with excessive wear. The rest were kind of random. I wonder if this one was run with a blown head gasket or something that caused the top to wear so much. Then someone cleaned it up and put a new piston in maybe. I guess it needs a .010" piston. I was hoping to get it fixed really cheap because I'm just going to sell this one.

 

 

[tntatro 181]

8 minutes ago, lynnmor said:

Yep, your cylinder is wore out.  Make sure that you have a good air filter and change the oil often to prevent this kind of wear.

Yeah, that makes sense that if it just wasn't well maintained and debris was making it's way in also, then that would cause wear at the top.  I was told it came off a Jacobsen Chief. It's in better shape than what I expected though, the last engine I got off the same guy that he said smoked and knocked was way out of spec on the bore, crank pin and the valves were really worn.

[pacer 3,175]

The last couple I have had with similar readings - actually a bit more - I decided to go ahead and throw a new piston and rings and see what happens. With the very inexpensive import piston, rings, rods, gaskets, etc so available I figured I didnt have much to lose. And these engines are  SO easy to work on..... Anyway , they both turned out very well, no more smoke and ran strong. 

 

Now the crank I do differently, I'll try a new rod with .001 or .002 , but no more -- if every thing else is good, and here again have had good luck with that.

 

I actually am sorta pushed into this because there is no where around me to do small engine work. If I had a convenient shop to do bore and crank, I'd most likely take advantage..........

[tntatro 181]

Thanks for the replies, I guess it's not that big a deal to bore it out. I see a new piston on eBay for $32.

[tntatro 181]

3 minutes ago, pacer said:

The last couple I have had with similar readings - actually a bit more - I decided to go ahead and throw a new piston and rings and see what happens. With the very inexpensive import piston, rings, rods, gaskets, etc so available I figured I didnt have much to lose. And these engines are  SO easy to work on..... Anyway , they both turned out very well, no more smoke and ran strong. 

 

Now the crank I do differently, I'll try a new rod with .001 or .002 , but no more -- if every thing else is good, and here again have had good luck with that.

 

I actually am sorta pushed into this because there is no where around me to do small engine work. If I had a convenient shop to do bore and crank, I'd most likely take advantage..........

Now you are making me want to be cheap and just throw in new rings. I'm lucky to have a very good machine shop nearby that has been in business for a long time. I bought a used Sunnen cylinder hone a while back and it works pretty well for boring cylinders. You just need a heavy duty low rpm drill. I have them do the crank pins and valves and I bore the cylinders and cut the valve seats.

 

On the similar readings you had, were they wide at the top like mine also?

[Ed Kennell 40,472]

2 hours ago, tntatro said:

The wear limit for out of taper is .002", according to the repair manual those numbers are still okay, it's the top that is way out and it seems odd that it is worn out at the top but maybe that is not uncommon.

What am I missing here?     You state it is 0.015"  (fifteen thoushands) of an inch  over spec at the middle.

[tntatro 181]

2 minutes ago, Ed Kennell said:

What am I missing here?     You state it is 0.015"  (fifteen thoushands) of an inch  over spec at the middle.

Oh sorry, that was a mistake. It is .0015" in the middle.

[richmondred01 2,289]

Short answer.

yes. 
Additionally If you are 015 over you will have to go .020 or .030 over. 

Edited November 1, 2020 by richmondred01

[tntatro 181]

1 hour ago, richmondred01 said:

Short answer.

yes. 
Additionally If you are 015 over you will have to go .020 or .030 over. 

I just had to edit the original post because the .015 was an error. The measurement in the middle is .0015". My concern was how the top of the bore from 3/4" down tapers from .003" up .006" in just that top 3/4". The rest of the bore is okay. 

[squonk 42,524]

Tapered wear is pretty normal on any engine.