Yet Another 044 hybrid project

[MattG]

Hello again OPE forum,

So hello again, I'm the crazy Brit who did the 044 hybrid back in 2017/18 with a 10mm wristpin case. Grinding the crankcases to give the 12mm crank the clearance etc. etc.

Well about 4 years ago, I bought another 044 this time a 12mm model, and I was even more crazy and bought a Hyway ms460 BB (54mm) kit. Thing is since then "life has tended to get in the way", so after stripping the 044 down, I never got much further than just basic clearance work (cylinder screw holes), jug sides and crankcase mouth and fitting the new bearings and putting the crank back in.

Since then my day job (programmer) gotten much much more stressful. I figured out that I really needed a break, distraction etc. so I've started getting back into this saw building malarkey.

Now I have deleted the BG and have ground my squish to about 0.52-0.66 (think that's good) and I'm down to wanting to post on here for advice.

What I noticed is that at BDC the piston is about 2mm below the EXH port floor. I've read that it's optimal when it's crown is flush at BDC. But at TDC I've got scarcely 2mm of skirt overlapping the port floor. So I wondered is safe to grind say a 1mm of my exhaust floor down? Is it worth it? I'm obviously wanting muchos power but free porting the saw seems like a a bad idea.

How close can I go?

thanks Matt

 

[Woodslasher]

Just to clarify, your squish is 0.66mm and 0.66 inches, correct?

 

[Funky sawman]

.66 inches would be enough squish that the saw would have 5 lbs of compression lol

 

[drf256]

My $.02

The big bore jug. More likely to make better power from a stock 52mm jug, the big bore jugs tend to encroach the transfer tunnels to gain the real estate needed for the bigger bore.

The aftermarket jugs are noted for issues. I’ve had a nice looking one eat through the plating in under 10 tanks. The castings can be out of round, the plating may chip easily when grinding. They lack the finesse of an oem jug in the transfers, and it’s a part that’s tough to see.

There’s already a mismatch in the 044/46 combo in terms of case vs jug displacement. That’s why they tend to be more high winding with less torque than a typical well done 046/460. There are exceptions, but you are accentuating this mismatch with a 54mm bore jug.

The exhaust port issue. Most saws at BDC will have a piston crown above the exhaust port floor. The majority of exhaust flow happens in the first few degrees of piston decent with diminishing returns as it continues its descent. I’d personally leave it alone. It’s had to imagine you actually are below the floor at BDC, it’s not typical on a Stihl.

 

[MattG]

Just to clarify, your squish is 0.66mm and 0.66 inches, correct?

Mil

My $.02

The big bore jug. More likely to make better power from a stock 52mm jug, the big bore jugs tend to encroach the transfer tunnels to gain the real estate needed for the bigger bore.

The aftermarket jugs are noted for issues. I’ve had a nice looking one eat through the plating in under 10 tanks. The castings can be out of round, the plating may chip easily when grinding. They lack the finesse of an oem jug in the transfers, and it’s a part that’s tough to see.

There’s already a mismatch in the 044/46 combo in terms of case vs jug displacement. That’s why they tend to be more high winding with less torque than a typical well done 046/460. There are exceptions, but you are accentuating this mismatch with a 54mm bore jug.

The exhaust port issue. Most saws at BDC will have a piston crown above the exhaust port floor. The majority of exhaust flow happens in the first few degrees of piston decent with diminishing returns as it continues its descent. I’d personally leave it alone. It’s had to imagine you actually are below the floor at BDC, it’s not typical on a Stihl.

I've gotta be honest. I'm not that impressed with the jug. But it's what I've got, and as it's just a play, destress me from my day job, I'm cool with continue to play.

BTW that piston crown is definitely below the floor at BDC. Will get a piccy in the next day or 2.

 

[MattG]

Just before BDC, crown flush with floor:


and now at BDC piston crown is below EXH floor.


so I'll ask my question again. If I have about 1.8mm of the bottom of the skirt overlapping the jug below the floor at TDC, how much can I grind off the floor before I risk wrecking the engine by free porting it? I'm assuming that at least 0.5mm of overlap should be left.

Matt

 

[huskihl]

Just before BDC, crown flush with floor:
View attachment 347523

and now at BDC piston crown is below EXH floor.
View attachment 347524

so I'll ask my question again. If I have about 1.8mm of the bottom of the skirt overlapping the jug below the floor at TDC, how much can I grind off the floor before I risk wrecking the engine by free porting it? I'm assuming that at least 0.5mm of overlap should be left.

Matt

None of it matters down there. As said previously, 90% of the exhaust flow is in the first 10% of the port opening. It would probably run better if the floor was lowered a little bit due to the added port area, even if it free-ported a little

 

[MattG]

None of it matters down there. As said previously, 90% of the exhaust flow is in the first 10% of the port opening. It would probably run better if the floor was lowered a little bit due to the added port area, even if it free-ported a little

Thanks Huskihl,

So you reckon that if I ground that floor a bit (say 1.5mm) it wouldn't really hurt it? Out of interest have you ever free-ported a saw or got damn close and still ended up with a decent machine?

thanks Matt

 

[huskihl]

Thanks Huskihl,

So you reckon that if I ground that floor a bit (say 1.5mm) it wouldn't really hurt it? Out of interest have you ever free-ported a saw or got damn close and still ended up with a decent machine?

thanks Matt

I’ve never attempted to create a freeport scenario, although it has happened. I used an 064 piston in a Dolmar 9010 because it had wider skirts.. Unfortunately, those skirts were also shorter. The bottom freeported quite a bit. But it runs good. I’ve never seen a bottom freeporting issue hurt performance. Many race saws have a notch at the bottom of the exhaust port designed just for that purpose

 

[MattG]

I’ve never attempted to create a freeport scenario, although it has happened. I used an 064 piston in a Dolmar 9010 because it had wider skirts.. Unfortunately, those skirts were also shorter. The bottom freeported quite a bit. But it runs good. I’ve never seen a bottom freeporting issue hurt performance. Many race saws have a notch at the bottom of the exhaust port designed just for that purpose

Wow. I never knew that!

Thanks for your help. I'll go ahead.

 

[drf256]

Wow. I never knew that!

Thanks for your help. I'll go ahead.

It’s like the effect a header has on a car engine. The inertia of the exhaust flow is thought to create a negative pressure area in the port when it closes. The freeport helps the case pull in fresh charge.

 

[MattG]

It’s like the effect a header has on a car engine. The inertia of the exhaust flow is thought to create a negative pressure area in the port when it closes. The freeport helps the case pull in fresh charge.

That sounds plausible. I did think it through the other day. I mean - were I to effectively zero the floor with the skirt at TDC, i.e. "on the edge" of a free port, then it's gonna take only like a degree or so until it's sealed back so probably not the end of the world.

Anyway I've degreed it now. I'm getting:

EXH 98-99
INL 77
TRANS 79

From memory 98-99 on the EXH sounds pretty aggressively tuned for something straight off the supplier. Am I right? I'd hoped for a strong work tune, but isn't 98-99 EXH quite high revving?

I guess I'm leaving the EXH height as is. Width wise, I measured it and compared with the bore dia. It looks like I can go 2mm wider on both sides, and still have 2mm+ skirt overlap, and be within 65% of the bore.

I'll probably widen the INL too, but excepting cleaning castings will leave the TRANS as is.

Have you guys got any comments on these ideas, and my numbers so far?

Matt

 

[huskihl]

That sounds plausible. I did think it through the other day. I mean - were I to effectively zero the floor with the skirt at TDC, i.e. "on the edge" of a free port, then it's gonna take only like a degree or so until it's sealed back so probably not the end of the world.

Anyway I've degreed it now. I'm getting:

EXH 98-99
INL 77
TRANS 79

From memory 98-99 on the EXH sounds pretty aggressively tuned for something straight off the supplier. Am I right? I'd hoped for a strong work tune, but isn't 98-99 EXH quite high revving?

I guess I'm leaving the EXH height as is. Width wise, I measured it and compared with the bore dia. It looks like I can go 2mm wider on both sides, and still have 2mm+ skirt overlap, and be within 65% of the bore.

I'll probably widen the INL too, but excepting cleaning castings will leave the TRANS as is.

Have you guys got any comments on these ideas, and my numbers so far?

Matt

The transfer timing isn’t right. Recheck that.

 

[MattG]

The transfer timing isn’t right. Recheck that.

Thanks. I'll check that when I go back to the workshop. I guess I could have accidentally done that measurement relative to BDC not TDC,

 

[huskihl]

Thanks. I'll check that when I go back to the workshop. I guess I could have accidentally done that measurement relative to BDC not TDC,

I thought about that, but it’s still off 20°

 

[MattG]

I thought about that, but it’s still off 20°

Yeah... I know. I'm outta practice! Lol. Re measured it earlier, it's 122. So I guess I got

EXH 99
INL 77
TRN 122

23* of blowdown should be fine, yeah? I've already widened the EXH and lowered it. Try and do photos tomorrow.

Any ideas for the INL degree wise? I don't really want too high revs, power will do me fine. Will widen if poss - I guess the issue there is how close the edges become to the ring pegs?

 

[farminkarman]

Yeah... I know. I'm outta practice! Lol. Re measured it earlier, it's 122. So I guess I got

EXH 99
INL 77
TRN 122

23* of blowdown should be fine, yeah? I've already widened the EXH and lowered it. Try and do photos tomorrow.

Any ideas for the INL degree wise? I don't really want too high revs, power will do me fine. Will widen if poss - I guess the issue there is how close the edges become to the ring pegs?

Not speaking from any experience with this platform, so take that for what it's worth...I would probably lower the intake 2-3 degrees and shape it to your liking...then let it rip.

 

[huskihl]

Yeah... I know. I'm outta practice! Lol. Re measured it earlier, it's 122. So I guess I got

EXH 99
INL 77
TRN 122

23* of blowdown should be fine, yeah? I've already widened the EXH and lowered it. Try and do photos tomorrow.

Any ideas for the INL degree wise? I don't really want too high revs, power will do me fine. Will widen if poss - I guess the issue there is how close the edges become to the ring pegs?

The ring ends are at the edge of the skirt and will be above the opening (unless you grind the roof corners too high). I’d lower and widen the intake enough to shape it if you want. And widen the exhaust a bit without raising it

 

[drf256]

That sounds plausible. I did think it through the other day. I mean - were I to effectively zero the floor with the skirt at TDC, i.e. "on the edge" of a free port, then it's gonna take only like a degree or so until it's sealed back so probably not the end of the world.

Anyway I've degreed it now. I'm getting:

EXH 98-99
INL 77
TRANS 79

From memory 98-99 on the EXH sounds pretty aggressively tuned for something straight off the supplier. Am I right? I'd hoped for a strong work tune, but isn't 98-99 EXH quite high revving?

I guess I'm leaving the EXH height as is. Width wise, I measured it and compared with the bore dia. It looks like I can go 2mm wider on both sides, and still have 2mm+ skirt overlap, and be within 65% of the bore.

I'll probably widen the INL too, but excepting cleaning castings will leave the TRANS as is.

Have you guys got any comments on these ideas, and my numbers so far?

Matt

I wonder what the total dimension is of your exhaust port. In general, the piston crown is above the ex floor at BDC. Being your jug is AM, it’s conceivable that you have a short height port. If that’s the case I’d lower it and avoid a freeport situation.

We all have seen this in AM big bore 066/660 jugs. The piston skirt is intentionally shorter than stock because it won’t fit into the case at BDC. I wonder if you have the same situation and they raised the floor to stop it.

Can you measure total port height with a pair of calipers? I have an oem 460 jug I can measure here.

 

[MattG]

@drf256

Hi mate,

TBH I've already done ahead and done the porting I wanted to do. So any measurements won't really be useful now. You're dead right with your theory re. short piston and lower exhaust height. These hyway kits are truly horrid IMHO. I had to do a lot of work just to get started, e.g. the exhaust flange was gross - most of my filing and grinding was in order to make this properly match a stihl EXH gasket!

The INL carb side was also rubbish. I needed to fill the top and file the bottom of the entry bore. I got around to doing some piccies. I've left the EXH opening at 98-99 but lowered (matches crown at BDC, about a 0.5mm freeport at TDC) and widened to 33mm.



sorry I'm utterly crap doing piccies with this stupid new phone that I had to buy to make my banking app work