what is a needle bearing

i am looking into purchasing a 70cc bigbore kit for my silver bullet and at mopedworld.com they say in order to use it on the a-3 u have to bore out the needle bearing to 12 mm, is this something hard? or can u do it at my house with a drill?

Re: what is a needle bearing

no

possibly on a drill press, a needle bearing uses tiny cylindrical tubes/bearings instead of balls or rollers for bearings,,, they are normally "pressed" into place and at only 12mm I'm guessing its part of the crankshaft bearing assembly,, but you should probably have it done at a machine shop

Re: what is a needle bearing

You'd better check into it with some other retailer.E-mail `Mopedwarehouse' and/or Steve's in New jersey and ask about THEIR bore kits and if that's a NORMAL requirement.Better safe than sorry.

Re: what is a needle bearing

the reason that they want you to bore the needle bearing is that the wrist pin in the new piston has a larger diameter (12mm) than the old one (probably 10 mm). I ran into this with a kit for a Vespa. However, the seller of the kit made available new needle bearings with the proper inside diameter to match the outside diameter of the wrist pin. Personally, I wouldn't bore the bearing. I'd worry about weakening it by thinning the wall or I'd worry about it being drilled off center or at an angle.

Chris S

Do not do this.

Reeperette /

The gudgeon pin ( or wrist ) pin is not the only difference between the A3 and A5 engine....the stroke is also longer, and the whole pistonarm/counterweight assembly is different.

As it stands, you can NOT mount the kit to an A3 engine without tearin it up...right now I am working with an A3 and A5 engine to see if a "Conversion" can be done, and if it is possible, I will let y'all know.

It would entail at the very least replacing the A3 pistonarm/counterweight with the one from an A5 transmission....and I hope to replace the points-based ignition with the A5's CDI unit as well....we will see.

But for now, listen to someone who knows these bikes....don't try it, at least not till we can see if a pistonarm swap is possible....you'll just wreck an engine.

-Ree

Re: Do not do this.

Way to go,Ree! I was waiting to see if you'd answer.It just didn't sound right to me(making `Joe Customer 'perform a difficult mod)and I figured you'd be up on the latest concerning Tomos.

Re: Do not do this.

is there a 60cc or 70cc head that i can just mount on my ped,

moped warehouse sells a 60cc head just for the A-3 they call it a replacement, i was just gonna buy that because i dont want a bigger carb and i already have a turbo pipe

i was just gonna buy anew jug and re-jet it

Not usually that simple.

Reeperette /

>>is there a 60cc or 70cc head that i can just mount on my ped,

moped warehouse sells a 60cc head just for the A-3 they call it a replacement, i was just gonna buy that because i dont want a bigger carb and i already have a turbo pipe

i was just gonna buy anew jug and re-jet it<<

Actually, The best (and apparently most effective) collection of Mods for the A3 Tomos is the BiTurbo, Amal 15mm Carb, 27Tooth Sprocket combined with a larger main jet, a timing advance and an optimised fuel/air mix.

The larger carb would in truth probably give you more performance with less hassle, and it's a hell of a lot easier to install and configure without screwing up than a larger cylinder.

Now, dependin on what you want outta the 'ped, you can re-arrange those mods a bit, especially if you have the two-piece Biturbo....cause you can slide that shorter for more low end, longer for more top end.

So if ya want power takeoffs and yer happy with yer current top speed, slide the pipe short and use a 25tooth sprocket, and if you want nasty top end and don't care how long it takes to get there, slide the pipe long and go with a 27tooth sprocket.

It's all in yer tuning, and the larger head kits are actually more trouble than they are worth in most cases - keep in mind the whole design is based around 50cc's...fuel mix, timing, everything...and with a larger head you would probably have to back it up with a bigger carb anyway.

Hope alla that helps some,

-Ree

Re: Not usually that simple.

listen to ree ... he knows tomos inside and out.

Re: Not usually that simple.

listen to ree ... he knows tomos inside and out.

besides ... i've heard too many 60cc and 70cc horror stories.

At least one thing's simple

Reeperette /

And don't hestitate to ask "stupid" or obvious questions....I wouldn't hang round this forum if I didn't enjoy answerin them...tho a lot of em are covered in Freds guide.

-Ree

« Go to Topic — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account