Ms660 low compression

[stihladdictt]

Can glazed cylinder cause loss of compression the chainsaw has very little to no compression and will only run for about 30 seconds at full throttle it is bogging the entire time and backfires at times as well it has a fresh top end but when I disassembled the cylinder appeared glazed

 

[singinwoodwackr]

Can glazed cylinder cause loss of compression the chainsaw has very little to no compression and will only run for about 30 seconds at full throttle it is bogging the entire time and backfires at times as well it has a fresh top end but when I disassembled the cylinder appeared glazed

Pics?

 

[thompsoncustom]

compression reading?

 

[cookies]

Yes glazing can cause compression loss...so can using the wrong size version of piston, weak rings, cylinder being out of round etc

 

[Gord404]

what make is the top end

 

[Bob Hedgecutter]

Can glazed cylinder cause loss of compression the chainsaw has very little to no compression and will only run for about 30 seconds at full throttle it is bogging the entire time and backfires at times as well it has a fresh top end but when I disassembled the cylinder appeared glazed

A little more background please- was the saw owned by you and running well before the top end swap?
Was this recently built out of a box of old saw wreck parts?
As others have already asked- who made the new top end? Was it new or secondhand?

 

[SteveSr]

Can glazed cylinder cause loss of compression the chainsaw has very little to no compression and will only run for about 30 seconds at full throttle it is bogging the entire time and backfires at times as well it has a fresh top end but when I disassembled the cylinder appeared glazed

Is this an OEM Stihl or an MS660 clone that I see on CL and FB from time to time. One guy around here has been trying to sell (scam someone) with a MS660 clone for about a year now. No takers yet.

 

[lone wolf]

Can glazed cylinder cause loss of compression the chainsaw has very little to no compression and will only run for about 30 seconds at full throttle it is bogging the entire time and backfires at times as well it has a fresh top end but when I disassembled the cylinder appeared glazed

It's apart now, or what?

 

[Bob Hedgecutter]

 

[stihladdictt]

It's apart now, or what?

Yes my apologies for the delay it is a all oem stihl saw with new seals no air leak or vacuum leak detected I know it appears to look scored but there is no scoring just very smooth and shiny the piston is like new as well

 

[stihladdictt]

My apologies I just uploaded the photos now

 

[Bob Hedgecutter]

I agree- piston looks good- cylinder I am not so sure of.
Ring end gap?
Piston skirt clearance?

Plus the other questions above.

 

[lone wolf]

Too bad you didn't do a compression test before you ripped it apart, did it feel like it had good compression when you pulled it? The Cyl and piston look good in the picture, is that an OEM piston? Take a ring off the piston and put it squarely in the cylinder and measure the ring end gap to see what the hell is going on there.

 

[lone wolf]

I agree- piston looks good- cylinder I am not so sure of.
Ring end gap?
Piston skirt clearance?

Plus the other questions above.

China crap possibly.

 

[Lightning Performance]

My 660 jug looks about the same. Ported and breaks starter parts if you don't use the decomp or TDC. No band cut. Swapping jug this week to a cut band and more compression. My cylinder was pushed hot once and has some glazing just like that. A mirror finish is fine on nikasil if the rings are mated to it. If not you are **** out of luck if you have low spots and low compression. It only happens with some AM jugs 99% of the time. Here is another jug off to be cut amd hacked on.

 

[Lightning Performance]

Another used 660 jug

 

[Bob Hedgecutter]

China crap possibly.

Yeah na, does not have to be China crap- can be an OEM cylinder that has been cooked up good and hot- got new piston and rings into a glazed up bore that is possibly a bit oblong into the front right (as viewed from the back of the saw) cylinder wall.

 

[Lightning Performance]

Can glazed cylinder cause loss of compression the chainsaw has very little to no compression and will only run for about 30 seconds at full throttle it is bogging the entire time and backfires at times as well it has a fresh top end but when I disassembled the cylinder appeared glazed

Let us see a good pic of the rings and ring lands please.

 

[Lightning Performance]

Yeah na, does not have to be China crap- can be an OEM cylinder that has been cooked up good and hot- got new piston and rings into a glazed up bore that is possibly a bit oblong into the front right (as viewed from the back of the saw) cylinder wall.

Possible

 

[Lightning Performance]

Stock used 084 cylinder. Looks about normal.