Ajs 650 csr 1963

What's the general opinion of these bikes?
Reliable?
Do they vibrate badly?
Anything engine wise to watch for?
Cheers

I have just sold my 1960 650 CSR. Always wanted to try one, & over the five years I've owned it I have enjoyed riding it. They seem to handle very well & the brakes, at least on mine seem okay. As for vibes, mine doesn't shake any worse than other Brit twins. A bike from 1963 should have the later SG iron crank, so should be fairly bullet proof. Between the owners club & AMC Spares the parts supply is good, & overall they are a nice thing to own & ride.
The only reason I parted with mine was to buy a S1 Interceptor, as it's another bike I've always wanted to try.

The achilles heel of AMC's biggest twin is the head gasket. Their attempt at sealing two surfaces at once (the spigotted surface AND the gasket surface) leaves one of them loosing, and usually it's the gasket surface (the spigot mates with head, and there is no compressibility there).
In short, insufficient gasket pressure leads to a blown gasket. The reported incidents are too many, for instance you may look up Doc Casey's report on his G12 combo. AMC designed this kind of joint with racing in mind, where mechanics have the time to fettle a perfect seal with no head gasket. For a road bike, this arrangement works only if you leave a tiny gap at the spigotted joint, i.e., gasket thickness in the compressed state has to meet a minimum figure. Additionally, the long 5/16"cylinder head studs stretched too much when subjected to prestress and combustion pressure load, which translates to reduced gasket sealing pressure. AMC dealth with it by increasing stud size to 3/8", which allowed a higher prestress load to be specified (25 vs. 16 ft-lbs). Early G12 engines may be comverted to the later spec. Beware of sub-standard head studs. The optimum solution is using high strength 3/8" studs with a reduced shank, allowing total strain to be maximized in the reduced section, thus preserving the threaded sections, which helps maintain the prestress load. This is particularly useful in the G12CS(R) engine.

- Knut

mdt-son said:

The achilles heel of AMC's biggest twin is the head gasket. Their attempt at sealing two surfaces at once (the spigotted surface AND the gasket surface) leaves one of them loosing, and usually it's the gasket surface (the spigot mates with head, and there is no compressibility there).
In short, insufficient gasket pressure leads to a blown gasket. The reported incidents are too many, for instance you may look up Doc Casey's report on his G12 combo. AMC designed this kind of joint with racing in mind, where mechanics have the time to fettle a perfect seal with no head gasket. For a road bike, this arrangement works only if you leave a tiny gap at the spigotted joint, i.e., gasket thickness in the compressed state has to meet a minimum figure. Additionally, the long 5/16"cylinder head studs stretched too much when subjected to prestress and combustion pressure load, which translates to reduced gasket sealing pressure. AMC dealth with it by increasing stud size to 3/8", which allowed a higher prestress load to be specified (25 vs. 16 ft-lbs). Early G12 engines may be comverted to the later spec. Beware of sub-standard head studs. The optimum solution is using high strength 3/8" studs with a reduced shank, allowing total strain to be maximized in the reduced section, thus preserving the threaded sections, which helps maintain the prestress load. This is particularly useful in the G12CS(R) engine.

- Knut

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Great information
Thank you

I have a 62 G12 CSR. It's not fast, shakes like hell, and has blown a head gasket twice. The front brake was awful, but I changed it to a Norton 2LS. That being said, it's an interesting motorcycle. I don't ride much anymore anyway.

rocketman71 said:

I have a 62 G12 CSR. It's not fast, shakes like hell, and has blown a head gasket twice. The front brake was awful, but I changed it to a Norton 2LS. That being said, it's an interesting motorcycle. I don't ride much anymore anyway.

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I've never ridden one
I was thinking they may vibrate a bit less than other Brit twins because of a supported crankshaft
But maybe not
Cheers

rocketman71 said:

I have a 62 G12 CSR. It's not fast, shakes like hell, and has blown a head gasket twice. The front brake was awful, but I changed it to a Norton 2LS. That being said, it's an interesting motorcycle. I don't ride much anymore anyway.

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Some say a gentleman’s motorcycle.

Others say oily vibratory heap.

Let’s improve rigidity with a three-bearing crank, but let’s make it worse again with separate cylinders and separate heads.

rocketman71 said:

I have a 62 G12 CSR. It's not fast, shakes like hell, and has blown a head gasket twice.

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G12's are usually gentle rides wrt. vibration. Do you have aftermarket pistons in it? Crankshafts were statically balanced at the factory. Dynamic balancing will make it even better.

- Knut

Triton Thrasher said:

Let’s improve rigidity with a three-bearing crank, but let’s make it worse again with separate cylinders and separate heads.

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How so? Heresay perhaps? Provided we are discussing a sound parallel twin, the vibration pattern is up-down and to a lesser degree back and forth, i.e., the entire motion is in the X-Z plane. I can't see how more top end rigidity will change this vibratory pattern. The cylinder and head is a fairly stiff lump that doesn't vibrate on its own.
Lots of engines have separate cylinders and heads --- think of all the V-twins, or the boxer engine. I've never heard anyone claim that separate heads amplifies vibration.
Vibration stems from the internal moving parts (crank, piston, conrod), not from static parts like cylinders and heads.

Increased vibration would be felt in the handlebars if you left out the head steady. What occurs is a torque reaction whereby the entire engine tries to rotate around the mainshaft.

- Knut

mdt-son said:

How so? Heresay perhaps? Provided we are discussing a sound parallel twin, the vibration pattern is up-down and to a lesser degree back and forth, i.e., the entire motion is in the X-Z plane. I can't see how more top end rigidity will change this vibratory pattern. The cylinder and head is a fairly stiff lump that doesn't vibrate on its own.
Lots of engines have separate cylinders and heads --- think of all the V-twins, or the boxer engine. I've never heard anyone claim that separate heads amplifies vibration.
Vibration stems from the internal moving parts (crank, piston, conrod), not from static parts like cylinders and heads.

Increased vibration would be felt in the handlebars if you left out the head steady. What occurs is a torque reaction whereby the entire engine tries to rotate around the mainshaft.

- Knut

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Who said separate cylinders and heads increased vibration?

Triton Thrasher said:

Who said separate cylinders and heads increased vibration?

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It's reasonable to construe your statement in #7 that way. If you didn't mean to put "vibration" and "rigidity" in a context, what did you actually imply by mentioning the latter?

- Knut

I bought a second hand (pre used is the modern term I believe) CSR 650 in 1963.
It had a particularly annoying vibration just before reaching 70 mph so I eventually stripped it down and had the crank dynamically balanced. While the crank was away I discarded the head gaskets and machined where necessary to make a metal to metal joint. This was all a long time ago and I can't remember the exact details, but it was a very different motorcycle from that time on., and a smooth running engine made it a real pleasure to ride.
I emigrated to South Africa in 1975 and gave the CSR to a very good friend on the understanding that he taxed and insured it and to all intents and purposes used it as his own, but if I ever came back to the UK I would take back ownership. I did come back in 2006, but never retrieved the CSR, and when my friend said he thought it might be time to sell, we shared the money.
In the years he 'owned' the CSR, my friend regularly took it on holidays, travelling all around Europe, and never once had a failure of any kind.
I would readily do it all over again, - if only I could turn the clock back !

PS in a letter to me Jack Williams stated that the CSR crankshafts WERE dynamically balanced at the factory.

Snotzo said:

I bought a second hand (pre used is the modern term I believe) CSR 650 in 1963.
It had a particularly annoying vibration just before reaching 70 mph so I eventually stripped it down and had the crank dynamically balanced. While the crank was away I discarded the head gaskets and machined where necessary to make a metal to metal joint. This was all a long time ago and I can't remember the exact details, but it was a very different motorcycle from that time on., and a smooth running engine made it a real pleasure to ride.
I emigrated to South Africa in 1975 and gave the CSR to a very good friend on the understanding that he taxed and insured it and to all intents and purposes used it as his own, but if I ever came back to the UK I would take back ownership. I did come back in 2006, but never retrieved the CSR, and when my friend said he thought it might be time to sell, we shared the money.
In the years he 'owned' the CSR, my friend regularly took it on holidays, travelling all around Europe, and never once had a failure of any kind.
I would readily do it all over again, - if only I could turn the clock back !

PS in a letter to me Jack Williams stated that the CSR crankshafts WERE dynamically balanced at the factory.

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It's interesting that JW said the cranks were dynamically balanced. A few years ago I rebuilt a G12 650 CSR & the very rare G15/45 engine both at the same time. Both cranks had been drilled for balance in a way that indicated a dynamic balance. The 650 crank in particular had been drilled far more in one side than the other, however, I have never seen any documented evidence of AMC dynamically balancing their cranks, only Royal Enfield.

Matchless said:

It's interesting that JW said the cranks were dynamically balanced. A few years ago I rebuilt a G12 650 CSR & the very rare G15/45 engine both at the same time. Both cranks had been drilled for balance in a way that indicated a dynamic balance. The 650 crank in particular had been drilled far more in one side than the other, however, I have never seen any documented evidence of AMC dynamically balancing their cranks, only Royal Enfield.

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JW stated that ALL twin engine cranks were dynamically balanced !
I have found some details for this engine in an old notebook, and see that the crank was balanced to 66% of the reciprocating weight, but unfortunately I never recorded what it was originally before re balancing was carried out.
JW's original letter to me went with the CSR when it was sold, but I still have scanned copies.

Snotzo said:

JW stated that ALL twin engine cranks were dynamically balanced !
I have found some details for this engine in an old notebook, and see that the crank was balanced to 66% of the reciprocating weight, but unfortunately I never recorded what it was originally before re balancing was carried out.
JW's original letter to me went with the CSR when it was sold, but I still have scanned copies.

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How long ago was your bike sold?
It'd be nice to know it's still out there
Still being used

baz said:

How long ago was your bike sold?
It'd be nice to know it's still out there
Still being used

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It must have been sold approx. ten years ago, and most unfortunately my 'joint owner' friend died in 2017, so I have no record of who the buyer was or where it went.
Before I emigrated. for a time I ran it with a 7R front wheel, which gave a rather 'special' look to it, but the brake was perhaps a bit too sharp for my liking, so eventually the original was re installed.

The earlier AJS and Matchless twins had problems with oiling to the drive side of the crank, breakages through the sizing hole in the conrods and thackery thwack in the valve gear. However in 1963, all the problens had been fixed. I have only seen one 650CSR - it was ridden by the New South Wales cop who booked us when we were on the way back from the Bathust races in about 1963. It had a 2 into one exhaust system as standard. It looked and sounded excellent. I think they were discontinued after 1963. But worth having.

Snotzo said:

It must have been sold approx. ten years ago, and most unfortunately my 'joint owner' friend died in 2017, so I have no record of who the buyer was or where it went.
Before I emigrated. for a time I ran it with a 7R front wheel, which gave a rather 'special' look to it, but the brake was perhaps a bit too sharp for my liking, so eventually the original was re installed.

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When I sold my Triton 500, it had 7R brakes front and back. That was the reason I sold it and built the Seeley 850 which has disc brakes. If I race, I now race in a different class, and I am still alive.

acotrel said:

The earlier AJS and Matchless twins had problems with oiling to the drive side of the crank, breakages through the sizing hole in the conrods and thackery thwack in the valve gear. However in 1963, all the problens had been fixed. I have only seen one 650CSR - it was ridden by the New South Wales cop who booked us when we were on the way back from the Bathust races in about 1963. It had a 2 into one exhaust system as standard. It looked and sounded excellent. I think they were discontinued after 1963. But worth having.

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Al, you are misinformed, or spreading hearsay. There never was a problem with oiling to the drive side of the crank as per design. Crank breakages appeared because a) owners neglected the centre main bearing when doing a regrind, and b) neglected cleaning the built-in oil filter.
As long as capacity was limited to 500/550/600cc, cranks were almost bullet proof. Problems related to fatigue breakage started apearing when capacity increased to 650cc and CR increased as well. In response to that, AMC introduced the nodular iron crankshaft, which has a much higher fatigue limit. (Nodular ductile cast iron is an excellent engineering material, with hard wearing surfaces, good fatigue strength, and good machineability to boot.)

Breakages through sizing holes in the conrod? Never heard of those. Perhaps a consenquential damage of a snapped crankshaft? Those conrods are bullet proof. The only problem is associated with creep plasticity at the big end, resulting in ovality on high mileage engines. Conrods can be machined to as new condition.

Sorry, I don't know what you mean by "thackery thwack". You are the first I've heard claiming the valve gear gave rise to problems. High mileage engines wear, it's normal. Valve seats, yes, in the heat of competition, they may drop in the old design. Post-60 heads were much improved in this regard, and even more so in 1963. The same year, stellited camshaft followers were introduced, also a high-capacity oil pump, ensuring better cooling of the engine.

The long line of AMC's sophisticated twin ended in 1966.

- Knut

Some of my mates had AMC twins in the 1950s - they were not as good as Triumphs. A G45 motor was probably very different.