372xp piston?

i have a 372 i've been gathering parts for to make a runner again. the stock piston was a 2 ring piston. the replacement piston from husky is a 1 ring piston. whats up with that? whats the advantage of one over the other?

kf_tree said:

i have a 372 i've been gathering parts for to make a runner again. the stock piston was a 2 ring piston. the replacement piston from husky is a 1 ring piston. whats up with that? whats the advantage of one over the other?

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There has been much controversy over this. The debate is whether the sealing gains against the cylinder wall justify the frictional losses of two rings. There are small cart engines with NO rings. They run a rich mixture of methyl alcohol and caster oil. If you have access to a ball-hone (sometimes called a Christmas tree hone) use that in the bore at about 500 rpm going rapidly back and forth to give a nice cross-hatch pattern. 15 seconds with a 240 grit will do it. Wash the cylinder religiously with solvent then soap and water then solvent again. Your cylinder should look new and work perfectly with a single ring piston. When re-installing the cylinder, throw away the base gasket and instead seal it with permatex Ultra-grey. Apply it as thin as a sheet of paper, you hardly need any. This will reduce your squish band by 0.012" and give better throttle response and a little more mid-range and top-end power. You can run the saw an hour later.
Cheers.

Ball hone? You mean one of these?



Don't those have a tendency to trash the ports?


Why that over a standard cylinder hone?



Just to muddy the waters, here is a interesting dissertation on the evils of honing and the great superiority of never honing unless it has been necessary to bore the cylinder. Just found it, so I'm not pushing the idea. Haven't digested it yet myself...

They actually do a nice job of chamfering the ports. Keep in mind the hone is in there for about 15 seconds which removes less than half a thou. With pinned rings like a two-stroke has, the ring cannot rotate. Having a semi-abrasive surface will seat the ring quickly and provide an excellent dynamic seal in short order. The biggest danger is in not cleaning the cylinder properly. I stressed this in my post. I have seen over-honing with a bar type hone that sharpened the ports and caused a ring to grab causing catastrophic failure at 13000rpm. It was not pretty and it convinced a fellow technician to go to a ball-hone from then on.

Hey Simon would permatex ultra copper orange work as good as the permatex Ultra-grey.I always use that since it is supposed to take heat beter than the blue.Thanx for the help.

dufrain said:

Hey Simon would permatex ultra copper orange work as good as the permatex Ultra-grey.I always use that since it is supposed to take heat beter than the blue.Thanx for the help.

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I prefer the Ultra-grey. There are many Loctite product out there for sealing cases on outboard motors etc, but many manufactures now recommend Ultra-grey. Ultra-copper will take more heat but doesn't seem to have the same resilience to gas and oil. In any case the temps are well below either products maximum.

Thanx for the reply.I agree the one that would have the highest resistance to oil and gas would be best on the saw.I will use the gray for sure

Is the Permatex Ultra-Grey in the same vane as Loctite 515?

Don't those have a tendency to trash the ports?

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Not hey do not. Avoid using spring loaded, brake cylinder type hones. Those trash cylinders.
I hone after every rebuild to aid in ring seating and speed up break in.

where is a good place to get the bead hones in chainsaw size

Google J&L industrial. They will have any size you need.

Well i did order a new piston for my 372xpg and my did only have one ring from the start, its a non epa saw ,,, the epa saws has two rings ,,, as it looks in the ipl ,,,
I did order a one ring piston again !!

/Kristoffer