Low profile 3/8 needs special sprocket?

[Pioneer]

I was at the Stihl dealer the other day and found out they make a outer rim sprocket for 3/8 LP and another one for regular 3/8. The owner insisted that you have to use the special sprocket to run the LP chain. Anyone have any problems running the LP chain on a regular 3/8 sprocket?

 

[heimannm]

You may not notice at first, but running LP on a full 3/8 sprocket or vice versa will cause problems. Since the LP chain has a shorter profile the sprocket to fit it correctly must have a smaller radius as well. SCarr52 runs LP on a milling rig to make the chain pull a bit easier, and modifies a .404 sprocket to work with it by turning/grinding off the O.D.

Make yourself a few sketches of the chain going around the sprocket and you will understand why the radius/diameter of the sprocket must be different to match the drivers even though the pitch is the same.

Mark

 

[grizz55chev]

You may not notice at first, but running LP on a full 3/8 sprocket or vice versa will cause problems. Since the LP chain has a shorter profile the sprocket to fit it correctly must have a smaller radius as well. SCarr52 runs LP on a milling rig to make the chain pull a bit easier, and modifies a .404 sprocket to work with it by turning/grinding off the O.D.

Make yourself a few sketches of the chain going around the sprocket and you will understand why the radius/diameter of the sprocket must be different to match the drivers even though the pitch is the same.

Mark

Love hearing all the tricks learned and tested by others on the forum! That's what keeps me coming back!

 

[blsnelling]

They are a slightly different pitch.

 

[Efisher26]

Stihl low pro is their "picca" chain, or somthing right?


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[Mad Professor]

This subject has been beaten to death on the milling forum.

To run 3/8 LP/picco you should have the correct drive sprocket and the correct bar sprocket.

Can you run regular 3/8 sprockets? Yes, but it's not pretty, and the drivers on the chain get beat up.

Stihl only makes LP/picco rims for the smaller spline sprocket saws. You can't find them for the larger saws unless they are custom made. You can find 3003 mount bars in LP/picco but they are hard to find, I'm not sure if logosol has a monopoly on those also?

Some people have turned down .404 rims to 3/8 LP/picco diameter, others have had custom rims made up.

Stihl makes a 3/8 picco spur sprocket for the 066, but it's only available through logosol in USA (1122 640 2006).

For small saws you can get the LP/picco rims, spurs, or bars no problem.

Years ago Andy/Lakeside53 mentioned you could adapt the early style 034/036 clutch drums that use the smaller bearing for bigger saws, then you can use the picco rims made for the smaller saws. But there was a reason stihl upgraded the bearing/clutch on those saws (I have genaded an early 036 bearing in a 036).

Here is a picture of a 066 drum, along with a 7T 3/8 rim and a custom 7T 3/8 picco rim. Note the difference in diameter of the 3/8 and 3/8 picco rims. That is why although the pitch is the same, the 3/8 picco chain drivers do not mate properly in a 3/8 rim. The LP/picco chain will ride up on a 3/8 sprocket and beat up the chain drivers.



P.S. I just noticed that the 3/8 066 drum kit I purchased was mislabeled as 8T, pictured is a 7T rim that came in the kit

 

[Mad Professor]

They are a slightly different pitch.

Pitch is the same the chain chassis is different. A 100' roll of each has the same # of drivers.

 

[heimannm]

The pitch is indeed the same, and really more like .365 not really .375 but due to the lower profile chassis they take a slightly tighter corner...

As you can see looking a the "similar threads" below, this topic is often discussed.

Mark

 

[blsnelling]

Thanks for the correction.

 

[Pioneer]

Well, I dug out a new 3/8 rim out of the tool box and grabbed an almost new spare 3/8 LP chain I had hanging around. Perfect fit, that's odd. Tried a new 3/8 regular chain- bound up like crazy- whaaaat! Found out that spare sprocket was actually meant for LP chain, so I saved myself some grief there.

Had a well worn 404 sprocket in the box and pulled that out- what do you know! an almost perfect fit on the LP chain. It would just need a bit of turning to get it right.

So I see the mechanics of it now, the base of the chain is farther away from the pins on the regular 3/8, meaning that when the chain is bent around an arc, the base describes a smaller circle than it would with a chain that has pins closer to the base, I.E. low profile. This is why the larger diameter .404 sprocket is actually a closer fit on the LP chain.

 

[PDXchain]

Pitch is "slightly" different between 3/8" LP and standard 3/8". For example, the measured pitch on the Carlton 3/8" LP is .3658", and the standard 3/8" is .3663". The old Windsor chain was the same at .3655". You will find the sprocket outside diameter slightly different because of the distance of the rivet holes to the bottom of the parts. The shape of the drive link tangs also dictate the tooth profile, so the two will be slightly different.