Theoretical custom case

[Rich Fife]

That is an echo case.

I've never worked on an echo

Stock is 32mm stroke. The generation prior is 34,36mm and the generation after has 37.6mm.

Bearings and seal diameter are good, widths are the same or less. And plenty of shaft to make the flywheels/clutch tapers/threads.

I have some Husky cranks 37mm stroke etc... a bit different in dimensions when compared to a 372.

Some hard turning is involved, but it's doable.

I have some good carbide and ceramics... I'm not too worried about the turning aspects... as I am about cutting threads seeing the hardness of some of these shafts.

 

[Rich Fife]

I've been playing around with cylinder to case volume ratios. I'm definitely learning more about these 2 strokes... there IS a delicate dance between these two.
My custom saw that I'm working on is an undersquare saw... should be a decent reving stump pulling lightweight.

 

[Rich Fife]

Sweet idea! But why not just make a crankshaft?

Profile the ends to match desired flywheel/clutch.

but it would be sweet to see custom case.

Here we go man... I'm starting the build, a new build. I'll have to do a separate post... I'll be using as many existing parts as possible... 880 gast tank, side covers, bearings, seals... plans are 51mm stroke 60mm bore... I'll be machining a full circle crank, the Material will be 4140 ph... Reed valve, big carb, pipe... should be interesting.

 

[Rich Fife]

After talking to others, and doing even more research... 51mm stroke and a 56mm bore is the route I'm taking... this will be a hodge podge of machined parts and modified parts until I get a product that's tested (running and cutting with satisfying results)... if it sucks, on to the next project... right?

 

[Ketchup]

Would you mind explaining why you chose that bore and stroke? It’s over square, but less than most chainsaws. I’m interested in going that direction with some of my own builds.

What are your considerations around case volume? The trend with newer saws has been to reduce volume around the crank and put it in the transfer tunnels. Some run a stuffed crank, some don’t. I don’t know of any full circle chainsaws coming out of a factory. I’m not sure if that is a balance thing or just weight savings.

Will this be a two piece cylinder or blind bore? There’s definitely opportunity to put a two piece bike cylinder on something like this.

 

[Rich Fife]

Would you mind explaining why you chose that bore and stroke? It’s over square, but less than most chainsaws. I’m interested in going that direction with some of my own builds.

The idea is to minimize the process of reinventing the wheel... so, the pre-94 YZ125cc had a 56mm/50mm bore and stroke. I ordered a cylinder and I'll use the base of the cylinder as the pattern for the case...

What are your considerations around case volume? The trend with newer saws has been to reduce volume around the crank and put it in the transfer tunnels. Some run a stuffed crank, some don’t.

Less case volume, I'm more so focusing on the lowers and transfers.

I don’t know of any full circle chainsaws coming out of a factory. I’m not sure if that is a balance thing or just weight savings.

I'll be machining a full circle crank... I'm working out the balancing portion of it... my buddies suggested 61% reciprocating mass as a starting point. I want a little more weight to the crank to act like a flywheel...
I'll have to play with rod lengths and pins... but, I'll figure it out. Lol

Will this be a two piece cylinder or blind bore? There’s definitely opportunity to put a two piece bike cylinder on something like this.

That's exactly the route I'm taking... a two piece. This should help dial the build in faster.

 

[Rich Fife]

So I switched it up.... Again. Final numbers will be 54mm bore, 50mm stroke... im waiting for a bunch of parts to arrive... the reed valve, big carb, pipe, bearings, seals, 660 case, 660 crank, etc. I don't know too much about clutches but I'm thinking I'll need something that'll handle the POWA... lol
Anyway...

 

[Rich Fife]

The case and crank are in.... I think it would be easier if I use Husqvarna 385xp case for dimensioning.
I guess I have a 660 build for the future.

 

[Hulpio]

Great project!

 

[Rich Fife]

I've been distracted by a bunch of other items/irons that this build went straight to the back burner... now that im ALMOST caught up... it's time to make some chips with a custom case.
As you read this thread... you'll see that I continously change my thoughts/ideas, etc... its the nature of the beast I suppose.
1st test 52mm bore / 45mm stroke
2nd test 56mm bore / 45mm stroke
3rd test 60mm bore / 45mm stroke
I'm debating if I want to machine a keyed crank so that I can swap rods... thinking if a keep reciprocating mass around 60% and the ends true it should be an issue... time will tell.

 

[Rich Fife]

1 side done, 5 more to go.

 

[Rich Fife]

All sides squared... I guess now I'll sit down and do some math... instead of just winging it.

 

[Powerstroke Cowboy]

Subbing. Looking forward to seeing where this goes.

 

[Rich Fife]

Subbing. Looking forward to seeing where this goes.

Hopefully it doesn't go into the scrap bin.... either way, it'll keep me busy for a while.
Just had a thought... I should machine different bolt hole spacing on the case halfs so that I can run various cylinders... perhaps, make spacer blocks with o-rings to seal and dowels for alignment.

 

[Hulpio]

Spacer is a good idea, you can play with different conrod lengths then too. At the end you can install whatever cyl you like

 

[NateSaw]

It’s worth your time to check out Twostroke Stuffing on YouTube. Not chainsaws, but he’s built several ground up theoretical engines for bikes and documented it well. It’s a lot of content though and not all of it is engine related.

The dude radical! He has a turbo moped engine.

 

[Powerstroke Cowboy]

Hopefully it doesn't go into the scrap bin.... either way, it'll keep me busy for a while.
Just had a thought... I should machine different bolt hole spacing on the case halfs so that I can run various cylinders... perhaps, make spacer blocks with o-rings to seal and dowels for alignment.

Hopefully it doesn't. It looks like you will be busy for a LONG time...

How about machining the case halves in a way the deck is replaceable? Basically machine the deck so you can bolt in different spacer/blocks that have different bolt spacing so you can run different cylinders? It would be kind of like and adaptor for different cylinder bolt patterns. Just unbolt the block and bolt a new one in to change cylinders and (or) crankshaft stroke length?

Just a thought. Thoughts are easy, making it works another story.

 

[Rich Fife]

Hopefully it doesn't. It looks like you will be busy for a LONG time...

I'm thinking so.

How about machining the case halves in a way the deck is replaceable? Basically machine the deck so you can bolt in different spacer/blocks that have different bolt spacing so you can run different cylinders? It would be kind of like and adaptor for different cylinder bolt patterns. Just unbolt the block and bolt a new one in to change cylinders and (or) crankshaft stroke length?

Exactly.

Just a thought. Thoughts are easy, making it works another story.

True. I have a case that I can take measurements from... and I can adjust dimensions where its needed.

 

[Rich Fife]

Spacer is a good idea, you can play with different conrod lengths then too. At the end you can install whatever cyl you like

Exactly. It'd be nice to have a case where I can swap out top ends to suit my wants for that day.

 

[Ketchup]

Are you going to incorporate an option for side and exhaust fed transfer cylinders? A modular deck plate would help with that.