I must be doing something wrong, because customers keep bringing me their old, decrepit machines to repair.
Today's headache is a Greenfield Tractor 11 with drive chain issues.

All my records show that the unit should be fitted with 1/2 x 5/16 chain (#40), but the lower sprocket on this machine appears to be more suited to 1/2 x 3/16. In other words, the big sprocket is too narrow for the chain...

Anyone able to shed some light on the original chain size?
Yes, it is possible to use wide chain on narrow sprockets, but it's bad engineering and increases wear rates by a ridiculous amount.

Tentimes, one of our members, aldot, has a Tractor 11 and can probably tell you the answer. If he doesn't join this thread you could send him a PM. Here is the chain drive on another member, KeithB's, 11-28:



The chain does look rather wide, but of course it may not be the original part - fitting wider chains and matching small sprockets could conceivably be a popular modification. However in the case of extreme chain drive ratios like that, I suspect that having a wide small sprocket might greatly outweigh the wear-life advantage of having the chain match the width of the large sprocket. I don't think we have ever had a completely worn-out large sprocket reported here.

I don't have the Tractor 11 with me at the moment but I can have a measurement for you by Saturday if that is any help.

Aldot, your measurements will be appreciated whenever you have time to make them.
With regards to the pic posted by Grumpy, it appears to be the same as the unit I have in my shop. 5/16 drive sprocket and chain, running to a 3/16 axle sprocket, so at least I'm not dealing with anything unique.
I agree about the added load capacity of 5/16 chain and primary sprocket and how this may have been a cheaper or more easily available solution, but chains are sneaky, devious little buggers that delight in going their own way, with the slightest provocation and usually when it proves to be most inconvenient. If you look at a rating curve for a chain, it's load capacity just about falls off a cliff as soon as you have any torsion (twist). Running a wide chain on a narrow sprocket (in this case 40% narrower) and running it in a hostile environment, is a good recipe for torsion.

Perhaps I can also tackle this from another angle....

The IPL for this machine gives the following part numbers:

Primary Sprocket : #252
Drive Chain: GT500

Can anyone tell me the specs for the original sprocket or chain?

Apologies Tentimes as I didn't have a chance to get up and see the mower. When I do I will certainly get the measurements if you haven't found something in the meantime.

UPDATE!!! I have just been in touch with the Greenfield Technical Department. In the past, they would only help their dealers, but this time they have been most accommodating. According to their records, the machines rolled of the production line with 1/2 x 5/16 chain and top sprocket. I can only assume that they also had the 3/16 sprocket on the axle as well. I've always thought the engineering principles behind this brand were a bit sus....and now I have the proof. Thanks Grumpy and Aldot for your replies. I'll stick #40 chain back on and cross my fingers.

I don't think it's a major problem, tentimes. Yes, the chain can wander from side to side on the axle sprocket, which will give uneven loads on the chain's sideplates, thus shortening its life. However because the sprockets are so close together, I don't think there is much opportunity for torsional oscillation as well.

Thank you for posting this thread, which I will now close. If anyone needs to post to it, just PM a moderator.