93 nsr250 mc21 se - Chicagoland Sportbikes
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post #1 of 14 (permalink) Old 01-10-2011, 02:47 PM Thread Starter
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93 nsr250 mc21 se

Bored yesterday and finally pulled the trigger to work on my NSR250 . Plan is to powder coat the Frame and Swing arm , Rebuild the engine and maybe go TYGA bodywork if funds permit.

Started with this. Blew the Rod bearing and heres what it looks like.







Got the engine out before midnight and its time to call it off.



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post #2 of 14 (permalink) Old 01-10-2011, 09:20 PM
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Nice project. Did you find out what caused the detonation that grenaded it? Crappy fuel, dirt in the carb, timing off??
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post #3 of 14 (permalink) Old 01-10-2011, 09:50 PM Thread Starter
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It was due or almost due for a crankshaft rebuild. Usually the crank for this street bike is around 20-30k kilometers for it to be rebuild or replace for a new one. My mileage is around 18000 kilometers on the speedometer. Who knows if its the right mieage? Plus I overreved it couple of times while I was on the track.
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post #4 of 14 (permalink) Old 01-10-2011, 10:33 PM
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Originally Posted by rvt2002 View Post
It was due or almost due for a crankshaft rebuild. Usually the crank for this street bike is around 20-30k kilometers for it to be rebuild or replace for a new one. My mileage is around 18000 kilometers on the speedometer. Who knows if its the right mieage? Plus I overreved it couple of times while I was on the track.
What I was getting at is that the top of the piston and the barrel look like the aftermath of piston meltdown from detonation. big ends don't often fail that way unless it's a complete lubrication failure.

I have pulled enough TZ and RD rods out after they failed but the top end rarely looks like that unless the pump failed or it ran out of oil for some reason.

I'm just looking at the pictures and that's how it appears. In the metal it may be clearer what failed first.
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post #5 of 14 (permalink) Old 01-10-2011, 10:50 PM Thread Starter
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I'm running premix. It looks like detonation but what I think is when the rod bearing blew up it causes the travel , clearance or distance(whatever you call it) out of whack causing the piston to hit the cylinder head.
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post #6 of 14 (permalink) Old 01-11-2011, 10:04 AM
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Could be right. It's hard to see in the picture, but it does look like the big end is overheated. For here it looks like the piston has seized as well.

I'd spend some time examining parts to be 110% sure of the cause. We don't often see that much top end damage from a simple big end failure. Of course that depends on how long it was run after the damage started. If it continued to run and bits of big end cage were coming up through the transfers, that might have caused the rings to jam and allow the piston to overheat and cause the seizures.

There is certainly a lot of debris in the top end and much of it is small balls which I took to be detonated piston, but it may have come from the cage.

That motor is very similar to the RS250R. Had a 96 to rebuild a couple of years ago. Transfers were much larger IIRC.

RSCycles for parts or is there a better source for street motors?
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post #7 of 14 (permalink) Old 01-11-2011, 10:44 AM Thread Starter
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It run probably ran half a min to a minute before I grab the clutch but will do check. It probably had a mild seized before the bearing blew up and the look like a detonation is from the debris from the bearing or it is really detonation. There's no way for me to know because this is my first time openning this engine. Eversince I got this from overseas I just ran it and never checked it. All I did is clean the carbs and jetted it. Yes the RS250R is very similar engine to NSR. NSR engine is like the detuned engine of RS250R. As for parts ordering I have a guy in japan that ordered NSR parts for me when I need coolant hose but I might try redline from cali or tygaperformance. Rgvspares sells nsr parts too. RSC doesn't sell parts for NSR only TZR's and GP bikes.
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post #8 of 14 (permalink) Old 01-11-2011, 04:37 PM
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I was just about ask how hard it was to find/get parts for an NSR. Always loved those bikes
post #9 of 14 (permalink) Old 01-11-2011, 05:04 PM Thread Starter
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Most of the MC21 & MC28(90-96) parts are still available. The MC18(88-89) are lil bit hard to find, like the whole crank assembly I don't think there's one stock available. Best way is to do rebuild although pistons,rings etc is still available. The older models 84-87 is quite to find parts or most are no longer available. Honda is not friendly to 2 strokes if you compare it to Yamaha and Suzuki.
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post #10 of 14 (permalink) Old 01-12-2011, 09:05 AM
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I just realized that you are only about 15 minutes away from me. If you need a hand to determine what went wrong so you can avoid a repeat, just pm me.
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post #11 of 14 (permalink) Old 01-13-2011, 01:52 PM

 
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that is a great offer... very cool to see stuff like that on the forum!

www.thepowderpro.com

Custom Powder Coating, custom bike builds, one-off machining work, custom LED kits..you want it, we can make it happen
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post #12 of 14 (permalink) Old 02-25-2011, 03:51 AM Thread Starter
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Will do.

Quote:
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I just realized that you are only about 15 minutes away from me. If you need a hand to determine what went wrong so you can avoid a repeat, just pm me.
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post #13 of 14 (permalink) Old 02-25-2011, 03:57 AM Thread Starter
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Got my frame and swingarm last weds.





Slowly putting it back. Still need the wheels pc'ed. I would guessed before i finish this thing it'll cost me $2.5k with everything. I should buy a new crank but that would be another $850 so ill just used the low mileage crank that i bought from japan.

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post #14 of 14 (permalink) Old 02-25-2011, 04:07 AM Thread Starter
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When its done it should look like this but in black(west scheme). Same with my old NS400R paint.




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