G3 Piston required ?

patchy-man · Post by **patchy-man** » Thu Nov 11, 2010 6:44 pm

On starting to my latest Matchless G3 restoration project, I have taken off the head and barrell, to discover the bore is std (74.00mm), but unfortunatley a piece of the piston between the bottom and middle piston ring has broken off at some stage and scored the cylinder bore. On inspection, I have my doubts whether a +0.60" piston would clean up the cylinder bore ?

Are 74.00mm oversize pistons available, or can any alternative pistons be used ?

I also have as part of my box of spares, a new BHB Piston (028127)which also measures 74.00mm, but has a lot lower compression crown than the one that was fitted to the bike.

Looking forward to any help.

paultbird · Post by **paultbird** » Thu Nov 11, 2010 7:18 pm

The piston fitted in my '63 AJS is also a BHB marked 028127, which the bike ran very well with, and I'm planning to re-use.

Parts list and Bacon states part no 028107.

patchy-man · Post by **patchy-man** » Thu Nov 11, 2010 7:40 pm

Many thanks for your reply Paul. I may have to look at fitting a liner and using the BHB Piston ?

pkr87 · Post by **pkr87** » Fri Nov 12, 2010 8:51 am

Hello Patchy.I had a similar problem with my 16mc(with aluminium barrel)I had it sleeved and fitted a piston from club spares and I have been riding it far and fast for the last 3 years with,so far,no problems.You must first ensure that the machinist knows about bike engines even if it means you have to pay a bit more for his work.Cheers,Paul

patchy-man · Post by **patchy-man** » Fri Nov 12, 2010 3:07 pm

Thanks Paul, Is there a recommended company for fitting or supplying cylinder liners ? I would also need to source a new set of piston rings for my new piston, who supplies piston rings for BHB Pistons ?

Groily · Post by **Groily** » Fri Nov 12, 2010 4:10 pm

Recently had a pair of (twin, iron) cylinders re-sleeved at T&L in Beds (01234 352418 and see ads in Jampots) if that's any help. They do quite a few I believe.
For rings, if suitable original rings for singles are as hard as for twins (which I don't know and maybe the usual suspects can help) . . . but FW Thorntons could probably dig up something. They did for me, although the radial thickness was a tad too big (they explained in advance, so no surprises) and I had to deepen the grooves a few thou.

ianselva · Post by **ianselva** » Fri Nov 12, 2010 4:48 pm

I got some rings for my Model 20 from
Cox and Turner ian@coxnturner.freeserve.co.uk. who were very helpful and quick.

Ian