660 clone port timing numbers for milling (torque)

[huramentzefix]

I smoked my cylinder on my 660 clone while milling by having the high adjustment too lean.
Now I am holding a new 36$ knock off cylinder in my hand and have just ordered a degree wheel to check timing.
By just measunring with the calipers I can tell that this cylinder is way off compared to the other one.

The upper edge of the exhaust is 3.2 mm lower than the stock holzfforma!
It's about the same for the lower edge. The entire exhaust port has moved down by 3.2 mm.
The transfers are 1.64 mm lower
The Intake is 2.6 mm lower
piston from top ring to Crown -0.5mm
from piston pin to crown -0.5mm
Blowdown is 3.8 mm instead of 2.05 mm (so there might be room to correct all this mess hopefully)

What squish and port numbers should I look for for a milling saw? I am looking for torque and don't want to breed a race-horse.
What I am after is a wide band, not a narrow high-power spike. I was happy with the power as it was (even without muffler mod) before I cooked it.
I will check timings once I receive my degree wheel.

What are good timings for a milling 660 and what squish? and how to achieve torque gain, polishing, widening?

 

[Lightning Performance]

I smoked my cylinder on my 660 clone while milling by having the high adjustment too lean.
Now I am holding a new 36$ knock off cylinder in my hand and have just ordered a degree wheel to check timing.
By just measunring with the calipers I can tell that this cylinder is way off compared to the other one.

The upper edge of the exhaust is 3.2 mm lower than the stock holzfforma!
It's about the same for the lower edge. The entire exhaust port has moved down by 3.2 mm.
The transfers are 1.64 mm lower
The Intake is 2.6 mm lower
piston from top ring to Crown -0.5mm
from piston pin to crown -0.5mm
Blowdown is 3.8 mm instead of 2.05 mm (so there might be room to correct all this mess hopefully)

What squish and port numbers should I look for for a milling saw? I am looking for torque and don't want to breed a race-horse.
What I am after is a wide band, not a narrow high-power spike. I was happy with the power as it was (even without muffler mod) before I cooked it.
I will check timings once I receive my degree wheel.

What are good timings for a milling 660 and what squish? and how to achieve torque gain, polishing, widening?

I'm ready start selling those in AM or OE just built for milling.
My 660 will pull a 60 but prefers the 36, 40 or something lesser. Anyway you can't get to where they need to be without heavy machine work. I figure 150 a jug should be about right for AM ones ready to mill. Doing a new stock one will be 110 machining and port work only. They need much less work as you can clearly see. Go here. 100+ E 122-124 T 78-9 I
The rest you can figure out. Just remember every crumb you take out increases case volume you can't get back without extra work. Your intake will need extensive work on any jug AM, OE, ect. If your not all in it isn't worth the trouble to bother imho. You will never find a solution without compression and timing being correct. Polishing is for turds. Your on your own with squish but I run 0.018 So... the peanut gallery will be along shortly to discredit that.
Enjoy

 

[huramentzefix]

It seems that you don't like peanuts?

Good Idea to sell those jugs for milling on amazon.

Well thank you so far I will have to wait for my degree wheel to see where I am at, and then see how much I would have to take off to get to your numbers.
What extensive machine work are you referring to?
I will possibly put it into the lathe to get my squish to where I want it to be.
What else is there to do?

And remember, I want a saw with a wide band for milling. No crazy screaming competition disc cutting machine that has a pointy narrow band. And I don't need to screw around to get the last % of power either. This saw has plenty for what I am doing already.

I think 100+ E 122-124 T 78-9 I is pretty much 661 stock?

It's said that the Meteor are the best, is that true? Does anyone here have the timing numbers of a meteor here?

I just stuck the cylinder on as is so that I have a running saw till I get the degree wheel. It runs and revs OK, just haven't tested it yet to see how it pulls.

 

[Sierra_rider]

I'm ready start selling those in AM or OE just built for milling.
My 660 will pull a 60 but prefers the 36, 40 or something lesser. Anyway you can't get to where they need to be without heavy machine work. I figure 150 a jug should be about right for AM ones ready to mill. Doing a new stock one will be 110 machining and port work only. They need much less work as you can clearly see. Go here. 100+ E 122-124 T 78-9 I
The rest you can figure out. Just remember every crumb you take out increases case volume you can't get back without extra work. Your intake will need extensive work on any jug AM, OE, ect. If your not all in it isn't worth the trouble to bother imho. You will never find a solution without compression and timing being correct. Polishing is for turds. Your on your own with squish but I run 0.018 So... the peanut gallery will be along shortly to discredit that.
Enjoy

I concur with these timing numbers in a milling saw, although I do prefer a bit wider squish.

 

[Sierra_rider]

It seems that you don't like peanuts?

Good Idea to sell those jugs for milling on amazon.

Well thank you so far I will have to wait for my degree wheel to see where I am at, and then see how much I would have to take off to get to your numbers.
What extensive machine work are you referring to?
I will possibly put it into the lathe to get my squish to where I want it to be.
What else is there to do?

And remember, I want a saw with a wide band for milling. No crazy screaming competition disc cutting machine that has a pointy narrow band. And I don't need to screw around to get the last % of power either. This saw has plenty for what I am doing already.

I think 100+ E 122-124 T 78-9 I is pretty much 661 stock?

It's said that the Meteor are the best, is that true? Does anyone here have the timing numbers of a meteor here?

I just stuck the cylinder on as is so that I have a running saw till I get the degree wheel. It runs and revs OK, just haven't tested it yet to see how it pulls.

Generally speaking, I like to arrive at my final intake timing number via machine work...i.e cutting the squish band and decking the cylinder to lower the intake. There are some variables to this...some cylinders have a gap in between the cylinder head surface and the top of the plating. Lower the cylinder too much and you can end up dropping the top ring into this gap.

As far as a wide powerband, don't go too high on the exhaust and have decent blow down numbers, and you should be fine. Blowdown and transfer ports are probably where most controversy and debate lies in porting, but I like 22-25* of blow down on the dual-transfer Stihls. Again, that's just my opinion and there are people that like more blowdown that that, so your mileage may vary.

 

[huramentzefix]

OK thank you guys so far.

it seems that most of the pros don't like the 56 mm bore kits because they supposedly don't make good power.
I have read that many of them have freeporting issues.
The 56 mm cylinder kit I can get for 23$, the 54 mm is 25$ I still ordered the smaller one.

What is wrong with those big bore kits for the 660's?

 

[thompsoncustom]

OK thank you guys so far.

it seems that most of the pros don't like the 56 mm bore kits because they supposedly don't make good power.
I have read that many of them have freeporting issues.
The 56 mm cylinder kit I can get for 23$, the 54 mm is 25$ I still ordered the smaller one.

What is wrong with those big bore kits for the 660's?

The problem with the BB kits is garbage timing numbers so if you just slap it on it might make less power than the stock holzfforma one did.

If your gonna do the work and alter your timing than I would go with the BB if not I would stick with the stock jug and just widen the ports.

As far as what timing number to use for milling, I would keep to exhaust roof as low as possible which will give you more compression and less RPM. The standard numbers for a good running 660 are 100/120/80 a lot of the time but for you I would like to see the exhaust 105+ if possible. As far as squish goes I like to run thing tighter than most the standard seems to be to take it do to .020 but I like to go to .015 which again ups your compression. Higher compression=More power through out the entire powerband. Blow down in the 20 to 25 range.

As far as numbers widening the ports for a work saw 65% of the cylinder diameter for the intake is a good place to be, the limiting factor is the piston skirt width but you want to have enough on there to stop/seal air flow and your not building a cookie cutter anyways so don't go wild.

Lowers: just try to blend them and take any lips off the bottom. Your trying to improve airflow without removing to much material.

Uppers: besides raising them (if needed) you can benefit from pointing the transfer more towards the intake (if needed) some do a good job from the factory and some AM cylinder just blow straight across the piston.

Exhaust: This is the only part I can see free porting being a issue as there is no support on the bottom of the piston at TDC which means I wouldn't widen the exhaust as much to support the piston more. One of those thing youll just have to see when you get into it. I fell that .050 of shirt support on each side is probably safe when free porting but you might want to check into that as idk without any lower support.

Go slow and check your numbers a lot the worse part of doing it is just taking the cylinder on and off all the time to recheck your timing numbers as you go.

And you said you already burnt one top end up running to lean so obviously you need more fuel but with milling I would also be running 32:1 but that's just my personal opinion. Oh and open up that muffler not only for the power but to get the heat out.

 

[Lightning Performance]

Generally speaking, I like to arrive at my final intake timing number via machine work...i.e cutting the squish band and decking the cylinder to lower the intake. There are some variables to this...some cylinders have a gap in between the cylinder head surface and the top of the plating. Lower the cylinder too much and you can end up dropping the top ring into this gap.

As far as a wide powerband, don't go too high on the exhaust and have decent blow down numbers, and you should be fine. Blowdown and transfer ports are probably where most controversy and debate lies in porting, but I like 22-25* of blow down on the dual-transfer Stihls. Again, that's just my opinion and there are people that like more blowdown that that, so your mileage may vary.

The ring of death isn't good. If he gets something can be cut 60+ to get the exhaust back the casting will be thin or gone on the top of the transfer ports. The cylinder will be out past 86 on the intake at that point so filling it isn't an "option" at that point. You want 200 psi in an AM jug you also need to cut the band and angle cut it to lay off for 50% no more or your just building unwanted heat. My oe is cut 42 on thick base 97 cylinder so it didn't need much with 126 transfers to start. They went up a good bit but we'll within reason. Next one gets the transfer lower up top filled to the BDC piston height. I want more flow there on the floor without chopping up my piston and ruining the quench area we just made. AM will need the casting fixed on top of the external transfer turns up top and fill the intake. Ain't no fixing the free port on stock height pistons. Live with it.

 

[huramentzefix]

thanks so far for the good tips.
@Lightning Performance it's a work saw, I am not building a fuel gurgling cookie monster. I am not intending to go extreme anywhere. My intention is to work with that saw and use it hard, and not to have it open all the time because something broke.
not intending to go below 25°. but let's wait for my digital degree level.
less power = more work achieved

 

[huramentzefix]

Ain't no fixing the free port on stock height pistons. Live with it.

for which cylinder is this? I just stuck the piston all the way in into the one that I have cooked (holzfforma) and there is no freeporting.
is this for the big bore?
If so then I would rather stay with something that has not freeporting.

how about shortening the skirt on the intake?

 

[thompsoncustom]

If so then I would rather stay with something that has not freeporting.

What is it about free porting that concerns you?

when some of the pro's do port/mill work on a saw they make it free port to get everything where they want.

 

[Lightning Performance]

What is it about free porting that concerns you?

when some of the pro's do port/mill work on a saw they make it free port to get everything where they want.

That post above yours is just grasping at straws unfortunately. The person doesn't understand the port timing is so far gone on the AM offerings you can just have your cake and eat it to.
Wanting to cut an intake skirt clearly shows that.

 

[huramentzefix]

I have just received my 22$ big bore cylinder kit.
when I push the piston all the way in then I have I tiny gap in the exhaust port.
With correct squish that gap would equalize out.

I was thinking about lowering the cylinder by about 2mm so that I have the skirt covering the exhaust by 2mm.
Is less also OK or is even more required?
It seems that there is plating till to the top but the hone marks don't go all the way up, even not in current condition.

I haven't taken the numbers yet, but by dropping the jug I will also reduce blow-down?

What would be an advisable piston if I want to go down that route?

Numbers will follow as soon as I am not using the chainsaw anymore for my current project.

 

[thompsoncustom]

I have just received my 22$ big bore cylinder kit.
when I push the piston all the way in then I have I tiny gap in the exhaust port.
With correct squish that gap would equalize out.

I was thinking about lowering the cylinder by about 2mm so that I have the skirt covering the exhaust by 2mm.
Is less also OK or is even more required?
It seems that there is plating till to the top but the hone marks don't go all the way up, even not in current condition.

I haven't taken the numbers yet, but by dropping the jug I will also reduce blow-down?

What would be an advisable piston if I want to go down that route?

Numbers will follow as soon as I am not using the chainsaw anymore for my current project.

as long as u have enough support on the sides you don't have to have anything on the bottom at all and may Freeport to get the numbers you want which is not a problem.

lowering the jug will not change blow down but it will bring the exhaust port down which is what you want.

I would put a pop up in it since your after torque.

start by posting your numbers and build your plan from there.

 

[huramentzefix]

As far as your free port versus squish compromise question, I’d adjust the free port to zero & just accept the 0.027” squish. For a 100cc saw, that squish will help keep the starter assembly in one piece!

I guess it's been too long since I did port work the last time (20 years +) and I have to correct my own errors here.
Of course I would have to raise the cylinder 2mm to get rid of the freeporting problem, not lower it.

freeporting might be acceptable for some, it is not for me though. hotshots idea is a good one but I would still prefer a longer skirt.

before I can get numbers I need to find a piston with a longer skirt so that I don't have any more freeporting.
I am not looking for a higher compression, I am looking for a piston with a suitable skirt.

by raising and lowering the cylinder you change blow down together with everything else.
the crankshaft has to rotate more ° at 0° or 180° than it has to at 90°, to sweep a certain distance.
don't remember though how much that has an effect?

does the hyway pop up 56mm piston have a longer, the correct, skirt length? Or any other non-pop up piston?

I will post numbers as soon as I can pull the saw apart.

 

[thompsoncustom]

I guess it's been too long since I did port work the last time (20 years +) and I have to correct my own errors here.
Of course I would have to raise the cylinder 2mm to get rid of the freeporting problem, not lower it.

freeporting might be acceptable for some, it is not for me though. hotshots idea is a good one but I would still prefer a longer skirt.

before I can get numbers I need to find a piston with a longer skirt so that I don't have any more freeporting.
I am not looking for a higher compression, I am looking for a piston with a suitable skirt.

by raising and lowering the cylinder you change blow down together with everything else.
the crankshaft has to rotate more ° at 0° or 180° than it has to at 90°, to sweep a certain distance.
don't remember though how much that has an effect?

does the hyway pop up 56mm piston have a longer, the correct, skirt length? Or any other non-pop up piston?

I will post numbers as soon as I can pull the saw apart.

nobody aims to be freeporting its just a worthwhile side effect in some cases.

if you can find a longer skirt that would be great but raising the cylinder is going the wrong way. if you changed nothing else you would lower compression, power, and torque.

 

[rola]

Hello all,my first message on here, have tried these BB kits and are currently working on a few idea's.
I suggest looking at using a MS661 or husq 395 piston and clearancing the case etc to make it work.Problem with the BB is they shortened the piston 2mm so it didn't hit the case, this caused all sorts of issues with port timing.
Have just made a hybrid ms361 clone with 440 crank and 460 cylinder and carb, 272 piston and ms360 flywheel. Still needs some fine tuning. But very pleased with the result.

 

[huramentzefix]

thanks guys for all your help so far.
I just started looking at timing numbers of the big bore.
And as has been said here further up, the intake is garbage!
I am getting 185° total intake and 189° total exhaust. Transfers I have just eyeballed at around 123°
If I drop the cylinder past 100° exhaust then I might be able to close the freeporting-gap.
I haven't checked squish yet.

Is this JB'ing the intake a reliable solution?

the AUMEL 54mm Cylinder Piston Kit For Stihl MS660 has timing of:
E190° I 186°

the Yindina YULI 56MM Cylinder Head Piston Kit Compatible for Stihl 066 MS660 has a timing of:
E 189° I 185°

the original holzfforma has timings of:
E164° I 158°

the holzfforma ran great.
what are timing numbers on hyway and meteor?

 

[rola]

Thanks, I have a Hyway will check that, the BB piston is about 41mm and the stroke is 40mm so with .5mm(0.020") squish there might be just enough length to stop the freeporting.
660 piston is 43mm long with 23mm comp height, 20mm pin to skirt
288XP (54mm bore) piston is 43mm long with 22mm comp height, 21mm pin to skirt
660BB piston is 41mm long with 23mm comp height, 18mm pin to skirt
661 piston is 43mm long with 28mm comp height, 15mm pin to skirt
395XP piston is 48mm long with 27mm comp height, 21mm pin to skirt
395XP piston is 49mm long with 27mm comp height, 22mm pin to skirt
the ideal would be if someone could get pistons made that were 2mm longer (1mm above and below pin) this would allow us to cut the squish and also set the intake timing easier.
Have found that the 660's seem to have about 25mm from squish to top of exhaust, this gives in effect a 25mm stroke, also the transfer heigh can vary considerably probably due to core shift or a dud pattern when casting.
I am looking at using a 395 piston and machining the top down possibly making a pop up or doming
cutting the squish band and spacing the jug to get closer to the preferred numbers.

 

[thompsoncustom]

thanks guys for all your help so far.
I just started looking at timing numbers of the big bore.
And as has been said here further up, the intake is garbage!
I am getting 185° total intake and 189° total exhaust. Transfers I have just eyeballed at around 123°
If I drop the cylinder past 100° exhaust then I might be able to close the freeporting-gap.
I haven't checked squish yet.

Is this JB'ing the intake a reliable solution?

the AUMEL 54mm Cylinder Piston Kit For Stihl MS660 has timing of:
E190° I 186°

the Yindina YULI 56MM Cylinder Head Piston Kit Compatible for Stihl 066 MS660 has a timing of:
E 189° I 185°

the original holzfforma has timings of:
E164° I 158°

the holzfforma ran great.
what are timing numbers on hyway and meteor?

Looks like you got duration. But at what degree is your exhaust opening? Transfers clearing the top of the piston? and Bottom of the piston skirt closing the intake port at?