My MC21SP has always been difficult to start. I did a crankcase compression and vacuum test, the crankcase would not pressure up.
After splitting the cases, I found the flywheel side crank seal was absolutely knackered. It had hardened and chewed itself up.



You can also see that dirt has passed through into the crankcase



That side outer crank bearing and the centre bearing have gone. A new crank I've got will be installed. This one will be repaired for 1st reserve (I've a new set of bearings).

Also found significant wear on both barrel exhaust bridges, plus the pistons are slack in the bores, so it will also get 2 x complete brand new top ends.

With the amount of miles I cover, this engine rebuild should last the bike, but its an expensive repair. Also a good lesson for everyone buying an NSR of unknown origin.....even if it looks shiny on the outside, it still needs the engine looked at internally.
_________________
Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

Hooker in a pretty dress - well said Dan!!!
You said that the seal could be the problem months ago - right diagnoses!
Actually, its somewhat rewarding mechanically to completely bottom one of these motors. Don't worry, I will take pride in rebuilding with new parts and making a 'virgin out of her'. It should run a bit crisper after the rebuild.
I'll be keeping the OEM forks, but I will have a set of great condition RVF Forks/ Yokes & Stems / CBR900 Nisin Breaks for sale in a few months time
_________________
Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

Mate, you're a milder man than many for not throwing the thing back through the dealers window!
The miles you've done on it there would be a half decent case for it not being "fit for purpose".

It's your call of course but from my point of view, new crank, new barrels, new, new, new just means it stings more when it eats itself again.

and it is "when" not "if"
_________________
Please do not PM me technical questions, if you can't find it on the Forum start a thread

fontyyy wrote:Mate, you're a milder man than many for not throwing the thing back through the dealers window!
The miles you've done on it there would be a half decent case for it not being "fit for purpose".

It's your call of course but from my point of view, new crank, new barrels, new, new, new just means it stings more when it eats itself again.

and it is "when" not "if"

Well there would have been a time when I'd have taken exactly that approach. Such is life. I really appreciate this rare bike, so on that basis I'm prepared to spend the cash to properly sort it. The engine is not being tuned and is on factory standard jetting, running on top quality synthetic oil, I'm not expecting to see many more problems in a short space of time. I'll only be racking up 500 miles per year max.
_________________
Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

I think mine has the same problem, very hard to start and not crisp enough, i'll see what i find too!!!

One method, perhaps the most accurate way to test the crankcase seals for integrity is a compression / vacuum test, I blanked off both exhaust outlets and made a blanking plate for the intake manifold, with a hose tail joint welded on. I had access to a Stihl 2 Stroke compression / vacuum test kit to allow testing of seals in both directions.

Or, as many folks do, spray carb cleaner around the edge of flywheel, if the revs rise on tickover the seals pulling air in at the very least.

My bike just wouldn't start from cold, but the problem manifested itself over time. When I first got the bike it started fine, then after a few spirited rides with a dry / hardened seal, it just got gradually torn up. To a point where the bike just wouldn't start without easy-start spray. After it had finally fired, and had air / fuel mix pulled through the cases and had warmed a little, it would start sooo easy. Initially I checked everything else to no avail.

Let us know how you get on and if you need any help.
_________________
Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

It can only get better from this point


The crankcases are now back together, gearbox & clutch assembled. Next job is to fit the new top ends, do a crankcase vacuum & compression test, then get the engine back in and reassemble everything.
_________________
Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

is that a certain 400cc project i see in the foreground...

mr smith.

Very close Dave, its a CBR250RR MC22. Just the engine is for the new project, a Honda RC163 Hailwood / Redman Replica. The RC161 - 164 models were the Honda GP Works Racers of the 1960's. They had a 250 cc 4T air cooled engine, and the CBR250 engine is the closest lump you can get for a Replica Project.



But no more talk of 4 Strokes, at least in this section
_________________
Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

Well, the engine is back together and now back in the frame. I took this shot before it went in. Practically a brand new engine with the new bottom and top ends


_________________
Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

You could eat yer dinner off that! Lovely job, Rich.

It'll doubtless run far, far better too. Ignore the cost and hassle and just enjoy the results . Summer's just around the corner...

and now the hard part comes. How to keep it looking that good over time

I know I spend more time keeping my RS engine looking like that weekend after weekend. But that engine comes out of the frame a couple times a year. And when it's in the frame, it's easy to get to pretty much all parts.

Most people dont pull their NSR engines, unless they are going to do a bottom end. And with all the extra stuff on a street bike, it's hard to get into the tight areas.

Thats one of the reasons 4-strokes drive me nuts, so much crap and so little space. How is a clean freak supposed to keep one clean all the time!

Keep the photo's coming, it's looking good so far.
_________________
Charles Gallant

will be embarking on the same journey mate, pulled mine to bits today and cranks looks a little rusty in places is towards to top of its service limit and has unkown mileage, was just gonna do the tops end today but looks like a full rebuild is in order. blumming two strokes!

also found another resaon for mine not performing too well up top, there was a ton of play in the pv cables and one rc shft thread is buggered so the bit thta the cables attach to moves all over the place rather than opening the valve!

At least the bores and heads are mint, one positive!

Trouble is Ricey is you just don't know what the perivous owners were like or how they treated.. or didnt treat the bike.

When you start an NSR up and gently blip it you can see the power valves often don't open togther even though the cable play seesm to be the same. It takes quite a bit of fine tuning to get them both to open together and reach full open at the same time.

Rememeber Billy's Andy. One power valve opened while the other closed!

Edit: For my damned spelling again.
_________________
If I have to take the carbs off once more...


Last edited by StephenRC45 on Sun Jan 25, 2009 6:38 pm; edited 1 time in total

Yeah, I remember that! I also remember the servo twitching like a schizophrenic with terets!
_________________
Andy.
NSR-WORLD.COM

Please keep all responses to Forum posts on the Forum so that others may benefit.

Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.

Check us out on Facebook! Please "like" our page!