Getting serious about lo-pro

[billstuewe]

I have been using Stihl "Picco" chain (lo-pro) since 11/2001 for milling with a Logosol. They supply a Stihl picco spur sprocket made for them from Sweden. It is not available to your Stihl dealer here in the USA. They say I am crazy until I produce the sprocket with the part number--which they cannot get. It works just fine and will not peen the back of the drivers. A regular 3/8 sprocket will in a matter of minutes. I have not gotten my head around that but I am told that it is because the picco is actually .365 ga instead of .375 (3/8). BUT, a 100' spool of 3/8 chain has 1640 drive links and a 100' spool of picco chain has 1640 drive links!!!!! Go figure? There is a difference however because one peens the drive links and the other does not. I know of no drive sprocket that will work on picco and fit the big block saws like 088 or 084, just the 066.
mtngun, If your theory of sprocket diameter is correct and you turn down a .404 sprocket I think you will then have a regular 3/8 sprocket??? If it works, let me know. Having a rim sprocket would solve the problem of getting a picco sprocket for the big block saw but then you sill have the problem of getting a .50 ga bar to fit a big block mount if you are wanting to use on an 088. I also thing the 088 will break more lo-pro chain due to its extra power.

 

[mtngun]

I have been using Stihl "Picco" chain (lo-pro) since 11/2001 for milling with a Logosol. They supply a Stihl picco spur sprocket made for them from Sweden. It is not available to your Stihl dealer here in the USA. It works just fine and will not peen the back of the drivers. A regular 3/8 sprocket will in a matter of minutes.

If the 404 rim doesn't work out, I plan to fall back on the Logosol spur sprocket. In fact, I will probably go ahead and order the Logosol sprocket. No one likes spur sprockets, but it is a solution, and the lo-pro speed advantage justifies the expense.

I have not gotten my head around that but I am told that it is because the picco is actually .365 ga instead of .375 (3/8). BUT, a 100' spool of 3/8 chain has 1640 drive links and a 100' spool of picco chain has 1640 drive links!!!!!

There is a lot of confusion about that. Both lo-pro (and presumably picco) and 3/8 are actually 0.367", give or take. However, the lo-pro side links are not as tall, and that changes the way it sits on the sprocket.

mtngun, If your theory of sprocket diameter is correct and you turn down a .404 sprocket I think you will then have a regular 3/8 sprocket? ?? If it works, let me know.

It'll have a larger OD than a 3/8 sprocket, similar to the small spline picco rim.

If it works -- big *if* -- I'd probably be willing to supply them to others.

you sill have the problem of getting a .50 ga bar to fit a big block mount if you are wanting to use on an 088. I also thing the 088 will break more lo-pro chain due to its extra power.

I'm not crazy enough to use lo-pro on a 120cc saw, just the 066.

My 084 will either use 3/8 or .325, 0.063" gage. It'll cost me quite a bit more to set up for .325, but Aggiewoodbutcher seems to think it is worth it.

 

[Brmorgan]

The unproven theory is that all rim sprockets are basically the same except for OD. The OD of a 3/8 x 7 is too small for lo-pro. The OD of a 404 x 7 is too big for lo-pro.

But, if I had a way to chuck the 404 rim in the lathe, I could turn it down to fit lo-pro.

Just a theory, and it may not work.

I've thought about using an old clutch rim as a starting point for the lathe mandrel, but bear in mind that the rim is hardened tool steel and very, very tough to cut on a lathe. The mandrel must have an iron grip on the rim.

I will probably have to make a mandrel from scratch, and heat treat it.

If I remember right, the ID of the standard large spline drive rims is very close to 7/8". I remember 4-5 years ago when I started fiddling around with building a carriage CSM (when I knew nothing about them) I was trying to figure out a way of driving the sprocket, and I remember it fitting very well over a piece of 7/8" threaded rod. What if you were to weld a little tab on some of that stuff to fit into one of the splines in the rim, and then spin a nut down on either side of it to lock it into place?

As for removing material, what about a good 1/2" cylinder carbide burr in a die grinder, rotating opposite to the lathe? I've done this with decent success on softer stuff.

 

[huskyhank]

I think "bushing" or "re-lining" a proper lo-pro sprocket with a large spline center my be the way to go. Or it may be possible to machine the larger spline directly into an existing lo-pro sprocket. Using EDM perhaps??? If the sprocket teeth and the drivers don't mate they'll bugger every time. So if you have that part whipped then figure a way to get that part on the large spline.

 

[mtngun]

Ordered the Logosol pico spur sprocket last night, $51.45 delivered ! :censored:

By the time it gets here, I'll probably have the 404 rim made and won't need the Logosol.

I am determined to make the lo-pro work right, one way or another.

 

[mtngun]

Some updates......

I painstakingly filed down the peened drivers -- all 228 of them -- wearing out 3 files in the process. I hope I don't have to do that again.

The Logosol picco spur sprocket arrived, so I am cleared to resume using lo-pro, assuming the Logosol sprocket solves the peening problem.

BTW, the Logosol spur is a Stihl part, #1122-640-2006. I dunno if you can order it at your Stihl dealer or how the Stihl price compares to the Logosol price.

I was going to order a bunch of 404 x 7 rims to experiment with, but it turns out all the new Oregon and Bailey's rims are "ported," cut away on the backside. Supposedly the porting helps clear chips, but I've never had any problem with non-ported rims clogging up with chips. More likely, the porting saves a penny in material costs.

The problem with the ported rims is that if you turn them down to fit lo-pro, then you may cut into the ported part of the rim and the chain will be free to fall off the rim. I don't know if it actually will fall off, but it could. Nor do I know for sure that it will be necessary to cut that deep, anyway. I'll just have to experiment and find out.

Since I have one non-ported 404 x 7 rim on hand, I'll probably go ahead and modify it, just to test the theory. If it works, then I'll try one of the new ported rims. This will all take a while, and I haven't started on it yet because I've been busy on the 084 project.

Left to right, Logosol sprocket for 066, NOS Oregon non-ported 404 x 7 rim, and new "ported" Oregon 404 x 8 rim wrapped tightly with lo-pro, which isn't meshing well..

As best I can measure, the OD of the Logosol spur is 1.436", compared to 1.433" for the Stihl Picco rim as reported by Trigger-Time. That's only 0.055" bigger than a 3/8" rim.

 

[KiwiTony]

Is there a chance that you could take a few shots of the 1122...2006 with
both a regular 3/8 chain,and the Lo-Pro wrapped around it? Similar to what you have on the 1st entry to this thread with the nose sprockets.It looks like the 1122...2006 sprocket has a different profile.Certainly different to the 1122/02 that I am looking at.Thanks.

 

[mtngun]

Is there a chance that you could take a few shots of the 1122...2006 with
both a regular 3/8 chain,and the Lo-Pro wrapped around it?

I'll try to remember to do that tomorrow night.

Tonight I made the mandrel for turning down rims. It was a late night in the shops so no pics yet.

 

[mtngun]

The Logosol picco spur tightly wrapped with lo-pro.

Logosol picco spur tightly wrapped with 3/8.

At first glance, there doesn't seem to be a big difference in how they fit. The proof will be in how the drivers hold up.

 

[KiwiTony]

In the top photo,virtually all the side links of the lo-Pro chain are snugged down onto the driving dogs.--The std chain actually goes "out of synch" as it progresses around the spur.Only 3 or so side links actually rest on the dogs.

To my way of thinking,the same would apply if a Lo-pro chain was put onto a regular 3/8 spur.The side links would come out of synch,thus more of the driving load would be transferred via the cutter tang. It is tricky to describe,but maybe that is the cause of your peening,and resultant hand filing.

The profile of the sprocket dogs are definately different between the Lo-Pro and standard spur.And by the look of your photos,the drive tangs on each chain seem to be a little different as well.

Great photos and interesting stuff.

 

[mtngun]

I used a CAD program to layout a 7 pin sprocket for lo-pro chain, 'cuz I'm getting ready to cut a 404 rim to fit lo-pro, and I'm trying to convince myself that I know what I am doing.

A lo-pro tie strap is 0.393" long, center-to-center, as best I can measure. It's very tough to measure accurately, so if you measure your lo-pro chain, you may come up with a slightly different number.

A lo-pro tie strap is 0.172" tall, mid-way between the rivits. It is actually a curved shape, and of course it wears with use, so once again, if you measure your lo-pro chain, you may come up with a slightly different number.

A lo-pro drive link is 0.339" long, center-to-center, as best I can measure.

Wait a minute, you say, isn't lo-pro supposed to be.366" per link ?

Well, if you average the .339" drive link and the 0.393" tie strap, you get 0.366".

Ah..........

Now, imagine a loop of lo-pro with 14 links -- 7 tie straps and 7 drive links. Lay out that imaginary 14 link loop on CAD and use CAD to determine the rim diameter that will fit that loop perfectly.

I came up with 1.426", but in real life lo-pro drive sprockets seem to be 1.433" - 1.436." It's possible that the difference is due to my measurement errors, but I suspect the sprockets are deliberately made slightly oversize to allow for normal wear.

Some quick and dirty measurements on 3/8" chain show about the same lengths for the tie strap and the drive link. The main difference is that a 3/8" tie strap is about 0.283" tall vs. 0.172" tall for lo-pro. A 3/8" rim must be smaller to allow for the taller tie strap.

 

[mtngun]

To my way of thinking,the same would apply if a Lo-pro chain was put onto a regular 3/8 spur.The side links would come out of synch,thus more of the driving load would be transferred via the cutter tang. It is tricky to describe,but maybe that is the cause of your peening,and resultant hand filing.

Exactly. Earlier in this thread, I posted a pic of lo-pro wrapped around a cut-away 3/8 rim, showing that only 2 lo-pro drive links were making good contact with the rim. The other drive links were "out of synch," as you put it.

I spent all evening doing the CAD drawing, and now there is no time left to cut the 404 rim sprocket. Oh, well, I'll try again tomorrow evening.

 

[mtngun]

Mandrel to hold rim in lathe. Mild steel, including the hand-filed keys. OK for this experiment, but if I get serious about modding rims, I may need to make a splined mandrel in 4140 pre-hard or something similar.

404x7 rim turned down to fit lo-pro (I hope). Darned hard to machine with carbide tooling ! ! ! If I do many of these, I'll either have to try some hi-tech bits, or else anneal the rims before machining.

Will it eliminate the damage to the drive links ? Dunno. I'm working today, but maybe later this week I'll find time to do a few short tests.

 

[huskyhank]

The surface finish of the part looks plenty nice.

Annealing will cause more problems than it solves. These things look like investment castings and there's no telling what they are made of - how could you re-harden and know what you will get? Some kind of exotic insert may be best.

If you do make a splined arbor for this, it might be worth finding an old scrap crank and re-using the splined end. Probably lots easier than making a new one from scratch.

Good luck with this and thanks for sharing the project.

 

[Brmorgan]

I dunno, and please don't take this the wrong way because I really admire all the time/money/effort you're putting into this, but I really cannot be bothered by worrying about measuring such things down to thousandths of an inch, especially parts which are DESIGNED to wear as the chain/rim get used. As long as my LP chain on regular rim/bar combo keeps cutting straight and not breaking I'll keep using it as-is without worrying about the numbers.

As for the drive tangs only fitting two or three drive splines really well - isn't that normal? I mean, if you have 7 drive splines/pins over a 360° rim, only 3 should be driving the chain at most at any given time. The chain only wraps around the rear ~40% of the rim (not 50% because most bar tails are wider than the rims so the chain usually leaves and re-enters the rim on a slightly angled tangent, not parallel). Wrapping a chain tightly around a sprocket isn't a good way to tell if it's going to cause premature wear etc. in my opinion because it's never used like that in the field.

 

[mtngun]

As long as my LP chain on regular rim/bar combo keeps cutting straight and not breaking I'll keep using it as-is without worrying about the numbers.

I have no choice -- a standard 3/8 rim was severely damaging the lo-pro drive links, which in turn damaged the bar and created tremendous friction. Even if I didn't care about damaging a brand new Stihl bar, it was just a matter of time until the peening would have led to a broken chain.

The peened area had swollen to 0.055" - 0.060" thickness, some were even thicker. Imagine dragging that through a 0.050" bar groove ! ! !

After running for just a couple of minutes, the bar was too hot to touch because of the friction created by the damaged drive links.

At first, I thought the friction was because the bar was brand new. I assumed it would go away as the bar broke in. Instead, the friction got worse and worse, which led me to examine the drive links.

One wonders how much power was wasted pulling the 0.060"+ peened drive links through the 0.050" bar ? How much faster would the chain cut if it didn't have to struggle with peened drive links ?

The damage to the drive links was in full evidence after making only 2 passes with a brand new chain -- about 4 minutes run time. That's a serious problem, my friend. :help:

Perhaps my saw is the only saw in the world that peens lo-pro drive links, but I doubt it. More likely I just happened to notice the problem because I was running a brand new bar, whereas the people who claim they don't have a problem are using worn bars ?

Reading back through the old threads on lo-pro/picco chain, I came across two or three reports of broken chains. At the time, it was always blamed on the inherent weakness of lo-pro chain, but now I wonder how many of those chains actually broke as a result of peened drive links ?

Where's BobL when you need him ?

All theory aside, peened drive links are not acceptable. They damage the bar, increase friction, and can eventually result in a broken chain.

I checked the drive links on some of my well-used 3/8 and .325" chains, to see if their drive links were peened, too. No, the old chains had little or no peening. So what is different about the lo-pro that causes peening on the drive links ? What else could it be other than the poorly fitting drive sprocket ?

Anyway, I should have some answers in a few days. I'll make a pass with the picco sprocket, and check for peening. If it passes that test, I'll make a pass with the modified 404 rim and again check for peening. Apparently, the peening is nearly instantaneous, so it shouldn't take long to see if the new sprockets solve the problem.

 

[Andrew96]

So what is different about the lo-pro that causes peening on the drive links ? What else could it be other than the poorly fitting drive sprocket ?

It could be the drive link itself.

Your assumption here that the drive tab on a standard and a low pro are the same...may not be correct.
Maybe the drive link is made to a different hardness standard knowing that it will be used on a lower powered head? Just a thought. You know the thickness of the link is the same...but maybe not it's strength. You seem to have access to everything else...can you access a hardness test on the drive link?
You have a very nice drive sprocket, with what looks like appropriate support...yet may still be peening the edges. Strange, unless the drive link of the lo-pro is as hard as frozen butter.

Without a hardness test, you could prove this theory but making an appropriate cut first with your setup. Assume lo-pro is good for say a 12" cross cut with low power. Try a 12" cross cut with high rpms but 1/2 throttle or something in order to mimic a low powered saw. See if you have any peening. It should only take one baby cookie if it's the drive sprocket (like you think). If it's the drive tab itself, it might be fine with low power and you'll cut the cookie and not have damaged the tang.

 

[mtngun]

Maybe the drive link is made to a different hardness standard knowing that it will be used on a lower powered head?

Santa hasn't dropped off a Rockwell hardness tester yet, but judging by how quickly files dulled while dressing the peened links, I'd say the drive links are plenty hard.

I inspected the bar last night, expecting to find massive damage. The grooves were only wallowed out at the very ends of the bar, still tight otherwise. The bar must have flexed to accommodate the peened links, like a snake swallowing a rat. No wonder the bar got so hot. :angry2:

Hopefully I'll have an update this evening. Decided to skip the Logosol spur and go straight to the modded 404 rim, because if the modded rim works, I'll want to sell the Logosol.

If the rim works, I'm still not out of the woods, because it remains to be seen if lo-pro will provide a decent service life on the 36" bar.

 

[Kicker_92]

Any thoughts on if an 8 pin sprockets would far any better being a larger diameter? You'd have more of the drive links engaged at a time.

 

[mtngun]

I'll be making an 8 pin rim this week, but my guess is that the 066 won't pull it well.