Help! Did I just kill my saw?

[Riles32807]

I have a little Poulan Pro 42cc. I cut down a small dead tree yesterday and it was idling very fast and I couldn't give it full gas without it stalling. So tonight I watched a couple of YouTube videos on tuning the carb and thought I had a pretty good idea of what to do. But no matter what I did it would idle high. So I cranked everything down until it stalled then figured I'd open them up little by little until the saw would start. But a half a dozen pulls in, it froze, and I can't pull it at all.

I pulled out the sparkplug and it looks like there's scoring on the cylinder. I pulled off the muffler and it looks like matching scoring on the piston.

Did I lean it out too far and kill it?

 

[Deleted member 117362]

I have a little Poulan Pro 42cc. I cut down a small dead tree yesterday and it was idling very fast and I couldn't give it full gas without it stalling. So tonight I watched a couple of YouTube videos on tuning the carb and thought I had a pretty good idea of what to do. But no matter what I did it would idle high. So I cranked everything down until it stalled then figured I'd open them up little by little until the saw would start. But a half a dozen pulls in, it froze, and I can't pull it at all.

I pulled out the sparkplug and it looks like there's scoring on the cylinder. I pulled off the muffler and it looks like matching scoring on the piston.

Did I lean it out too far and kill it?

View attachment 607446

Stop. Do not try to run it. You have a ring scored into piston. Maybe able to pull and clean up cylinder, add a new ring and piston. If you can remove ring, clean up piston might be able to save it with new ring. Your compression is gone.

 

[Riles32807]

That's what I was afraid of. ..

I stopped as soon as it wouldn't pull. Im done messing with it for tonight. Any tips on how to get it out without doing more damage?

 

[Deleted member 117362]

Unbolt cylinder and try to pull it off. Have seen worse come off. Best part of it. You get to learn how to remove aluminum transfer and rebuilt a saw.

 

[cus_deluxe]

Scoring looks pretty light, should be salvageable with a little bit of time and effort. Should be able to find all the info you need on here, try searching the chainsaw forum.

 

[Streblerm]

I would bet the fast idling was caused by a vacuum leak and that is what caused the scoring.

 

[Riles32807]

I would bet the fast idling was caused by a vacuum leak and that is what caused the scoring.

Thanks, I'll keep an eye out while I'm taking the saw apart & plan on rebuilding the carb.

 

[ironman_gq]

I'm guessing your issue is an air leak, could be intake boot, impulse passage or crank seals.

 

[Jackbnimble]

I'm just curious. I know nothing about engines in general, (except I have this knack for destroying them with great ease) and less about chainsaw engines. Why would a leak in a vacuum line, intake boot, impulse passage or a crank seal cause scoring?

 

[cus_deluxe]

An air leak (crank seal/pulse line/intake boot...) can cause a lean running condition, as it can introduce air that has not passed through the carb, and so has no fuel (more importantly no oil).

 

[Riles32807]

With a little elbow grease and a lot of swearing, the saws apart. The ring doesn't look too bad, same scoring as the piston. I'm going to order a new ring at least. Here's the piston, & the cylinder. What do you guys think? Is it save-able?

I haven't taken the carb fully apart yet, but the gaskets, & intake boot look good. Looks like there were a couple of air bubbles in the RTV between the cylinder and the bottom plate. The bottom plate was clean no RTV stuck to it, in fact there's ano oil sheen in the bottom plate gasket groove, making me think it came loose.

 

[Jackbnimble]

Scoring is damaging because it leaves streaks of removed metal from the piston which breaks the "seal" in a sense which causes a loss of compression? Is that the idea?

 

[Riles32807]

Someone is welcome to correct me if I'm wrong, but yes, scoring breaks the "seal" and reduces compression. Scoring on the piston itself is bad, but the piston ring or rings should be able to cover that. Scoring on the cylinder is worse because the piston ring won't be able to fill that gap. Also the material removed by the scoring can then become debris that can cause more damage.

 

[Jackbnimble]

Thanks. Never knew why scoring was bad before. If I can learn to shut my trap and listen, I may just keep learning important stuff around here.

 

[Marshy]

The largest problem you have is you don't know why it happened. Just putting a new piston/ring or cylinder on the saw is fixing the symptom, not the cause. You need to be diligent after you put it back together to determine cause or it will ruin your new parts.

Start simple and check you had mixed gas in the tank and not straight gas. Dump some in a clear bottle or glass and check color.

Check all the rubber hoses for rubs, cracks or holes. Any air in-leakage can cause a lean condition.

Only way to test the crank seals is to block the exhaust and intake ports and pressurize the case through the impulse line. Once pressurized use soapy water on the crank seals and look for leaks.

 

[stihl sawing]

With all that scoring , you'll probably spend more getting it fixed than a new one cost. If you're just wanting to mess with it that would be fine, but seriously I wouldn't put a lot of money into it.

 

[Riles32807]

Yup, if I was going to replace the cylinder & piston it would cost about $80. I paid $75 for it used. I've gotten my money out of it. Mostly I want to play with it and learn more about 2 cycle engines.

I took a fine file to the piston, and ring, just light enough to remove any burs. And did the same to the cylinder with a high grit dremel bit (by hand). It moves easily now. I'll get a new ring before I put it back together.

Next step is to clean the engine 2 or 3 times to make sure I didn't leave any debris. Then I'll go through the rest of the saw cleaning and looking for anywhere it could be leaking. Clean the carb and replace the gaskets and diaphragm.