Matchless G12 650 oil seal mod

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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AJS 500
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Joined: Wed Aug 05, 2015 5:27 pm
Location: KENT UK

Matchless G12 650 oil seal mod

Post by AJS 500 »

G12 crankcase chain case oil seal
Please read pdf file as it has photos as well.

I've had issues with my chain case overfilling with oil via the open main bearing into the crankcase. This occurs especially when left on the side stand directly after a ride. I Also found some cross contaminating occurring.

This has caused the following problems:- Oil ingress into the clutch, smothering the plates causing slip and drag.

Oil egress from behind the clutch smothering the chain, rear wheel etc.

Remedying this I purchased a nitrile rotary shaft rubber oil seal 2" x 3.25" x 0.37" oil seal from simply bearings for £5.46 ex VAT

Fitting the oil seal:

Drained oil, split chain case, split and remove primary chain, strip and clean clutch with petrol.

Remove primary drive sprocket from the end of crankshaft.

Remove original spacer and using the sprocket ease the oil seal into place using the sprocket and sprocket nut to drive in gently and plumb.

Mark where the extra outer rim of the seal protrudes as it will not fit flush due to the depth Difference.

Holding the seal via inner ring gently in a lath chuck, With a sharp blade rotate the seal by hand and remove the rubber from the steel outer rim. this will give the necessary clearance for the primary chain.

Refit the clutch

Using the lathe, machine a new spacer to suit the inner dimensions of the oil seal while maintaining the correct alignment of the sprocket teeth in relation to the clutch teeth.

This can be checked using a steel ruler once the clutch is refitted,

Fit all parts and check chain clears the outer rim of the seal, then remove all parts again.

Degrease all surfaces the outside oil seal will fit into.

Using medium strength bearing lock, smear it sparingly onto the outside rubber of the oil seal. Again refit using the drive sprocket and breather nut to fully locate the oil seal in position as pictured.

Tap the sprocket if necessary with mallet to ensure its all the way home.

Remove nut and sprocket. Clean off all excess bearing lock, if you used it sparingly there will be no excess.

Fit the machined centre spacer.

Refit the sprocket and nut as pictured and tighten

Refit the primary chain

I suggest Leaving overnight to allow bearing fit to go off.

Now there should be no more oil getting into the chain case from the crankcase.

I've left chain case dry, and check the chain periodically

I've found a small amount of oil does egress via the output shaft splines.

No more clutch slipping or excessive oil loss or cross contamination.

If you unsure about any of this do not carry it out, refer to a qualified mechanic who is familiar with these machines and open minded.

If you are reassembling an engine I suggest buying a sealed bearing for the side in question, removing the inner part of the seal (the side facing the crankshaft) flushing any lubricant from it.

the outer seal left in place should do the same job.

 

//cloud.tapatalk.com/s/5b588766f13 ... %20mod.pdf

Sent from my SM-G935F using Tapatalk
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ajscomboman
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Location: HAMPSHIRE UK

Re: Matchless G12 650 oil seal mod

Post by ajscomboman »

There is a major issue with leaving the chaincase dry. The original design of the clutch is designed for the rollers to be lubricated by the oil flung around by the chain. Unless you have converted the clutch to use a sealed bearing as used on belt drive conversions the rollers will wear very quickly. No amount of sprayed chain lube will overcome this issue.
bob121
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Location: WEST MIDLANDS UK

Re: Matchless G12 650 oil seal mod

Post by bob121 »

I maybe being a bit thick. But with the seal fitted as it is in the photos, it looks the wrong way round. With the 'dish' side of the seal facing into the crankcase, the case pressure would normally push against the seal, compressing it against the spacer, giving the best possible seal. The way it is in the photos, the pressure could force oil past the seal.
JEAN-NOEL
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Location: FRANCE

Re: Matchless G12 650 oil seal mod

Post by JEAN-NOEL »

I agree with bob121 : on the pictures the seal is obviously fitted wrong way round.
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dave16mct
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Location: LANCASHIRE UK

Re: Matchless G12 650 oil seal mod

Post by dave16mct »

He's only put it in the wrong way to mark how much to machine off. In the later picture it's fitted the correct way. I agree with Rob, put just enough oil in to touch the bottom of the chain. Thanks for posting it, I may do this mod. Nice clear pics and description.
Dave.
Mick D
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Location: Aberdeenshire

Re: Matchless G12 650 oil seal mod

Post by Mick D »

Hi

I wonder what effect this will have on the breathing.

Regards Mick
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dave16mct
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Re: Matchless G12 650 oil seal mod

Post by dave16mct »

It shouldn't make any difference, the original breather is still in place (holding the sprocket on).
Dave.
Groily
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Location: NORMANDIE FRANCE

Re: Matchless G12 650 oil seal mod

Post by Groily »

It is a worthwhile mod I think. I have seals on 3 twin engines and I do think they help. Can't remember off hand the seals used but narrower as they fitted flush. Just had to turn down the scrolled flingers and then re-tempered by quenching. They have lasted well and I think have helped keep excess oil out of the primary. And by a minor miracle my primaries retain (most of!) their oil. So a win-win really.
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