Play time?

[srcarr52]

Transfers open
122 on intake side then 129 ex side.

Primary/secondary

Factory coil is 39* btdc stock could try the more tame 590 coil, it is around 32* total

Wow, that is a lot of transfer port stagger. 7deg is like 0.060" in height! Must have been beer:30 on a Friday when those cores got installed in the mold.

 

[Red97]

Wow, that is a lot of transfer port stagger. 7deg is like 0.060" in height! Must have been beer:30 on a Friday when those cores got installed in the mold.

I was thinking that, along with the stroke/rod ratio stretching things more crank rotation per .001" traveled down bore.

 

[MG porting]

Echo (saw) is 37.6 stroke

046 (cylinder) is 36mm stroke

The stock echo has a really tall piston for 45mm

After base cleanup I didn't have to take much out of the band.

As assembled
103
122s 129p
75
79.85cc

Which I was pretty happy with all but not having a lot of skirt to play with.

Would guess comp is still over 200psi

Have not timed the big bore jug yet, but should be in the same ball park.

So far I like the port timing numbers that you're coming up with you should be able to run a good size bar and chain.

 

[Red97]

Well, the case is together.

 

[Red97]

Now to remember where I put the seals......

I remember putting them somewhere i shouldn't forget.

 

[Red97]

54mm at bdc.

 

[drf256]

Looks great Joe.

I was more referring to the difference in port heights as it relates to longer strokes and the difference in piston speeds at different points in the sine-wave like cycle.

For example, the fact that a 120 roof height transfer on a 32mm stroke crank can be the same physical height as 112 on a 36mm stroke. The longer the stroke on a saw, the more the transfers move in degrees vs. the exhaust roof when we drop a jug. The piston speed is the fastest @90*, so more physical movement per degree mid bore.

Cant wait to see the results of what you come up with.

 

[drf256]

Whats the original stroke and what stroke are the cylinders designed for? I've found it's easier to destroke a cylinder than go to a larger stroke. When going to a larger stroke the intake and exhaust durations can get out of hand quickly.

Are they all the dual transfer strato design like the 562?

I’m still trying to wrap my head around transfer timing, strato effect, case volume, etc...

Am I correct to say that regardless of strato design vs non, if you don’t have a enough blowdown, you’ll backstuff the uppers anyway if the exhaust pressure isn’t vented enough to be less than transfer pressure when they open?

 

[Fruecrue]

Great thread!

 

[Red97]

Looks great Joe.

I was more referring to the difference in port heights as it relates to longer strokes and the difference in piston speeds at different points in the sine-wave like cycle.

For example, the fact that a 120 roof height transfer on a 32mm stroke crank can be the same physical height as 112 on a 36mm stroke. The longer the stroke on a saw, the more the transfers move in degrees vs. the exhaust roof when we drop a jug. The piston speed is the fastest @90*, so more physical movement per degree mid bore.

Cant wait to see the results of what you come up with.

Thank you Al

I know exactly what you are saying about the long stroke, and the difference in the numbers. Ported some pretty strong stock versions with that approach.

Guess i need to order a few extra pistons.

File the crown instead of wasting a jug.

My original build has higher numbers than I would to have likes.

97,117,80 on a 50mm bore. That one has the attitude/feel I'm looking for. Just want to work my way up to it.

Probably get these other 2 saws (86 & 92cc) built first.

Then go back and start trying to port for gains.

Really do appreciate the info from you, and the other's that have taken the time to reply. Keeps the ideas flowing.

 

[srcarr52]

Are they all the dual transfer strato design like the 562?

I’m still trying to wrap my head around transfer timing, strato effect, case volume, etc...

Am I correct to say that regardless of strato design vs non, if you don’t have a enough blowdown, you’ll backstuff the uppers anyway if the exhaust pressure isn’t vented enough to be less than transfer pressure when they open?

The OP is using a 460 jug so it's a non strato saw.

If you are referring to the Husky 550, 572, yes they are all the same design as the 562.
There are more factors to having backflow in the transfers than just blowdown. Crankcase compression is the biggest factor which is affected by your intake duration, also longer exhaust duration lets the gasses expand further and lessens the cylinder pressure before opening.

 

[Red97]

Ok, elastostart? Or D handle?

This 52mm did not cooperate while trying to get a compression reading...

First saw I've ever had fight me this bad.

Maybe the recoil is bad, (I'll swap on a different one) pulled the carb off so I didn't flood the saw. Normally pull 15 times to get a good solid reading.

Got to compression stroke number 4 and was stopped in my tracks....

Gauge at 150 psi.

1 foot in the handle, other on the bar Both hands pulling the rope....

Thump...... thump...... thump...... dang...


That was a first...

Maybe I would be able to check it with a 95 exhaust...

 

[Definitive Dave]

decomp and D handle

 

[Czed]

 

[Red97]

decomp and D handle

Good thing these are decomp jugs...

 

[spencerpaving]

Another thing to think about....I think smaller saws have smaller starter pulleys...That means less leverage to pull on....I might be wrong though...

 

[Red97]

Another thing to think about....I think smaller saws have smaller starter pulleys...That means less leverage to pull on....I might be wrong though...

I think you are correct.

 

[Red97]

Decisions, decisions...



Finish the 54mm, or attempt making the 56mm cylinder from my spare big bore jug today.

 

[Red97]

Might even be lighter than a stock 620...

 

[Red97]

Got the band cut.

Might have to open the chamber on this some...