Meteor Cylinder Porting for Holzfforma G372XP

[Paul Fithian]

Received a clone 372XP the other day to learn how Husky's are set up and to have another go at porting. Ran it for ~ 5 minutes out of the box with 24:1 synthetic, worked and sounded right. Here's what I've found so far in a teardown:

- Unlike a recent G660 clone I ported, none of the fasteners on this one were loctited

- Timing as built with and without a base gasket. Very high transfer numbers seem odd


- Piston and single ring look OK, however there was some minor scuffing on the intake and exhaust sides:


Cylinder intake, some ragged edges are cause of minor scuffing on piston


-Cylinder Exhaust, more ragged edges


Muffler is completely open inside, here's a concept for a deflector (thanks @drf256 !) to braze on the top. Gasket opening on the cylinder discharge is 0.94 square inches, plan is to drill a pair of 3/8" holes in the top of the muffler, open these up to an oval, then braze on the deflector.


Many thanks to folks that have posted tips on porting this cylinder. Goal for port timing numbers is 102/120/78. Special thanks to @huskihl for info on this thread that shows moving the transfers up to 120: https://opeforum.com/threads/372xp-port-timing-numbers.29031/

New Husqvarna 577 57 24-01 piston pin bearing will be used in rebuild, plan is to keep everything else stock.

 

[Maintenance Chief]

Depending upon your intended use the exhaust port that you added may ignite a fire?(ask me how I know)!
Anyway, I put them on the back half of the muffler now. They still fit under the cover.

 

[huskihl]

I don’t modify the stock top deflectors on 372s or 390s any longer because once you promote more flow from there they start to burn your hands when you get up against a big log. At the very least I would make sure you turned it on an angle to the right

 

[WI_Hedgehog]

I've always considered the Chinese saws a pre-assembled parts kit you then have to tear down, find and modify/repair the problem areas, buy 20% of the remaining parts OEM or there's a good chance they're going to let go, put it back together, run LOTS of oil in the pre-mix (which is good for fogging mosquitoes and causing cancer), tune the carb so it runs "best" for whatever that means for the carb (or replace it), and then the saw is good to go for 250 hours at which point it's time to tear it down for inspection and see what's failing, though it seems they're getting better at putting out more that make it 500 solid run-time hours at 80% of the OEM power output.

I think they're possibly/probably good to learn on because parts are cheap, though if one batch of a particular part is bad you may keep getting bad parts until they make some good ones, or pony up some clams at the STIHL dealer (because I'm reading Husqvarna shut down quite a few of their gasser plants and went to Chin-lectrik saws). On that, STIHL is focusing on electric saws also, but nobody I know runs one; batteries are expensive and the da#n brain-box locks out the go-switch after 1.375 seconds of inactivity. A friend has a Milwaukee Electric (I live in Milwaukee, so no surprise) and they're really torque-monsters and run great on drill/power-tool batteries. In a tree they're really handy as they're so quiet you can yell at your ground squirrel (for no good reason, of course), that plus they're instant-on/instant-off. Chain speed isn't...well, it's an electric saw, and it cuts pretty fast for an electric saw, I'll give Milwaukee that. Down-side is it "may be" best to change out batteries at 1-bar because the saws "seem" to kill them otherwise (I've never let one go dead and they've been fine, so I can't really say either way). Wow I got lost.

To get back on track, some people have had great luck with the Chinese "generic" saws, though prices went up in order to gain that reliability improvement. Maybe some day I'll pull the trigger on one, but while I'm "young" I'd rather keep the bar buried than the saw on the magic fix-it bench. (meaning I'm still an OEM fanboy)

 

[srcarr52]

Your numbers seem a little off. I've never seen a 372 with 33° blowdown.

Also removing the 0.021" gasket on a with numbers I have from a Holzfforma cylinder should yield:
-3.6° reduction in exhaust duration, opening moving from 101.1° to 102.9°
3.2° increase in intake duration, moving the opening 71.4° to 73°
0.6° increase in blowdown, moving the opening from around 122.7° to 125.1°

So, in all, your measurement of the transfer ports seems pretty suspect. In order to have 33bd with 158 ex duration, and the stock squish clearance of around 0.043", the transfer ports would have to be 1.3 down from the squish band. Which is about 0.095" lower in the bore than usual.

Even if I plug in a transfer port that low it still only gains 1° of blowdown by removing the gasket thickness.

Note, this is all done with math and measured port heights from the squish band. The equations can be found in A. Bell's book "Two-Stroke Performance Tuning".

 

[Paul Fithian]

I thought the same, @srcarr52 they looked off to me. But check this picture that @huskihl posted on the thread I referenced above to get his transfers to 120 deg:

Before:



After


I 'll set up a ring to find out where 120 degrees is, the desired top of the transfers. Mine looks like Kevin's before picture above

 

[huskihl]

I thought the same, @srcarr52 they looked off to me. But check this picture that @huskihl posted on the thread I referenced above to get his transfers to 120 deg:

Before:

View attachment 391256

After
View attachment 391257

I 'll set up a ring to find out where 120 degrees is, the desired top of the transfers. Mine looks like Kevin's before picture above

Those pictures are after removing .050 from the squish band and cutting the base. Stock on the 372 is around 24 blow down

 

[Paul Fithian]

Here’s the ring set at 120 degrees and marked with a sharpie






Visual check confirms similar

 

[huskihl]

That’s a lot of chikasil and chaluminum to grind. You’ll likely grind through the roof

 

[heimannm]

Just to confirm one point that has already been made...I was running my 372 clone today (orange version) with a stock muffler and the dead ash I was cutting was smoking and glowing.

Normally I like to get my firewood home before I start burning it.

Mark

 

[jacob j.]

That’s a lot of chikasil and chaluminum to grind. You’ll likely grind through the roof

That's how the early 375k cylinders were - lots of blowdown. Many a porter had to seal up the roof of the transfers with JB Weld.

 

[Paul Fithian]

That’s a lot of chikasil and chaluminum to grind. You’ll likely grind through the roof

Looks like that to me also. Any suggestions on OEM or aftermarket P/C setups for a 372XP?

 

[farminkarman]

Looks like that to me also. Any suggestions on OEM or aftermarket P/C setups for a 372XP?

I wouldn't waste an OEM top end on a clone saw, but that is my opinion. I'm a little surprised the transfers are that low on the FT jug. I recently ported a pair of 372xp FT jugs. One was a 50mm and one a 52mm. I cut 0.040" from the band on the 50mm and only 0.030" on the 52mm. I cut ~0.055" from the base on both...even with that machine work, I didn't have to grind that much to raise the transfers to get my 18 degrees of BD. Maybe get another FT p&c? Definitely don't waste your money on a Hyway set.

 

[Ketchup]

OEM 50 or 51.4mm will be best, but they’re getting expensive. Some people like the Hyway and Meteor jugs but I think they’re harder to port than the cheap no name kits at 3 times the price. An off brand 52mm can be had from the Duke for cheap and can be returned if the timing is junk.

There can be a lot of extra grinding in an AM jug. The tunnels and ports can be under sized and the cooling fins so thick there is no air gap between.

You might as well epoxy the tops of the transfer
tunnels on the jug you have and give a try. Nothing to lose there but time.

 

[MG porting]

It's been a long while since I've been in here since I had to sell all my saw and truck because of my landlord decided to demo the place I lived in for ten years I'm getting back on track and got a good home to live in and lots of trees my new landlord even has a sawmill but anyway I've been looking at all the new clones that they've been coming out with I've built a ton of Stihl clones and got good at reworking them I've decided to turn to the dark side and try out the Husqvarna 372 clone and of course I'll be porting it from what I've learned from porting Stihls is don't touch the intake just clean them up exhaust 102 or 105 depending on what saw it is torque is king her still need bar lengths 28" to 36" I prefer 32" so I'll be porting the 372 I ordered for torque so being this is a 372xp what would be a good start on porting it for torque other than opening the lower transfers which I have no clue why Husqvarna did them the way they did??

 

[Paul Fithian]

Plan B in process

 

[srcarr52]

That's how the early 375k cylinders were - lots of blowdown. Many a porter had to seal up the roof of the transfers with JB Weld.

On the BB kits I would well on the top of the transfer tunnel before I even started grinding on them. It's a lot easier to weld when there isn't a hole to fill.

 

[Paul Fithian]

Muffler mod finished, deflector brazed on and high heat paint

 

[Maintenance Chief]

 

[Woodslasher]

Muffler mod finished, deflector brazed on and high heat paint
View attachment 391341
View attachment 391342
View attachment 391343

I usually make the hole in the muffler about the same size as the outlet's footprint, any particular reason you left it that small?