G3LS Cylinder standard bore limit wear

[KEES_MATCHLESS]

Hi there

I am struggling to find info about the minimum diameter after which a cylinder is worn too much. The only thing I can find is the tolerances for piston rings, but they not necessary say something about the cylinder.

The thing is I bought a new piston standard (69), with rings.The motor has started a few times since then, so they are practically new. For some reason I doubt whether the cylinder is ok, I did a leak test and it seems that it leaks via the piston rings. When I poured some oil in the cylinder the leak test was ok. Both valves are leak free etcetera.

Are there any figures about the cylinder bore limit wear of a G3LS 350 '53, for instance the limit wear is 68,80, when less it should be re-bored or replaced?

In my case I have the standard bore.

Regards Kees.

[Mick D]

Hi

It is not good practice to replace rings and piston without carrying out a re-bore at the same time, especially if the engine has been well used. The bore, rings and, to a lesser, degree piston all wear to an approximate elliptical shape, fit new rings into an old cylinder and the rings will be circular and the bore elliptical, hence the poor seal.

If it runs OK you could leave as is confident that things will improve over time or get a re-bore and oversized piston and see an instant improvement.

What was wrong with the old piston and rings? They could well be a better option than the new ones.

Regards Mick

[KEES_MATCHLESS]

Hi Mick,

Thanks & Understood, maybe foolish cost saving. The piston I replaced because the diameter was 68,50 assuming this was out of limit. The cylinder looked rather well, so I decided to leave that, besides that I thought I have measured the bore, but without wear limits.

Anyhow are there figures about cylinder bore limit wear? If not how do you measure whether or not the cylinder should be re-bored?

Regards Kees

[Greybeard]

Rather than take measurements which would need to be taken with specialised instruments, have you checked for a ridge around the top of the bore? Thats 'as far up as the rings get so there's no wear above that point. If you can feel a ridge there with your fingernail it will give an indication of the degree of wear. If it's slight then you may get away with new rings but ideally that ridge needs to be honed out as it may break the new rings that will have a sharp top edge. New top rings with a stepped upper edge used to be avaiable to clear it but Ive not seen any for years.
It is good practice to at least glaze-bust a bore if fitting new rings in order to help them bed in.
Judging at what point to rebore is largely a matter of experience. Does it burn oil, is there an excessive amount of piston slap when its warmed up? You also need to consider whether it's worth doing the work given the anticipated mileage. These old engines will plug away quite happily for many thousands of miles even when quite worn. A rebore may not give you a noticeable improvement in performance unless the engine was very worn by which time thered be other symptoms showing.

Id suggest taking the barrel along to someone with experience of the engines. Your local section would be a good starting point.

Steve

[clive]

Hi

It is not good practice to replace rings and piston without carrying out a re-bore at the same time, especially if the engine has been well used.....
If it runs OK you could leave as is confident that things will improve over time or get a re-bore and oversized piston and see an instant improvement....

Regards Mick

I am sure Mick is right from the engineering point of view. From a practical point of view I have mixed and matched on a number of occasions, including a couple when I have filed down the gaps in oversize rings so they will fit a smaller size. Rarely seemed to make much difference to performance. I would go with the second comment and leave it. If the rings are leaking too much you will see an oily smoke drifting up from behind the primary chaincase as the crankcase vent works overtime!

PS having seen greybeard's entry I agree that you need to hone away any ridge (although I have got away with installing two base gaskets when trying to get a ride to work bike sorted over the weekend and no hone was available).

[SPRIDDLER]

Are there any figures about the cylinder bore limit wear of a G3LS 350 '53, for instance the limit wear is 68,80, when less it should be re-bored or replaced?

Hi Kees, you will find recommended wear tolerances relating to cylinder, pistons, rings and every bush, bearing and shaft for your '53 bike in the 'Army G3L Technical Handbook - Inspection Standards' here:

http://archives.jampot.dk/book/Workshop ... ndards.pdf

[SPRIDDLER]

I'd suggest taking the barrel along to someone with experience of the engines. Your local section would be a good starting point.

I could be wrong but I don't think there are many AMC sections in the Netherlands.

(Yes Steve, you're right: I am a cocky little sod.).

[KEES_MATCHLESS]

Hi Spriddler, clive, Mike and Greybeard,

Thanks all of you, some answers below:

There was/is no significant ridge around the top, no scratches or other wear on the cylinder.
I agree with Clive, it is not always necessary to bore the cylinder, but care should be taken as stated in the answers!!!. Anyhow that is why I am asking about the wear limits to be sure.
I am not worried about the performance as such, it should run smoothly, somehow it just does not.
I am in the possession of inside micrometers, so measuring the wear will not be an issue, although these kind of measurements are not that easy.
There were some tiny oil spots coming out of the exhaust, this might be explained by the wear of the cylinder.

There is by my knowledge only one matchles / ajs club in the Netherlands, but they do not have a Forum. I am a member of that as well and I am also happy with that.
The Army G3L Technical Handbook - Inspection Standards was already in my possession, but I found it difficult to read until now then, after reading again. This was also were I was looking for. Sometime you don t know what you have yourself.

If the wear is too much I will go over an oversize cylinder, piston and rings.

Thanks for the help so far.

Regards Kees

[jackstringer]

Rather than take measurements which would need to be taken with specialised instruments

One person's specialist tool is another person's common tool. A Very Near will do fine for measuring a bore, just need to check top and bottom, unless we start talking temperature controlled areas then it isn't worth the faff. I must admit I thought the sets of these were cheaper but a Mitutoyo 155-131 (or a set of them) would be ok for basic bore measurements, though a bore micrometer or dial bore comparator might be better but costly and not much use without standards to compare to. I did wonder if you could turn a 3d printer system into a cheap CMM if you just attach a touch probe to it.

Hi Kees, you will find recommended wear tolerances relating to cylinder, pistons, rings and every bush, bearing and shaft for your '53 bike in the 'Army G3L Technical Handbook - Inspection Standards' here:

That is rather interesting, I can see my basic table of AJS & Matchless Pistons getting some more Data on wear allowances.

https://1drv.ms/x/s!AoQU31lH3_fGhYJ6_Qu ... A?e=7bl8Wi <-Work in progress.

You can get a basic idea of bore sizes from my spreadsheet linked above.


Jack

[bitza]

Is a rough guide trying a new piston ring in the bore in three positions top to bottom , and comparing the reccomended gaps.