Matchless G12

[Rainmanshaun]

Hello all - I am thinking about buying a 1959 Matchless G12 650 that I have my eye on and was wondering if anybody could pass on any pro's and cons of this model to help me make my decision ??

Cheers Shaun

[Blue]

Ask the seller about the oil system and whether or not he/she has modified it in any way.  The AMC twins are notorious for oil starvation to the left cylinder because the crankshaft is supported by a central web.  This web is supposed to increase the rigidity of the shaft but also added another plain bearing for the high-pressure oil to be pumped through - subsequently, when this bearing wore from use the oil lost pressure before it could properly lubricate the left crank journal (resulting in many a con-rod making a break for freedom through the crankcase).

This problem is usually circumvented with a few minor alterations and the use of later-model/aftermarket oil pumps, coupled with new bearings and modern oils and filters BUT it does mean that they can be particularly sensitive to poor rebuild jobs and poor filtration.

That's all I really know about the AMC twins - they're a fine looking bike and will no doubt give you a lot of joy if well cared for (like any british twin)

[Rainmanshaun]

Thanks Blue for that very useful info - I have also just had an email conversation with a very old mate of mine who says that he can recall the 650 twin also had a weak bottom end due to crankshaft whip at high speed - presumabably the third main bearing that was added was in an effort to counteract this problem. Ok if you keep the revs down, but buying a bike with an engine that hasn't been re-built or at least re-built properly could be risky!!

[RichP]

The AMC twin engine had the three bearings from the begining and it is probably the extra rigidity that can make the bigger ones real shakers.

There have been stories of breaking crankshafts, especially the alternator equipped models which AMC went some way to curing with the introduction of a nodular iron crank.

A friend of mine ran a Model 31 Ajay (the same model) and it was incredibly uncomfortable due to vibration. He replaced the crank with a dynamically balanced noddy one which ran for about 1500 miles before it broke !

As with many makes, the earlier smaller capacity twins were often nicer to ride. I remember riding a jampot 500 which was very pleasant.

[Rainmanshaun]

Thanks for that info Rich - think I will now continue to look for a reasonable BSA A10 or an AMC 500 single or twin

Shaun