039 scored piston on intake

[Jza]

Bit if background on the saw ...

Got it off a work mate . was a p.o.s saw needed and overhaul anyway , so I told him I'll swap it for this little 50cc chinese saw I had .

So I go about my day . Fuel it up 50:1 with stihl synthetic oil ( the red one ) .. done about 5 tanks of fuel and it starts to bog ..

I'm no expert so went to YouTube and watched a video on tuning

This is where it gets interesting. I counted the turns (clockwise ) to set them again. I got 1 turn out of low jet and when I went to seat the high I got none ... which made me really concerned...


Anyway from what I gathered from YouTube and the internet was roughly u want about 1 turn anti clockwise from being seated then go from there .

Did that , things where going good then it seized...

So my question is did it seize from being way to lean on the hi jet for 5 tanks of fuel or did I damaged it when I adjusted the carb ?

 

[Mad Professor]

The damage on the intake is from something hard getting loose inside. Either came in intake or bearing parts.

Lean seize will be on ex side, worse towards clutch as it gets hotter there first.

The saw was well worn/lots of use.

4 posts? Welcome to AS!

 

[J D]

I agree... Was just typing words to the same effect

 

[Jza]

Thanks for the reply , it makes sense . In a way I'm relieved it wasn't from me adjusting the carb but something coming in ...

I've ordered a aftermarket piston assembly . So hopefully get abit more life out of it

 

[Mad Professor]

Thanks for the reply , it makes sense . In a way I'm relieved it wasn't from me adjusting the carb but something coming in ...

I've ordered a aftermarket piston assembly . So hopefully get abit more life out of it

Is the cylinder OK on intake side where the piston gouges are?

Look over all the bearings real well.

 

[J D]

As above, & I'd also flush the crank case out really well... catch & inspect whatever you get out of it.
Whatever did all that damage has gone somewhere & if it did all that damage going in it would likely have left some evidence on the other side when exiting

 

[Mad Professor]

As above, & I'd also flush the crank case out really well... catch & inspect whatever you get out of it.
Whatever did all that damage has gone somewhere & if it did all that damage going in it would likely have left some evidence on the other side when exiting

+1

Is there any pocks on the piston crown/cyl squish area? And check muffler too for debris. The spark screen should keep things inside.

 

[J D]

Are the ring locating pins present? It's hard to tell from the pics

There also looks to be damage from something in the transfers so check the cylinder for damage there too

 

[Jza]

Is the cylinder OK on intake side where the piston gouges are?

Look over all the bearings real well.

The cylinder got gouged pretty bad too .

Once the a.m parts arrive I'll pull it all apart and have a good look .

At first when u said it's been hit i thought maybe a wrist pin so I had a look but there still there..

I pulled the muffler off and it's wrecked.. I shake it and it rattles inside but I assumes that's the baffle?

Yes both pins are there but seized . I will try keep this updated with pictures once I've got it all apart

 

[angelo c]

When scored on intake side I look real close for intake leaks through air filter as well as all of the above comments.

 

[Jasonrkba]

Its a clamshell so replace the seals and bearings. You will be there anyway. It's an older saw so I would replace all the rubber parts. Use an OEM air filter.

 

[keithto]

couldn't the damage on the intake side be from running to hot. like the carb was to lean?

 

[Jza]

Its a clamshell so replace the seals and bearings. You will be there anyway. It's an older saw so I would replace all the rubber parts. Use an OEM air filter.

Cheers . Will I get away with replacing rubber parts with after market ? Or should I get oem

 

[Woodslasher]

couldn't the damage on the intake side be from running to hot. like the carb was to lean?

Muffler side should get hotter quicker, so it should score first if the saw's lean.

 

[Jasonrkba]

Cheers . Will I get away with replacing rubber parts with after market ? Or should I get oem

If fuel touches it get OEM.

 

[Mad Professor]

couldn't the damage on the intake side be from running to hot. like the carb was to lean?

Intake damage is from something solid and hard, that it ingested or came apart.

 

[a. palmer jr.]

If you're going to buy a new fuel line get an OEM one. The aftermarkets don't do too well with this part, the sharp bend is prone to kinking.

 

[Brushswamper523]

I am very interested in what happened. What ever did it it did a number on it. I would love to know if you find anything in the exhaust.

 

[keithto]

Intake damage is from something solid and hard, that it ingested or came apart.

I had been told in the past that intake side scoring was because of to much air like with a bad seal of an small intake leak. But maybe that is if the exhaust side AND the intake side are BOTH damaged and not just the exhaust side.
On the op's pictures the intake side looks severe but I can not tell if the exhaust side is scored at all.

but why would debris only damage the intake side? If it was one particle I could see it making a groove and then blowing out the exhaust but that is a lot of scoring in the op's picture. So I would think a lot of debris but then why not the exhaust side? very curious to learn.

 

[cookies]

exhaust side only scoring is caused by a air leak or adjusted too lean, both intake and exhaust scoring is caused by straight gassing, intake side only damage is caused by foreign objects being sucked in. As others have said get oem rubber parts that contact fuel, too often aftermarket parts come defective or fail quickly and on that model its not worth having to diagnose and do it twice. It should take common sizes bearings you can source from ntn/koyo/fag etc. Their most commonly sold (cheapest version) with metalized rubber side shields you can easily remove with a pick and then use. I would use a water hose and bucket to flush out that muffler and find the source of the rattle, its likely the cause of your engine damage.