Triumph 650/750 Crank bearings

OK here’s a subject I refuse to get into debates about – life is too short.

We specify 70-2879 as the correct drive side roller bearing and list it for all 650 and 750 twin motors 1963-80. According to Jack Shortland and Edward Turner it is made by RHP to Triumph’s specifications.

The frequent complaint is that it is too tight with its C2 clearance.  However Mr Turner insisted that it be tighter than RHP recommended for a cold motor and said that anything else (especially C3) would have too much clearance when the engine was hot.

We do supply the bearing with C3 clearance for those people who insist on using it (Part No 70-2879/C3).

In conclusion it is recommended that slight negative clearance on assembly should be considered to be correct.




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Here’s an article I wrote some time ago.  To experienced restorers it will sound too basic but from the number of questions we get at the shop it needs to be understood.


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Single phase vs three phase

Most of the bikes we deal with are 1966-77 models and all have single phase alternators. In good shape these are perfectly adequate. The biggest problem is that the magnetic rotor gradually loses its magnetism and this causes a drop in output.  I am not sure I totally trust the ammeter fitted to bikes up to 1970 although it will give you some indication if there’s a real problem and it is very useful, especially on singles, to get the piston/s in the right position for starting.

We frequently get customers who want to buy a 3 phase stator or high output single phase (as fitted to 1975 Commando’s)  because their batteries keep going flat when the real culprit is  the rotor.

2 quick tests – hook up a DC volt meter to your fully charged battery. turn on the ignition and the lights and the voltage reading will drop well below 12 volts.  Start the bike up and see how many rpm you need before the meter reads 12 volts or more. If it reads less than 12 volts at the rpm you usually cruise at it will only be a matter of time before you are stranded with a flat battery.

You can also take the 2 AC wires off the rectifier and connect them to an AC volt meter.  Start the bike up and at 175o rpm you should get a reading of 20 volts AC.

Single phase stators have 6 laminated coil windings, three phrase have 9.  Early single phase units have 3 wires, the later ones 2. They are actually exactly the same electrically – with the later ones the green and yellow and green and black wires are joined internally to enable the alternator to produce maximum output at all times.

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Trimming Horns

Had a customer return a horn today, because “it doesn’t work”.   Worked fine for me.  Most, if not all, horns have a trim adjusting screw on the back and are very delicate and sensitive. This screw often has to be adjusted to get the optimum sound.  The current arriving at the horn when it is activated will vary from one  bike to another. This according to the resistance in the wiring which is a factor of it’s length and diameter.

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1958 G12 650 Matchless

58-g12Here’s an unusual bike. This particular picture courtesy of Jim Thomas in Florida.  Officially, or so the UK club informed us, the first  G12’s were introduced in 1959. They had no knowledge when we asked of the 1958 model however we have come across several over the years and even the occasional AJS version.

At least 200 of these bikes were specially built for Coopers for USA export.  They are really 1958 G11’s (600cc), the only difference being longer stroke cranks and special pistons with higher wrist pins and the skirts fly cut to miss the tops of the cranks.  They use the regular 7 fin G11 cylinder, not the later taller 12 fin G12 type.   Scott Apger in Ohio owns one of these and did a lot of research.   Jerry Wood also has one and describes it as one of his nicest bike to ride.

The place where guys get into trouble is ordering parts.  Every single part other than those mentioned above is G11 and that’s  the parts book to use.



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Warning to all AJS, Matchless & P11 Owners



The problem with Matchless, AJS & P11 rear wheels locking solid, with disastrous results, keeps coming up and I heard about another one this week. This is caused by the right hand seal cup 018094 being shown the wrong way around in several of the original parts books, as it is in the 1960 book shown above. This seal cup MUST be installed the other way around with seal 014387 to the outside.  The speedo drive 021583 screws into the hub so it can hold the lip of the cup tightly against the outer race of the r/h bearing.(014868). If you install this seal cup the other way around it will only be a matter of time before your rear wheel locks solid.


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Daughter Steph promoting Walridge at the Calgary Bike Show.  Will send some catalogues for her to hand out next year – if I ever get the new one written!

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