Dolmar 123

[ppj690]

Well if it's .040" you shouldn't have to worry about piston contact with the top of the cylinder. I think I saw a pic in this thread showing a very tiny combustion chamber, so .040" may be what your saw needs. On the other hand, you will have to determine what caused the marks on the top edge of the piston. Any chance there may be some debris inside the saw? Are there corresponding marks in the combustion chamber?

After investigating I think the marks on the cylinder may not be too suspicious, a little carbon build up and once cleaned with a little emery paper there was no actual indents in the piston. The shiny cylinder wall on both exhaust side and intake side correspond with the shape of the skirt so I assume this is piston slap? If so, what is usually the most common cause and is this a major issue? thanks again..

 

[Sepia]

After investigating I think the marks on the cylinder may not be too suspicious, a little carbon build up and once cleaned with a little emery paper there was no actual indents in the piston. The shiny cylinder wall on both exhaust side and intake side correspond with the shape of the skirt so I assume this is piston slap? If so, what is usually the most common cause and is this a major issue? thanks again..

The shiny areas on the cylinder are normal and not an indication of piston slap. If you have inside and outside mics you could measure the piston diameter at various locations and compare to the cylinder inside diameter. Alternatively you could slip the piston into the cylinder and measure the clearance between the skirt and cylinder wall with a feeler gauges. Anything over .003" clearance is questionable.

 

[ppj690]

The shiny areas on the cylinder are normal and not an indication of piston slap. If you have inside and outside mics you could measure the piston diameter at various locations and compare to the cylinder inside diameter. Alternatively you could slip the piston into the cylinder and measure the clearance between the skirt and cylinder wall with a feeler gauges. Anything over .003" clearance is questionable.

I have .004” clearance between skirt and cyl wall

 

[Sepia]

I have .004” clearance between skirt and cyl wall

I think I would be looking for a new piston and rings but that's just me.

 

[ppj690]

I think I would be looking for a new piston and rings but that's just me.

Absolutely agree. An aftermarket piston and rings here in the uk is about £35... will grab one just to be on the safe side. if this is all it needs to be a runner again I’ll be happy. Bottom end bearings etc seem to be fine. What are your thoughts on base gasket given the squish clearance?

 

[Sepia]

Absolutely agree. An aftermarket piston and rings here in the uk is about £35... will grab one just to be on the safe side. if this is all it needs to be a runner again I’ll be happy. Bottom end bearings etc seem to be fine. What are your thoughts on base gasket given the squish clearance?

Many like to do the base gasket delete to gain some compression (clearances allowing). You seem to have plenty of clearance so that isn't an issue. Only issues I can think of are assembly clearances on the muffler and carb/intake tract, ability to start without a decomp valve, and port timing changes. Since you are using a demolition saw cylinder, the port timings may be the wild card here. If you are ambitious, you could install the gasket initially and do some timed cuts, then remove the gasket and repeat the cuts to make a comparison, then decide what you prefer.

 

[ppj690]

Many like to do the base gasket delete to gain some compression (clearances allowing). You seem to have plenty of clearance so that isn't an issue. Only issues I can think of are assembly clearances on the muffler and carb/intake tract, ability to start without a decomp valve, and port timing changes. Since you are using a demolition saw cylinder, the port timings may be the wild card here. If you are ambitious, you could install the gasket initially and do some timed cuts, then remove the gasket and repeat the cuts to make a comparison, then decide what you prefer.

Great... thanks, will decide when I get the new piston. Does the 47mm piston from the 119 and 120 fit the 123..?

 

[Sepia]

Great... thanks, will decide when I get the new piston. Does the 47mm piston from the 119 and 120 fit the 123..?

Sorry, can't help you there. Maybe pop over to the Dolmar forum and post your question there.
https://www.arboristsite.com/community/threads/sachs-dolmar-chainsaws-thread.143945/