Stihl 066 RUD during milling

[buzz sawyer]

Lot's of good info so far. It looks to me like the clutch was slipping and overheated. Could be caused by a dull chain and/or pushing the saw too hard in the cut. Keep the RPMs up, try leading with the tip of the bar forward, cutting at a slight angle.
Hope this all works out for you, it's a great learning experience.

 

[Mad Professor]

I just found this thread.

066 P/C are sized and cylinder and piston should match. You want about 0.0025" clearance at the skirt. Look for an "A" or "B" stamped on top of cylinder and on piston crown. On newer Stihls the replacement pistons are a compromise and stamped "A/B". A new takeoff piston could be either.

I've seen Meteor replacement pistons stamped "A" or "B", I've not seen an "A/B". Not sure about mixing and matching with used Stihl cylinder with those. You could check with machinist tools, or crudely with feeler gauges. Too tight would not be good on a milling saw.

Consider buying the gasket set, it comes with crank seals and costs less than seals alone. Good to get a new upper rod bearing too.

Go to the "Beg for Manuals" thread here. Someone will set you with a service manual and IPL.

 

[huskihl]

I’d clean up the cylinder and replace the piston with a Meteor. I would see how it runs once you get it back together before replacing a bunch of carburetor and intake bits. Sometimes the parts we take out are better than the parts we’re putting back in. Looks to me like it was just tuned too lean (exhaust side scoring) and not enough oil in the mix (intake side scoring). Somewhere between 20 and 32:1 depending on the oil you’re using is common for a mill saw. Tune the saw so it 4 strokes wide-open throttle out of the cut and barely cleans up when you’re milling.

 

[muddy42]

Hey,

Quick update and question if anyone would be so kind. I've bitten the bullet and got a Mityvac and have pressure/vac tested the crankcase. Results are:

Pressure - 8 to 7 psi over 6 mins. There were no bubbles I could see from soapy water on the seals on either end of the shaft.
Vacuum - 15 to 12 inHg over 6 mins (hopefully I'm remembering that unit correctly)

What do you think about those results?

===

To answer a couple of questions further up:

The marks on the piston top are from me scratching off some of the carbon.

And I'm sure that I used a 50:1 mix of gasil. The gas I used contains no ethanol. If anyone reads this far - would you recommend a lower ratio for high and long intensity applications like milling?

Regarding the pressure test, do you mean 8/7 psi was maintained constant for 6 minutes or that the pressure dropped to 0 over 6 minutes? If the former, that is fine. You should rotate the crank during the test, the pressure/vacuum may spike or drop but always return to 7 psi.

Regarding fuel, certainly its advisable to run more oil at first with a new piston, as it beds in. Thereafter what you run is more contentious. You’ll find long debates online. More oil = more lubrication, but tests have shown it makes the saw run hotter.

I run about 40 to 45 to one. Probably more important is using fresh, ethanol free fuel and decent two stroke oil. And I tune saws slightly rich for milling.

 

[huskihl]

Regarding the pressure test, do you mean 8/7 psi was maintained constant for 6 minutes or that the pressure dropped to 0 over 6 minutes? If the former, that is fine. You should rotate the crank during the test, the pressure/vacuum may spike or drop but always return to 7 psi.

Regarding fuel, certainly its advisable to run more oil at first with a new piston, as it beds in. Thereafter what you run is more contentious. You’ll find long debates online. More oil = more lubrication, but tests have shown it makes the saw run hotter.

I run about 40 to 45 to one. Probably more important is using fresh, ethanol free fuel and decent two stroke oil. And I tune saws slightly rich for milling.

If more oil makes it run hotter, the heat would cause it to run lean. A simple H adjustment adds more fuel and the 4 stroking comes back. It’s no different than if you had it tuned too lean at 50:1 or too lean at 20:1. Running it lean causes heat and running it hot causes it to go lean. Just add more fuel.

 

[muddy42]

If more oil makes it run hotter, the heat would cause it to run lean. A simple H adjustment adds more fuel and the 4 stroking comes back. It’s no different than if you had it tuned too lean at 50:1 or too lean at 20:1. Running it lean causes heat and running it hot causes it to go lean. Just add more fuel.

Thanks, that is a good explanation. So tuning is key.

 

[tom_]

I just found this thread.

066 P/C are sized and cylinder and piston should match. You want about 0.0025" clearance at the skirt. Look for an "A" or "B" stamped on top of cylinder and on piston crown. On newer Stihls the replacement pistons are a compromise and stamped "A/B". A new takeoff piston could be either.

I've seen Meteor replacement pistons stamped "A" or "B", I've not seen an "A/B". Not sure about mixing and matching with used Stihl cylinder with those. You could check with machinist tools, or crudely with feeler gauges. Too tight would not be good on a milling saw.

Consider buying the gasket set, it comes with crank seals and costs less than seals alone. Good to get a new upper rod bearing too.

Go to the "Beg for Manuals" thread here. Someone will set you with a service manual and IPL.

This is great info, thank you, I'll see if I can find whether it's an "A" or "B". I've already purchased a new Meteor piston and cylinder to worst case is I can just use both of those.
The aluminium transfer seems to be cleaning off the inside of the cylinder with a little elbow grease and 240 grit sandpaper.

Regarding the pressure test, do you mean 8/7 psi was maintained constant for 6 minutes or that the pressure dropped to 0 over 6 minutes? If the former, that is fine. You should rotate the crank during the test, the pressure/vacuum may spike or drop but always return to 7 psi.

Regarding fuel, certainly its advisable to run more oil at first with a new piston, as it beds in. Thereafter what you run is more contentious. You’ll find long debates online. More oil = more lubrication, but tests have shown it makes the saw run hotter.

I run about 40 to 45 to one. Probably more important is using fresh, ethanol free fuel and decent two stroke oil. And I tune saws slightly rich for milling.

Sorry, I wasn't very clear. I mean the pressure dropped from 8 psi to 7psi over a period of 6 minutes. Same with the vacuum, it dropped from 15 inHG to 12 inHG over 6 minutes. Is that a concern? Asking because I'd ideally like to avoid splitting open the crankcase - I'm new to this and that feels like a big job (though one I'll do if necessary to get the saw running well).

If more oil makes it run hotter, the heat would cause it to run lean. A simple H adjustment adds more fuel and the 4 stroking comes back. It’s no different than if you had it tuned too lean at 50:1 or too lean at 20:1. Running it lean causes heat and running it hot causes it to go lean. Just add more fuel.

This is great info again, thank you.

 

[J D]

I mean the pressure dropped from 8 psi to 7psi over a period of 6 minutes. Same with the vacuum, it dropped from 15 inHG to 12 inHG over 6 minutes. Is that a concern?

That's fine, & well within spec

 

[muddy42]

Agreed. That should be OK.

That's fine, & well within spec

 

[Mad Professor]

This is great info, thank you, I'll see if I can find whether it's an "A" or "B". I've already purchased a new Meteor piston and cylinder to worst case is I can just use both of those.
The aluminium transfer seems to be cleaning off the inside of the cylinder with a little elbow grease and 240 grit sandpaper.


Sorry, I wasn't very clear. I mean the pressure dropped from 8 psi to 7psi over a period of 6 minutes. Same with the vacuum, it dropped from 15 inHG to 12 inHG over 6 minutes. Is that a concern? Asking because I'd ideally like to avoid splitting open the crankcase - I'm new to this and that feels like a big job (though one I'll do if necessary to get the saw running well).



This is great info again, thank you.

Try using some dish detergent with the wet/dry paper. When you get most of transfer off you can go to finer paper. Check the plating well once cleaned up. You can lightly hit the whole inside with fine paper it will help new rings seat.

I mill with an 066 also, using the lo pro/picco Stihl bar/chains 63 PMX. The 63 PMX chains have gotten way expensive in USA

 

[J D]

You can cut a slot in the end of a piece of metal rod & stick a piece of scotch pad in it to make a cleaning flap wheel you can run in a drill to remove the last of the transfer

 

[tom_]

I just found this thread.

066 P/C are sized and cylinder and piston should match. You want about 0.0025" clearance at the skirt. Look for an "A" or "B" stamped on top of cylinder and on piston crown. On newer Stihls the replacement pistons are a compromise and stamped "A/B". A new takeoff piston could be either.

I've seen Meteor replacement pistons stamped "A" or "B", I've not seen an "A/B". Not sure about mixing and matching with used Stihl cylinder with those. You could check with machinist tools, or crudely with feeler gauges. Too tight would not be good on a milling saw.

Consider buying the gasket set, it comes with crank seals and costs less than seals alone. Good to get a new upper rod bearing too.

Go to the "Beg for Manuals" thread here. Someone will set you with a service manual and IPL.

I've taken a look at my cylinder and it does indeed have an "A" stamped on the top of it. Conversely, the Meteor piston I have has a "B" on top. Do you have any more info on this please? I'm struggling to find a retailer/seller that distinguishes between the two types - if you know any please feel free to pass them on

That's fine, & well within spec

Agreed. That should be OK.

Phew! Thanks!

 

[Mad Professor]

I've taken a look at my cylinder and it does indeed have an "A" stamped on the top of it. Conversely, the Meteor piston I have has a "B" on top. Do you have any more info on this please? I'm struggling to find a retailer/seller that distinguishes between the two types - if you know any please feel free to pass them on




Phew! Thanks!

Two ideas.

Call Meteor ask them for skirt diameters, A vs B, and if they know how they fit OEM cylinders?

If you have a machinist friend, have him measure up all the parts. You can do it crudely with feeler gauges. Get 0.0015, 0.002, 0.0025, 0.003 and 0.004". Use them as go/no go, gauges

I was building a 038S---->038M conversion years back. I had access to all the tools...

These were NOS 038S, 038M, and Tecomec 038M P/Cs. Should give you a feel of what to look for for clearances. 038M is 52mm, 066 54mm bores.




P.S. I can't remember if A or B size is large or small? You are shooting for ~0.002-0.003" clearance.

 

[huskihl]

Two ideas.

Call Meteor ask them for skirt diameters, A vs B, and if they know how they fit OEM cylinders?

If you have a machinist friend, have him measure up all the parts. You can do it crudely with feeler gauges. Get 0.0015, 0.002, 0.0025, 0.003 and 0.004". Use them as go/no go, gauges

I was building a 038S---->038M conversion years back. I had access to all the tools...

These were NOS 038S, 038M, and Tecomec 038M P/Cs. Should give you a feel of what to look for for clearances. 038M is 52mm, 066 54mm bores.

View attachment 1079731


P.S. I can't remember if A or B size is large or small? You are shooting for ~0.002-0.003" clearance.

A is small.

 

[tom_]

Got some numbers from Meteor on the piston sizes for "A" and "B":

"A" is 53.95mm

"B" is 53.96mm

Can anyone please comment on whether this difference is significant?

Given that 0.01mm is 0.39 thousands of an inch, and the variability for the tolerance (not the clearance itself, the fact that it's between 0.002-0.003") is c. 1 thousands of an inch I would have thought that you can use either piston effectively?

I'll caveat this with I know nothing about engines and this is my best guess!

Thanks, Tom

 

[Mad Professor]

Got some numbers from Meteor on the piston sizes for "A" and "B":

"A" is 53.95mm

"B" is 53.96mm

Can anyone please comment on whether this difference is significant?

Given that 0.01mm is 0.39 thousands of an inch, and the variability for the tolerance (not the clearance itself, the fact that it's between 0.002-0.003") is c. 1 thousands of an inch I would have thought that you can use either piston effectively?

I'll caveat this with I know nothing about engines and this is my best guess!

Thanks, Tom

Tom, what are loops of Stihl 63PMX in Britain? 60 and 84 drive links? (16" and 25" bars)

Clearance one will fit better. I'd not go less than 0.002".

 

[ericm979]

As long as you have the correct piston clearance, the letters don't matter. I don't know the 660's clearance spec but it may be in the shop manual.

As an example, for a Yamaha RZ350 (64mm bore) the factory spec is .060- .065mm, or .0024-.0026"

Given that spec, .01mm could put you into or out of spec, depending on your parts.

I'd measure the cylinder bore and then select which Meteor piston to use based on Meteor's clearance spec, and then measure it to be sure before you install it. That's the best way to do it. Selecting the parts with matching letters and not measuring should get you something reasonable most of the time but it's depending on the manufacturers to get everything right.

I say to use Meteor's spec for their pistons because their pistons may be of different alloy than OE, which can change their expansion rate.

 

[Mad Professor]

As long as you have the correct piston clearance, the letters don't matter. I don't know the 660's clearance spec but it may be in the shop manual.

As an example, for a Yamaha RZ350 (64mm bore) the factory spec is .060- .065mm, or .0024-.0026"

Given that spec, .01mm could put you into or out of spec, depending on your parts.

I'd measure the cylinder bore and then select which Meteor piston to use based on Meteor's clearance spec, and then measure it to be sure before you install it. That's the best way to do it. Selecting the parts with matching letters and not measuring should get you something reasonable most of the time but it's depending on the manufacturers to get everything right.

I say to use Meteor's spec for their pistons because their pistons may be of different alloy than OE, which can change their expansion rate.

A friend here had wiscos, made for 166 Dolmars, they were forged, needed 0.004-0.005"


Where has @leeha been?

 

[leeha]

A friend here had wiscos, made for 166 Dolmars, they were forged, needed 0.004-0.005"


Where has @leeha been?

I'm still around, Haven't been on the saw sites in awhile.

 

[ZeroJunk]

I know it could be a hobby. Or, where you are. But, around here I can get a lot of lumber cut by somebody who knows what they are doing for the cost of a burnt up saw.