Britbike forum Forums British Motorcycle specific Brands Ajs & Matchless forum Early and Late Twin Cranks?

So looking at G9 Cranks, one I am being offered the drive and timing cheeks are fully round - others I am looking at claiming to the timing and drive cheeks are "triangular" shaped. What does this mean? That the cheeks changed at a certai year, maybe after engine no 7000?

https://www.britcycle.com.au/wp-content/uploads/2021/03/P1020268.jpg

vs

https://www.picclickimg.com/d/l400/...-AJS-Twin-Crankshaft-1952-to-1956-G9.jpg

One presumes the later crank will fit the crankcases, with the narrower centre web that accepts thrust washers?

Thanks

Hi Peter,

I had to refer back to my AMC guru David DeLapp here in Australia, who sold me my first Matchless G12 basket case in the late ‘80’s. He is quite a busy man, though has previously penned this info, hopefully the following should help with your questions.
In summary:
Series 1: 1949 - 1951 : Lightweight Crank using lightweight section conrods
Series 2: 1952 - 1955 : Crank with triangular outer flywheels. Conrods had the 'H' stem section thicker but still with not much metal around the small end
Series 3: 1956 - 1957 : Heavier 550 crank (possibly with round outer flywheels). Conrods had the series 2 improved with more metal around the small end
Series 4: 1956 - 1958 : 600 crank (same as 500 crank with different balance factor of 60%). Conrods had more metal again on top of the small end
Series 5: 1959 - 1962 : 500 crank with or without alternator spigot. Conrods for the 650 had series 4 rods with chamfered edges.

P.S. I note that the G45 crank is similar in weight to the early 49-51 cranks.
This may not be 100% accurate, but it shows the variety of cranks available. You must also remember that there are at least 4 different sets of con rods (all with the same part number) and these must be matched to the crank as well.

That is incredible information....it's a complete minefield out there.

So why cannot the later con rods which appear stronger, be used with the earlier flywheels? The only journal change I am aware of is the earlier cranks up to maybe 51 used a narrower centre main.

This is a crank I am looking to get from USA..except the seller is weird in that he simply does not answer queries to measure up parts....the cranks are made of Meehanite ( perlitic grey cast iron of a good strength) before they went nodular... I believe you can either Gleeson weld or spray then up if the journals are too ground ( some examples for sale are 0.80 on the centre main using BMC Mini Bearings!). The problem is to get the radiuses right..they are very sensitive to that. A guy in UK does it...quoted me 600 quid for the job!

Here is the crank I am looking to buy. This would be correct for a 51 prior to engine 7000 would it not? https://www.ebay.com/itm/383610417468

Thanks enormously for your help.

No idea on cranks, but if you do the business with that chap, make sure you agree on postage.
I bought something, and he insisted it be sent as 'legal papers'. !
Complete ^^^^^^^^^ ?

Hi Rohan..from MachivMotors? He's very strange. I wrote about 4 x times trying to get him to measure a crank...no reply..even using their Facebook messenger and email.... bought another thing off him and could not ask a postage ? afterwards as Paypal informed me he does not take messages.

Then he wrote a long paragraph finally, explaining that he is short staffed and training someone to do measurements.. For the time he took, he could have taken out his caliper!

It looks like a good crank... and I'd buy it and then have myson in USA measure it and return it if it was not useable. But am scared he would refuse the return.

And he has a 100% rating.... ebay can be a weird place!

Hi Peter, sorry for the late reply, I missed your question the first time I read it. My immediate thought was Dave simply meant matching rods to cranks regarding factory balance factors(Which he has confirmed). I think these days if I am going to the expense of building an engine, balancing (static or dynamic) would be path of the course. Why is it hard to get the correct radius done in Kenya? And why would it be more expensive? As a machinist I would just buy the correct tooling or grind my own?
Cheers
Adrian

Hi Adrian, it would seem that for the centre web on Matchless cranks you need to dress the grinding wheel it correctly to the radiuses, which are not the same on the journals and centre web...... it might be hard to get some of our machinists attention on that!

I agree with you the balance factors need to be worked out...but even if unknown, I think someone who understands dynamic balance would figure it out if given piston, rings and pin plus a rod?

Peter, as a long time AMC Twin owner I would respectfully suggest that you have bigger issues to investigate with used cranks than journal radii. The first thing is to have any cast iron crank crack checked, magnetic particle or dye penetrant, either will expose the flaws at the radii where they break. In the unlikely event that the crank has no cracks, then work out the journal sizes. I would be reluctant to have one spray welded, if the journals are below 0.030" undersize, then the reduced diameter is already reducing the load they can carry and spray welding does not give that back. (in the aircraft industry where I worked as a machinist, machining cold spray weld build ups amongst other things, I referred to cold spray welding as having a similar structural integrity as throwing shite onto a wet stone wall)

I would recommend that you look around for a replacement steel crank. We have a bloke here in NZ who makes them. I can chase contact details if you wish.

I would also recommend replacement conrods. I fitted Triumph/BSA Triple rods to a late G9, then fitted 600cc barrels above them in the late'70's.There are now better designed alloy rods available from the UK. I am about to fit a pair to a G45 for a friend. Can get you details if you wish.

What is "cold spray welding" though ??

Now I've been for a ride on a bus, in India, that must have been on about its 7th incarnation
(wild guess, but it was more than one., this bus was quite elderly.)

I've also got a pic, someplace, of a welder out on the footpath giving another Bedford crankshaft
a hefty dose of hot spray weld with an oxy torch - talk about red hot ...
The machine shop inside was ready to machine it back to serviceable.
Now I'd say these guys were experts, but if they can do that, then anything is possible.
And the era and materials would be rather similar even. ?

I've also recently seen an even older crank,1920s, that had been built up by electroplating - hard chroming -
and ground back. Likewise they've done many.

That crack testing first is important, like you say.

Rohan, cold spray welding is so called because the molten metal powder particles are sprayed onto a "cold" material base, like a crank, where they stick with little more adhesion than a turd flung on a wet stone wall. "Hot" spray welding is where the molten metal powder particles are sprayed onto a red hot base to which they metallically bond. From your description it sounds like the Indian repair guys may have been using hot spray welding, Eutectic Eutalloy or similar.

As for the material technology, Bedford truck cranks may be forged or cast steel, sadly, AMC Twin cranks are simple grey Mehanite cast iron.

I did have my Model 31 AJS (Pre nodular) crank hot sprayed with Eutalloy back in the '70's. I didnt run it long after that and never had confidence in it.

AMC cranks are cast iron and notorious for breaking. If you wish to ride one reliably, fit a steel crank.

Yes, we've all heard of that foible of AMC twins.
Dang centre bearing, who's idea was that ...
Noddy iron solved that though ?


I must look into that.
Steel cranks for many a year were seriously expensive, but maybe thats all they had earlier on that could go the distance.
There is an engine shop down the road here, they'd know.


Most brit singles have iron flywheels, but the shafts were steel.
An all steel crank was a serious bit of kit, racing only. ?
Singles are somewhat different to twins though

Hi Peter, can you foward the details of the person making the steel crankshafts as mentioned in your post.