Rim sprocket questions (2024)

I few questions about the use of rim sprockets. I know all of their advantages over spur sprockets, and most of my chainsaws use them.

First: As far as the sprocket is concerned, is there a difference between using regular 3/8 pitch chain, and low-profile 3/8 chain? I have a saw that is currently using an 8-tooth .325 sprocket, and for convenience of using the same bar and chain as my other saws of similar size, I would like to convert it to 7-tooth 3/8 low profile. Will low-profile chain run correctly on a regular 3/8 rim sprocket? Or is there any place one can get special sprockets for low-profile chain?

The chainsaw in question is unusual: It's a Greenlee hydraulic pole pruner. We use it on our bucket/crane truck (yes, we're a normal household that owns and regularly uses a digger-derrick). We just managed to get a replacement spline sprocket for it (after a 6 months wait), so now I can finally convert the saw to any pitch and bar I want. Since all other chain saws of that size class we have use low-profile 3/8 chain, it would be convenient to switch that one.

Second question: I always mount rim sprockets one way, with the writing (like "325-6") towards the outside. But does that make a difference? Would I get some more life out of them by flipping them over when they are halfway used?

Final question: Three of my saws use 6-tooth 3/8 low profile spur sprockets (an Echo top-handle CS-3400, Makita battery powered, and Echo pole pruner). To make maintenance easier, I'd like to convert all of them to use rim sprockets too, but I can't find 3/8-6 rim sprockets, nor can I find the spline mount for them specific to these saws. Am I looking in the wrong places?

ralphbsz said:

First: As far as the sprocket is concerned, is there a difference between using regular 3/8 pitch chain, and low-profile 3/8 chain? I have a saw that is currently using an 8-tooth .325 sprocket, and for convenience of using the same bar and chain as my other saws of similar size, I would like to convert it to 7-tooth 3/8 low profile. Will low-profile chain run correctly on a regular 3/8 rim sprocket? Or is there any place one can get special sprockets for low-profile chain?

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No not really run correctly. While the pitch, the distance between the pivot points or rivets is the same (1640 drive links per 100') the 3/8lp rivets are closer to the sliding surface hence the sprocket is somewhat larger. Stihl for their smaller saws has a mini spline (Stihl specific) that does have proper sized 7 tooth rim sprockets for the 3/8lp chain in their code it is picco 63. I think the difference is 0.060 in diameter but could remember wrong. It sort of works, basically all the pull comes from the last tooth of the sprocket instead of the whole ring of drive links.

ralphbsz said:

Second question: I always mount rim sprockets one way, with the writing (like "325-6") towards the outside. But does that make a difference? Would I get some more life out of them by flipping them over when they are halfway used?

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I never thought about flipping the sprocket, the places that the tie straps wear into it likely are going to be the same places. There are radially ported rims that have a kind of void in the middle of the hole for the drive link. .325-7 usually is this way. Other sprockets would have openings for chips to get squeezed out and those I put what way the chips could get out easiest.

ralphbsz said:

Final question: Three of my saws use 6-tooth 3/8 low profile spur sprockets (an Echo top-handle CS-3400, Makita battery powered, and Echo pole pruner). To make maintenance easier, I'd like to convert all of them to use rim sprockets too, but I can't find 3/8-6 rim sprockets, nor can I find the spline mount for them specific to these saws. Am I looking in the wrong places?

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.325-7 and 1/4-9 are the smallest rim sprockets. At least for 7 spline small. For the Makita battery sprocket, at least the one I have it is a spur but has alternating filled in sides, not filled in far enough so the tie straps ride on but if one really wanted to they could turn one down to the size of the Stihl mini spline and weld or braze or solder on a 7 tooth rim sprocket.

Rim sprockets all splines and sizes
https://www.6kproducts.com/sprocket-lo7s_bore.html

Unsure about their pricing, but they’ve got the sprocket you need.

@Franny K
Difference is 0.167

Stihl Picco 7T rim.....1.433 dia = 4.502 circumference
Reg. 3/8 7T rim 1.380 dia = 4.335

For what it's worth,.......

I have been playing around with an 18 inch 3/8lp a041 bar and chain on a 54cc Poulan (k041)with a well used 3/8 7t rim.

Pulls around smooth......no issues thusly,.... other than the bar is pretty flogged out.

Not a fan of 3/8lp,......but I have around 80 loops,....so......

NSEric said:

I've ran a bunch of loops of 3/8lp oregon and cheap chinese chain on oregon or chinese regular 3/8 rim sprockets.
It works totally fine but everyone tells me it doesnt work lol.
I held the rim sprocket in my hand and put the chain on it, the chain matches the rim perfectly. I've never ran stihl picco chain tho, it may not fit perfectly.
I too had a bunch of 3/8lp bars and chains that fit my 54cc saw(cheapy zenoaha clone), all I had to do was drill a new hole for the oiler.

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I am not sure who the everyone is that tells you it won't work. The drive links are smaller for the 3/8lp so of course the chain fits fully into the sprocket. What happens when in use is that the chain is pulled by the first tooth in that rim sprocket not pulled by a bunch of teeth with the tie straps resting on the rim. Push the chain back and forth in the process of getting a good adjustment and get a cut on your finger when it kind of hangs up and you might change your opinion.