Idler sprockets distance

[Will D 0]

I have an ST324 snowthrower and I am adding the second idler to the chain drive system. Can someone please tell me how far apart the two idlers are on the 65 and up models? Thank you.

[ri702bill 13,042]

You may wish to reconsider your measurement parameter. The lower idler is in a slot to allow adjusting the chain tension and will be used that way when done. Where it is now is not where it may end up.

Perhaps fixed dimensions ftom the top & end of the housing? The 2 portions of chain moving up and down over the new idler are really close and must not collide!

Another thing to consider - even though #40 or 41 chain has a 1/2" pitch, you need a length of chain to the nearest inch to be able to use a standard external Master Link.

If the chain length comes out to xxx and a 1/2", you need an offset or half link as you would need to couple an inner & outer link together.

"Measure twice and cut once" applies here.

[Will D 0]

1 hour ago, ri702bill said:

You may wish to reconsider your measurement parameter. The lower idler is in a slot to allow adjusting the chain tension and will be used that way when done. Where it is now is not where it may end up.

Perhaps fixed dimensions ftom the top & end of the housing? The 2 portions of chain moving up and down over the new idler are really close and must not collide!

Another thing to consider - even though #40 or 41 chain has a 1/2" pitch, you need a length of chain to the nearest inch to be able to use a standard external Master Link.

If the chain length comes out to xxx and a 1/2", you need an offset or half link as you would need to couple an inner & outer link together.

"Measure twice and cut once" applies here.

 

Ok, I think I see where you're headed. I just need to know where to drill the hole for the top sprocket. I know the bottom one is slotted for adjusting. I assumed it would be vertically aligned with the bottom one, just need a reference for where to center the hole... Like "6.25" down from top edge of auger housing" or similar. But you're suggesting laying it all out and picking the top location to ensure an even number of chain links. ✅

Edited Monday at 08:03 PM by Will D

[Will D 0]

6 minutes ago, Will D said:

 

I just need to know where to drill the hole for the top sprocket. I know the bottom one is slotted for adjusting. I assumed it would be vertically aligned with the bottom one, just need a reference for where to center the hole... Like "6.25" down from top edge of auger housing" or similar.

 

[ri702bill 13,042]

That logic should work... as I recall, the idler I added has the same number of teeth as the lower. It IS positioned directly above it as the run of the chain is parallel to the opening. My snowblower is burried in the back of the garage right now, facing the wrong way. If you can bear with me, I may be able to get your dimension in a day or two... Another larger project is disassembled in front of it now.

 

[ri702bill 13,042]

@Will D - I did not forget you - here is the info, as promised.

These dimensions only work if your new fixed upper idler is the same size as the OE lower, as I did.  

If yours is different, do not use these; you are on your own.

 

Measuring from the front bend line on the flat side, it is 2 inches to the right, the same as the OE sprocket idler inline below. (Picture is rotated

Measuring down from the top of the flat side, it is 2-7/16 inches.

 

I suggest drilling a smaller starter hole, and finish by drilling a 1/2" hole - that should give a slightly bigger diameter, about .505. The 1/2" thru, but  with little clearance.

You are using a 1/2" hexbolt, correct?. If not, the location stays the same, you need to adjust the size of the clearance hole accordingly. I purchased mine from McMaster-Carr; it required a 1/2" bolt.

"Measure twice, cut once" applies here.

 

 

Edited Thursday at 07:34 PM by ri702bill

[Will D 0]

On 10/8/2026 at 3:31 PM, ri702bill said:

@Will D - I did not forget you - here is the info, as promised.

These dimensions only work if your new fixed upper idler is the same size as the OE lower, as I did.  

If yours is different, do not use these; you are on your own.

 

Measuring from the front bend line on the flat side, it is 2 inches to the right, the same as the OE sprocket idler inline below. (Picture is rotated

Measuring down from the top of the flat side, it is 2-7/16 inches.

 

I suggest drilling a smaller starter hole, and finish by drilling a 1/2" hole - that should give a slightly bigger diameter, about .505. The 1/2" thru, but  with little clearance.

You are using a 1/2" hexbolt, correct?. If not, the location stays the same, you need to adjust the size of the clearance hole accordingly. I purchased mine from McMaster-Carr; it required a 1/2" bolt.

"Measure twice, cut once" applies here.

 

 

 

That's great, thanks for the help! Yes, I have two 41BB18 idler gears. The 41 pitch / 18T idler is what the original parts diagram calls out.