Husky 570 Crank Stuffers. Keep or Ditch?

[Brewz]

Hi folks.
Been a while…. Hope all are well.
I’m building myself a Husky 570 X-torq auto tune saw that I was given after it got strait fuelled.

I was just sitting here looking at these crank stuffers and thinking how they would stop a lot of the pulse driving the lowers as the crank lobes go past as the uppers open.

Interested to know if anyone has tried these saws with and without the stuffers to see what makes better power when ported.

Cheers

 

[Kiwioilboiler]

I know less than nothing Tony, so where does the reduction in case volume afforded by the stuffers trump what you're seeing you reckon old mate? Husky use them for some perceived reason yeah?

 

[67L36Driver]

I’d run rabbits and bay at the moon before deleting a crankcase ‘stuffer’.

A two stroke develops compression at both ends.

 

[Brewz]

If run rabbits and bay at the moon before deleting a crankcase ‘stuffer’.

A two stroke develops compression at both ends.

Yeah but the 371/372 didn’t use them, nor do any of the Stihl saws.
Something tells me they are not there to increase power.
If they lower the pressure pulse of tge crank lobes pumping the front feed lowers, that would technically lower emissions

 

[Ketchup]

My 2 cents.

In general I feel that lowering the intake and raising the transfers negatively effects case compression. Removing the stuffers seems like going farther in the wrong direction.

Edit:
What about widening the transfer lower in the case to flow on the sides of the stuffers?

 

[Stump Shot]

Only practical experience I have regarding this is putting 357 top ends on 359 cases. Which makes for a saw in between the two, or a 357 with more grunt if put another way.
The 570 was probably one of if not the smoothest saw I ever ran as is.
I can think of about just as many reasons to take them out as leave them in.
I'd hazard to say though, that if you like a peakier saw then leave them in, if you like more grunt down low, take 'em out.
A 575 top end will fit on the 570 if the cylinder has had it and will give some more power, the 576 however is a different design and will not fit.
There was an update on the seals of the 570 and the replacements should be sought for purchase if shopping places other than a dealer like Ebay, Ereplacement and any other outlet that may have old stock on hand. This will go far in the lessening of future failures.

 

[srcarr52]

Yeah but the 371/372 didn’t use them, nor do any of the Stihl saws.
Something tells me they are not there to increase power.
If they lower the pressure pulse of tge crank lobes pumping the front feed lowers, that would technically lower emissions

But 372's have less than 1/2 the transfer port length of the 570's.

 

[Brewz]

I’m in Australia and out timber needs different porting and power curves.
Yeah power is power, but where it makes it and how it spreads it across the rev range makes a huge difference in out hardwoods.
Max peak power numbers are not the goal here.

I’m just thinking outside the square on this…. Certainly not saying I know more than Husky’s design engineers but something has always bugged me about those stuffers.
I’m gunna go with my intuition and leave them out and see what it does.
I have never been impressed with the 570/575 but never ported one either,

Yes case compression is needed but I think there are other factors at play as well.
Case compression implies the fuel/air mix is compressed to create pressure.
When the uppers open the energy stored by this pressure releases up the transfers
Crank stuffers don’t compress so cannot add to this energy release.
Take a bike tire and a truck tyre and pump them both up to the same pressure, then punch a hole in the tyre.
The higher capacity of the truck tyre, even at a slightly lower pressure will push air out harder and longer due to the added volume and energy stored in that volume under pressure.

This is my line of thought.

Why did they use them…. And persevere with the stuffers even when they were plagued by bottom end bearing failures, which I suspect is due to reduced oil to the bearings due to the stuffers?
I think it’s emissions driven.

yes they have a long transfer path compared to the 372 but it’s also fed from bottom and top via the side of the piston to help bring that pressure back up faster.

Im gunna try them out.
If it sucks balls I will strip it and put them back in

 

[Brewz]

Well…. I guess we may as well turn this into a bit of a build thread to follow along with progress.

while the cases were split I took the opportunity to round out and smooth the restrictive lower feeds from the cases.
Squared edges and casting lips gone.
Not enlarged, just port matched to the cylinder gasket and the cylinder will get the same.

should improve pumping efficiency.

 

[Brewz]

 

[TreeLife]

I'll be completely honest, im one of those weird guys that feel the 576 never got the love it deserved. Insanely smooth, reliable and plenty of torque for the platform. People pissing about power to weight? It might be half a pound heavier than a 72 and you don't need to touch a screw driver...

 

[Brewz]

I'll be completely honest, im one of those weird guys that feel the 576 never got the love it deserved. Insanely smooth, reliable and plenty of torque for the platform. People pissing about power to weight? It might be half a pound heavier than a 72 and you don't need to touch a screw driver...

Yeah they do go good.
I just rebuilt a non auto tune 576 for a friend that got cooked.
This 570 is auto tune

 

[jacob j.]

Yeah they do go good.
I just rebuilt a non auto tune 576 for a friend that got cooked.
This 570 is auto tune

I got one of these to do also, so I'm keen on what you find out. I got mine for free for helping an old boy rescue his old Jeep out of a ravine.

 

[67L36Driver]

View attachment 342726

Wait! That space filler thingy rotates WITH the crankshaft?

[emoji848]

That’s an entirely different type of ‘stuffer’ than the old McCulloch cart engine were retrofitted with.

 

[Brewz]

Wait! That space filler thingy rotates WITH the crankshaft?

[emoji848]

That’s an entirely different type of ‘stuffer’ than the old McCulloch cart engine were retrofitted with.

Yep
Sits between the crank lobes and the bearing

 

[Ketchup]

For science!

I was thinking take this part away if you left the stuffers.



But better to try both!

 

[Stevetheboatguy]

Juzt a heads up....... If you need to order a cylinder for any of the 570-575 saws. There were two designs and they don't interchange. The early 570-575 were their own. The later second generation 570-575 used the same cylinder base as the 576.

Love to run that series saw. Seriously dislike ordering parts for them. So many variations.


Steven

 

[Brewz]

For science!

I was thinking take this part away if you left the stuffers.

View attachment 342769

But better to try both!

No that’s structural and the crank lobe sits there and is wider while transfers are open so no point.

I don’t look at transfer feed as flow like water down a pipe, its more lots of short controlled puffs, we just need to improve the ability of that air to to flow at each puff.
Too big a hole and you lower velocity.
Sharp edges and lips create drag.
I try to create a smooth even path for the flow to travel over.
There is plenty of capacity in the lower feed area to supply from.

 

[Brewz]

Juzt a heads up....... If you need to order a cylinder for any of the 570-575 saws. There were two designs and they don't interchange. The early 570-575 were their own. The later second generation 570-575 used the same cylinder base as the 576.

Love to run that series saw. Seriously dislike ordering parts for them. So many variations.


Steven

I didn’t know that.
That explains why I had to trim the cylinder gasket to get it to fit properly…. All OEM.

just about to cut the base.
Timing is 102/116/72 stock…. Nice
I doubt I will change it much at all

 

[Brewz]

Correction on stock timing
It was 104/116/72
I took .030 out of band, squish at .022
Now at 101/116/74
Exhaust widened from 55% to 65%
Intake and stratos just smoothest out and left stock
I wanted more blowdown cause the uppers were full of black burn from exhaust gas backfill.