AMC conrods, yes or no?

Information relating to the Matchless G12 or AJS Model 31 650cc twin
mdt-son
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AMC conrods, yes or no?

Post by mdt-son »

For my first venture into the AMC twins domain, I would like your valued advice: Are used AMC conrods any good or should I opt for Carillo rods? I read somewhere that Triumph T120 rods may be used as well (will need modified pistons though). One of the new crankshafts will be fitted for this rebuild eventually.

I read the advice of having the big end eye machined to ensure a perfect fit. Rods will be meticulously checked and polished in either case.

Knut Sonsteby
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milos
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AMC conrods, yes or no?

Post by milos »

At "Twin connrods AJS M30 searching" topic I was looking for a pair of them. If you read the topic you will find that there is possible to find australian ones which look great and they are much cheaper as Carillos. At the end I decided to buy a good pair of used ones.
Don Madden
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AMC conrods, yes or no?

Post by Don Madden »

The factory conrod big ends have a tendency to stretch in the 650cc engine. I have gone through several of them but others may not ride as hard. The Australian ones have an better cap fastning setup & Carillos are steel although lighter than the originals. T140 rods are 1/2in shorter than T120 & can be used in AMC twins with special pistons. With a good crankshaft & good rods, these engines can be thrashed without concern. Ed Crowell in So. Cal. builds 750cc engines & is working on one of 850cc using stroked noddy crankshaft & Carrillo rods. Cheers, Don.
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GSAX1
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AMC conrods, yes or no?

Post by GSAX1 »

Hei Knut.

Jampot Spares had some Ridgecrest rods for sale a while ago, perhaps they still have some in stock. I bought mine directly form the Australian club.

Regards from Trondheim
Michael

Original rod in the middle:
zwarts
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AMC conrods, yes or no?

Post by zwarts »

Also, Thunder Engineering do new rods for the G45 which are similar to the Ridgecrest rods and will fit in the G12. Their website is at
www.thunderengineering.co.uk
The G45 rods are not mentioned on their website but they are listed in their OBM advert, and have been for some time. If you want the ultimate, then the Carillos are probably the best choice - being steel, I always assumed they'd be heavier than the originals but it seem this is not so. A lot depends on what state of tune you are going to build your engine to and how you intend to use it subsequently. I have always used carefully selected AMC rods, polished and balanced to equal weights at each end. I have not had any problems with them going out of shape in use (yet!), but my engines are not too highly tuned as I like to finish races with the engine in one piece. The original rods were a well designed and strong product but, depending on how hard a life they have had, may be getting to the age where fatigue failure is a possibility.
Bob.
rayswadling
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AMC conrods, yes or no?

Post by rayswadling »

When I approached Carillo about the rods I bought from them, they were also G45 rods. I sent one of my originals over and they examined it and thats what their database came back with.
The steel rods are no heavier as they are an "H" section like a steel beam.
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GSAX1
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AMC conrods, yes or no?

Post by GSAX1 »

As a curiosity; I read in an interview from the early '50s with AMC engineers that the conrods (on the 500 twin) were designed to last for 50 years - at full throttle! And that they could be expected to fail at the small end due to fatigue fracture at the end of their service life.

It now seems they where wrong, since small end failures are not common as far as I know, the most common fault is as mentioned above that the big end gets oval.

About the Ridgecrest rods; these have a feature I think the Carillo's lack: An extra slot in the big end (and cap) to accomodate Austin Mini main bearings, which are the same size according to sources.

The Ridgecrest rods weigh exactly the same as the original rods, so no need to rebalance. And they are beautiful, I take them out of the drawer once in a while and admire them .

Michael
mdt-son
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AMC conrods, yes or no?

Post by mdt-son »

Thanks, fellows. Lots of good advise here. I think I will go the Carillo route for my hopped-up 750. Does anyone know the Carillo part number? Their catalogue lists the G80CS (?) item only.

It should be noted that total weight isn't the main issue. For balancing, the big end and small end weights as measured by a special balancing scale using 'knifes' are the figueres to look for. I will post the figures if I can obtain them.

Knut SonstebyEdited by - mdt-son on 06 Feb 2012 4:08:06 PMEdited by - mdt-son on 06 Feb 2012 4:10:55 PM
mdt-son
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AMC conrods, yes or no?

Post by mdt-son »

quote:
Ed Crowell in So. Cal. builds 750cc engines & is working on one of 850cc using stroked noddy crankshaft & Carrillo rods.

Hi Don,
Does Ed have a web site or at least an email address? I would like to discuss a few things before starting out on my 750 project which will be based on a '64 650 engine.

I remember talking to another Californian Matchless guru around 1990, the late Bud Ekins. It was a pain reaching him, a word of advice was even more difficult. Eventually he sold me a pair of 1964 shortstroke crankcases - probably his last set.
rayswadling
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AMC conrods, yes or no?

Post by rayswadling »

The part number they provided for me was MT_BG12_0HS_575B5S

I dealt with Barry Deane at Carillo (bdeane@cp-carrillo.com). I guess if you mention my order then it will help to match up the parts. I confirmed the order dated 19th August 2010 and its 4-6 weeks manufacture.

I sent over a sample rod and shell to be used a s a pattern. The 650 rods are "similar" to their G45 rods. I initially sent over some dimensions taken from the original rod before I actually sent one over.

Cheers,

Ray.
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