New Crankshaft

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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New Crankshaft

Postby mdt-son » Sun Oct 07, 2012 12:00 am

quote:

Where is the sludge trap you are talking about? As far as I can see the design is very sound. My own crank did not have any blockage after 50 years.



GSAX1

As can be seen in the image, oilways extend right out to the crank cheeks. There will be a sludge trap there which can't be cleaned out, unlike the design used for the Dominators. The trap shouldn't have been there in the first place.

Good for you that you didn't experience a crank seizure. Have you measured the journals lately?

Knut Sonsteby

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Postby mdt-son » Sun Oct 07, 2012 12:00 am

Hi Geoff and Bob,
Your discussion about the economics of ABSAF products is a complete derailment of the topic discussed here. Please take your dispute elsewhere. I think Jan de Jong's engneering qualities can't be disputed as he has developed and supplied championship race engines for years. His G80 engine is also utterly reliable. From my brief inspection of his premises, workmanship and products were second to none but that's also irrelevant in this context. Let's get back on track here.

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Postby rex.webb » Sun Oct 07, 2012 8:26 am

HERE ! HERE ! i HEAR the CRY !!!!!!!!!!!!!!!
RIDE with CARE and LIVE LONG to ENJOY your Bikes and Scooters.
r w webb

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Postby zwarts » Sun Oct 07, 2012 8:38 am

Knut -you are quite correct! We have digressed and are well off topic. For this I apologise.
Bob.

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Postby dave16mct » Sun Oct 07, 2012 10:11 am

Why do you say the sludge traps can't be cleaned out? There are screwed plugs which have to be removed. Then they can be cleaned easily. If an in line filter is fitted on the return oil pipe they will probabely never need doing again.

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Postby MG » Sun Oct 07, 2012 10:30 am

Hello gents!

Knut, thank you for you input. While I fully agree that the old centre bearing design was superior in terms of bearing surface, we have clearly decided against major changes in the original design. While there is room for optimisation indeed, it is well proven and the majority of people are happy with their cranks, also for racing use, so we have opted for a direct 1:1 replacement part.
When talking to members, we have had the impression that 99% were not up to spending additional money on new centre webs or other experimental parts. Quite understandable, when you consider the cost of a proper engine rebuild, compared to the (highly underestimated, imho) overall market value of our bikes...

However, if you so wish, I can ask the company that do the machining to supply your cranks with raw-machined (read unground) journals. Then you can have a go at it yourself. Machining material off the inner sides of the crank webs and subsequent grinding of all three journals should give you exactly the crank you desire. Just let me know if this is viable for you. Leaving the crank unground shouldn't be a big problem, but making one-offs during machining of the serial production run will cause tremendous additional costs I'm afraid (re-designed 3D model, CNC programming and setup costs, and we'd need at least one additional prototype with the inherent risk of rejects). So I hope you will understand that this is out of question unfotunately.

Ref the oil ways: Erny Merryweather indeed considers the short length between the plug and journal drilling a "sludge trap", see the last page of his article: [url="http://archives.jampot.dk/Technical/Specific_Models/AJS_Matchless_Twins__Ernie_Merrywater_in_British_Bike_Magazi.pdf"]Merryweather_twin_article[/url]
It's not a bug, it's a feature.
I'm not familiar with the Triumph system of drilling oilways, but if you can come up with a solution that can be incorporated without causing additional costs for machining/drilling, additional plugs, etc, I shall of course be more than happy to discuss things!
If you are not happy with sludge accumulating beneath the plugs, I am sure a skilled engineer such as yourself will be capable of making his own prolonged, tuned or whatever verision. The plugs for the new cranks are bog standard M6x10 countersunk bolts. If you need any further dimensions or information, please feel free to contact me any time.

All the best, Markus

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Postby 242017 » Sun Oct 07, 2012 2:07 pm

Dear All,
I agree about the de-railment of the topic..
But I dont agree about the comments about ABSAF and his idea of how a matchless engine should be.
He is barking

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Postby zwarts » Sun Oct 07, 2012 3:26 pm

You are welcome to your opinion and I see no point in prolonging this any further.
Bob.

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Postby GSAX1 » Wed Oct 10, 2012 2:25 pm

quote:

As can be seen in the image, oilways extend right out to the crank cheeks. There will be a sludge trap there which can't be cleaned out, unlike the design used for the Dominators. The trap shouldn't have been there in the first place.

Good for you that you didn't experience a crank seizure. Have you measured the journals lately?

Knut Sonsteby



The oilways that extend towards the cheeks contain only stagnant oil, therefore no large amount of sludge will be deposited. And any debris will anyway pass this "trap" and go directly towards the journals.

For 1953 AMC changed the design to the one shown in the picture. The pre '53 oil tunnel at this point was parallel to the mainshafts and was indeed a sludge trap and AMC therefore specified a 20000 miles cleaning interval. For the new (post '53) design no cleaning interval was specified, since cleaning is not needed.

My own crank showed some wear when I rebuilt the engine 7 years ago, but the reason for dismantling it was worn main roller bearings. The centre main journals where still good. All crank journals was standard size, and the crank had not been touched since it left the factory (full history is known). When I opened up the oil gallery in the crank (there is a 2BA screw each side) there was some sludge inside the small "blind" passage, but this deposit was nowhere as hard as it usually is on BSA and Triumph twins. The main passageways where both clear.

This design is sound, I would advise against modifying it.

Edited by - GSAX1 on 10 Oct 2012 2:27:53 PM

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New Crankshaft

Postby 242017 » Wed Oct 10, 2012 4:12 pm

I agree with Michael Gregor on this...

The design of the sludge trap is as sound as it can be for this crank....

Not quite sure why a Mech.eng would need to take his motor to someone else to fix?

and then come away with any number of ideas

Are they as sound as the Matchless factory who spent a lot of years developing that engine?


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