G2 timing side main bearing renewal

Information relating to the Matchless G2 or AJS Model 14 250cc Lightweight
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G2 timing side main bearing renewal

Postby Richard Hyatt » Tue Apr 02, 2019 7:44 am

good morning,
we are slowly stripping the engine down to explore a poor oil feed to the rockers.
we are down to the crankcases now and need to buy an extractor for the timing pinion and get that nut off and pinion off - then split the crankcases from the crankshaft.
a few questions please??
1) is the timing pinion nut LEFT or RIGHT hand thread please?? before I start swinging on it in the wrong direction!!!
2) once the nut is off , I can use the extractor to pull the timing pinion off --- any problems here please??
3) then I can carefully extract the crankcase from the crank to check wear in bushing as a possible route for oil loss , thereby reducing the flow to the top end(we never had any oil out of the rocker jets despite everything being poked clear etc)
4)if we have to replace the bush, is it just a matter of pressing in or does it need reaming to size afterwards(in which case , I'll need to find a reamer)
5) when we check the drive side mains - what reassembly hints are there with regard to the bearings and their timed breather please??
basically , any hints and tips on this strip would be appreciated.
thank you.

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Re: G2 timing side main bearing renewal

Postby Ozmadman » Tue Apr 02, 2019 10:10 am

Richard Hyatt wrote:good morning,
we are slowly stripping the engine down to explore a poor oil feed to the rockers.
we are down to the crankcases now and need to buy an extractor for the timing pinion and get that nut off and pinion off - then split the crankcases from the crankshaft.
a few questions please??
1) is the timing pinion nut LEFT or RIGHT hand thread please?? before I start swinging on it in the wrong direction!!!
2) once the nut is off , I can use the extractor to pull the timing pinion off --- any problems here please??
3) then I can carefully extract the crankcase from the crank to check wear in bushing as a possible route for oil loss , thereby reducing the flow to the top end(we never had any oil out of the rocker jets despite everything being poked clear etc)
4)if we have to replace the bush, is it just a matter of pressing in or does it need reaming to size afterwards(in which case , I'll need to find a reamer)
5) when we check the drive side mains - what reassembly hints are there with regard to the bearings and their timed breather please??
basically , any hints and tips on this strip would be appreciated.
thank you.


1) As far as I remember it is RHT
2) no issues just pulls off
4)There is a small retaining pin just tapped into the casing on the face of the bush, probably just there to stop it turning in the casing. Yes it is pressed in and mine did need reaming so I took it to an engineer with the crank and other half of the casing and bearings so they could line ream it accurately, some have said that theirs didn't need reaming though??
5) Think clanger has a link somewhere with some tips on this... there are three types of timed breather early one where the breather tube screws into the casing but the end is just a press fit in the breather stator ring and they waer causing a rattle. intermediate one where the breather tube actually screws into the stator ring. third type where there is no breather tube, just a hole in the casing and the stator ring is is secured by a bolt in the casing. All of the rotors on the crank are the same and that is kept in place by a very small woodruff key. If you have two ball bearings then when you replace them use the later roller bearing, which has a removable outer track as the inner (nearest to the crank) bearing which makes life so much easier to fit. The stator sandwiches between both bearings so I would fit the first bearing (the outer one) heat the casing first and it should just drop in, then put in the stator and fix it in place by putting the breather tube through the casing into the hole in the stator or bolt depending which version you have as this will ensure all holes line up otherwise you may have a hell of a job lining it up once you fit the other bearing!!. last of all fit the inner (Roller bearing )track using the same heating method and either loctite it in place or just peen the casing with a centre punch to retain it. The roller bearing itself is just pushed on the crank an yes it will just be a push fit and that is correct but once all is back together and tightened up it will be tight and will not spin on the crank.
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed

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Re: G2 timing side main bearing renewal

Postby Ozmadman » Tue Apr 02, 2019 10:17 am

Some pics
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Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed

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Re: G2 timing side main bearing renewal

Postby clanger9 » Tue Apr 02, 2019 7:14 pm

Hi Richard,

This thread may help:
viewtopic.php?f=159&t=22646

To answer your questions:
1) Right-hand. There's only one left-hand thread on a Lightweight (the gearbox sprocket)
2) You may need a puller if it's stuck. I improvised one (see above thread)
4) You need to press it in from the outside. There's a small pin to hold it in position. It shouldn't need reaming. Mine was a perfect fit out of the box.
5) Drive side bearings are easy enough to change, just warm the cases & drop the races in. Don't forget the breather rotor ;)

Good luck!
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: G2 timing side main bearing renewal

Postby Richard Hyatt » Tue Apr 02, 2019 7:20 pm

Thank you both.
Hope we get the oil up to the rockers after all this !!!

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