After a top end rebuild, new pistons etc. on my MC21 I think I may have just suffered a seizure.
I also chopped the airbox, hi-flow reed stuffers from Tyga, HRC electronic derestrictor and HRC front cylinder head modification and removed the air bottle below the carbs and plugged the holes with fat bolts, HARC-PRO chambers and cans. Using a BR9 plug.
I guessed at a 135 main jet, and used that for the engine heat cycling, then after it was run in I followed the instructions on the tuning page here and found it was fine holding at 4000 RPM but at 7000 RPM it would rise in revs indicating leaness. So I moved up to 140 main jets and it then held solid at 7000RPM. Went out for a plug chop and held it flat out in 4th probably for 10 seconds or so (all I could manage on local roads) and the front plug came up a light tan colour on the electrodes and the ceramic -defintely not white anywhere-. From the plug guides I'd seen this looked perfect, but not on the OK-but-rich side. I rode the bike on the road for 100km or so then went to the track and hammered it for several sessions and 3 fun races (won one of them too) -no monster long straights-. Somebody told me to check for crack-McPop from the exhaust on overrun after chopping the throttle from wide open (indicating lean) and I didn't have that at all. Decided to go and get it dynoed and do a plug chop on the way. On the expressway I had it maxed out at 10000-11000 RPM for a good 10 seconds in top gear throttle full open. Now I am not quite sure what happened because I simultaneously chopped the throttle, hit the kill switch and pulled the clutch ... but I got a rear end slide somewhere in there which I wasn't expecting. Thinking: hmmmm! Was that a seizure or just hitting the kill switch before the clutch?
So I stopped and pulled out the front plug and to my horror the ground electrode is melted and everything is covered in a grey furry deposit. Bike started up OK and rode home fine but would no longer idle, and compression seemed down maybe when kicking it over.
Hmmmm! I can't make sense of it, I was expecting a really white lean plug if it was a seizure. Looking at plug reading guides, the melted electrode indicates pre-ignition. Now I read somewhere that the HRC box advancs the timing ... And the furred up plug is due to addatives or type of oil used, which doesn't make sense. So I am guessing that the grey furry stuff is melted and atomised aluminium from the piston, but that seems a bit extreme.
When I get over the demoralisation I'll pull the front head and cylinder off and have a look in there, but either way it begs the question: how is a plug chop going to tell me I'm lean if it seizes the engine first? Or if I was so lean as to cause seizure, then should it not be possible to detect beforehand?
Where did I go wrong? _________________ MC28 SE -sold-
MC21 with RS250 engine -for sale-
MC21 race bike -soon for sale-
Are you using the jet kit HRC or JHA?.Premix or pump(you may have lost lubrication),what oil?.
On my race bike i have a similar set up but am using a 210 on the front and 200 on the rear,the rear is a bit rich so will co down a size.
Plug chops can work but not with unleaded pump gas you need avgas or race fule to get good results.
Long straights and 2 strokes do not mix very well.
Let us know what you find.
I am using no jet kit, everything stock in the carbs apart from the main jets and I am using the oil pump set to maximum. I am using Honda Ultra GR2 2-stroke oil (top of their line I believe). The choice of fuels here at the pump are unleaded 'regular' or 'high-octane' and I was using the 'high-octane'.
I suppose next time I'll put in the biggest jets I can find and see if it runs, then work down from there. 200 sounds insanely large to me, but what do I know? I'm the one that just screwed something up _________________ MC28 SE -sold-
MC21 with RS250 engine -for sale-
MC21 race bike -soon for sale-
Holy crap!! Just took off the front cylinder and the piston is impressively destroyed (after only 275.6 km). The crown is melted in the middle and to one side; I'd be impressed if it wasn't for the fact my barrels look scored all down the sides. It looks like deposit from the piston rather than scoring in the cylinder but I suppose it is irretrievable? Can the barrels be cleaned out and used again?
I'll post a picture later if I can ever get the piston retaining pin out. I am considering just grinding the piston off!
Looking at the barrels on the tyga website and in the parts manual, there seem to be a great range of possibilities, ranging from $157 for a Cylinder B 12002-KW6-840 to $535 Cylinder A 'SP' 06121-KV3-980 or $472 for a cylinder A 'R' etc.. What is the difference? Presumably so long as I am matching the piston correctly to the cylinder I can use any type right?
Also do I need to check the rear cylinder before ordering new ones? I want to have it rebuilt for a race coming up, so I'm in a bit of a rush. I mean is a seizure like this always in both cylinders? _________________ MC28 SE -sold-
MC21 with RS250 engine -for sale-
MC21 race bike -soon for sale-
It sounds like a detonation seizure. I did the same thing when I first had mine. Too small mains and low octane fuel will do this. Advance will also cause it but I don't know how much the HRC box pushes the timing. If it was oil, you would most likely get a 4 corner seizure and both cyclinders would be done in. It's no big deal, anyway.
If you are using the PJs, start around 170 and work down. You'll probably end up about 150-160. At least that was my experience. CHOP, chop, chop, or go on the dyno. Pump gas will work fine for plug chops, but be consistent and use the same gas every time.
Buy a new piston and send the cylinder and piston to the Nikasil plater for a replate. Be sure to tell the plater to reinforce the exhaust port bridge and refit the power valve. Eric Gorr does a great job with this. He will also heat treat the cylinder to relieve welding stress prior to plating. You can clean the cylinder with hydrochloric acid. Maybe it can be saved.
Already replaced the front head with the rear before the problem.
I'm in Japan so I'll have to find someone locally rather than Eric Gorr. I'm sure there are people here as good, probably better but communicating with them? My Japanese skills would amount to \handing them the parts and mentioning I race and then saying 'how much?'.
Interstingly my seizure is more than 4 corner .. it basically has marks on the barrel at the edge of every port, about 8 places. Also the crown has a black sunken circle in the centre, and a seriously melted edge. I did not run out of oil, wasn't using low octane fuel. The piston is just a smear, the spark plug melted.
Interesting what you say about the pilot jets, because I'm fairly certain that the main jet is responsible for the wide open top gear seizure at over 11000 RPM, that's 180+ kph with the rear wheel locked and fishtailing round a slight bend!
I really want to do this properly. I'm going to get on a dyno, I can do plug chops, but I just feelo very short-changed since I've been trygin to be conservative with the mod.s and keep the oil injector and pilot jets to sustain reliability. My first plug chop on a dual carriageway looked great. So I go ahead and do one flat out in top as suggested and am rewarded with a meltdown. I must be doing something wrong! _________________ MC28 SE -sold-
MC21 with RS250 engine -for sale-
MC21 race bike -soon for sale-
The differance in load on an engine from 4th gear to top is quite alot. Detonation will nearly always take place not because of rpm but because of load. Your plug may well of looked perfect in 4th gear but the engine is not under the kind of load it would of been under had you been in 6th. Im sure you would of found the plug looking alot leaner if you had done the chops in 6th.
Next time try going up a couple more jet sized and doing the chops in 6th. You dont have to hold it there for 10 seconds to start with, not untill your confidant that youre on the safe side of jetting. I would say youre at least 2 sized to small going by the damage you did to the piston. _________________ If I have to take the carbs off once more...
Julian,
that is definately a detonation seizure. With your setup, most the NSR racers there use the HRC 0.6mm base gasket on the front cylinder to help prevent this. Looks like you were just a tad on the lean side with the jetting.
HARC PRO should be able to fix your cylinder. I believe they do replating. Rich had his RS125 cylinder repaired by them, and I believe it was alot less than the price of a new cylinder.
If you do get a new cylinder, just make sure it is off the same model bike as the other cylinder you have (ie, MC21R or MC28P, etc). The bore, A,B,C, will make no difference. _________________ Paul Herr
'88 FZR4/GSXR/YZF Frankenbike
MY BIKE PICS
invigiator wrote:
Interesting what you say about the pilot jets, because I'm fairly certain that the main jet is responsible for the wide open top gear seizure at over 11000 RPM, that's 180+ kph with the rear wheel locked and fishtailing round a slight bend!
Sorry. That was Power Jet, not Pilot Jet. You are right about it being the mains, but whether or not you retain the power jets will affect the main size.
Wrench, should I use the 0.6mm base gasket on just the front, or on both next time?
Triman5, do ever find you have to change jetting for conditions/weather?
Looks like I'll have to build up very gradually to the plug chop in future ... I think I didn't make myself clear, I haven't checked the rear cylinder yet but I am assuming it is in the same condition as the front. So I'll be looking for a pair of used cylinders and I'd very much like to know the difference between the cylinders from different models since the new price is so wildly different.
You can be pretty sure that only the lower cylinder has let go! I won't gaurantee it, but I would put money on it... not a lot though!!
I'm just about to swap to the 0.6mm gasket on my front cylinder. Funny how Paul has just mentioned it too! I had a detonation seizure a few weeks ago. This is running an HRC head and RS plug too.
I'm assuming your piston looks something a little like this:
I was right on the edge with the jetting, and was heading back to richen it up a little, but it was going like an absolute missile and I just couldn't get off the throttle!!
That'll teach me! Then again... maybe it won't!! _________________ Andy.
NSR-WORLD.COM
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Yep! Just like that but a bit worse. See the thread titled 'cylinder damage'.
So should I only use the HRC gasket on the front? What are the best plugs and HT leads to use? With the head conversion the HT lead no longer mounts where it should, what do you do with yours?? _________________ MC28 SE -sold-
MC21 with RS250 engine -for sale-
MC21 race bike -soon for sale-
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