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Suffolk Super Colt - chain too loose?

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DFulton Sun, 07/05/2023

Looking for advice on what I'm doing wrong here:

The drive chain on my mid-70's Super Colt is constantly coming off - it seems far too loose, but I don't seem to be able to adjust it any tighter.

I did fit a new (second-hand eBay purchase) cutting cylinder at the end of last year (and also replaced the ball bearings).  There's no obvious play in either the cog on the blade, or in the drive cog coming in.

I've tried fitting a new bottom blade too yesterday, in case that made a difference, but no luck.

Is there something else I need to adjust, or have I fitted something incorrectly?  Bizarrely, it cut the the lawn perfectly two weeks ago, but now I can't even run the engine for more than about 15 seconds before the chain comes off.

I've included some pictures of the cylinder set up and the chain.  Any suggestions very gratefully received!

Just in case it's relevant, the clutch on the driveshaft hasn't been behaving correctly for a while.  I cleaned out the carb and adjusted the fuel mixture and since then, I've not been able to get it to idle to the point where the blades stop spinning.  I expect this is unrelated (it's been like that for months), but thought it worth mentioning.

Forums

wristpin Sun, 07/05/2023

Check the spherical bush on the top shaft. It may be worn and letting the shaft drop. Another possibility is that it’s been run with a worn out bottom blade and an extra link was added to the chain to allow the  cylinder meet it, and still there with what looks like a new blade.

Also looks as though the tensioner may be incorrectly assembled but those two pics could do with better lighting.

 

DFulton Mon, 08/05/2023

Thanks Wristpin - I'm off to have another look.  I don't believe the chain has ever been altered, so I suspect the problem is one of your other suggestions.  I've attached another couple of photos of the adjuster mechanism in case there's something fundamentally wrong there that I've missed.  I have noticed that the bit of the adjuster that has the nylon washer(?) on it is angled away from the chain (you can just about see it in the last photo).  I wondered whether it was just a bit bent or whether it's meant to be that way?  Not sure that will be enough anyway, but might help tighten things a bit.

 

wristpin Mon, 08/05/2023

Well, the tensioner bracket and its nylon slipper look ok .  Unhelpfully, none of my parts books give a link count for the chain but your chain doesn’t appear to have an added link, but that’s not to say that someone just fitted a new longer length rather than add a link to an existing one. It will be interesting to hear what you find with the spherical bush on the top shaft.

DFulton Fri, 12/05/2023

I'm struggling to work out how to get to the spherical bush - I've removed the chain and the top sprocket, but I can't work out how to remove the shaft - do I just unbolt the engine from the base and slide everything along?

What I would say is that there doesn't seem to be any significant movement in either the drive shaft or the cylinder blade.  I did find part of the chain linkage lying inside the casing (it was just held together by the outer clip, so I'm wondering if that's a factor).

Two other thoughts:

1. The nylon slipper / adjuster mechanism is angled away from the chain (i.e. it's not 90 degrees to the mower body).  Is it meant to be like that?  Do I just need to bend it a bit?

2. Have I got the lower sprocket on the right way round?  It looks good to me in that the two sprockets are roughly aligned, but if I were to turn the lower one over, it's much closer to the body of the mower.  That feels wrong, but it would make the chain tighter and would also make the chain align to some grooves that are worn in the nylon slipper.

Two further pics - one showing the top drive shaft (no real play visible), but the grooves in the slipper can also be seen; another showing the slipper angled away from the chain.

wristpin Sat, 13/05/2023

If you want to take the top shaft out, yes, engine off. But you can check for bush wear by just trying to lift the sprocket/ shaft in situ.

Just so happens that I have a similar machine that became accessible to day!