Stroked to 650 - which PCC fits?

Information relating to the Matchless G11 or AJS Model 30 600cc twin
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Stroked to 650 - which PCC fits?

Postby Velossembly » Tue Jan 31, 2017 11:19 am

My AJS M30 has been "stroked" to 650cc by a previous owner; no idea why unless the engine suffered a crank breakage and the owner couldn't obtain an equivalent. It was running really well but utterly oil incontinent. The cause was obvious when I removed the PCC outer - no gasket whatsoever! In order to clear the 650 crank's alternator, an alloy PCC has been fitted (Part Nos. 025017 & 025020 - outside the range of my lists) and Previous Proud Owner had installed two 1/8" thick alloy rings to fit between the inner and the original M30 crankcase.

However, my examination revealed that the primary chain was misaligned by about 1/4 inch. Why it didn't break or jump the sprockets I don't know but the old chain bent like a dead snake in every plane. I "cleverly" re-arranged the engine sprocket spacers and managed to align it with the clutch sprocket but then the chain ran hard up against the PCC inner.

Now, there is nothing amiss about the the positions of the engine and gearbox; after all, they're constrained by the mounting plates. The clutch is standard AMC with, thank goodness, shock absorber rubbers included. I mention this because the engine dates from that crossover period '56-'57 when the engine shock absorber was dispensed with.

My question: is there a twin PCC that fits directly between the AMC gearbox and M30 crankcases and, if so, which one? Is it the one shown in the 1958 Parts List: Nos. 024153 & 024008? My guess is that outer cover won't clear the alternator and a true 650 outer won't bolt up to that inner. AMC appear to have made over 22 different PCCs since WW2.

Maybe this is an Old Chestnut but I've scrolled back to John Drew's question in 2003, with Duncan's helpful reply, but it doesn't quite cover my problem.

Thanks for trawling through all the above. Brian B.

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Re: Stroked to 650 - which PCC fits?

Postby bjork » Tue Jan 31, 2017 9:18 pm

PCC? Primary Chain Case I'm guessing? Not seen that used before.

If you've moved the sprocket in a 1/4" is the case rubbing without the two 1/8" spacers still?
As you have found there are many chaincases to choose from, but I would expect the 1958 type to work as that is when the alternators were introduced.
I don't think this is 'an old chestnut' either-I've not heard of it before! Good luck though!
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Re: Stroked to 650 - which PCC fits?

Postby Velossembly » Fri Feb 03, 2017 5:39 pm

Sorry, thought PCC for Primary ChainCase was in common usage but then, I have Velocettes. Any oil retention problems that may occur with the AMC 'tin' chaincases pale into insignificance when compared with those on Velos, which have big holes at each end in order to ensure that the oil is sure to get flung out! Still, they only used two types of chaincase on all the big singles between 1951 and 1970, which is very helpful.

I'm more or less resigned to machining the back of the chaincase inner to clear the camshaft blanking plug now, as this will enable me to dispense with at least one of the spacers. It should also place the rear end of the chaincase further back onto the final drive bush - it was more or les floating about in space before and rubbing on the back of the clutch. The only other option that I have for aligning the primary chain is to shift the clutch sprocket out and I don't think that's either possible or advisable.

My gearbox is numbered M 12642 but I don't know to what year that relates. Roy Bacon's excellent book doesn't appear to list gearbox numbers. Previous owner managed a couple of thousand miles on this bike over three years but who knows how many primary chains he went through? By the way, the clutch has friction plates with internal tangs; can anyone tell when they were introduced?

Thanks, BB.

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Re: Stroked to 650 - which PCC fits?

Postby ajsph » Fri Feb 03, 2017 7:09 pm

on crankcases from 1958 and later, is the recess for the blanking plug milled a little bit deeper, to clear the alu chaincase, the crankcases from a dynamo and an alternatormodel is also different in the part around the main bearing, the alternator chaincase fits in the crankcase and the dynamo chaincase fits around a recess on the crankcase
Best regards Poul

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Re: Stroked to 650 - which PCC fits?

Postby Groily » Fri Feb 03, 2017 9:10 pm

You could remove a bit from the outer face of the inlet cam blanking bush BB - it's what I did to get an incorrect alloy PCC to fit one of mine. Lot easier than trying to machine the inner chaincase maybe, and a less valuable part to be modding? Made all the difference for me, but who knows what will or won't work with some of the parts combinations we find ourselves ending up with!

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Re: Stroked to 650 - which PCC fits?

Postby Velossembly » Sat Feb 04, 2017 11:48 am

Thanks Poul and Groily for the advice, really helpful. I'm not going to waste any more time snooping around other members twins at Jampot rallies now it's fairly clear that a different chaincase isn't going to solve the problem. Maybe one day I'll convert my M30 back to 600cc; just need a crank, a steel chaincase, a dynamo and.....
BB.

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Re: Stroked to 650 - which PCC fits?

Postby kbs1240462 » Tue Feb 28, 2017 8:32 pm

Hi I had a similar problem on my Model 30 that should have a tin case but has an alloy one fitted. It fouled the camshaft cover. I used a tungsten router bit in a wood router to create a pocket for the cover - fits a treat now and looks neat as well.
Kevin

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Re: Stroked to 650 - which PCC fits?

Postby clive » Wed Mar 01, 2017 1:37 pm

Velossembly wrote:.................... By the way, the clutch has friction plates with internal tangs; can anyone tell when they were introduced?

Thanks, BB.


I am wondering if you have more than one complication. Your profile suggests that your bike started off as a 1956 Model 30. This would have had a Burman GB (B52) gearbox and a tin primary chaincase. The part number for drive side crankcase changed between 56 and 58 when the alloy chaincase was introduced. On my 58 G11 CS there is about an eigth of an inch clearance between the chaincase and the rear camcover. So machining out the case sounds a good option especially as another member has done this succesfully.
Then we move onto the gearbox. You have the later (and better) AMC gearbox (confirmed I think by the number you quoted) to my knowledge its not a GB box number anyway. You ask about clutch plates with internal tangs. My AMC clutch friction plates have tangs which are external and are driven by slots in the clutch outer basket. Looking at 63-4 parts list they are still illustrated like that. The clutch that went with the Burman GB box however had friction plates with recessess in them and the clutch outer basket had no slots in it, instead there were inserts on the inside of the basket to engage with the friction plates.
It is possible you have this clutch fitted and it is causing some of the alignment problems? Perhaps another member will be able to confirm if the AMC clutch ever had similar friction plates without external tangs.
clive
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Re: Stroked to 650 - which PCC fits?

Postby zwarts » Wed Mar 01, 2017 4:37 pm

Clive - Just to confuse/complicate things slightly more - Fred Neill's handbook clearly shows that prior to 1962, the AMC clutch friction plates had external tangs which engaged with slots in the clutch drum and transmitted the drive, via plain plates, to the clutch centre. Post '62, the friction plates had internal tangs and were driven by the plain plates which had external tangs. there are other differences but not of relevance to this discussion.
The friction plates with external tangs were also as used in Norton clutches from way back in the mists of time, the 'AMC' clutch (and gearbox) being a direct descendant of these.
One thing I have often discovered from looking through the parts books is that the illustrations are not always up-dated from previous editions, so they do contain quite important errors. The same applies to component dimensions given in parts lists e.g. the length/gauge of spokes when the hubs changed from single-sided to full width in two stages, 1954/55.

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