G15 Cylinder Head Removal

Information relating to the Matchless G15 or AJS Model 33 750cc twin. This also includes the G15 Mk II and the G15/45
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Joker_Bones
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Re: G15 Cylinder Head Removal

Post by Joker_Bones »

Mick D wrote: ↑Sun Jul 26, 2020 3:48 pm
Is it actually possible to remove the head on a AMC Duplex framed bike without taking the engine out? If so any tips?

Regards Mick
I read this thread earlier having failed to remove the head by the method described in the manuals. I also read some threads on Norton forums. There were posts telling how it is done ie as per the manual, but I didn't find anyone saying they had actually managed it. So I am posting this as a conclusion, it may help someone one day.
ajscomboman wrote: ↑Sun Jul 26, 2020 3:54 pm I'm led to believe it is possible but many many others have struggled and said no way! The other alternative is to let the motor drop down between the plates and swing forward allowing the head to be removed. I've never attempted this myself.
I say "no way!" There just isn't enough clearance to get the longer push rods over the barrel by about 1/4 inch.
Solution, as Rob said, was to drop the engine a little which wasn't as bad as I feared...
IMG_20220908_192849~2.jpg
Removed the three front frame studs and one of the back pair which allowed the engine, plates, box and primary to rotate together down about the remaining rear stud
IMG_20220909_195704.jpg
This is as far as it would go before resting on the centre stand spring where it hooks into the engine plate... But it was enough 🙂
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Groily
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Re: G15 Cylinder Head Removal

Post by Groily »

To Mick's original Q about 'head in a duplex framed bike', I can say that I've done it without moving the engine on my P11, but it was a horrible way to spend a morning, with a worse one to come getting it back on. Not sure if dimensions and clearances are the same or not between different hybrids though.
Even with a Featherbed where the twin top loops offer just enough space to get the head off and on 'sideways' through the tubes, the job's a lousy one owing to the pushrod problem.
Removal of exhaust rockers and shafts helps or may be a 'must' for reassembly, along with much cursing.
I rate this job FAR worse than that 'worst job in the world' of fitting pre-unit BSA twin rocker boxes. That's a cinch, compared!

Makes me really appreciate the design of the AMC twin engine more and more, even if the execution wasn't perfect in some respects.
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Joker_Bones
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Re: G15 Cylinder Head Removal

Post by Joker_Bones »

Groily... Yes, I read your earlier post in the thread about the P11.
Knowing little of P11s it prompted me to search for some photos... A different looking duplex frame to the G or N15, but I didn't come across any photos where you could judge the relative clearances. I guess there is a bit more clearance on the P11 coz you said it was a horrible way to spend a morning... I've been on this, one way or another, for the last three days! ðŸĪŠ
Groily
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Re: G15 Cylinder Head Removal

Post by Groily »

I was told by another member who knows more than I do by miles that on the G15 you can get the head off if you remove the inlet rocker shafts - but I don't know and never want to go there!
g80csp11
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Re: G15 Cylinder Head Removal

Post by g80csp11 »

ive always taken rockers shafts out on P11 and G15 head removal as you can get push rods higher in the head
I agree its tight but possible to remove in situ
Dropping the engine down on the G15 of course helps a bit
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ajscomboman
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Re: G15 Cylinder Head Removal

Post by ajscomboman »

g80csp11 wrote: ↑Wed Sep 14, 2022 5:12 pm ive always taken rockers shafts out on P11 and G15 head removal as you can get push rods higher in the head
I agree its tight but possible to remove in situ
Dropping the engine down on the G15 of course helps a bit
Got got some special tools just for that job from a very nice person in Sussex. ;) :rofl:
Nomad
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Re: G15 Cylinder Head Removal

Post by Nomad »

It is possible to remove the cylinder head from a G15 or N15 with the engine still in the frame. The head studs were shortened by 3/8 of an inch, to facilitate this removal on the hybrid bikes. The rear of the cylinder barrel was made wider on the hybrid bikes before this became standard on the rest of the Norton models. This was so you could gain access to the rear stud nut. I have been taking that cylinder head off of my bikes since my first G15CSR that I first bought back in 1970. It is difficult but it can be done. Ray Lightfoot who worked at AMC as a tester and on the production line, and he managed it without removing the exhaust rocker spindles. This was much to the annoyance of his foreman at the time, who had tried and failed. He left the cylinder head on the track where the bikes were being assembled for his foreman to find it. I had to take the cylinder head off my 1968 G15CSR after the cylinder head gasket blew out on the A10 coming back from Royston. I did it on my friend's drive, and I changed the head gasket, and put in the correct valve springs in, after the dealer it went to had put in the earlier Dominator ones. I then rode it home, from Hoddesdon.
g80csp11
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Re: G15 Cylinder Head Removal

Post by g80csp11 »

Ive always put engine in to frame without barrels / head fitted then built up the engine in the frame
As Anthony says , its is possible to remove head in the frame
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