REAL 80+ CC Happy Times!



HI All,

I was just looking at an old partially disassembled engine today and was thinking of a low $$ way to increase displacement and power...

Recasting an entire cylinder would probably be expensive so I thought to myself....what about just making a spacer that fits on the bottom of the cylinder jug and make a new connecting rod (of course slightly longer studs would be needed too).....the longer stroke will add displacement and many additional cc would 1/8 more give you?....How about 1/4 inch more?...Of course hopefully there will be enough clearance inside the crankcase?

I know connecting rods can be made of aluminum so machining a rod shouldn't be too difficult....of course the balance issue comes into play BUT since we are using the same piston maybe it won't be too far off?

Minor porting for the additional displacement may be necessary but then again maybe not.....same fuel / air mix with a longer stroke should yoiels tons of torque...

So what do you think? Seems like it wouldn't be too expensive to get more from our engines!

You'd need to change the crank to change the throw of the rod as well to get the displacement change.

If you cant change the crank, then you have to increase the piston diameter to up the displacement.
datz is right,

might aswell put the spacer uptop it'll still do the same - stock rod length - lower compression, increase the rod length - return it to normal cc

You could have a 1 foot long spacer and a 1 foot long rod, it will still be original cc.

A stroker kit involves crank and rods.

Nothing wrong with thinking about how things work, every day since I first started
my bike and It roared into life, Ive been thinking about how to Improve it.

Even if you can stroke another 1/4 inch both up and down your max RPM would go down because your piston is working harder. Vibrations would probably go up as well unless you can balance it all.
A good example of the RPM thing is crotch rocket engines. They can go 10,000 RPM because they have very short strokes.
In contrast on a Harley Davidson they pretty max out around 6,000 RPM because they have a longer stroke.
But they also have more bottom end power.
So a stroked out Happy Time would work but you may need to get that tooth count lower in back.. unless you don't mind burnouts.
as datz sed...without a crank mod, there's no way to get more stroke. and re: larger piston...i'd be wary of adding any more mass to the already-"heavy side" of the crank unless i was gonna re-work it.
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HI Guys,

Hmmmm...interesting thoughts....I was looking at the 383 Chevy where they took a 400 crank on a stock 350 block to get the increased displacement.....So I guess simply increasing the the cylinder height and rod length won't do anything Hmmmm.....I seem to recall something though about rod length affecting the characteristics of the engine but I think then one would have to alter the piston too (I think it was raising the location where the rod joins the piston and having a longer rod (or maybe vise versa) and that somehow altered the torque output or power of the engine.....without need of crank alterations or cylinder alterations....But one would then have to mess with a rod and piston which I would think would be easier and cheaper than messing with the crank itself....(making a crank sounds more expensive)...In keeping with the "cheap" theme I am wondering if it would be possible to cut and weld the crank assuming good welds?...Of course maybe heat treating is needed too then....Hmmm


I just found this post & it seems to fit here too.

Which will eventually be the downfall of the motorized bicycle as states create new laws due to injuries sustained by these types of riders or complaints of reckless motorized bicycle riders. Those that are old enough will remember such laws being created in the 70s for mopeds due to similar careless riders.

This is something the vendors should not contribute to. They would better serve the community and their long term profits by focusing on reliability. Which would increase both the reputation of the bikes as a alternative means of transport as well as the reputation of the vendor.

I think boring the thin walls of the cylinder may ruin it....not to mention having to replate the cylinder wall and having to make a custom piston....I though simply adding a spacer would be the solution but appears I didn't figure on the crankshaft needing a longer throw to boot...

FWIW - I contacted a company in Ohio to see what the would charge to make a custom crank for our engines.....the answer was $4000!! ....And that was EACH for a production run of 15 Cranks....I would guess there there wouldn't be too many takers here? ;-)

I'm still looking! I love to tinker tho....