Hi guys just asking for a bit of advice here.I have a 91 nsr 250 r7l which I use as a race bike in f3 in NZ.I have just replaced both cylinders on this bike almost,I checked the parts numbers on this site and my cylinders that i ordered are for a mc 28 250 r2r and the piston rings for the rr.its not a problem exchanging and re ordering but are these items inter cangable on these bikes i've already checked the tyga site but not enough info hope you can help as i want to get racing.This bike is an r model not an SP Thanks Bruno.

Pretty sure cylinders are the same between 21 and 28 , I also race a mc21 in f3 in nz , where do u race , what ya done to it and how does it go

Hi paul i'am in auck was all geared up to race the club and some F3 races this year had done some serious practice at Pukekohe some reasonable lap times consistant 1.14 's and 1.13's so i would have been on the pace but started to have probs on start up top cylinder not firing at first start up.Turns out when I stripped it down there was enormous wear in top cylinder lining with some nipping on the exhast bridge so i guess a lack of comp on start up in that cylinder.Have not dynoed it yet but will post when I re-build and set up.As for the bike all road gear gone running pre-mix 30:1 sp front forks sp rear shock magtek wheels Super Cosa tyres De-restricted as per tyga guide lines,hrc jet kit air box mods.Belive it or not but even with the shagged cylinder the bike was running well.The 400's would only pull away on the back straight but only just,guess i need to lose weight.The only gripe i have with the bike is the suspension is to soft.But the reason i posted is I want the bike to at least run as well as before i dont want cylinders that have specs for a different stroke or piston size this would just knock me back even more and don't even mention the cost as this has knocked me for six.Hav'nt seen any other MC 21's up here but there is a guy ho hoon on a rgv and another on an aprilia rs.where do u race?,what your bike do could be interesting.See ya .Bruno

Bruno,

All MC21 and MC28 cylinders/heads are interchangeable, but there are differences between the R and the SE/SP models:

The R model heads are low compression.
The SE/SP heads are high compression.
The SE/SP barrels are taller than the R barrels.

The piston rings are the same across the board for all models now. Just make sure they are gapped correctly.

If you use SE/SP barrels and heads on the R bottom end, you will be fine, you will simply have stock compression.

If you use SE/SP heads on R barrels, you will increase the compression, consequently R heads on SE/SP barrels will give a low reading.

The ideal way to go therefore, is R barrels with SE/SP heads, if your class doesn't allow modification of components. Even if it does, this is the best starting combination before you begin the port work.

Andy.
NSR-WORLD.COM

Thanks,our class lets us do pretty much anything bar remove the airbox.The main things i was worried about was losing comp or changing the timing via higher or lower porting.So i will keep the cylinders which are stamped A.But they gave me unmarked pistons so wrong pistons if the chart on tyga is right.I'am off now to change the pistons.Once i'am done i will post my dynos and update you guys on the racing[though its now heading into winter over here it wont get cold but it will rain alot].Thanks Bruno.

hi bruno , I live in nelson and race at the south is street races and at ruapuna but hopin for a few missions to manfield soon , my mc21 has rs 250 pipes , hrc cylinder head conversions , modded airbox , racetech modded suspension , wire splice , braided lines , and a dogfight racing crank.
Its primary function is a road bike but it has mutiple sets of body work for racin , at ruapuna I was runnin 1.45 - 1.46 min laps which is pretty good , but it depends who else is there yo how fast you look , only the real fast 400 , s or sv 650s are faster on the straights but it does seem to lose out on drive out of corners .
what were they going to sting you for a barrell?I,ve bought most of my second hand parts from bikes and bits and they have been very expensive but have found it much cheeper to buy out of nz for large new purchases

oh and last time I bought pistons the only ones I could get were the b pistons ( unmarked ) and honda nz said to put them in my a barrells and it would be fine , I did and they were but wouldn'd trust waht honda nz says cause when I had first tried to order the pistons they told me honda don't make 2 stroke road bikes!!!

Hi Paul,the cost oh the cost ALMOST 3000 bucks.I know i'am nuts now.But in my defence I can only offer this I wanted to do it right and then take it from there.Plus i now have a spare set of shagged cylinders awaiting re- plating and porting should i ever be able to have cash again in this life.I also have a set of older ethos pipes for the bike now.As for the B pistons yep Honda NZ tried it on me as well but my parts are now on ex-Japan order.You should dyno your bike and post it you never know someone out there might have some tips for more ponies theres a guy on the Aprilia site with a claimed 70hp on an aprilia rs 250 and he says they have no probs with the sv's he did some serious squish band work though.

$3000 , sounds steep but I also have a list of reciets as long as my arm , nsr owes me about $14000 now , I got cheeper prices in the end from my local yamaha shop than from the honda dealer when I wanted to go local

prices were
barrell $ 1100 new with power valve and gasket
$500 second hand for bare barrell from bikes and bits(the only part I ever bought where the credit card bill was what I was quoted mind)
circlip $2.95
base gasket $21.95
piston pin $28.60
piston $211.00
ring set $107.00
head gasket $34.60

I had lots of dramas getting the right part first time out of honda too , normally took them 3 goes with the part coming from japan each time so getting your own part numbers helps , but hopefully for you the learnt from me

and where did ya manage to source a jet kit , all I can get for mine is mains and it runs like a dog on constant throtle at 5500 rpk

Hi Paul,well red baron have just contavted me with a re-fund of 700 bucks never had that before.There were a few xtras in that seals rubber mounts for the exhasts etc the parts are about the same prices as yours give or take a few dollars.My carb kit is the JHA one from japan it contains everything,loads of main jets emulsifier tubes[they have twice the number of holes in them]blanked pilot jets,3 different profile needles and replacement x and y parts.Cant tell if they made a difference as have not run the bike still waiting for cylinder studs and i need some heads as i now have the sp cylinders.I would really like to do the top cylinder conversion but cant get the hose for it at this time have contacted Tyga they replied saying they would check on that also contacted Jamie's web site where he has the part listed for sale but no reply to date.Red Baron got my jet kit but you can get the hrc kit from Tyga performance.They use pay pal so its very easy and safe to pay.I have bought a few bits off them ie highflow reed cages and stoppers and they arrived exactly 2 weeks later,i will order my heads from them as well once i know whats happening with the pipe.My objectiv is to show that the NSR is still competetive in our club and F3 races.Jujing by the practice and track time sessions with the bike in shagged form i would say it will just need to get out there again.You still need to dyno to see where to start from as it saves a lot of time my Yzf is living proof of this as the flatsides were real gits to set up,would have taken all year without a dyno.Let me know wat colour your spark plugs are do a plug chop from top speed cut yor motor stop the bike remove plugs let me know the colour and we can take it from there.See Ya

I also had dramas getting a pipe to fit for the head conversion and as the tnsr bills were starting to mount up I maed one from a piece of thin walled alloy pipe with a short section of rubber hose at each end where it joins to the head, my plugs are a coffee with lots of milk colour on a top speed run with 150mains