Advice please......
Today I decided to gap the NEW rings in my barrels. Looking at the workshop manual it stated that the sevice limit was .43mm and to replace the rings if over this! I was horrified to find that the gap with the NEW rings was .508mm.
Does this mean that the liners need to be re-nikasilled?

What sort of cost is this to be done and can anybody recommend anyone in the Somerset area?

I thought that this was just going to be a simple oil seal and ring service. If I have to go for a new crank then it is going to cost me a small fortune.

Mike
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Anyone please..

Hold on. New crank? It just sounds like your rings may have been pre-gapped to an idealized barrel. Check to make sure the piston clearance isn't too far out of spec. If your piston to wall clearance is okay, it is likely that something is wrong with the rings you have (i.e pre-gapped).

Thanks for that but why would a new set of rings be 'pre gapped'. Both pairs came in sealed boxed!
Accepted there are 3 different size of piston but surely there is only one size of ring.

The crank is a different story!

Mike

My manual gives ring end gap as .5mm although that doesnt solve your problem, it doesnt seem to specify where abouts in the bore you measure the ring gap which could make a difference.

I would guess the next step is to measure your bores, with 3 sizes of cylinder and one size of ring if you have the largest barrel it gives you a smaller margin for cylinder wear before you go out of limits on your ring gap.

You are only measuring .008 out of limits which could be down to the tools you are measuring with or the way you are measuring. Personally speaking I would bang it together and do a compression check, if thats good I would run it as it is and monitor the compresion readings. You can do a lot of ring changes for the price of a pair of cylinders but its really up to you and what your expectations/budget stretches to.

Hobbit210 wrote:Looking at the workshop manual it stated that the sevice limit was .43mm and to replace the rings if over this! I was horrified to find that the gap with the NEW rings was .508mm.

Where in the bore did you measured the gap and how did you get such an accurate measurement?
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2t-racelab.com

2Tracelab wrote:

Hobbit210 wrote:Looking at the workshop manual it stated that the sevice limit was .43mm and to replace the rings if over this! I was horrified to find that the gap with the NEW rings was .508mm.

Where in the bore did you measured the gap and how did you get such an accurate measurement?

I put the ring into the top of the bore and then pushed it down about an inch with the bre piston to make sure it was level in the bore. I suppose about 15mm above the exhaust port.
I used a Snap-On (accurate to within 3 feet!!!) feeler guage which has imperial and metric. The ring gap with the 'flat blade' of the feeler gauge flat against the bore was 20thou (0.508mm).
I moved the ring up until it was still in the 'working area' near the top of the bore and the gap was virtually the same.

Mike


Mod edit:20 thou is 0.508mm not .0508mm as you had typed
FY
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I don't mind dying...I just don't want to be there when it happens!

Paul's right, the service limit is 0.5mm.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread

Mike, what was the ring gap on the old rings ? Seem to go too well for it to have been too far out of tolerance.
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I don't know the NSR specs but my vintage Vespa's have 2.0mm service limit on the ring gap, I found them at 3 mm once and the bike still ran fine: 45mph on a 50 y.o. bike. Put it back together and it still runs like a champ!

I say tun it, 0.495, 0.500 or 0.508 is virtually the same gap, I doubt snap-on gauge can provide such an accuracy. if you had a 0.490 feeler it would "feel" the same as 0.508 going through the gap,

Mike - what mark are your barrels or are there any numbers stamped onto them from a previous nickasil ? I am guessing that there are 3 different ring sizes ?

Neal wrote: I am guessing that there are 3 different ring sizes ?

And you are guessing wrong.
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The barrels are B but there is only one ring size.

Okay, a hypothetical question.

If I have a .508mm ring gap, if I have the bores re=plated what sort of gap should I then expect ... i.e. Very roughhly what thickness is the plating.

Question 2. Can anyone recommend a good company to do the work in my part of the world.

Thanks
Mike

Thanks for clearing that up Fonty .

The best ring gap to work to is 0.24 mm

Hobbit210 wrote:The barrels are B but there is only one ring size.

Okay, a hypothetical question.

If I have a .508mm ring gap, if I have the bores re=plated what sort of gap should I then expect ... i.e. Very roughhly what thickness is the plating.

Question 2. Can anyone recommend a good company to do the work in my part of the world.

Thanks
Mike

The manual lists all cylinders having a service limit of 54.02mm, a "B" cylinder is 54.004 - 54.008 mm as standard so thats the size you would get it plated to. Have you measured the cylinder?

Les reckons it ran strongly before so cant be to much wrong with it.