Engine rebuild thread

Information relating to the Matchless G2 or AJS Model 14 250cc Lightweight
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Engine rebuild thread

Postby clanger9 » Fri Oct 13, 2017 7:14 pm

Hi all,

Now that I've got my engine to pieces I thought it might be useful to post updates & questions on my engine rebuild here.

Parts are definitely a challenge at the moment, with the club spares out of stock of almost everything for a Lightweight engine. My engine has severe wear on the oil pump teeth and timing side shaft & bearing and the drive side roller bearing has failed completely. The big end is good but has small amount of lift. It will hopefully be OK once it's fitted with a new set of rollers.

I managed to get the following from the ever-helpful Les at Russell Motors:
042239 Timing side bush
010079 Oil pump pin
042104 Oil pump plunger [edit:] this is the wrong oil pump for a CSR - the correct one is longer stroke, but unavailable new
012542 Outer main bearing
012543 Inner main bearing
044059 Duplex primary chain
042173 Timing side axle
000075 Crankpin rollers (28 off) [edit:] these are incorrect for some CSRs - mine has a single row of 1/2" wide rollers
041097 Chaincase retaining screws (6 off)

Club spares provided the following:
042100 Inner camshaft bush
042101 Outer camshaft bush
042183 Camshaft oil seal
Engine gasket set

New cam followers (042071) are unavailable at present. I will see if I can get mine re-profiled.

Some interesting things from the strip down:
- You can improvise a slide-hammer puller to remove the advance-retard mechanism. Use one of the long retaining bolts for the toolbox covers (it screws straight in) with a large washer and a heavy socket.
- You can improvise a puller for the timing pinion using a 22mm brass pipe fitting and a flat-bladed puller.
IMG_1686.jpg

- The wear on the oil pump teeth was surprising. It might not have been long before it failed. The worn one is at the front of this photo - you can see how thin the teeth are.
IMG_1709.jpg

- The wear on the timing shaft was enough to make the shaft a loose fit in a new bushing. You can see the visible wear grooves on the shaft when compared to the new one.
IMG_1710.jpg

Next up: vapour blasting the crankcases & crankshaft rebuild...
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Last edited by clanger9 on Mon Oct 30, 2017 7:50 pm, edited 1 time in total.
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: Engine rebuild thread

Postby shifter » Fri Oct 13, 2017 8:07 pm

Cracking job
shifter
?

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Re: Engine rebuild thread

Postby clanger9 » Sat Oct 14, 2017 11:02 am

Well, the crankcases are off to get vapour blasted. All the bearings and bushes came out easy enough once the cases were heated in the oven (approx. 150 deg C).

Fun observation: whoever last had the crank to bits forgot to align the breather rotor keyway with the crankpin:
IMG_1715.jpg

This means the timed breather isn't timed correctly, which would explain why my engine has never breathed properly. So that's both crank axles that need to come out...

The curse of the P.O. strikes! :headbang:

[edit:] it turns out that the alignment shown above is correct.
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Last edited by clanger9 on Mon Oct 30, 2017 7:51 pm, edited 1 time in total.
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: Engine rebuild thread

Postby dodger » Sat Oct 14, 2017 1:45 pm

I have just received back from Alpha Bearings my G2 CSR crankshaft and your post prompted me to go and check the position of the breather keyway and it is in exactly the same place as yours, but, that axel is located in the flywheel by two keys and cannot be assembled wrongly, apart from being 180 degrees out I suppose.
If you remove the remains of the bearing pictured on your axel you should see the two keyways clearly.

Laurie

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Re: Engine rebuild thread

Postby clanger9 » Sat Oct 14, 2017 2:20 pm

Thanks Laurie, that's very helpful. I'm sure Alpha will have put your crank together correctly.

The manual says: "...the keyway for the rotor is pointing to the crank pin."

I've removed the bearing inner race now and the keyways are clearly visible. The manual is probably misleading (again!) - I guess they were trying to explain how not to get the rotor timing 180 degrees out...
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: Engine rebuild thread

Postby clanger9 » Sat Oct 14, 2017 2:30 pm

...the manual goes on to say "The correct shaft location is shown in the engine breakdown (see Fig 28)."

Looking at a zoomed-in version of that diagram, the orientation of my shaft now looks OK.
Untitled.jpeg

I guess they meant to say "...the keyway for the rotor is pointing towards the crank pin and not away from it." :headbang:
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Re: Engine rebuild thread

Postby Ozmadman » Sat Oct 14, 2017 6:38 pm

Complete red herring then :headbang: what made you think yours wasn't breathing properly in the first place?
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed

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Re: Engine rebuild thread

Postby clanger9 » Sun Oct 15, 2017 7:32 am

It was chucking engine oil smear down the left hand side of the bike when ridden hard - presumably from the breather.
I also had trouble getting it to stop throwing oil out of the rocker cover.

I assumed there was something wrong with the breathing, but the fact that the piston ring gaps weren't spaced properly (two were in line!) certainly won't have helped...
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: Engine rebuild thread

Postby Ozmadman » Mon Oct 16, 2017 1:19 am

clanger9 wrote:It was chucking engine oil smear down the left hand side of the bike when ridden hard - presumably from the breather.
I also had trouble getting it to stop throwing oil out of the rocker cover.

Don't think that is unusual as some of that oil spray is "designed" to lubricate the rear chain (all the more reason to keep the full chain guard which interestingly has an oil drain hole in it) mine has a drip from there now and again. Have a look at this picture taken from a German Model 8 road test, looks like he has the same issue!! Anyone read German/ It would be interesting to find out what the caption for that picture reads
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Re: Engine rebuild thread

Postby dave16mct » Mon Oct 16, 2017 9:09 am

It just describes what you see in the picture.

' Airfilter for the carb. Horn (too quiet!) Spring rear leg and rear cover. The chain is sufficiently covered , no water enters. The English chain lasts a long time.'

Something like that. Dave.

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