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Old 02-23-2010, 02:42 PM
BarelyAWake's Avatar
BarelyAWake BarelyAWake is offline
Motorized Bicycle Elite Member
Join Date: Jul 2009
Location: Maine
Posts: 7,212
Default Re: How to rebuild and balance these engines

Tinkerin' on these is indeed at least half the fun - it's why I got into this blasted addiction FTW

The fuel air mix from your carb goes through the crankcase too w/a two stroke engine, when the piston moves down it exposes the transfer ports and draws in the mix - to be compressed then detonated like you'd expect. This way the fuel/oil mix can be used to lubricate the crankshaft and assorted bearings - thus the marvelous simplicity (and disproportionate power/weight) of teh two smoker

Pics of the transfer ports in our HTs (Grubee Skyhawk 66cc btw), the squarish indentation in the side of the case and passages next to the sides of the cylinder... also note the destroyed base gasket heh (click to view larger);

A perhaps overly simplistic & general explanation (but better than mine lol) can be found here: a more in-depth definition and various alternatives wiki provides here:

The specific torque specs... varies depending on whom you ask - and the Chinese ain't tellin'. I try not to worry about it too much, mostly I get em "snug" and resist the urge to "check" them by just tightening them a lil more - which can lead to fastener failure and stripped threads. Despite the lack of loctite (I'm not a huge fan, personal bias tho) I've not had any problems with fasteners loosening or failing... I am however a big fan of lock washers, including replacing them after use and disassembly. I'm sure someone else will drop by with torque specifics, it's defo handy to know them - sorry I can't be of more help (betcha Pablo from SBP knows tho).

TBH I'd care more if the engine cost more I think *shame*

I've not checked out the "racing" carb from Pirate, I did however just get a CNS from Spooky... but I've not had a chance to run it yet. I've heard good things mostly, but anythings gotta be better than stock lol

As for the 'Damp Pro' - well, it's 'nother product I've not tried as I simply lined the inside of just the clutch cover with a coupla coats of rubberized undercoating. Easy n'cheap and best yet unobtrusive, it works well to help shut up the clutch noise... the vibration? Only a sprung seat and good, soft handgrips will do anything to "damp" that with these motorized bikes.

lol - 'nother missed question *second helpin' of the shame*

No, you'll not need any special tool for the piston rings - they're small 'nuff to easily compress w/yer thumbs (being sure to put the gap over the alignment pin) as you put the piston back in the cylinder. Gently get the first one aligned and in, then work the second. If it's tough, stop and look again 'cause yer doin' it wrong, it outa be easy.

The pesky lil alignment pins;

Last edited by BarelyAWake; 02-23-2010 at 03:27 PM.
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