Reducing squish - seems like a lot

[Ma Barker]

White-top Husqvarna 50 Rancher. Measured the squish w/the original gasket & a new piston at .062. Seems kinda high. Did my best to see if the dimensions of the original piston match the new (supposedly OEM) piston & can't tell that they're any different. So it seems that this saw was running w/a squish of .062.

I can always slap it back together as is, but I was hoping to reduce the squish to .020. If I reduce it that much, will I have to do any porting? How low can I go without porting?

I tried a couple of searches on this and wound up getting about a zillion unrelated results . . . search engine throws out common words like "not enough", etc.

Thanks,

Ma

 

[mtngun]

I can always slap it back together as is, but I was hoping to reduce the squish to .020. If I reduce it that much, will I have to do any porting?

What is the squish with no base gasket ? 'Cuz that's probably where you are headed, unless you plan to mill the jug.

As you reduce the squish, intake duration will increase, and exhaust duration will decrease. Nothing you can do about the intake. You may wish to raise the roof of the exhaust port the same amount that you reduced the squish, to restore the original exhaust duration -- but you don't have to.

 

[tdi-rick]

Yes, it can be that wide.

All components are made to a +- tolerance and the minimum allowed squish clearance will be with the maximum length rod with the tallest piston and shortest cylinder height.

If you are unlucky to get a rod at the shortest centre to centre length with a piston with the shortest gudegon centreline to crown height with the tallest cylinder height you'll get a large squish measurement.

 

[Ma Barker]

What is the squish with no base gasket ? 'Cuz that's probably where you are headed, unless you plan to mill the jug.

Haven't removed the original gasket yet, but I pulled a corner of it up and it's about .010 thick. I'll definitely be setting this up w/o a gasket for whatever those marginal gains will be. Milling the jug is beyond my knowhow & resources, so I'm not gonna sweat it. It worked fine before, it'll work fine again.

Thanks for the answers,

Ma

 

[Zombiechopper]

I just checked my 357 prior to tearing it down and it was .042 which explains why I never really liked the way it ran...

Stihls I have torn down were in the .030-.035 range.

 

[btbill]

I've done a Husky 61, a 268 and a 272. All of which I just removed the base gasket. However at the same time I also did the muffler too, to open it up some. All three I got excellent results without doing any port changes to the cylinder.

Just go easy with the sealant you use on the cylinder when you put it back together. Just the merest smear and make sure you don't block the pulse hole which in effect works the fuel pump of the carb

BTW, if you port the muffler... you should..... put some heat reflectant tape on the plastic just above it as its gets noticeably hotter.

You'll need to retune the carb and if you do the muffler retune it a lot at the the High end. Do this in wood. I find the best way is with the saw at full throttle get it so the revs peak. You'll here it. The richen 1/4 tune. Then get some big logs and tune it properly in them.

 

[woodshave]

As you reduce the squish, intake duration will increase, and exhaust duration will decrease.

How can the intake duration increase?

 

[timberwolf]

When the cylinder is lowered effectivly the bottom of the port is moved down so the skirt opens the port sooner as it leaves BDC and closes it later as it returns to BDC making the durration longer. If you have high squish values you also likely are lat the ower end for compression, for that reason I would leave the exhaust port height alone to minnimize any loss of compression.