I can see that the .325 rim is significantly smaller than the .375, but I am wondering how they compare to a 6-tooth, 3/8 spur supplied on some old Echo 280Es? I don't over tension my chains, but I still see rapid wear of the spurs on other small saws. Would switching to 1/4" pitch allow me to use a rim while staying closer to the low ratio provided by the 6-tooth? (MAKE JOKE HERE ABOUT PITCHING ANEMIC ECHO.) Don
How does a 6-tooth spur diameter compare to small-spline 7 tooth rims?
- Thread starter BigDee
- Start date
Help Support Arborist Forum:
Brent Nowell
Addicted to ArboristSite
Well the torque is going to be different if the diameter changes. Larger = less torque and smaller = more.
It’s a good question, I myself have never seen a 6 tooth. But with a full comp chain I couldn’t see a dramatic speed difference. If anything a smaller diameter rim with 6 teeth would be easier on the motor...
Another note too is the more teeth the less wear on the rim, maybe this is the balance that was found with the common 7 tooth rim.
It’s a good question, I myself have never seen a 6 tooth. But with a full comp chain I couldn’t see a dramatic speed difference. If anything a smaller diameter rim with 6 teeth would be easier on the motor...
Another note too is the more teeth the less wear on the rim, maybe this is the balance that was found with the common 7 tooth rim.
Yes, and conversely chain speed. That's the reason for the question.
Van462
ArboristSite Member
On Stihl going from a 6 tooth spur to a 7 rim changed the diameter from the center of the rivets from 1.36" to 1.53". The additional tenth of an inch on the rear of the sprocket usually changes requires an additional link to allow removal of the chain without having to remove the bar. Not sure its a direst comparison but this was the case on a MS241.
There are 9 tooth 1/4 inch pitch sprockets in small 7 spline. They are a bit smaller than the .325 7 tooth. You will half again as many cutters cross a given spot per batch of revolutions as the 3/8 6 tooth so the relative tooth size would seem to come into play. It is a small top handle saw reed valve carb forward?
That's what I'm talking about, thank you very much. I'm thinking the r-squared business makes the change in ratio more than just 1.36/1.53. I am math challenged but I will work on it. And report back. And I will take some similar measurements on the Echo 280e.
Yes, carb forward, reed valve Echo 280e, but I think I see the same on the old top handle homelites and others, I'm sure. the echo hasn't any power to spare so while I want to use a rim, I don't know if the 28cc echo can afford the higher gearing. Can I file the rakers higher?
I do not have a 9 tooth 1/4 rim to compare to the .325/7, so this is new useful information for me. Thank you. Don
Huskybill
Addicted to ArboristSite
In the past I changed all my husky saws over to rim and drums. I went up in rim size not down. I was looking for more cutting speed. I went a 7 pin rim to a 8 pin rim on my husky 266/3/8” I went from a 7 pin rim to a 9 pin rim on my husky 240/325”, on my 2100 I went from a 404”/7 to a 404”/8 pin. I just make sure I keep the chains razor sharp at all times.
With that said what are u trying to achieve by going with a 6 pin rim.? These rims are smaller and thinner. Won’t they wear out sooner.?
My thoughts have always been go to a larger diameter 9 pin rim, go with a full skip 404”chain on my 2100/100cc with the rakers set max depth. I feel a faster chain speed with less teeth will surpass the 404 w/ full chisel.
With that said what are u trying to achieve by going with a 6 pin rim.? These rims are smaller and thinner. Won’t they wear out sooner.?
My thoughts have always been go to a larger diameter 9 pin rim, go with a full skip 404”chain on my 2100/100cc with the rakers set max depth. I feel a faster chain speed with less teeth will surpass the 404 w/ full chisel.
I would be delighted to go to a 6 pin rim but I don't think it exists. Please correct me if I am wrong. I am trying to get away from the 6-tooth spur than wears quickly and seems inefficient, but I suspect that even the small increase in size to a 7-tooth .325 rim will overpower the 28cc saw. However, it does have 175# compression and I have yet to free up the exhaust. I am waiting for a carb kit to come in the mail.
Are the small rims thinner? Will they wear out sooner?
Years ago I put an 8-tooth rim on one of my 266s, but ultimately I switched back for the grunt of a 7 pin. Maybe I need to keep my chain sharper. I do have 8s on the 288s.
Huskybill
Addicted to ArboristSite
I had the govenor plugged on the 266 with an 8 tooth rim.
The six tooth spur sees more wear because of the smaller diameter. Think about it, it wraps the diameter of the chain more tighter, more friction. I would try a 7 tooth rim. With a 325” full chisel chain. Chisel chains cut faster less load on the saw.
The six tooth spur sees more wear because of the smaller diameter. Think about it, it wraps the diameter of the chain more tighter, more friction. I would try a 7 tooth rim. With a 325” full chisel chain. Chisel chains cut faster less load on the saw.
When I go smaller on sprocket size the 2 biggest things I have notice have been increased fuel consumption( may not be the case on all saws ) and higher torque with less chain speed. Sprocket wear from 1 less tooth difference seems so minimal to me I don''t consider it. If the power is your biggest concern go with the smaller. Fuel economy go with the bigger but I would try both and find out how your saw responds to both and u will probably like 1 over the other depending how u most use your saw. keeping the chain nicely sharp will have the biggest effect on chain wear cause your chain will stretch more when its used dull and cutting dirty wood. When your chain gets stretched out it climbs higher up on the sprocket wearing the sprocket out very significantly faster.
The 6 tooth 3/8 lp spun for me will last for a few bars. Similar type of saw. I get Stihl 44dl 0.044 bar and chain, make the bar fit. If you have a rim drive drum your choice is a 3/8 non lp 7 tooth rim sprocket.
1/4 chain has different nose propert's. Derailing issues are enough to usually use the 3/8 lp stuff. Might be an 8 tooth spur for that saw. The rim won't bang up drive links on throwing the chain.
1/4 chain has different nose propert's. Derailing issues are enough to usually use the 3/8 lp stuff. Might be an 8 tooth spur for that saw. The rim won't bang up drive links on throwing the chain.
With thanks again to Van462, I have answered the question. Measuring from rivet to rivet as he reported was the tip I needed to get good measurements. The Echo-supplied 6-tooth spur diameter measures 36mm; the 7-tooth rim with the same .375 oregon 91 lp chain measures 41mm; and the .325 7-tooth measures 37. So the .325 should give 97.3% of the power of the spur while the 3/8 is 88%. As for speed, the numbers are 103% and 114%. So now I am wondering about a short .325 bar that will fit the little Echo.
Thanks for all the responses. Don
Thanks for all the responses. Don
Van462
ArboristSite Member
I'm glad you mentioned the measurements of 375 compared to 325. I hadn't thought of that in regards to drive diameter. On 375 LP chain 6 tooth barely looks round. I wonder if there is any sort of loss due to "cogging". Another member used the term rollerizing in this case. I like the concept of a smoother chain line.
Yes and that's why I would rather be using a rim. And thank you again for understanding my question and responding in a way that furthered the answer. I suspect that even thought the .325 is larger than the 6 tooth .375, it may have less mechanical loss, yielding more output. But finding a small .325 bar is challenging.
