1953 / 4 G3LS build

[SPRIDDLER]

Spriddler,
Thanks for your reply.
The problem with the piston is that it is oval by 22 thou and will not fit inside the barrel. But skimming it with a lathe won't work because the small "diameter" is too small for the bore. 2.7187 - 2.700 would leave almost 0.019" clearance. I am resigned to the piston being scrap.

Ah, I hadn't realised that the piston didn't even fit inside the cylinder.

Now a rebore of 0.020" is (I thought) + 0.020" on the diameter, which would mean 0.010" off the thickness of the liner. I.e. 10 thou off 0.051". N'est ce pas?

Yes Eddie, you're quite right. I added that comment later when I was in the process of getting my lunch and just did the maths without giving any thought to the application.

TBH I don't have the level of engineering experience to be able to assess the desirability of a reboring the current liner although it does seem surprisingly thin, especially considering that the near standard size piston is too large to enter the cylinder (but we don't know if it is even an AMC piston do we?). Knowing the bore of your cylinder would give a clue as to how far it may or may not have been rebored already.

If I was sufficiently well off to winter in Nairobi I wouldn't faff about with unknowns but I'd give a new standard size piston to an engineering firm and have the cylinder relined to suit it.

[EddieDay]

Thanks Spriddler.
Strangely enough the liner bore is pretty close to standard but after cleaning off the rust and pitting it will probably be a bit too large for a standard piston. My two options are:
A) The one you suggested. New standard piston + new liner to suit.
B) New + 0.020" piston and rebore the liner to suit.

The cylinder is currently in the hands of a very nice Sikh gentleman who runs a small engineering shop in Nairobi's industrial area. His dad, who is 73 but still comes into the shop, said immediately "new liner". It is the more expensive but safer option. I will sleep on it.

By the way I now have a club dating certificate. It is a '54 frame with matching number '54 engine, shipped to Dar es Salaam in January 1954.

[EddieDay]

Spriddler,
Ref your quote " if you deduct the standard cylinder bore of 2.7187" from the liner O.D. of 2.8460" it will give you a good clue to an acceptable liner thickness (e.g. 0.1273")."
The dimensions are diameters, so the liner thickness is 0.1273" / 2 = (say) 0.064". A bit thicker than mine in the G3LS.

[SPRIDDLER]

Spriddler,
Ref your quote " if you deduct the standard cylinder bore of 2.7187" from the liner O.D. of 2.8460" it will give you a good clue to an acceptable liner thickness (e.g. 0.1273")."
The dimensions are diameters, so the liner thickness is 0.1273" / 2 = (say) 0.064". A bit thicker than mine in the G3LS.

Indeed so, thanks Eddie. I should take more care as I've only been giving superficial thought to the finer details because in view of the possibly alien piston and apparent lack of liner (pitted) wall thickness I'd just get a standard piston and have a new liner bored to suit, (assuming you have a reliable engineer in Nairobi).

[EddieDay]

"I'd just get a standard piston and have a new liner bored to suit, (assuming you have a reliable engineer in Nairobi)."
Spriddler I have taken your advice and have ordered a standard piston and asked the engineer to insert a new liner to suit. We know that will work.

[EddieDay]

Continuing the restoration since the last post.
Frame parts, brake pedal, mudguard stays, chain cases and other assorted parts sand blasted, primed and sprayed in 2 pack black. I have welded up a crack in one foot peg and had the other straightened.
The cylinder is at a small engineering works for repairs to two broken fins using a sacrificial iron cylinder head.
The cam followers were seized in their guides but a lot of WD40 and some judicious tapping using a block of hardwood (for one) and piece of aluminium for the other has freed them off.
I am concerned about what I think is the oil feed channel that runs from the timing side crank axle bush to the small cutaway on the top of the crank case wher it ends in a brass bush between the cam followers. It is blocked. A small diameter wire will not go much more than an inch either down from the cylinder base face on the case or up from the timing side bush. First of all is this what I think it is? The top Secondly I guess an air line might clear it. Or there any other tips?

[SPRIDDLER]

I am concerned about what I think is the oil feed channel that runs from the timing side crank axle bush to the small cutaway on the top of the crank case where it ends in a brass bush between the cam followers. It is blocked.

It's an oil feed to the cylinder wall. You don't really need to clear it if it's blocked as it was discontinued in '56 and the cutaway for it in the cyl base gasket was discontinued.
See pic and text on page 10 here:

http://archives.jampot.dk/technical/Spe ... hanics.pdf

[Duncan]

There is a ball and spring behind the bush, if you follow Neville's link to remove the bush you can then check the oil passage.

[EddieDay]

Neville and Duncan,
Thanks for your guidance. That is a really useful article. It carries several insights that the workshop manuals don't include. Presumably that oilway was abandoned in later engines because the cylinder wall gets enough splash lubrication from the crank.

[EddieDay]

Next question. The outer and inner races for the big end bearings are showing slight pitting. It is very light and only discernible with a finger nail. The outer race is called the "Liner for big end bearing" in the spares book. The inner race is a sleeve on the crank pin. I have photos but for some reason I can't upload them.
Do you think that with new rollers they are serviceable or should i just bite the bullet and replace them?