New Piston Taper

[dsell]

I'm putting together another Husky 51 and have an aftermarket piston from Baileys. The skirt is too tight at the bottom of the cylinder and the new piston tapers .008 from top to bottom. It's also a bit egg shaped on the bottom. Is there any way to make this work or should it be tossed?

 

[Four Paws]

Call customer service and inform them of the problem and return it for a refund.

Then, buy a meteor piston from one of our site sponsors.

 

[ChoppyChoppy]

How long ago did you buy that? That piston is only $20 now.

 

[Mad Professor]

You need 0.0025-0.003" clearance at the skirt.

OEM pistons have taper.

Round pistons are good pistons.

 

[scallywag]

Two stroke piston should be slightly oval shape when cold, expanding to round at running temperature.

As a guide, .001" per inch of bore, piston to cylinder clearance, ie: two inch bore=.002" clearance.

 

[drf255]

Two stroke piston should be slightly oval shape when cold, expanding to round at running temperature.

As a guide, .001" per inch of bore piston to cylinder clearance, ie: two inch bore=.002" clearance.

Was thinking the same. Why don't you heat it up with a propane torch, nice and easy, and see it it straightens out. Obviously, only if it won't ruin the potential of a return.

The crown of an MS250 piston grew over .010 on me when I heated it up to weld a dome on it. I was shocked. It reverted back to original size when it cooled. The crown grew more that the skirts BTW.

Cold, a stock OEM piston was 1.666 at the crown and 1.690 at the skits for me. From a running motor.

 

[scallywag]

Can you get a reading using this method?

 

[Nitroman]

Remember if you measure clearance like that, you halve the measurement. That is 0.001" if the 0.002" feeler is snug.

 

[dsell]

Can you get a reading using this method?

View attachment 399881

No, there is no clearance. The cylinder measures 1.771 slightly in from the bottom, 1.770 at the bottom and the piston skirt is snug.

 

[dsell]

How long ago did you buy that? That piston is only $20 now.

I bought it last summer off Ebay. The person that originally bought it in 2008, sent the receipt with it. I'm not worried about returns, just wonder if there's a way to make it work.

 

[dsell]

Two stroke piston should be slightly oval shape when cold, expanding to round at running temperature.

As a guide, .001" per inch of bore, piston to cylinder clearance, ie: two inch bore=.002" clearance.

I have slightly used OEM piston which is round and measures 1.767 at the skirt, 1.765 just under the ring groove, and 1.763 above the ring groove. So, I'd have .003 clearance at the bottom.

 

[blsnelling]

Pitch it.

 

[Mad Professor]

Remember if you measure clearance like that, you halve the measurement. That is 0.001" if the 0.002" feeler is snug.

No need to halve the measurement, unless you put a feeler on both skirts.

Use the feelers like go- nogo- gauges. If a 0.002" fits and and a 0.003" does not you are fine. A 0.004" is showing wear but not too bad. If a 0.0015 or 0.002" does not fit good chance it will seize.

Aftermarket forged pistons (wiesco) need more clearance as do much bigger saws/pistons

 

[LegDeLimber]

That's the shape that piston is supposed to be cut.
The aforementioned heat expansion is the reason.
you'll need to do the math from the clearances these guys gave you
to check if it's the right size.
http://www.engineering-dictionary.org/Cam_ground_piston
they worked just dandy in our motorcycles.
Can't speak of modern ones, but this was how they were made, back in the 70's.
Every one that I had a chance to put a mic or calipers on, was cut this way, back then.