Full Circle Cranks

Arborist Forum

Help Support Arborist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
How about balance? If the filler material is a different density, would that throw off the balance?

I dont think so, from what I understand, a single cylinder 2 stroke is only "balanced" at one particular rpm, so either side of that it is "unbalanced" to begin with

I think :msp_unsure:
 
I dont think so, from what I understand, a single cylinder 2 stroke is only "balanced" at one particular rpm, so either side of that it is "unbalanced" to begin with

I think :msp_unsure:

I have read the same. I have no experience modifying cranks, therefore have nothing constructive to offer. I am watching this thread to learn how your mod works out for you.
 
Im good with that. Just trying to learn and understand whats going on. Carry on experts. This is good stuff.:rock:
 
hey Im learning to...buggered if I know 2 5ths of F... all. I just wanted to try it. When I get done witha few of these Husky resto's and parts sorting, I will be going to see my SUP shaper...he has foam, carbon fibre and resin that id like to try...Not to sure about the heat but have been told most epoxies are similar. I have also read the crankcase shoul only see about 120c. Who knows??? I want to fill the 272 crank first and put it in a stock saw, stock jug and piston and see what it goes like....
 
The balance does matter, on my single cylinder motorbike engine, when changing to a heavier piston (bigger bore) the vibration got out of control. I balanced it, and it was very smooth again.

I think you need to balance 100% of the rotating mass and 50-60% of the reciprocating mass from memory. Measure these and make a counterweight reflecting this, and put it on the big end with no rod fitted and drill holes etc in the crank until it doesn't turn when you have it on knife edges.

Look it up, there is plenty of information about it on the net.
 
I don't think balance is that critical in a chainsaw. Husky uses exactly the same crank in the 357/359. They just bolt on a resin stuffer onto the crank in the 357 and call it good. I don't think there is enough mass in a resin stuffer to upset the less-than-critical balance in a crank where balance is already suspect at best.
 
Echo uses nylon spacers in one of their new saws.

239308d1337901035-fullround-jpg
 
I'm wanting to start building full circle cranks. What kind of filler material/epoxy should I use? Any pics, tips, suggestions would be appreciated.

If you run down some of the old MAC kart materials you'll see that some used to use exopy and balsa wood. I believe there were some links post at one time to these materials. Ron
 
Higher crankcase compression pushes the point of maximum delivery ratio of the transfers up higher in the rev range. Both the point of max torque and max horsepower end up higher in the revs.

Here is a webpage with a graph to illustrate the concept, its down about halfway on the page -

Moped
That's interesting - does it extend the peak to a higher rpm, or move the peak? Poorly written probably - what I mean is, with higher crankcase compression the peak is at a higher RPM, but if you go down to the RPM where the peak was with lower crankcase compression is there less than there was?
 
According to 2 Stroke performance tuning by A. Graham Bell, the japanese were working on incresing the primary crankcase compression ratio in their GP racers. The effect was that they were able to get more power out of the engine, but the engines became very peaky.

These days they don't worry about having a high primary compression ratio and just use a more effective expansion chamber to suck all the gasses out of the crankcase.

However this probably isn't the case on a chainsaw as they don't really seem to have any expansion chambers due to a lack of room, so probably going down the road of higher primary compression is nececcary.
 
Back
Top