I am busy preparing my barrels before plating and threw a dummy assembly I
found on both cylinders that on the one side the piston is level with the intake
port and on the other side the piston is about 0.5mm over the port.

Any advice on fixing this problem? This is never been worked on barrels
and tops. I'm asking this because there is so much that has to be looked
at when skimming a barrel.

You'll need to rephrase this question, as at the moment it doesn't make any sense!

Why would you want to skim the barrel (or a head) on an NSR, unless of course you want to turn SP heads into R heads? The NSR needs absolutely no more compression that it has as stock.
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have you measured the barrels to see if they are different? Could it be the pistons? WHat about going with a thinner base gasket?

If you mean the ports aren't level it's just production tollereance issues. Leave it.
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I was just wondering about this as both barrels measure the same and was wondering if there isn't something one can do to fix it. The squish on these barrels are around 1.3 -1.4mm so I would just do something about that, take it down to 1.1 because I am running on AVGAS witch is over a 100 octane. Sorry for the simple question, I am also still on the learning curve and would just like to have a perfect NSR250 MC21SE.

To Andy: The problem was that the 2 intake ports on the one side does line up with the piston edge when at the lowest. At that same stage the 2 intake ports on the opposite side are lower than the piston edge.

But thank you, I would just then leave it just like that and work on the squish.

Howzit Harold ,Don't think that you can just skim your heads , you need to measure your volume too and set it for the octane that you will use . Squish depends on the type of track that you will ride at .I may come to the october race , can you get me some of that jungle juice you are using ?

Harold wrote:I was just wondering about this as both barrels measure the same and was wondering if there isn't something one can do to fix it. The squish on these barrels are around 1.3 -1.4mm so I would just do something about that, take it down to 1.1 because I am running on AVGAS witch is over a 100 octane. Sorry for the simple question, I am also still on the learning curve and would just like to have a perfect NSR250 MC21SE.

If the squish is 1.3-1.4mm are you sure you're not mixing SP spec cylinders (marked L1,L2 or L3) and R spec heads (marked KV3H)?

Stock NSR parts (either matched R cylinders and heads or SP) tend to measure up around 1.2mm squish.
The usual trick of R cylinders and SP heads measure 1mm squish which is OK on 97ron fuel if you're careful with your jetting.

Much tighter than that seems to cost power (in my experience) even if you do have the fuel for it.
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These tops are marked KV3H and the other one is marked KV3L.
The standard Tops that I bought my bike with is both marked
KV3L. Does this make a big difference Fontyyy? The barrels with that was
B barrels and the new ones are A barrels.

I checked my new barrels and tops and that seems to be the case.
My barrels are L2 and L1. My tops are KV3H and the other KV3L.
Could you maybe help me to sort this out, witch would work best where?

Regards, Harold

I would talk to the person I know that could organise me AVGAS.
This unfortunately does come at a price. I think almost R280-R300 for
20litres. How much would you need? And please let me know when you guys
come down to Cape Town. Would be nice to share a word or 2.

Regards, Harold

I would strongly advise for the time being to use R cylinders with R heads, or SP cylinders with SP heads. Don't mix anything up! (I.e. don't even run one side R-spec and the other side SP-spec.)

Either spec, well set up and maintained will give 61~63hp on a stock NSR.

Once you have a good base to work from, then you can be confident to modify.

As Fontyyy already mentioned, differences in port heights are generally just down to manufacturing tolerances. It doesn't hurt in the least to clean up the nikasil on each port window so they all match!

Finally, R and SP barrels are different heights, and R and SP heads have different combustion chamber volumes. Make sure you have the correct combination of parts. It doesn't matter what bottom-end it's all fitted to, what PGM-III you run, or what set of carbs you are using... that stuff is all interchangeable with no measurable differences in power.
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Can you maybe help me on the code of the tops. I know now that the
KV3H is R-model tops but what is the KV3L ones? is this SP tops?

Thanks for the advice, this sure does explain a lot of things to me.

My barrels seem to be both SP ones as the one is a L1 and the other L2.
I just need some help on that KV3L top now. Thanks a lot ones again Andy.

Harold

Yes, L is SP (and SE as they share the same cylinders and barrels). Like Andy said if your starting point is a set of L barrels, make sure you use L heads.

Also note there are different codes on the cylinders noting what size they are, so you'll have to take that code and look at the chart to find out what piston you want to run. What I mean by that is the code for the cylinder is not the same as the code for the piston (that would be too easy).

Thanx for that. I will look for another standard L top then and work from there.
The problem with the A,B,C cylinders is that there isn't pistons available any more for them, what I mean is that there is only one size piston available threw Honda at this stage so you have to make that piston fit.