Where do I go, where do I go, where do I go now?

[Greybeard]

That barrel looks more than slightly scored, Chris (theres a lot of it) and the piston looks like its nipped up at some time going by the scuffs on it. You cant do it now, but you could have put a drop of oil in through the plug 'ole to see if compression was restored. If it was then itd be a ring/piston problem.
I cant recall now but had you had it running before the thorspark venture?

Steve

[spookefoote1956]

Morning Steve. It was running with the Thorspark then not. With the "new" mag I put some oil down the barrel and the compression did go up to 90+ psi. I am concerned about that JP piston. Really I would like to replace it with a hepolite one. The bike has only done about 500 miles!

[SPRIDDLER]

I can't say how much effect that Spooky's cylinder scoring would have on the cylinder pressure. However on my return trip from one of the Hampshire Jampots many moons ago my G3LS started fine although it seemed a bit out of sorts during the 60 miles ride home but I was quite surprised when I took the barrel off.

P3 Scored cylinder.jpg

[spookefoote1956]

Would this one go in OK?
https://www.ebay.co.uk/itm/265583301662 ... Swm9diJhLQ

[dave16mct]

I'd say no because it has the wrong deck height. If you look at your piston the gudgeon pin will be lower. You'd probably have a compression ratio of about 4:1. Notice it has 4 rings too?
Dave.

[Greybeard]

If you contact John Harding (either through VMCC or his regular ad in OBM) he has comprehensive details of pistons and stocks of same, he should be able to help. Youll need to know the over size you need so I would take the barrel to whoever is going to rebore it for accurate measurements before seeking out pistons. The cost of a rebore by my local engineering company is around 30-35 quid.

Steve

[dave16mct]

Chris, if you go to Farmyard Ales on tuesday night look out for a bloke called Tony Keegan on a '54 blue AJS 16MS. He'd give you good advice or may even sort it for you. We used to watch him racing a G80 in Vintage racing. I'll look out for him. He's one of those guys who make things sound so simple!
Dave.
PS sorry, just seen Greybeard's reply. Good advice but wouldn't do any harm to speak to Tony as well.

[ajscomboman]

I'd not be overly concerned about the JP piston as there are several members who swear by them and have had none of the so called horror stories that always seem to follow every type of piston that isn't a Hepolite or BHB.

[spookefoote1956]

If you contact John Harding (either through VMCC or his regular ad in OBM) he has comprehensive details of pistons and stocks of same, he should be able to help. Youll need to know the over size you need so I would take the barrel to whoever is going to rebore it for accurate measurements before seeking out pistons. The cost of a rebore by my local engineering company is around 30-35 quid.

Steve

I know of John from the VMCC Forum

[spookefoote1956]

Chris, if you go to Farmyard Ales on tuesday night look out for a bloke called Tony Keegan on a '54 blue AJS 16MS. He'd give you good advice or may even sort it for you. We used to watch him racing a G80 in Vintage racing. I'll look out for him. He's one of those guys who make things sound so simple!
Dave.
PS sorry, just seen Greybeard's reply. Good advice but wouldn't do any harm to speak to Tony as well.

Will do Dave