playing with a pop-up, 066 BB

[Brmorgan]

Ya, raising the entire port 2mm on the new kits was a dumb idea.

They could have merely raised the floor and left the roof alone. The floor should have very little impact on flow, since the majority of the flow occurs when the port is first cracked open.

650 ? I'm hoping to stumble upon a pre-emissions 066 jug. Supposedly they had more compression and saner porting.

I'm not quite sure what the engineers of those cylinders were thinking...

I have an old 066 cyl. in great shape that's even pre-decomp . It doesn't even have the spot to drill out for one; just a nice curved casting. I haven't decided whether I'm going to use it or the newer one that I found at the scrap (with decomp but with one broken fin and some aluminum smear that should clean up) in the 066 I have apart on the bench right now - the porting etc. appears to be pretty much identical on both. Just waiting for a case gasket and muffler heat shield foil to come in at my dealer and I'll be putting that one back together finally too. If I do end up building with the decomp cylinder though, I'd need to find another top cover since the two I have don't have the spot for the decomp at all. Not that I ever use them anyway.

 

[mtngun]

I have an old 066 cyl. in great shape that's even pre-decomp . It doesn't even have the spot to drill out for one; just a nice curved casting.

I wish I could borrow it for a day just to measure it and see if the old jugs are as good as they are cracked up to be.

Brad, is there any chance you would make a pencil & paper port map of that jug ?

Just cut a piece of paper to fit inside the cylinder -- factory edge of the paper tight against the squish band. Then use a carpenter's pencil to lightly rub around the outline of the ports. When you are done, take the paper out and use calipers to measure the distances from the tops of the ports to the squish band (except on the intake, where you need to measure to the bottom of the port).

I found this little tidbit of 066 wisdom from Timberwolf on an old thread. He makes an awful lot of sense -- too bad Baileys doesn't hire him to review the specs on their jugs.

Check your squish height if if its an older 066 then it is likely close to 0.040, pulling the base gasket will get you down close to 0.020 and give you all the compression you will want, if it is a newer 660 then squish is likely tight from factory.

If you have a tight squish already and want more compression then the easiest decent way is a slight pop up piston and milled base, best done on a metal lathe. You don't want to go over much over 170-175 psi on a saw that is going to get heavy use.

Don't raise the exhaust at all [edit:Grande Dog must not have got the news], or at most just the amount the cylinder is lowered. Don't raise the exhaust at all on on a new 660 even if you lower the cylinder the durration is higher than ideal when stock.

Widen your ports out so you keep about 0.100 coverage on each side of the narrowest part of the piston skirt.

Intake durration can be raised a little, but going more than about 1mm deeper on the lower side is not needed on a stump and milling saw and will start to hurt low end. Lowering the cylinder also increases intake durration.

Bell mouth the entry into the transfers, if you have the tools to work the upper transfers they can be re-aimed a bit rearward, but don't raise them.

Open your muffler up, add a good 3/4 of a square inch of outlet area. Reset the carb.

Smooth all the rough edges and match everything up and you will have a runner.

There is much more that can be done to chase a few percentage points but that does not make much sense for a heavy duity work saw.

 

[Meadow Beaver]

Ya, raising the entire port 2mm on the new kits was a dumb idea.

They could have merely raised the floor and left the roof alone. The floor should have very little impact on flow, since the majority of the flow occurs when the port is first cracked open.

650 ? I'm hoping to stumble upon a pre-emissions 066 jug. Supposedly they had more compression and saner porting.

Smaller bore, packs a better charge and it has a smaller combustion chamber. More punch if ya get my drift.

 

[mtngun]

650 -- Smaller bore, packs a better charge and it has a smaller combustion chamber. More punch if ya get my drift.

Not really.

I look at:
-- uncorrected compression ratio (displacement divided by chamber volume at 0.020" squish).

-- port durations. It only takes a few minutes of grinding to increase port duration, but I can't decrease duration.

I've never played with a 650, so perhaps it does have better specs than the post-emission 066/660 (what doesn't ?), but the displacement would be working against it for a milling saw.

Anyway, I just checked the BB/pop-up port timing with a degree wheel. Actually, I rechecked the timing over and over again, until I was convinced I had it exactly right. I'm getting better at this with practice, which is the whole idea.

Exhaust duration = 172 degrees (compare that to 174 degrees according to the paper map in post #6.)

Intake duration = 168 degrees (169 degrees according to paper map)

Blowdown = 24 degrees (25.5 degrees according to paper map)

So...... the paper map method is within 2 degrees of the degree wheel method, as long as you know the rod length. Close enough.

Next task is to mod the new muffler.

 

[parrisw]

Not really.

I look at:
-- uncorrected compression ratio (displacement divided by chamber volume at 0.020" squish).

-- port durations. It only takes a few minutes of grinding to increase port duration, but I can't decrease duration.

I've never played with a 650, so perhaps it does have better specs than the post-emission 066/660 (what doesn't ?), but the displacement would be working against it for a milling saw.

Anyway, I just checked the BB/pop-up port timing with a degree wheel. Actually, I rechecked the timing over and over again, until I was convinced I had it exactly right. I'm getting better at this with practice, which is the whole idea.

Exhaust duration = 172 degrees (compare that to 174 degrees according to the paper map in post #6.)

Intake duration = 168 degrees (169 degrees according to paper map)

Blowdown = 24 degrees (25.5 degrees according to paper map)

So...... the paper map method is within 2 degrees of the degree wheel method, as long as you know the rod length. Close enough.

Next task is to mod the new muffler.

Man what a pain. I think a 395 would solve your problems.

 

[Brmorgan]

Man what a pain. I think a 395 would solve your problems.

I'll try to get a rubbing of the ports on that old cylinder done shortly. Never done it before though.

 

[mtngun]

Man what a pain. I think a 395 would solve your problems.

Or a 120cc saw. One of these days.........

New current production muffler with teeny weeny exit hole.

Big hole. Done with air pencil and carbide burr. The spark screen (not shown) will be retained, as required on public lands.

Inner baffle.

Baffle-B-Gone. Had a heckuva time cutting the baffle out.

 

[mtngun]

I'll try to get a rubbing of the ports on that old cylinder done shortly. Never done it before though.

If I can do it, anyone can.

The squish band needs to be halfway clean though, cuz you're pushing the paper snug against the squish band and then measuring the distance to the squish band.

A short carpenter's pencil works well to do the rubbing.

 

[Brmorgan]

OK buddy, think I got what you want here:

I left this one at 1024 wide since I thought you might rather have a higher-resolution image in this case. I had a brain fart and didn't make sure both were aligned the same, so the ports aren't in the same spots on both maps. Sorry!

 

[mtngun]

Thanks, Brad, I really appreciate the data. So much that I won't even complain about the 1024x image. I'll try to rep you again if it'll let me.

Here's the results for the no-decomp jug. Distance from crank axis to squish band = 20mm (Half of stroke length), + 68mm (rod length) + 23mm (Piston offset) + .5mm assumed squish (approximately .020") = 111.5mm

Note that I assumed 0.020" squish, but Timberwolf suggests the older 066 jugs usually came from the factory with 0.040" squish.

So....... the exhaust port on your flattop is 1mm lower than my OEM jug. I like that, but 168 degrees exhaust duration is still up there.

Now for your other old jug with the decomp. Again, assuming 0.020" squish.

Now THAT is how 066 port timing SHOULD be. I hope you can clean it up, it should be an ideal milling jug.

This is good info. Thanks again, Brad.

 

[parrisw]

Thanks, Brad, I really appreciate the data. So much that I won't even complain about the 1024x image. I'll try to rep you again if it'll let me.

Here's the results for the no-decomp jug. Distance from crank axis to squish band = 20mm (Half of stroke length), + 68mm (rod length) + 23mm (Piston offset) + .5mm assumed squish (approximately .020") = 111.5mm

Note that I assumed 0.020" squish, but Timberwolf suggests the older 066 jugs usually came from the factory with 0.040" squish.

So....... the exhaust port on your flattop is 1mm lower than my OEM jug. I like that, but 168 degrees exhaust duration is still up there.

Now for your other old jug with the decomp. Again, assuming 0.020" squish.

Now THAT is how 066 port timing SHOULD be. I hope you can clean it up, it should be an ideal milling jug.

This is good info. Thanks again, Brad.

Hey, the old flat top 066 I had no decomp, had .019 squish with factory steel shim gasket.

 

[Brmorgan]

Thanks, Brad, I really appreciate the data. So much that I won't even complain about the 1024x image. I'll try to rep you again if it'll let me.

Here's the results for the no-decomp jug. Distance from crank axis to squish band = 20mm (Half of stroke length), + 68mm (rod length) + 23mm (Piston offset) + .5mm assumed squish (approximately .020") = 111.5mm

Note that I assumed 0.020" squish, but Timberwolf suggests the older 066 jugs usually came from the factory with 0.040" squish.


So....... the exhaust port on your flattop is 1mm lower than my OEM jug. I like that, but 168 degrees exhaust duration is still up there.


Now THAT is how 066 port timing SHOULD be. I hope you can clean it up, it should be an ideal milling jug.

This is good info. Thanks again, Brad.

OK, I'll take your word for it... The exhaust on the newer one is only 1mm shorter, is that really that big of a deal? There isn't much modifying I could do to it - I doubt there's 1/16" clearance to the skirt wear marks on the cylinder wall. There's a bit more room with the intake, but even then I could maybe only go an extra 1/16" on each side. Transfers are pretty clean; I might drag them down a bit to smooth them into the case more, but other than that I don't think they'd need much.

As for squish, the topend that's on the 066 I just fixed that had the smashed piston had MAYBE .005" clearance with the Meteor piston I put in it. It was around .025" with the new .5mm gasket I put in it. I haven't measured either of these cylinders though, so I have no idea where they'll end up.

 

[mtngun]

The exhaust on the newer one is only 1mm shorter, is that really that big of a deal?

The critical thing is the distance between the roof of the exhaust and the squish band. That determines the exhaust duration which supposedly has a big impact on the character of the powerband.

170 - 180 degrees of exhaust duration makes more power at high revs but hurts the low end. Conventional wisdom says that is too much duration for a working saw.

That's the theory, anyway. I'm a newbie at this game, Timberwolf, Jacob, Brad, or some of the other experienced porters would have a better feel for what the ideal port timing should be.

I'm not sure if Stihl changed the port timing specs somewhere along the way, or if the timing differences between the various jugs reported on AS are merely due to normal production tolerances ? Seems like buying a used jug is a crap shoot.

 

[Meadow Beaver]

With all the time and money you've got into this so far you could have bought an 076 and called it a day.

 

[Brmorgan]

With all the time and money you've got into this so far you could have bought an 076 and called it a day.

LOL, p[robably true but the way at least I look at it is that, for better or worse, you don't learn anything doing things the cheap & easy way or getting someone else to do it for you.

Nevertheless, it's a worthy project because I'd much rather mill with a modded 066 that can compete with an 076 than an 076 itself, at least in average-sized wood like mtngun and I frequently work with. I don't have the cash for spare parts to fiddle with, or the machining equipment to do a lot of the work, so I have to let him make the mistakes for me! Then if something works well I can try it later too.

 

[Brmorgan]

The critical thing is the distance between the roof of the exhaust and the squish band. That determines the exhaust duration which supposedly has a big impact on the character of the powerband.

170 - 180 degrees of exhaust duration makes more power at high revs but hurts the low end. Conventional wisdom says that is too much duration for a working saw.

That's the theory, anyway. I'm a newbie at this game, Timberwolf, Jacob, Brad, or some of the other experienced porters would have a better feel for what the ideal port timing should be.

I'm not sure if Stihl changed the port timing specs somewhere along the way, or if the timing differences between the various jugs reported on AS are merely due to normal production tolerances ? Seems like buying a used jug is a crap shoot.

Well, I'm 99% sure that the jug on the last 066 I just rebuilt is identical to this one with the decomp, and it is indeed a very strong milling saw in stock form, noticeably moreso than when I was running this older one w/o the decomp. However I'd assumed there were other factors involved there too, since it was so old and dirty and I'd never done much for maintenance on it; not to mention that the piston skirt and rings are a bit worn but still serviceable for now. Next time I place an order with Bailey's I'll likely get another Meteor for it too.

It's odd though, I've never heard anyone infer that the older non-decomp cylinders were ported worse than any of the subsequent ones. Maybe they are better for firewood use but less ideal for milling. Both pull pretty good IMO.

 

[mtngun]

It's odd though, I've never heard anyone infer that the older non-decomp cylinders were ported worse than any of the subsequent ones.

It seems like Jacob once said the flat tops were among the better 066 cylinders ?

After looking at the specs on your two old jugs, I'm inclined to think that we are seeing normal manufacturing tolerances....... and it's just my luck to end up with jugs that are on the wrong end of tolerances.

Are both of your jugs made by Mahle ?

Meadow Beaver, other than the used 066, which I didn't pay top dollar for, I've gone through one BB kit and one NWP piston, less than $150 in parts -- and I'll probably spend another $50 - $100 for a used OEM jug and new rings, since I'm pretty sure the popped-up BB is going to suck.

I regret buying the BB kit, but I didn't buy the BB for this saw. The kit was purchased in 2008 for an 064 project that I no longer have, and then the kit sat on the shelf for a while. Since I already had it, I figured it was worth a try (now I know better ).

If I had to do it over again, I would have skipped the BB and gone with a used OEM jug and a Meteor. About the same cost as a BB, with the option to do a sane pop-up.

Maintenance items like the new muffler would be required on any milling saw. At least with the 066, parts are readily available for not a lot of money.

I haven't kept track of how much lumber the 066 has milled, but it's been a bunch. It's paid for itself, plus -- if I ever get the top end sorted out -- I could always sell it for what I originally paid for it, so it has really cost me nothing except maintenance. Admittedly, quite a bit of maintenance.

Even if I get a 120cc saw, I'll hang on to the 066, so it's worth maintaining. It's a classic saw. Everyone needs an 066.

 

[mtngun]

I had a hard time making up my mind whether or not to port this jug, but in the end I decided that since the purpose of this project is mainly educational, I'd go ahead and port it just so I could learn more about porting.

I tried to follow Timberwolf's porting guidelines to the best of my (limited) ability.

Piston windows before modding. The windows on the NWP pistons are actually pretty good, bigger and better finished than OEM.

Piston windows opened up a little bit.

Originally, the edges of the piston skirt cleared the exhaust port by about 0.150". As per Timberwolf's recommendation, I widened the exhaust port to 0.100" from the edge of the skirt, as shown. The port height was not changed at all (it is already too high for my taste).

Likewise I made the intake port about 0.050" wider on each side. There was plenty of room to widen it more, but I decided to widen it only as much as I widened the exhaust. Again, the port height was not changed.

The lower transfer was brought down a little bit, but I didn't get carried away because the jug wall is pretty thin in that area. The upper transfer was widened on the intake side.

 

[mtngun]

This little round stone was used to chamfer the edges of the ports. It worked perfectly.

This stone was used on the upper transfers. It's a little bulkier than ideal, but it worked OK, especially considering I had never attempted an upper transfer before (it's nerve wracking to stick a grinder INSIDE the jug, because there's a chance that it can nick the walls).

The sanding mandrel at the top of the photo is bent. It was a brand new mandrel, but it only lasted about 5 minutes. Apparently, it was designed for dremels and does not hold up to the 56,000 RPM pencil grinder. I'll try to make a homemade replacement that is shorter and made of hardened drill rod.

The round file on the left has a piece of old vacuum hose on the end, to prevent the end of the file from injuring the jug. The round file worked well at shaping the ports, but it caused some small pieces of plating to flake off, so I abandoned the file and went back to the pencil grinder.

The saw started on first pull, but didn't idle so great, to be expected with the free port. After a warm up period, I tuned the H screw and found it would 4 stroke to 14,000+.

However, after about 10 minutes of break-in, compression was only 120 psi hot (there's not really much to break in, since the piston and rings and jug are old friends).

Shining a light through the ports, there are no vertical scratches or broken pieces, but I do see horizontal chatter marks in at least a couple of places. The chatter marks were first noticed when I pulled the top end a couple of months ago. They aren't that severe, but ....... the rings don't seem to be sealing well, and never have seated well, and other than the horizontal chatter marks, I'm not seeing anything stopping the rings from sealing.

So ..... as expected, this top end sucks. If it had worked well, I probably would have had a heart attack. I may go ahead and do some timed cuts, just for the record.

A used OEM jug and a new Meteor piston are en route for the next, and hopefully final, top end. I learned a lot from this project and honed my porting skills, and it didn't cost me anything except my time, so it's all good.

 

[parrisw]

Wow you'r really having a time with this saw. At least its a learning experience.