18CS Replica Chain Rub

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Re: 18CS Replica Chain Rub

Postby AMacD » Sun Apr 04, 2021 9:20 am

Thanks all, really helpful.

I will investigate because I want to be sure the sprocket isn't loose. I notice it has a left hand thread and a lockplate.

The chain is slack which is something else I need to sort - think one adjuster is bent so need to get a new one. But it looks clear that the rubbing is on the sliding seal - I didn't know how the PCC accommodated adjustments to the primary drive chain tension.

It is my first brit bike so I don't have much to judge it against, lots to concentrate on when riding with limited brakes and gears on the right, but I wanted different challenge. Seems like a lot of fun.

I'm looking to make some other minor improvements so will probably be pestering you all with more questions.

Thanks again
Alex
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Re: 18CS Replica Chain Rub

Postby Duncan » Sun Apr 04, 2021 9:10 pm

I find the camera on a phone very good for placing under the engine and photographing back up to see what is there, you have to take several to get what you want and may need to do it in a darkish shed/garage possibly with the flash.

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Re: 18CS Replica Chain Rub

Postby AMacD » Thu Apr 08, 2021 7:51 pm

Thanks Duncan. It's remarkable the images you can get from a phone camera. I also have a borescope, but couldn't get anything conclusive on this occasion hence I've disassembled.

Seems my bike is fitted with a non-standard sliding seal made of brass and it was that that has been rubbing. For the record here is a pic:

Sliding_seal.jpg


It was fortuitous that I did investigate because I discovered that the primary drive chain was much too tight and the clutch nut was loose & there was no locking washer fitted. I can't see any damage on the splines so I'm hoping it'll behave with a locking washer fitted.

Will get a new sliding seal and see how the clearances look before deciding whether the PCC needs to be moved outboard slightly. The gasket was missing at the joint with the crankcase so that will make a small difference.

Will let you know how I get on with reassembly in due course.

Thanks again for all of the helpful input.

Regards
Alex
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Re: 18CS Replica Chain Rub

Postby Mick D » Fri Apr 09, 2021 6:38 am

Hi

If the integrity of the sliding seal is OK there's no need to replace it, just clean it up.

To help you decide where the alignment anomaly stems from you need to review the alignment of the primary and secondary sprocket pairs - not much point in moving the PCC if the sprockets are out of alignment.

Regards Mick

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Re: 18CS Replica Chain Rub

Postby AMacD » Fri Apr 09, 2021 7:54 pm

Hi Mick,

Thanks - I agree, the sliding seal actually looks quite well engineered. Clearly it's been rotating in the chaincase but I think that's only because of the chain rubbing.

There's no major problem with either primary or secondary sprocket pairs alignment but I will try and take some more accurate measurements before I reassemble. Worth spending the time to get it right.

I wondered about doing something to stop / deter the sliding seal from rotating - it's a very close fit on the gearbox output shaft - there was an o-ring fitted on the stub of the output shaft which feels like a bad idea. The central bush has an oil flinger groove in it but the o-ring will pretty much defeat that.

Any further thoughts much appreciated!

Cheers
Alex
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Re: 18CS Replica Chain Rub

Postby Mick D » Sat Apr 10, 2021 6:12 am

Hi

The sliding seal originally had about 0.5mm clearance over the mainshaft and there was no O ring seal there.

It would be a good idea to post photos of your clutch, gearbox and sprocket components, that way we can see what combination of parts you have and take a better stab at where the solution lies.

Regards Mick

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Re: 18CS Replica Chain Rub

Postby AMacD » Sat Apr 10, 2021 5:25 pm

Thanks again Mick!

Here are some photos - hope they confirm what I think I know... AMC gearbox and clutch. These and the PCC are from a later model year than the rest of the bike.

Today I confirmed that the primary chain alignment is good. Haven't checked the final drive yet as the rear wheel is out.

I fitted the clutch and chain and measured the clearance between the clutch and chain - 9mm. This sliding seal is 6mm thick. Hence there really isn't much space to play with. I will be ordering some spares from AMC Classic Spares - I will get one their sliding seals and then decide whether it frees up useful space or not. A gasket (or two) between crankcase and PCC might just be enough to give clearance. Now I understand the lay of the land rather better I think I can probably make some measurements whilst partly reassembled to check for adequate clearance.

Next task - lots of cleaning & awaiting a parcel of parts!

Will let you know what happens. Any observations prompted by the photos or my plan would be much appreciated.

Regards
Alex

LHS.jpg


gearbox.jpg


Clutch.jpg
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Re: 18CS Replica Chain Rub

Postby Mick D » Sat Apr 10, 2021 5:44 pm

Hi

This is an original factory sliding seal:

Chaincase Seal.png


Regards Mick
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Re: 18CS Replica Chain Rub

Postby dave16mct » Sat Apr 10, 2021 6:47 pm

If your footrests fit on the outside of the frame there should be spacers on the inside between the engine plate and frame. Check the sizes in the parts list but from memory 13/16" on the left, 1" on the right and 3 1/2" in the middle. Old handlebars make good spacers for these.
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Re: 18CS Replica Chain Rub

Postby AMacD » Sun Apr 11, 2021 1:19 pm

Mick,

Thanks for the picture - looks like the original part is a bit slimmer so changing may be worth the effort.

Also comparing a similar photo of mine seems to confirm that my PCC is slightly further inboard.

Dave,

Thanks - those spacers are missing on my bike - I get similar measurement for the centre and RHS but the gap on the LHS is more like 9/16". I will fit some. Thanks for the handlebar tip - I can certain make some one way or another.

Both, All,

Today I've checked the final drive chain alignment - difficult to be certain but it looks like the small sprocket is maybe 3/8" inboard of perfect. There is also some wear of the inside of the sprocket teeth - none on the outboard.

I have no obvious method of rectifying this - the engine plates seem correct - the rear wheel spacers seem correct. This might be something I have to tolerate - possibly a consequence of the conversion to the later clutch, gearbox and PCC.

The sprocket is dished - is that normal?

On the PCC whilst cleaning I noticed that a spacer piece has been made for the joint to the engine. I might need to make a slightly thicker one if a gasket between each joint doesn't give enough clearance.

Regards
Alex
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