3120xp "safe" squish

[Dave27483]

hey there everyone, I have a 3120 that had straight mix seizure and I've just spent the whole morning cleaning up the OEM cylinder, and thanks to a few guys on this forum who told me its most likely salvageable, turns out I think it is!!! Yay.
The cylinder has cleaned up real nice.
I'm now going to order a new OEM piston and rings.
Anyways my question is what is a safe squish in one of these saws for a "work" saw.
I just measured it and I have 40 thou squish with the origanal piston ( I will re measure it with the new piston)
The base gasket is 26 thou, so by tossing the gasket I will be left with 14 thou which I think will be to tight? Right?
Where I work I have accsess to shim material (brass or steel) and I was thinking maybe a 7 thou base gasket might be ideal to bring the overall squish to 21 thou...
Would this be ok?

 

[Dave27483]

 

[Nitroman]

I think Randy made mine 28.

 

[Dave27483]

This is the worst of it and you can only just feel one score line with your fingernail.

 

[Dave27483]

Well I now have all the parts for this saw and its going back together tomorrow, I have a gasket I made to throw in which will give me 27thou squish can someone please confirm this is ok. I started with 40thou.
I have read a few post where saws are getting down to 18 thou but I can't find info on the big 3120xp did not know if it would be different.
Any info would be appreciated!

 

[Chainsaw Jim]

Was it lightly used before you did this? If it had a lot of time on it then maybe for starters you should just use the oem gasket and run a few tanks through it to see how you like it.
You'll be ok with 21 thou as far as the saw goes, though it may not go so well for your arm when you pull the cord.

 

[Dave27483]

Was it lightly used before you did this? If it had a lot of time on it then maybe for starters you should just use the oem gasket and run a few tanks through it to see how you like it.
You'll be ok with 21 thou as far as the saw goes, though it may not go so well for your arm when you pull the cord.

Overall this saw has not had a heap of use. It had a straight fuel mix go through it.
I have inspected the rod bearings and they feel tight and smooth.
The only mods I'm making are tightening the squish to 27 thou and a dual port muffler.

 

[Dave27483]

Was it lightly used before you did this? If it had a lot of time on it then maybe for starters you should just use the oem gasket and run a few tanks through it to see how you like it.
You'll be ok with 21 thou as far as the saw goes, though it may not go so well for your arm when you pull the cord.

As you can see lightly used

 

[Chainsaw Jim]

Overall this saw has not had a heap of use. It had a straight fuel mix go through it.
I have inspected the rod bearings and they feel tight and smooth.
The only mods I'm making are tightening the squish to 27 thou and a dual port muffler.

Nice. That thing should really chew some wood. Are you planning on running some test cuts on video?

 

[Dave27483]

Nice. That thing should really chew some wood. Are you planning on running some test cuts on video?

I sure will. One with a 20" bar and the other with a 36" bar plus skip chain. I have a 40" pine to cut

 

[Chainsaw Jim]

I sure will. One with a 20" bar and the other with a 36" bar plus skip chain. I have a 40" pine to cut

Sweet

 

[drf255]

IDK, I'm a porting junky. I have a hard time leaving anything alone.

In this case, I'd leave it alone and maintain the stock gasket and squish. It's a 120cc saw, you've got a lot of power there, period.

Plus, it's a BIG saw. There's gonna be proportionately more expansion than a saw half its size.

Increasing the compression will make it run hotter and Is Tougher on the bottom end.

I'd leave it be, totally. (can't believe I'm saying this)

 

[Dave27483]

IDK, I'm a porting junky. I have a hard time leaving anything alone.

In this case, I'd leave it alone and maintain the stock gasket and squish. It's a 120cc saw, you've got a lot of power there, period.

Plus, it's a BIG saw. There's gonna be proportionately more expansion than a saw half its size.

Increasing the compression will make it run hotter and Is Tougher on the bottom end.

I'd leave it be, totally. (can't believe I'm saying this)

I know what your saying, I was origanlly going to run with 0.021" but I felt it might be a bit much on this big saw which is why I am now going to run 0.027"
Ahhhhh now your giving me doubts

 

[Chainsaw Jim]

I know what your saying, I was origanlly going to run with 0.021" but I felt it might be a bit much on this big saw which is why I am now going to run 0.027"
Ahhhhh now your giving me doubts

I'm leaning towards the advise drf255 gave you. But you'll be ok with your idea. Slap it together and go cut wood.

 

[Rx7man]

Try it the way it is, see how you like it, and see if you really need more power... At most at this point I'd look at just cleaning up the stock ports without altering the timing

 

[blsnelling]

.027" would be a very conservative number for an otherwise stock saw. I would shoot for closer to .020, no more than .025". Randy likely used a greater squish due to the squish band being wider after machining.

 

[Chris_In_VT]

If this saw still has a fixed H jet on the carb I'd be careful modding it too much. I think there is one or two guys on here who will add an adjustable H jet to the 3120 carb.

 

[blsnelling]

If this saw still has a fixed H jet on the carb I'd be careful modding it too much. I think there is one or two guys on here who will add an adjustable H jet to the 3120 carb.

An adjustable H needle is for sure ideal, but it's quite simple to ream out the fixed jet. The carb doesn't even have to be removed. Remove the top cover of the carb, remove the fixed jet, ream it out, and replace it. Repeat as necessary.

 

[Dave27483]

An adjustable H needle is for sure ideal, but it's quite simple to ream out the fixed jet. The carb doesn't even have to be removed. Remove the top cover of the carb, remove the fixed jet, ream it out, and replace it. Repeat as necessary.

Here's a question for you brad, for every thou you tighten the squish does the torque increase always.

 

[Dave27483]

Ok so it's all built, squish set at 0.022" (yes I did) and muffler opened up a bit more. Brand new 36" bar and full chisel skip chain.
I will be putting it through this huge pine tomorrow and post a video.
And here it is with a 20" bar, looks like a joke on this saw.!