when are new piston rings enough?

[ohiofarmer 3,157]

I am picking away at the k series on the raider10. Basically the Piston blew through at the ring grooves as it appears the rings may have had too large a gap. I can feel a slight erosion of the bore where the ring gaps All lined up, but not even close to catching a finger nail.

I am hoping just hoping out the bore will get it back to round close enough that a ring job will do .

In any case I can measure the bore and report back. Discipline demands that I do not tear this engine down right now as too many things are taking up my time.

Just hoping the gurus can offer a bit of guidance

 

 

[WHX?? 46,797]

One word farmer .... measure.. your finger nail is not a measuring tool. Sorry to have to break it to you in your time of no time but it sounds like you need to take the motor down and do a rebuild ... 10, 20, 30 over or whatever it takes. I have gotten by on just re-rings for show cruzers  but a worker... go whole hog. 

[ebinmaine 63,157]

6 hours ago, ohiofarmer said:

measure the bore and report back.

That's the thing to do.

 

 

[953 nut 51,721]

8 hours ago, ohiofarmer said:

I can feel a slight erosion of the bore where the ring gaps All lined up

Sounds like a ring job was done ad the rings were not staggered as they should have been. If you can feel it with your finger it is too much! After tear-down, put the old compression ring in the cylinder and square it up with the piston then shine a light form below all around the cylinder. Chances are you will see a beam of light passing the ring where this "slight erosion". If the light can get by the compression can too and a hone won't make it round.

[richmondred01 2,205]

To do it correctly you need a cylinder bore gauge.

If it’s out of round, or out of spec, simply honing the cylinder is a waste of time, money and energy.

The cylinder is checked at several locations.

If it needs to be bored simply installing a new piston and rings isn’t going to solve the problem.

The crank should also be checked. 

Chances are both need to be machined. 

A quality machine shop will do the measurements for you I’m sure. 

[ohiofarmer 3,157]

Yeah,I asked for advice. All I can say for now is that I can barely feel anything with the pad of my finger. A machinist once stated that that could be a very small amount. The story will develop once the crank pin can be measured.   I have a very tired 14 HP that is almost 1/16th inch out of round that still runs, but no way am I running it.. I can actually move the piston with my hand in the cylinder on that engine while the 10 HP appears very tight.

 

     i will measure the cylinder bore when i can with just the head pulled. Two things i have are a friend with a vast machine shop, but I do not want to take advantage of his generosity. Maybe I will since he has the free use of my bobcat 853....  i also bought a spare 10 or 12 horsepower engine that we cannot determine the power without removing the head. 

 

 The good news is that the Raider engine appears rebuildable if ever there was one...I have no experience in this, so I may be asking some questions later. If I am successful, it will mean that i have three 10 HP Kohlers up and running...Back with more soon

[pacer 3,159]

Over the years I have had ..... more than one engine, small & large that I got not knowing the history. I would do a cursory examination - similar to what youve done - and if got a good impression with the obvious checks, I would throw a set of rings at it. Of all I ever tried I got from 'a definite improvement' to a surprisingly good improvement. With the Kohlers I think I did 3 of them that way and was well worth the effort. Maybe some light smoke & light oil burning but running quite well.

 

Your description of the condition of yours, i think I would go that route. I think what Im leading up to is with the amazingly inexpensive piston/rings/gaskets, etc that are available now and the relatively little work to do adding rings ----- why not?