Is this piston good?

[Stevo Bambino]

I am rebuilding a saw and this piston has some wear on the intake side, bottom of the skirt. The machine marks or grooves or whatever you want to call them are worn off on the bottom 5/32's. That is the only wear. I was always told the machine marks were there to carry oil to lubricate the piston and to replace the piston if it is worn. I ordered a Meteor piston but it fits significantly looser in the cylinder than this original. The original had 160 PSI of compression, so that was not an issue.

 

[lone wolf]

Dont look very bad if it had 160 why replace it?

 

[Mad Professor]

Check them with a micrometer and bore gauge. New is ~0.002-0.0025" at skirt. Pistons will have ~0.005" taper top to bottom.

Feeler gauges can be used for crude measurement (go vs no go). Be careful not to mar piston.

I'd be interested in what the new Meteor measures.

 

[lone wolf]

Check them with a micrometer and bore gauge. New is ~0.002-0.0025" at skirt. Pistons will have ~0.005" taper top to bottom.

Feeler gauges can be used for crude measurement (go vs no go). Be careful not to mar piston.

I'd be interested in what the new Meteor measures.

That piston is good the 160 compression is telling. Most of the machine marks are on it still. Looks like it ingested some dirt get a new air filter if it looks questionable.

 

[mountainlake]

That one looks good but if they are wore too much on the skirt on the down stroke they will blow mix back though the carb instead of up through the transfers causing hard starting and crappy running. Steve

 

[lone wolf]

That one looks good but if they are wore too much on the skirt on the down stroke they will blow mix back though the carb instead of up through the transfers causing hard starting and crappy running. Steve

I wonder how many people got driven crazy troubleshooting that one?

 

[Stevo Bambino]

The cylinder is 1.890 in. I measured it at the bottom twice, 90 degrees apart and as far in as I could twice, 90 degrees apart. Same numbers no matter what and it really looks good.

The oem piston (Mahle) is 1.883 at the top measured in two positions, intake side to exhaust side and side to side. It is 1.888 in the middle. I put it into the cylinder halfway and used the cylinder to stay square. And, it is 1.885 at the bottom.

The meteor piston is 1.882 at the top measured the same way. 1.887 in the middle. 1.887 at the bottom.

The saw did not start well. Mountainlake might be onto something.

Edit: I also noticed the sides of the Meteor piston are different where they interact with the transfer ports.

 

[lone wolf]

The cylinder is 1.890 in. I measured it at the bottom twice, 90 degrees apart and as far in as I could twice, 90 degrees apart. Same numbers no matter what and it really looks good.

The oem piston (Mahle) is 1.883 at the top measured in two positions, intake side to exhaust side and side to side. It is 1.888 in the middle. I put it into the cylinder halfway and used the cylinder to stay square. And, it is 1.885 at the bottom.

The meteor piston is 1.882 at the top measured the same way. 1.887 in the middle. 1.887 at the bottom.

The saw did not start well. Mountainlake might be onto something.

Edit: I also noticed the sides of the Meteor piston are different where they interact with the transfer ports.View attachment 993136

Well if it dont have a new carb on it you cant rule the carb out yet and typically carbs go bad a lot with the crap ethanol gas . Now whats your next step? I think you should pressure test it and take it from there.

 

[Stevo Bambino]

I have it apart already. The rod and wrist pin bearings were shot. I straitened the twisted crank from my 034 and I am going to put that in it. I got new wrist pin bearing and main bearings and gasket set. I need to do some cleaning on it before I start putting it back together. I saw this wear on the piston so I bought this Meteor piston and ring kit and I am not all that happy with it. The carb was definitely going to be getting cleaned, I just have not gotten that far yet.

Could I take that meteor piston and use a die grinder to open up the transfer port windows on it to make it match the oem piston? Or would that not be a good idea. According to my trusty (not so trusty) didital calipers, there is a .048 difference between the two.

 

[bwalker]

This type of wear on the bottom of the skirt happens very fast and is mostly caused by poor port chamfers on the intake port.
I'd say piston pictured has very few hours on it.

 

[Hipastore]

Looks good

 

[cookies]

Wrist pin and wrist pin bearing damage caused that by allowing the piston to cock out of square during combustion. If a new oem pin still fits the pin bosses in that piston properly I'd reuse it with a set of new rings and a bearing.