Serious Question here. Re: Bike Seizing up?

[crashe]

Ok can you guys and gals please answer these few questions for me...
It will help me and most likely quite a few other riders out there.

Yesterday 10/9/05 at Pukekohe race track, a rider crashed his bike when he was going flat-tack around the track.
A few of you said the bike seized.....!

Now I understand about a engine seizing when the car, mower, truck or bike is sitting for a very long time and hasn't been used.
But I am guessing that this is a totally different thing.

1. What did you mean by the bike seized up?

2. How can we stop this happeneng?

3. What should we do at the time it happens?

4. Is there anyway to prevent this from happening?

5. What causes it to seize up?

Ok there maybe a few other questions that I haven't asked...
But I think you all know what I am getting at here.

Thanks for your answers in advance.



SpankMe and Moderators: Sorry if this is in the wrong section.

[James Deuce]

I'm assuming it was a two stroke.

Engine seizures are caused by a starvation of oil and a build up of heat. Get the pre-mix (two stroke oil/petrol mixed in either the tank or a petrol can) slightly wrong and at peak revs there's not enough oil to lube the upper cylinder and the piston/rings binds to the cylinder wall because it's melting, MELTING, help me mummy, I'm meltingg..

Anyway. Seizures. Can't avoid them completely. Two strokes, the oil/petrol mix has to be just right for peak rpm, compromising performance across the rest of the range. You can avoid 4 stroke engines seizing by making sure that you put oil in your bike. Sometimes though, mainly with older bikes who weren't designed with high RPM race track abuse, you can get oil starvation under heavy braking or acceleration. Basically the oil races to one end of the sump, and there is no way to pick up the oil to keep every thing lubricated. That sort of surging usually destrys top ends (valves Cams), but if the crank is being uncovered by the surge, you could have a, "Big-End" seizure. I find prunes helpful in that situation.

To avoid crashing when the engine seizes, you should cover the clutch. This means you disconnect drive to the back wheel the instant it feels like the engine is tightening by pulling the clutch lever in. If you don't pull the clutch in the rear wheel locks up when the engine stops rotating, causing the type of accident caused yesterday.

[Pixie]

Nothing to worry about as far as the virago is concerned.Short of running it with no oil in the motor,it is extreeeemely unlikely to suffer this problem

[SPman]

I'm assuming it was a two stroke.

An RZ 350

There is also a possibility the chain may haved jumped the sprocket but it was hard to tell until back in the workshop - it may have just come off and jammed after the event!
Phil may have a broken arm

[Sniper]

Ouch. Not nice for that guy.

Crashe, just read what Jim2 wrote (Ignore the by-comments ) and you should be fine. Keep an eye on your oil if you are worried.

[Motu]

2 strokes have an exhaust port on one side of the cyl,and an inlet port on the otherside,so you get huge distortion in the cyl because of temp differentials - of course the manufacturer knows this little design problem and takes steps to minimise it.In the bad old days of 2 strokes the proper way to run them in was to sieze them,remove the piston and file down the high spots until it stopped siezing,rather time consuming.Before synthetics race bikes used to run heavy oil mixtures - 12:1,16:1 were common.Most street 2 strokes use an oil pump,there will be an oil supply even with the throttle shut,but you still learn to open the throttle a few times on down hills.

Sidevalves have cyl distortion too from the exhaust valve and port in the barrel,they were set up with wide clearances and copious oil supply to the cyl - I seized my M20 BSA when running it in,just filed the high spots and put it back together.

[merv]

Its not so much about "melting" as Jim has said but the fact that if the engine gets too hot for whatever reason the piston basically expands to be too tight of a fit in the cylinder and it just locks up. In doing so on a 2 stroke they sometimes score the bore a bit but most times when the engine cools down you can fire it back into life and hardly notice any difference in it. Its generally a good idea to strip the head and barrell off anyway just to see how bad the damage is if any. Also its a good idea to find out why it did it.

The old aircooled 2 strokes ran fairly loose tolerances to try and stop this but even then seizures were a common thing especially with new tight engines. One problem was alloy pistons in a cast iron barrell with quite different expansion rates.

The RZ350 is watercooled and they weren't so prone to this as the expansions are controlled better with the more consistent heat in a watercooled engine so the owner would need to delve closely into why it happened. Maybe cooling system failure or any number of things.

[Ixion]

What they all said. I've had just about every sort of bike seize on me - usually at the most "oh shit" moments.

But it is VERY unlikely that you would seize a modern four stroke road bike. Very very unlikely indeed. Seizures on modern non-racing 4 strokes are almost always actually mechanical jamming after a conrod has broken, or a cam chain jumped its sprockets, cam belt broken etc. I really think that any 4 stroke riders have no need to worry.

Two strokes are another matter. The later Jap ones are much better than they used to be. I've still seized them. Cover the clutch. Always cover the clutch.

So long as it doesn't tip you off , a two smoker seizure isn't too big an issue often (sometimes is, if it snaps the rings).

And bear in mind that the extreme conditions of the race track do not (well, should not, anyway) apply to the road. Racers will seize two smokers. It goes with the territory. Riding a four stroke on the road ? Forget it. Two stroke on the road? Don't lie awake at night worrying about , odds are it wil never happen. But, just to be safe COVER THE CLUTCH. And keep a religious eye on oil level.

[crashe]

Cheers thanks for all the replys.....
Much appreciated...


I guess when it seizes up.... you just go with the bike when it goes down....
as this rider did.

Or can you keep them upright... when it happens????????

Speed factor depending.........

[Motu]

No,you pull in the clutch and stop...but on the race track it can happen faster at higher speed.But SP mentions the chain was off as well,you certainly can't get out of a chain locked rear wheel lock up easily.

[R6_kid:Me]

as said if you are on the road and it happens just keep you clutch covered. Had it happen (not engine sieze but similar) on my old vespa, just clutch in and roll to stop in a safe place.

Also this hardly ever happens on four strokes, and if you look after your bike like you are supposed to the engine will die for other reasons well before getting to a seizing state.

[Big Dave]

But it is VERY unlikely that you would seize a modern four stroke road bike.

Depends if you count wheel bearings seizing or not.

[froggyfrenchman]

if youthrash a hot bike when cold, the piston gets hot real quick and the barrels take a while. heat = expansion. piston gets too big for barrels, cant move and ceises (sp)

[FROSTY:Me]

as per all the above posts seizure of a modern 4 stroke bike is rather unlikely -but always possible.
Unfortunately Mella yella did just that to me at taupo
But it was a a bored out motor
Something to keep in mind with a racing 2 stroke is that they are trying to get every ounce of performance out of that engine.So the mixtures get thinned out to just below seizure point. --For those that dont know a stroker goes best just below seizure point.
Jennian is a fairly high speed corner just after a reasonable straight -prime place for a nip up.

[Ixion]

..
I guess when it seizes up.... you just go with the bike when it goes down....
as this rider did.

Or can you keep them upright... when it happens????????

Speed factor depending.........

Ask Mr Pyrocam ! He seized his RGV150, didn't think/know to pull in the clutch and rode out the skid from 100kph to a stop. Quite impressed I was !

In general, providing you're upright when it locks, and have enough straight road , a locked and sliding rear wheel is not too disastrous. A locked chain or gearbox may lock the wheel, and pulling in the clutch WON'T help with that one.