Hey guys,

Wondering what alternative pistons you have tried for your rs's ? I would tend to lean towards the NX5's as this is what I have but any info should be good...

I have some Wiseco pistons which are meant for an early cr125, for them to work I have to cut the barrel down by 1mm which I don't really want to do to a stock standard bike.

Are NXA barrels shorter than the NX5's ?

Any ideas ?

Cheers
Mario

I'm new to owning an NX5 RS so I do not have any info on using different pistions, although I have heard and read plenty of stories regarding problems with Woosner and Vertex pistons. I'm lucky enough to have a couple of sets of HRC domed pistons for my RS and for all the miles I'll be doing they will probably (hopefully!) last me a good while. In fact for what I'll be using my RS for (trackdays mainly) I would think that any of the pistons mentioned above would be okay as long as the clearances are okay and the bike is set up on the 'safe side'?
As for NXA barrels, the basic dimensions of the NXA barrel is the same as the NX5 barrel. I do not know about port heights though.
You do have to machine the bottom of NXA barrels to suit NX5 crankcases.
I would think that machining down barrels to suit pistons is a bit extreme thought. No?

Hi I,

Yeah I also do not want to cut my barrels but if piston prices keep going up then I won't have any choice !

One of my mates found a German company who sell pistons for the RS's, I've sent them a mail to find out more. They are about one third cheaper than HRC.

I'll will also only be using the RS for track days...

Cheers
Mario

As you are only using it for trackdays it wont be getting no where near the treatment it would if it was being raced, so i would stick with the hrc pistons, its not like you will be changing them halfway through a race weekend. All depends how many trackdays a year you do, if not many then a pair should last you. Different when the hrc ones dry up, (like they have for my nf5), but if you intend keeping it for a while it might be advisable to stock up. Another thing i will say though, an RS250 or 125 come to that, is not a bike to be run on a budget. Enjoy it though Cheers Les.
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Lesviffer750 wrote:
...Another thing i will say though, an RS250 or 125 come to that, is not a bike to be run on a budget.

Absolutely. It's a GP bike... treat it like one. If not, then stick with a proddy 250. Simple.

Hacking barrels to fit sub-standard pistons? You'll be hacking the cases about and screwing grub screws into the oil feed holes next to use the wrong main bearings after a Heath Robinson crank rebuild!
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Hacking barrels to fit sub-standard pistons? You'll be hacking the cases about and screwing grub screws into the oil feed holes next to use the wrong main bearings after a Heath Robinson crank rebuild!

LOL, not likely, my name is not Andy...

All I can say is each to his own, if we can use alternative pistons, which may or may not actually be better than the ART OEM stuff then why not ?

Yes it is a GP bike but I am not a GP team nor have I got the funds of one. To pay close to $500USD for a set of pistons is a bit steep, next year it'll be $1000? If I have to then I will buy the OEM pistons but for now I am doing my homework if there's not maybe an alternative option.

Don't get me wrong, I am not for cutting barrels but if that is what it's going to cost to keep on riding the bike on a regular basis then so be it. What's the point on having something which you can just look at ?

I'll have you know the latest cranks we're building are built with genuine Honda main and big-end bearings. I resent that remark. I will go as far as to say they are better than new, as they're only rebuilt if they are well within OEM spec, and are trued to HRC specifications.

You won't catch us using anything non-Honda in our motors, and have cranks in NF5's that have done the Manx GP for the last couple of years now without incident.

When someone can come along with an NSR250 (or 300) that can outperform the F3, that incidentally has never had an engine failure, and prove us wrong in what we advise, then you can maybe remark on the quality of our work.

Edited for typos/grammar.
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Last edited by Andy on Tue Aug 28, 2012 8:55 pm; edited 1 time in total

What are these crank rebuilds Andy? Can the RS ones be done?

I am doing a fair few trackdays on my NXA, i've done 7 in 2 years and i am planning an Oulton before the year is out (if anyone is interested )

It is costing me a fortune so i am interested in alternative piston supplies IF and only IF they are of sufficient quality and i am not hacking bits off my crank cases or cylinders either

What is the story with the Vertex ones?

I did a spread sheet the other night as i have a new spare crank and the current one is due replacement soon.

My thoughts were that you know the life of the crank will be 1200 miles, the pistons/rings etc etc 300 miles. This being the case you may as well by enough spares for the life of the crank right now before the prices increase further or the stock finally runs out.

It worked out at £1600 per crank ... that would probably do 12 track days so £133/trackday which isn't too bad i guess for the fun they are to ride.

I take it the cylinders can be replated, does this buy you another 1200 miles per cylinder or do they have a shorter life than OEM once refurbished? (I have just read 2smoke's thread in the NSR250 section so i now know the answer to this question ... ) add the cost of two new cyliners to the bill per crank then and call it £3200 per crank

So many questions, so much to learn and unforunately i dont pick things up or learn as quickly as i used to...

Alzazorg, sorry for the thread hi-jack.
Simono, you'll have to get your cylinders replated as Honda do not make cylinders anymore for either the NXA or NX5 RS's.
Maybe Padgetts have some new ones as old stock?
As a side note, the markings on one of the cylinders on my RS suggest it has been replated four times!
Now, I may get shot down for this, but here goes...
With regards to cylinder plating I have just had my RS cylinders replated by Aptec. I have not used them yet (ahem...*cough*) so cannot comment but they are 'round' and the piston / bore clearance is correct.
I have also had MC21 cylinders replated (twice) by Langcourt and never had any trouble.
According to IanE cylinders should last a very long time unless there is major damaged or have been replated 'X' amount of times. Same for crankshafts, they will last many miles longer than stated by HRC. But and this is a BIG but how long do you run them before you replace them??? It would be nice to replace them every 1200 miles but how many RS riders in the NG /ACU National 250GP Championship replace the cranks at 1200 miles??? It would be interesting to find out!
The crank on my RS has unknown mileage, according to the former owner (who never kept any notes about the bike but that is another story...) there is 'around' 500 miles on it. Yeah, I bet thats right! The crank does 'feel' good and all bearing run smooth as silk so I will use it for the mean time. The crank has also been apart at some point and has plastic stuffers fitted to it, so it could even be an old crank rebuilt!
I'm only using my RS for track days (at the moment...) and the way I ride I doubt any of the above will be of relevance until I'm a very old man!
As for pistons, I'll be using HRC pistons and rings as long as I can buy them.
P.S. Samba exhausts... luverly!


Last edited by sennidott on Fri Aug 31, 2012 8:25 am; edited 1 time in total

No problem Innist, I sit with the same situation. The previous owners never kept any form of history or log about the bike and parts being fitted and what not. This bike came into the country about 4-5 years ago.

Until now no one has ever ridden it properly, it's been to the track twice in the past 4-5 years and the rest of the time she was just standing in some bloke's garage getting full of dust. The first owner also mentioned that he never could get the bike to handle properly, when I looked at the bike now and measured the geometry I noticed that it was way way off from standard spec. E.g The rear ride height should be around 488mm, theirs was 540mm Same goes for the front...

I have no idea of how many miles the crank has done, but as the same in your case everything feels and looks fine. The pistons however have serious blow by and the rings are way way out of spec...0.63mm gap. I think if I would have just gone to the track with the bike as is then it would have most probably threw a ring or something.

Luckily I do have a new spare set of barrels and a very low mileage crank from an NXA.

I have also read about folks in the US who Teflon coat the pistons and TiNi the rings which then lasts almost triple the mileage compared to OEM with no incidents. They also don't run them in as per the norm/manual, I think they do something stupid like two warmup laps and then from there is full on.

Samba Pipes : Do you have any dyno graphs or something which you can show us how they compare to stock pipes ?

Andy

You mentioned that you have run rebuilt NF5 cranks, are these using the road NSR bearings or are you sourcing the full original HRC bearings?
Also with regards to the conrods are you measuring them up and refitting if within spec, we have heard they are of very good quality and last longer than what Honda recommend.
Given that the NF5 conrods are the same as what Honda put into the NSR F3s they should last a reasonable time.

Very interested to hear about the bearings for the NF5 cranks

Cheers
Philip

This is getting an interesting thread now.

As you all know, i am new to my NXA and i know very little about them.

Learning slowly.

There seems to be mistry, conflicting infomation and no solid facts or evidence surrounding these bikes which i dont quite understand.

Whilst we should all be a club of enthusiasts helping each other and sharing experiences, it all seems very closed doors so i appreciate the comments above .. all very relevant to our ownership and ongoing upkeep of these bikes.

The Sambas are producing 70bhp on unleaded, we didnt have time to test the standards back to back but will do so soon.

They seem to have made a good difference but jetting is in the frame too and when compared to running on Elf 2T 96.7 with a totally standard bike .... but very rich, i would say the bike now is not quite the same in terms of the spread of power available.

I love this bike and am running 4-5 track days a year, its addictive, so any info on non text book longevity blurb is very highly appreciated, its an expensive game yet pure and beautiful.

simono wrote: the pistons/rings etc etc 300 miles.

The guy who won our Open400 (now called Mini Thunderbike) class last year ran the same pistons/rings in his NX5 all year, 7 meets, 32 races, about 340 laps total running including practice, warm up and cool down laps - well, well over 800 miles + the odd TD.
I won't tell you what he said about the crank
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That is a lot of modification for a pretty weak justification. Just cause your doing track days, doesn't mean the engine doesn't need to perform as designed. If you want long interval between top ends and cheaper costs, get a street based 2-stroke of a 4-stroke.

I looked into a couple after market piston options for the RS and didnt really come up with anything that was determined to be reliable.

As fonty mentioned, you can go longer then Honda "recommends". I know of people that went 4-5 full seasons on a crank, as well as multiple weekends on pistons with no problems. Proper jetting, good oil, and non-leaky engine will give you a pretty decent run on a top end.

But using cheap oil with a low mix ratio, putting your bike away after a weekend without going through it and checking tolerances and you get what you deserve (says the guy with a seized Aprilia RS250 after letting his wife play with it for a weekend).

sennidott wrote:I have just had my RS cylinders replated by Aptec. I have not used them yet (ahem...*cough*) so cannot comment but they are 'round' and the piston / bore clearance is correct.

I've seized twice on a barrel plated by Aptec, both seizures were due to the ring pin hopping out and the end snagging in a port (so, not a plating issue), both times the plating survived intact as much as you could reasonably expect and the barrel was cleaned up and ran again that weekend.
No peeling of plating whatsoever, very happy with Aptec's plating.
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