Not wanting to spray my original 6500km Rothmans all over the track, I decided to find another MC21 and build a track bike. The search started and ended with a friend and the other night he dropped it off. Here's what I started with Thursday evening:



The front end is from an RVF400 and no, I have no idea what's up with the green wheels. Bodywork appears to be Hong Kong sourced.

I took that pic today but when I got it the engine had both top ends off for inspection. Saturday my dad and I removed the engine and cleaned the cylinders & powervalves. We flushed out the crankcase and rebuilt the top ends. Then the engine went back in the frame.

Today I put on the exhaust, coolant hoses, radiator, oil pump, and some bodywork to check fitment (the tail is coming back off to do something about the ugly license plate bracket and reflector sticking down below it). So here's where I'm at now:



Still need to replace the carbs, connect them up, and then it's time to recheck everything before adding fluids and trying the startup.
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Craig
MC21 SP Rothmans
MC21 R fake Rothmans - track bike
MC21 SE R9N

If your going to do regular track days Craig, a dedicated track day bike is a much better option than your shiny streetbike!

A voice of experience, are you confident you know enough about the bottom end of the engine? (Crankshaft & seals). How many km has the bike done? Has it ever had a bottom end rebuild? Tired seals, or at worst main or big end bearings reaching their fatigue life, will soon present problems with regular track riding on WOT.

The worst position to be in is not knowing what platform you are operating on. See my experiences........

http://www.nsr250.net/forums/viewtopic.php?t=7023&highlight=difficult

http://www.nsr250.net/forums/viewtopic.php?t=6956&postdays=0&postorder=asc&start=30
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

I do see your point, but here's the info I've had in the past about my bikes;

Castrol '28, nothing known, presumably original Honda, 1993, probably around 4000 road miles, raced for 2 seasons and around 20 trackdays.

Rothman's '28, nothing known, presumably original Honda, engine came off Ebay taken from a '21, so 1992 at the latest, a few thousand road miles, three or four track days.

Race '18, allegedly a new crank 2 years ago, but then again allegedly a decent race motor setup for avgas, reality was 2mm squish and still restricted. 3/4 of a seasons racing and 4 trackdays.

Road/race '21, motor allegedly built by Apex, that's 3rd hand info though and it certainly wasn't set up by them. Thousand+ road miles, couple of trackdays and a days racing.

So presumably that's 4 bottom ends you'd have ripped apart? As it is I've just run them and they've been fine.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread

Ripped apart. Not exactly, but if I'd gone to the length of taking the engine completely out (as Craig did), yes I probably would have split the cases, at least to check the seals and seen how much play were in the bearings.

Your bikes seem to have had less than 5000 miles on each bottom end John, so if that was me, I'd have probably left them as is, unless there was some issue like starting due to lack of crankcase compression.

That's why I asked Craig what mileage / km was on the clock. If its say 'high mileage' of 15,000 miles + with unknown history, I would definitely have a look at the bottom end before embarking on track days.

Once the engine is out, its not exactly a difficult job, even first time around.

But all of this is much less of an issue if you have 2 bikes to take to a track
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

Craig, have you considered the TYGA option?
The TYGA subframe will get rid of all the plastic fender, and the race bodywork looks great, to match your TYGA GP pipes

Going to a track only bike, you may want to consider putting your oil injector system onto your road bike, which is running on premix isn't it? Then set the track bike up towards HRC SS/SP spec, premix, HRC reeds / stuffers, open carbs, block the power jets and look for a HRC Carb / Jet kit on Yahoo Auctions Japan or through Moriwaki Man.
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

Rich you are absolutely correct. The bottom end condition is unknown (previous owner did not know history and never attempted to start it) and I did have the engine completely out of the bike. But there were 2 things working against me - time and money.

My next track day is 9/12. Between then and now there's one weekend and that's a holiday. So I had one weekend and less than two weeks of evenings (we'll be away for the holiday) to put the whole thing back together and I still need to remove the forks and install new seals. I didn't want to be scrambling to make the deadline and who knows what else will pop up in the meantime. Also, I had some but not all of the gaskets and seals needed to do a bottom end rebuild. Yes, I do have a 6000 km crank in perfect shape but see below. So I checked what I could, made sure it was all clean, and will have to hope for the best till I can do a proper rebuild. One good thing is that it appears somebody has been in there at least once so hopefully it wasn't too long ago and with any luck they knew what they were doing.

Second issue - instead of buying a total piece of junk and having money left over, I basically spent all I could and then some to get a nicer start at this project. I wanted a 21, and this one was very close to home and complete. Considering that I know of 3 bikes in my entire state and I now own 2 of them I think that's pretty much the best option I could have.

Without extra money to buy the rest of the stuff I needed and combined with the time factor, I decided I had nothing to lose by putting the engine back together with good top ends and hoping it's ok. If it "seems" ok, I'll flog it on the street as much as I can for a test and then take it to the track. After 9/12 there's only 1 more day in early October and then we're done for the winter. That's when I can do a complete engine refresh and put some extra parts on the shelf and come out of the gate next year being prepared like we know I should be now.

Hey, it's all for fun anyway so if it scatters like last time all I can do is smile and rebuild it again, right? As long as I know the SP is safe in the garage instead of on the track I'll be happy.

Craig

RichG wrote:
Your bikes seem to have had less than 5000 miles on each bottom end John, so if that was me, I'd have probably left them as is, unless there was some issue like starting due to lack of crankcase compression.

Those miles are what I did on them;
the 'Castrol '28 had 24000k's on the clock before the 030 card was added (and that was by the owner before last).
The Rothmans engine was apparently "Barrys old motor" according to Leigh.
The '18 is a total unknown, it's a '21 motor for starters.
The '21, well apart from coming without a speedo cable........

You are right in theory of course and all other things being equal a new crank is the way to go. But this is the real world, time, money and patience aren't in infinite supply.
Maybe I've been lucky, maybe both cranks will let go at the next race, maybe both bikes will run for another five seasons without issue. Whichever, I won't be ripping the bottom end apart until I'm pretty sure it's the cause of problems unless I've got the money to spend having it trued, the cases done etc.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread

I think you got very unlucky Rich.

I've personally never had a crank fail. And seen some which should of done and havn't!
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If I have to take the carbs off once more...

I probably should swap engines - the "race" bike has the injection setup and the "street" bike doesn't. The "street" bike also has everything you mentioned except open carbs. I really can't justify doing that, as my understanding is that it really tears up a motor quickly and I'm not "racing" just trying to impress the ladies!

Now that I've installed an injection system I was considering putting the other one on my streetbike. The difficulty level was pretty minimal once I sorted through all the parts and looked at my manual (best $100 spent on this whole adventure so far).

Craig

StephenRC45 wrote:I think you got very unlucky Rich.

I've personally never had a crank fail. And seen some which should of done and havn't!

I tend to agree, probably more bad luck than anything and my specific experience has made me over sensitive. Coming back down from DEFCON 5 (ripping cases apart)
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

2 day old news.....

The bike was back together and seemed to run ok enough that I'm not afraid of the engine. I rode it around the block several times and was pretty happy at the performance after simply bolting everything back together. I had a couple issues. First was a leak at the plastic splitter above the water pump. I guess there's a reason the manual says to use a new O ring. Second issue was one cylinder not firing below a certain rpm. When I put it together I noticed one slow jet was plugged so I opened it up, but maybe the passage in the carb is also clogged. I should also check the air screw settings and see where they are. Third issue is me discovering there should be a washer under the oil pump driveshaft. Fourth issue is a set of leaky forks. I have the seals but haven't ever replaced fork seals before. Fifth issue isn't really an issue but I need to derestrict it as it's pretty much stock except the Tyga GP exhaust.

So now I'm back down to no carbs, no oil pump, and leaky forks. I'm hoping to still get it together for October 3rd, the next trackday at the track where I had lots of fun with the other NSR (yeah, yeah, before it blew up).

Craig

Jaime's got a page on servicing forks on his website. I think Tyga matt wrote it.

Yep.....just checked it was Matt.

http://www.dreamgate.ne.jp/NSR/technical/mc28SE_forks.html

Guys it's the dead of winter here and I dug the bike out today. Going to drop off the wheels this week for powder coating and need to decide what to do with the engine. I have the complete bottom end rebuild kit here (thanks again Matt @ Tyga!) and don't have a problem doing that if it's needed. Here's why I think it *might* be, but please tell me what you think.

Below a certain rpm, the bike almost feels like it has a dead cylinder or maybe in fact it actually does. Once it passes a certain point while revving up, it catches the other cylinder (or something happens???) and it seems to be running on full power. Does this sound like a bad seal in the bottom end? If it's a carb, pv, or electrical issue I'd obviously rather leave the engine alone and rebuild it later after a thorough thrashing during this season's track days. I tend to agree with Fontyyy on this one due to the parts availability, cost, and time issues for me.

Yes I have a good working set of carbs on the SP and am just waiting for someone to tell me to yank them and give it a try.

Have you done a compression check?Also check your battery condition,do NSR's suffer carb icing?it might be only that!

Engine has brand new top ends and a battery from the street bike that worked fine. No idea on the carb icing though. Anyone know a source for the oil pump block off plates? They didn't come up on a search of Tyga's website.

I'm seriously considering swapping engines, as I have 2 more new top end kits (D pistons, B barrels or could use the D pistons/A barrels from the current engine) and the engine from my street bike has the oil pump blocked off, HRC reed items, and only around 1800 miles on a fresh bottom end including new crank.