Thread: Honing cyl on Stihl 026 PRO for new piston/rings?

I have a Stihl 026 PRO that I bought used with stuck rings and gaulded piston from apparent lean high-side setting. The saw is really clean, appears to have seen little use but now needs new piston/rings. I need advice. The cylinder has minimal, if any, aluminum deposits from the trashed piston. It had one very tiny "bump" of a deposit in the cylinders lower portion in line with the exhaust port and I was able to clean this up with fine sandpaper and a delicate touch. Will this saw respond well to just putting in new piston and rings or does the cylinder need to be honed first? If it does need to be honed, what type hone is best to use (ball hone, stone hone, diamond hone?). Last, if it is your opinion to alwayd replace saws in this state with a NEW cylinder along with piston and rings let me know. The saw isn't worth spending the high $ for a new cylinder but it is worth $78 for new piston and rings. Any advice is appreciated. Thanks.

Do not hone the cylinder or you will ruin it. The NiCaSil is only a few thousandths thick and should never be honed. to remove the deposited aluminum pure muriatic (may not be spelled right) will eat the aluminum and not damage the cylinder. Just do not get it on anything else. You may have worn through the NiCaSil already with the sand paper. Even emery cloth can be too much. Make sure the lean condition was not caused by an air leak or it will happen all over again.

Howdy,

Huskyman gave the good advice there, except myself , I would not use the acid even on a Nicosil cylinder. These things are often porus, and the acid can get in a pore, and cylinder start to go away. If you can not feel any damage with your finger, consider it done, put her together and try it out. It will take a couple runs to seat up and come up to full compression. I just stick them in a log, and let them idle through a tank of gas, jazzing it once in a while if I think about it.

Kind of keep an eye on it for over heating and don't work it long and hard until it has gone through a couple tanks.

Be sure you really wash the inside of that cylinder before use. Abrasive from the sandpaper can get in there and be hard to get out. Be sure your new rings are free in the land, and all debris has been removed from underneith. A broken piece of the old ring makes a good cleanning tool.
Be sure to protect that ring pin while doing this!
I've seen people cut it out of there, and then their new ring will turn in the land, trap an end in a port, and crash the engine!

If you are going to have any real problem, it will be evident right at first as a rule. Tune to good steady idle, right up next to clutch engagement, and make sure it holds idle speed.
Remember that engine scored for a reason. If you have not found the cause, you have to assume that the problem was behind the handlebars, but this might not be true. The idle test will help diagnose.

Regards,
Walt Galer

Walt and Huskyman, thanks for the "heads-up". I had heard such about NiCaSil cylinders but was not sure about honing them. I have rebuilt many engines in my day but most experience has come from domestic autos/trucks where honing is the norm and a must. My only concern with buying the piston/rings for $75 and sticking them in an unhoned cylinder is will the rings seal and do the job? I am not arguing but how do new rings get a "bite" in a used, unhoned cylinder? I can't even measure the cylinder for wear because the internal micrometer set I have won't measure less than 2". I know if the saw was run without the air filter (I don't think it was) the area right under the intake and exhaust ports would be "washed out" badly. I can't stand that I can't measure this cylinder to make sure it's good before throwing $75 at it!!! Anyway, I will put the saw back together correctly so as to eliminate any leaks there might have been. I understand full well how to tune a saw so that it runs a little "fat" on the high side and gives that "4-stroke grunt" every once it a while. This looks like a classic case of no oil in gas or a lean high-side condition. Thanks.

Dont forget to check for an air leak on the seals or the intake boot. Saw motors are not like auto engines. Auto engines have cast iron cylinders that are designed to wear and be honed over and over again. Saw motors have the cylinders exposed in "jugs" with thin walls to transfer heat quickly because they are air cooled. In an auto engine the rings are as hard as or harder than the cylinder, but in a saw the cylinder surface is much, much harder and the rings are designed to give. An undamaged cylinder in a saw will hold its bore for 2-3 re-ring jobs at least. If it is smooth to your finger it is safe.

air filter Or carb setting problem ? If the cyl. is scared on the intake side its the filter. On the exaust side it fuel or as in heat.
Just add a little lube as in w-d 40 or something when instaling the piston & rings.