I was told with no effort a rs250 piston and ring could be fitted into a nsr.
I was just wondering could anyone clear this up and also would they be pre93 rs piston and rings and would there be any mods required.
regards k

For a start you will need the special HRC F3 small-end bearings - virtually impossible to source these days!

The RS pistons will go, but it's not a straight swap. It's not worth the effort for the small gain unless you are going all out for racing.

Andy.
NSR-WORLD.COM

thanks andy for you reply

I just finished cutting some 300 cylinders and it's now peeing down with rain outside so i can't be bothered to go home.

Decided to have a trawl through some old posts and this one sprung up.

As Andy says the F3 special part is required to fit the F3 piston because of it's 14mm piston pin, but it's obviously not common knowledge that the RS125 NX4 and RS250 NX5 have a 15mm pin so will basically pop straight on.

The piston heights are different to std NSR so machining of cylinders is necessary, but that's quite an easy task.

Both NX4 and NX5 actually use the same piston pin as the NSR. Yes it's a KV3 part.

I have a set of NX4 kit pistons that I've never got around to using, but maybe one day when I've got nothing to do I'll fit them into something.

Not exactly a breakthough but someone might find this info useful.

Oh, and I can still get the necessary bearings to run the lighter 14mm pin with the RS125 pistons and stock crank if anybody want them.

If i use those bearings are the RS 125 pistons a straight replacement?
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These bearings mean that you can use the NF4 pistons which have a 14mm pin.

As I said, the later model NX4 has a 15mm pin so it fully compatible with the NSR conrod.

Both pistons (NF & NX) are different height so pay attention to this.

So Matt,

Using the RS pistons that are taller means that they need to be matched to a cylinder to allow proper deck height.

What is the difference in height? Would a fat base gasket help? What about a VHM head with a custom insert?

What is the deck height to look for on this setup?

Also, what is the real reason to do this? You go from two rings to one ring meaning wear and tear will happen quicker, meaning more top ends sooner. What would the difference in compression be? Is the port timing still going to be the same? I know the sides of the RS piston have indents, while the NSR is all smooth. What do these indents do for port timing?

thanks
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Charles Gallant

Here's a chance for all you budding tuners to learn about the NSR motor and make some comparisons against race components.

Measure the standard NSR deck height, squish clearance, combustion chamber volume and piston crown height, then try the same with the RS piston. This will show you the differences so you will have an idea of what to do.

I could tell you the figures but that takes the fun out of it doesn't it?

An RS piston is lighter, so better response when you turn up the volume.

The single ring offers less friction so saps less power, but doesn't seal as well at low rpm as a twin ring design.

The side cutouts have do effect on port opening or closing.

If anyone's worried about reliability or regular top end rebuilds then stick to the standard parts.

See what happens Matt?! Sometimes it just better to keep yer head down!
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Andy.
NSR-WORLD.COM

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Matt@TYGA wrote:Here's a chance for all you budding tuners to learn about the NSR motor and make some comparisons against race components.

Measure the standard NSR deck height, squish clearance, combustion chamber volume and piston crown height, then try the same with the RS piston. This will show you the differences so you will have an idea of what to do.

I could tell you the figures but that takes the fun out of it doesn't it?

I got enough fun lined up already with my RS! I don't know many people who have deck height gauges (Ye, I got one for the RS). I am still trying to figure out the proper way to measure the crown height... The tuner wrote numbers down on the new piston like +0.00213 on it. I was told by the previous owner I could never reproduce the measurement, so just measure the height on my own, and get the deck height as close to 2.0 as possible (1.98 on the lower, and as close to 2.0 on the upper as possible). I useally get an idea of the taller piston by measuring from the wrist pin hole to the top of the corwn, and use the taller on on the top. I then use the base gasket collection I have to get the proper deck height for each cylinder.

So how is the proper method for measuring the crown height, etc...

Matt@TYGA wrote:
An RS piston is lighter, so better response when you turn up the volume.

Hmm, never thought of it, but yes you are right... the RS piston is WAY lighter.

Matt@TYGA wrote:
The single ring offers less friction so saps less power, but doesn't seal as well at low rpm as a twin ring design.

ye, thats what I meant

Matt@TYGA wrote:
The side cutouts have do effect on port opening or closing.

I am guessing since the NSR port timing is SO close to the RS, using the RS pistons in the NSR with the cutouts will help.

Matt@TYGA wrote:
If anyone's worried about reliability or regular top end rebuilds then stick to the standard parts.

If it were me, and I had a street NSR, I would stick with stock NSR parts. Now for the race NSR's, you got me thinking I am already buying top end kits by the crate load (useally six at a time), so adding a couple more here and there for the NSR wouldn't be a big deal.

Thanks for the Info Matt
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Charles Gallant