MOPED ARMY

I didn't pull the cylinder off yet to see if they swapped pistons or not. Both being 38mm would it work if they took the bottom end plus the conn rod, piston, etc from the A3 and put the A35 top end over it? No other mods? I'm told it's not uncommon of a combination but I don't know if there are any other required modifications that needed to be done to make it work.

Edit: just found a post from 2016 stating an A3 piston will run in an A35 cylinder, but stated the piston windows need to be opened up to reap the benefits of the A35 top end. I'm guessing this is the same reasoning as with the A3 head where you trim the piston skirt to open up the intake?

Question still stands, are there any guides or photos of this trimming? I'd like to do it right and make sure I take the right amounts off in the right places. Thanks.

If you're running the a35 cylinder you don't need to trim the piston skirt because it's reed valve. Trimming the skirt is for using the a3 cylinder which is piston port and trimming the skirt changes intake timing which if done right would make it faster.

I usually draw the window, drill holes in the 4 corners then use a Dremel to finish it up. I've done it quite a few times. Don't be scared, get in there!

Thanks for the photos, seems doable. Dumbing it down a bit, is there a special process to determining the location and size of the window? I'm guessing shine a light into the intake as I move the piston between TDC and BDC and try to ballpark where to cut so that at no point is the side of the piston blocking the intake?

Is there any other purpose as to cutting a window instead of just a slot without a bottom, aside from structural integrity of the piston? I wouldn't do it, but just to understand the intention of the window. I see that a stock A35 piston actually has 2 windows. (edited)

Currently running a35 cyl/head on an a3 crank/rest. Havent cut holes on the piston and it works great, pulls over 50kmh with half throttle(havent tried wot yet since its in a process of breaking in).

Just make sure that the bottom of the piston opens intake port all the way when i tdc.

My crank was made for 10mm pin and piston uses 12mm pin, so i had to use bronze bushing instead of needle bearing.

Folks On other forum(croatia forum which has a lot of tomos mopeds and users) claim that if you make holes in the piston it gonna make you slower since holes were designed to make sure mopeds dont go over 45kmh which is illegal (not sure about this claim). check out so called L piston in attached pic, i use it as i said without cutting any holes.

My piston has 12mm pin and conrod is 14mm. I dont think such thin needle bearing exist.

Question.

For those of you that just did a A35 cylinder swap and left your stock A3 piston and crank, why are you changing the wrist pin and bearing and not just leaving those stock ? Durability ?

the op just fell off the map, bronze is not as robust as needle bearing but some say the inner surface of the conrod is not prepped for a needle bearing.