Was ripping on the freeway just about an hour ago, slowed for someone that wasn't moving over.... I went around on the right and was on it through a couple of gears.... Can't really remeber how it happened, don't know if it lost a little power or sounded different. What ever, I pulled the clutch and she shut down in a hurry???? Popped the clutch to see if I was dreaming and she skidded at 70mph or so...

Coasting with the clutch in and went for the kick starter, locked solid.
Coasted as far as I could and stopped. Bumped it backwards, Kicked it a few times and rode it home?????????

What happened? This bike only has about 2500 miles on a full rebuild.

Steve
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MC21
04 NSR50R
93 CBR F2
98 CBR F3 track bike
95 VFR750
89 FL400R Pilot
90 FZR 4/600

seizure I'm afraid - pull the pipes off and have a look at the pistons.
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-Jim
'93 MC21

definitely a seizure.......take some pics too please, it will help us amateurs debate over what caused it

Heat zeized,

If the motor can still run, take the radiator cap off while runnig and check for bubbles. If there are the head gasket has gone.

Other than that its down to overheating / wrong carb setting / not enough oil( pre mix ).

I didn't let it sit at all after I came to a stop, just bumped it backwards and it was free..... If it were that hot it'd have taken a few minutes I think.

The engine temp gauge was at normal reading, was a nice cool night, bike actually runs rich...

Also I still have the oil pump, and after I rode it home and let it sit a while I wanted to see if the compression felt right, it did, fired right up, and had blue smoke so it's getting oil.

It was seized for sure, but seems more of a mechanica lock up to me...

Anyway, what's up with oil pumps??? How much oil are they pumping in there at high rev but closed throttle? That could have been the killer right there.

Well, gonna pull the fairings and check the cylinders with a scope through the spark plug hole first.

Keep ya posted.

Steve
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MC21
04 NSR50R
93 CBR F2
98 CBR F3 track bike
95 VFR750
89 FL400R Pilot
90 FZR 4/600

So I got the scope and peak in the cylinders...

First off, both spark plugs mostly black with just a touch of brown. That was a wide open run with cool temps putside..... Like I said, this bike runs rich.

Top cylinder looks great, only a minor wear patch just above the exhaust port. The rest of the walls you can still clearly see the cross hatch marks. Compression test shows 130-132, that was wet as I noticed a little fuel drops running down the wall.

Bottom cylinder doesn't look as nice. Has a bigger wear mark above the exhaust port and some minor wear above some of the intake ports. The exh port bridge looks as it may have seen some damage, the edges look a little messed up. And it seems like there may be a mark on the power valve. The compression on this cylinder was 120 dry and 130 wet.

So, do I keep running this thing? It doesn't make any weird noises and seems to run fine... Why the hell did this thing seize up????/

Steve
_________________
MC21
04 NSR50R
93 CBR F2
98 CBR F3 track bike
95 VFR750
89 FL400R Pilot
90 FZR 4/600

Hopefully others more expert than me will chime in, but I wouldn't ride it as is. Maybe I'm just old and cautious, but I think things like locking up happen for a reason (as opposed to by chance), and it's likely to be a reason that will not just go away (I've tried that approach ) ...which means you're likely to lock up again, and you may not be so fortunate next time avoiding a crash. I would still favor pulling off the pipe to get a good look at the pistons.
_________________
-Jim
'93 MC21

Just took it for a spin after putting it back together.
Still runs like a scalded cat, but has a little piston rattle at low revs... No doubt that bottom cylinder.....
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MC21
04 NSR50R
93 CBR F2
98 CBR F3 track bike
95 VFR750
89 FL400R Pilot
90 FZR 4/600

Like Jim said, next time might be your last ! Sooooo...rebuild the bottom cylinder !

You've got to get the barrel off and check for damage, it's not like it's a big job to do, not just bore damage either, mainly you're looking for piston damage.

You can run barrels that are pretty heavily scored, after all what is a groove in the plating actually going to do?
However piston damage is another matter, the piston is soft and it only takes a tiny bit to lock it again.

You also want to find out why it did it, running too lean if it detonated or not enough piston/bore clearance if it didn't are my bets.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread

As Fontyyy said, get the barrels off and inspect the pistons. There is obviously something wrong for it to lock up, and it will happen again unless the fault is rectified.

Some piston diagnosis info here http://www.smellofdeath.com/lloydy/piston_diag_guide.htm

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

On your rebuild, were the cylinders plated here in the U.S., if so by who?

In doing mine the plater thought that 1.5 thousands was enough piston to bore clearance until I told them otherwise.

With the damage you described I'm sure it's going to lose compression each time you ride as the rings are getting nicked running over the scoring.

Well guys, I rode the bike today like an idiot.... Seems to be running just fine... No issues.

Question.... How likely is the crank getting thrown out of true on a "minor" seize like this? I don't know if it was cause I wasn't winding it up or what, just seemed to make my hands go numb a bit faster than normal....
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MC21
04 NSR50R
93 CBR F2
98 CBR F3 track bike
95 VFR750
89 FL400R Pilot
90 FZR 4/600

I've never heard of a sieze wreaking a crank.

The bike could be fine and you may have jst been very lucky, I've seen one minor sieze (Dave Reynolds racing with DP) when there was no piston damage, both rings still free. But that was a 4 point sieze so there was a issue with something still.
Other than that every one I've seen had a level of piston damage.
For the sake of about $2 (that's if you do replace the base gasket) I'd always check.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread

Yeah... I know.. I have a few base gaskets here. I even have a used perfect piston that I could put in there....

I did email the previous owner, he told me this was the same cylinder that he seized... That's why the bike got the full rebuild... He went down when it locked on him, so I'm talking a fairings,cases,crank,pistons,pipes kinda rebuild........ But, reused the jugs. I suspect that that lower jug to be out of specs.

Was thinking 300, but just worried about the crank now.

Thanks for the input so far guys.

Steve
_________________
MC21
04 NSR50R
93 CBR F2
98 CBR F3 track bike
95 VFR750
89 FL400R Pilot
90 FZR 4/600