Is .024 even worth the bother

[rms61moparman]

I've been wanting to see just how well a 3400 could be made to run without going the "full Monte".

I figured a decent port job, popup and cylinder shave for starters.

The perfect candidate arrived this week thanks to ModifiedMark and the transformation began today.
The piston and cylinder are very nice. No scoring or marks anywhere and a very nice "polish" typical of a good 3400.
(Wish I knew what oil this saw ran on before because the piston crown and combustion chamber are unbelievably clean. But that is another thread.)

The saw started with 130lbs of compression and a VERY uniform .050 squish.

When I pulled the cylinder and measured the piston there was only .124 of "meat" between the top of the top ring and the piston crown.
Conventional wisdom says that we must leave .100 above the top ring, so my question is:

Is an .024 popup going to be worth the trouble.

This is an interference fit wristpin so it will be a B!+ch to remove and replace, but if any saw could benefit from more compression a 130lb Poulan would be the one.

Anyone care to hazard a guess what the difference will be with and without the popup???

Thanks


Mike

 

[wigglesworth]

Mike, is it one with a chrome plated piston? If so, a pop up aint feasible.

I decked and ported a 3400 a while back, and it was a strong runner, but it was a chrome plated piston and an aluminum bore. Strange they did it that way??

 

[mtngun]

The saw started with 130lbs of compression and a VERY uniform .050 squish.

Dropping the squish to 0.020" will net the biggest and easiest gain, 0.030" of full bore diameter.

A 0.024" pop-up is not going to be full diameter. Dunno what diameter it would be, but let's say the volume of the pop-up is 1/2 the volume of full diameter, equivalent to dropping the squish 0.012".

Considering the interference fit wrist pin, I'd say no, it's not worth messing with the piston. Just drop the squish.

 

[blsnelling]

I'd turn the base of the cylinder to get a squish of about .018" and be done with it. That's what we did with the 4000 I had. The 245 I just got has 163 PSI compression with only removing the base gasket. Squish is still greater than my .030" solder.