MOPED ARMY

I heard something about a Hobbit jug being made to work on a case inducted e50. Seeing as the stroke is the same on a Tomos as a Puch, how would that be done?

I can't find anything about what stroke a Hobbit uses. It must be similar.

Why are you so worried about the stroke of the cylinder? You really could use anything in the 40-50mm range and you would still have to make.a.spacer.

"_Why are you so worried about the stroke of the cylinder? You really could use anything in the 40-50mm range and you would still have to make.a.spacer._"

Stroke matters a LOT for port timing and performance. Connecting rod length differences can be fixed by either milling the engine or adding a spacer.

Connecting rod length differences can be fixed by changing the conrod or spacing the cylinder. Stroke length differences can't be adjusted the same way.

That is true but generally if the stroke is close enough, and you space the cylinder correctly, the port timings won't be too crazy.

hobbits when at bdc don't completely uncover the transfers with the stock stroke so can handle a few extra mm stroke no problem.

pa50 ii cylinder approx measurements from top of cylinder

exhaust roof = 30mm

exhast base = 39mm

transfrers roof = 34mm

transfer base = 41mm

rear transfer roof = 34mm

rear transfer base = 46mm (tapers towards centre kind of triangalar)

hope these measurements help

So long as the wrist pin to crown distance is the same and the ring gaps are in the right place there is no reason you couldn't use a 12mm piston of the right diameter.

rough (tape measure) measurements for a hobbit/camino piston are

piston height =50mm to where crown starts = 47.5mm

piston skirt to bottom of wrist pin hole = 18mm

with the tape measure curved round the piston the ring pins are approx 29mm apart at the rear/intake side of the piston.

So for a 12mm wrist pin you need those measurements but with the hole starting 17mm from piston skirt

If your planning on a big bore kit you could see if it has enough material so you can just bore the wristpin hole out to 12mm or ask if the supplier has a suitable 12mm pin piston in stock as a replacement.

Planning on overcoming the cylinder height (spacer or machine some down), stud spacing (weld up the old holes, drill/tap new ones), piston port/case induction (changing an A3 bottom end to case induction via machining/welding) and case material for transfers (at the same time as changing to case induction).

Stroke is the biggest obstacle. I would prefer not to change the crank from the one I'm already going to use. I want to keep my A3 clutch and use ZA50 CDI, so I'd like to stick with my A3 crank with an A35 needlebearing conrod. Any further and I'd be better off just doing a full engine swap.

I'm looking more at the Hobbit Athena kit. I'll ask around about a possible piston replacement that uses a 12mm wristpin. If one can't be found, I'll machine a bushing.

Its not that hard to adj for stroke.

Pick your rod length and assemble the bottom end.

Use your spacer thickness to set your transfer timing.

Port the exh as needed.

If exh timing is too high, you can run a thinner spacer and remove material from the piston to fix the transfer time. Which will decrease exh timing.

Its funny, all that time welding on cases and moving studs and shit, and then to get scared by a couple mm.

So this is all hypothetical then Adam?

Well in theory I'd tell them that if they were going to spend all that time and money on making a Tomos engine fast, they should start with an a35... but you would know that already if you were this 'someone' planning the build in question.

All things being equal, the spacer will be half of.the difference in strokes. If you're off by 1mm then you need a .5mm spacer.

Even if you find a 43mm stroke kit, you'll probably have to do one of the following:

-Have a longer connecting rod pressed into your crank

-Have a shorter Connecting rod pressed into your crank

-Mill the engine cases down and add an aluminum plate to relocate studs

-Fill in old cylinder stud holes and drill/tap new ones

-Add a spacer between the kit and motor to convert stud pattern and/or compensate for port timing

-Mill kit down to adjust port timing