I am just about to go ahead with upping capacity of my 175 majesty to 200cc (199 cc with a 250 + 0.75 piston) only thing I need sorting now is the process of bushing the piston to accept the smaller gudgeon pin from the 175, anyone done this or know just how to go about it, I have lathe and reamers etc so making a bush is no problem, just wondered how the bush is fixed in the piston, any comments help appreciated.

This is something I've been pondering recently as I'm planning a similar conversion.

I was thinking of a cap type bush that will fit over the ends of the 175 pin then in through the hole in the 250 piston.

I gather the 175 pin is shorter?? So the cap ends will take up the end gaps and be able to hold everything in on the clips.

You may have to drill the ends of the cap outby the ID of the 175 pin to allow oil in and out.

I think you'd need to drill out the bush in line with any feed holes inside the piston as well.

(though I think the gen 250 piston doesn't have these holes like the gen 175 does)

Does that make sense??

I have done this with a Lambretta to get a Suzuki piston to fit. The gudgeon pin needs to be shortened to take the end caps of the new bushes so it fits inside the circlips. The bushes were made by one of the top tuning workshops but any of the scooter racing workshops will tell you what you need to do and might even make them for you.

A different day and a different thought, but couldn't the 250 pin be utilised?

Cut the middle out of the 250 pin so you have 2 ends that will already fit the holes on the 250 piston (and the clips will hold in) but won't interfere with the space for the little end.

Then from the inner end of these two 250 pin pieces, open the ID just enough to take the 175 Pin, but don't go all the way through.

You may have to shorten the 175 pin a little, but if you measure the two end pieces of the 250 pin correctly any difference between the space for the little end in the 250 piston and the 175 little end can be taken up.

You're also not having to machine a bush from scratch to fit the holes in the 250 piston, the 250 pin already fits the 250 piston perfectly!!

Edited May 17, 201214 yr by Goudrons