Poor me. I live in Hawaii. The riding season here only runs from January to December. I have to order all my bike stuff online. Sometimes things are not as described and I have to live with that. Shipping costs preclude returns. Ok - bear with me here.

"Wheezer" needs a top end rebuild. I keep telling people she doubles as a fogging machine for mosquitoes but pretty sure the locals are on to me.

This is what I have - due mainly to an unfortunate series of events:

1. the old jug has quite a few fins missing. Piston is STD and I'm using a quart of oil a week.

2. Some time ago, purchased another jug in nice shape except it had been bored to 85mm. (it came with what looks like a goldie piston).

3. Spotted a piston on Ebay - listed as a genuine WM20 piston with rings. Images follow. With a diameter of just under 85mm, obviously not for an M20. Before realising this, I ordered a new std liner from Draganfly. side-note... at first they sent me a sleeve for an Ariel SQ4 but they rectified this fairly quickly.

So, my question is: what next? Can I use the B33 (or whatever it is) piston in the 85mm jug? To me that would be the best solution. Does anyone else have a better idea?

jeez - when I screw-up, I do it good...

email (option): cas.vanderwoude@gmail.com

Hello Cas,

If what you have is a B33 piston of the "Long conrod" type,
You can fit it to the WM20 and also have the benefit of a larger
Engine displacement and a bit higher comp' ratio.
I would compare the piston you got with an M20 piston to see
If the location of the dudgeon pin is the same as the M20 one,
Relatively to the piston top.
If so, you can use it.

Cheers,
Noam.

['If what you have is a B33 piston of the "Long conrod" type,
You can fit it to the WM20 and also have the benefit of a larger
Engine displacement and a bit higher comp' ratio..']

Not so I'm afraid...What you have is a 'long conrod' B33 piston and this can only be fitted in conjunction with an M21 crank..

The M20 piston has a greater gudgeon pin (wrist pin) centreline to piston crown dimension...

The 'short rod' B33 piston is more likely to fit an M20 though I have never checked the pin to crown height of that one against an M20 piston...

Forgetting B33 pistons altogether you're going to need an M20 piston...Russell Motors may still have some of those..

Whenever you are looking at pistons a key identifier for a side valve piston is that none of them have valve clearance cut outs....Ian

email (option): ian@wright52.plus.com

Did you find one of those for me Ian?

Ron

email (option): ronpier@talk21.com

Sorry Ron...The one I had in mind turned out to be the high compression M33 version when I got it out of its box.....and thus not suitable for a side valve...Ian

email (option): ian@wright52.plus.com

Thanks for the correction, Ian.

I remembered that I bought a B33 piston in order to fit into M20, some 8 years ago,
But I did not remember that I must have also replaced the flywheel with an M21..

Best regards,
Noam.

OK so the one I need is for a long conrod B33, like the one Cas has? Ron.

email (option): ronpier@talk21.com

Yes...Ian

email (option): ian@wright52.plus.com