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My nephew siezed his KDX and went out and bought a new yzf450. He gave me his KDX. I tore it down hoping to find the top end froze up...not my lucky day, there was metal in the bottom end and the top end looked like new. The bike is in overall good condition as he had kept it well maintained.

I have come to the experts to find out what you would do. Do I have the lower end rebuilt or start looking for a used lower end/motor? Funds are limited, what are my best options?

Please HELP!!!
Jim

Top end in good shape is great news. Seems to me like you need to determine where the metal in the bottom end came from. Sounds like it did not do the typical Seize if the top end is in good shape. Seize the lower rod bearing???? Your description leaves alot for the imagination.


Rod up/down play? Clearance between thrust bearing and rod? Any play detectable in main bearings? Where was the metal in the lower end found i.e. below the rod in the case OR when you drained out the oil?? What did the metal look like? Shavings, chunks, grindings.????

Top end in good shape is great news. Seems to me like you need to determine where the metal in the bottom end came from. Sounds like it did not do the typical Seize if the top end is in good shape. Seize the lower rod bearing???? Your description leaves alot for the imagination.


Rod up/down play? Clearance between thrust bearing and rod? Any play detectable in main bearings? Where was the metal in the lower end found i.e. below the rod in the case OR when you drained out the oil?? What did the metal look like? Shavings, chunks, grindings.????

There does not seem to be a problem with the lower rod bearing it still pivots fine on the crank with limited side to side play and no up/down movement. The metal can be seen in the bottom of the case and some on top of the crank mostly shavings with some pieces the size of a clipped fingernail.

Jim

Check the wrist pin bearing. If all is well, then check your main bearing inner retaining ring/bands. Sometimes the metal retainer ring for the balls on a main bearing can come free (although I've only seen this when a main bearing has been completely worn out and I would think you would have either in/out play or up/down play on the crank shaft itself).

Another possibilty would be a reed has been sucked into the engine and what you are seening is broken reed parts - carbon fiber reeds resemble metal in looks but would be flexible.

P.S. Metal looking clippings attracted to a magnet?

Gonna have to split the cases....More than likely want to have a pro do that unless you have experience, and the equipment needed to split and align a 2-cycle crank. Eric Gorr is a very reputable engine builder, and can do some mods while he's at it if you're so inclined.

What do the kicker mechanism and KIPS activation assembly look like?

Does the trans work? Meaning, with the clutch lever pulled, can you rotate the rear wheel?

That, honestly, won't work too well...'cuz even if everything is fine, that doesn't work too well. You could take the clutch basket out and try to move/shift the trans. With the basket out, there is no clutch plate 'stickage' to fuss with.

Is it seized (mechanically welded somewhere)? ...or just 'stuck' (something impeding movement).

Did the 'stickage' happen under power? A 'locked up rear wheel screeching' stop?


Definition: Experts

'Ex'= has been
'spurts'= drips under pressure

Not a good thing in most...uh... 'cases'.........

fuzzy wrote:Gonna have to split the cases....More than likely want to have a pro do that unless you have experience, and the equipment needed to split and align a 2-cycle crank. Eric Gorr is a very reputable engine builder, and can do some mods while he's at it if you're so inclined.

My thinking is that it is too early to decide to split the cases. If the former owner said it "seized" and his experience was putting along at a relatively slow engine speed the engine may have done nothing but sucked a reed into the engine and wedge it between the piston and cylinder thus seizing the engine. If there is truely metal chunks in the lower end in the area of the crank then determining where it came from and splitting the cases would be in order.

Certainly could be so something in the transmission or between the main gear and clutch gear that locked up the engine also but with metal looking particles in the lower end near the crank I would continue to focus attention in that area and things which could have entered into the lower crank area.

After that I would go down the path being established by CC if it were my engine.

there was metal in the bottom end

Never good....No sucked reed there! BTW, a sucked reed will usually blow right through...Not get stuck in the piston/cyl clearance. WOn't really run after that.

RE: 'there was metal in the bottom end..'

And...'what did the metal look like?'


A refocus on a previously asked question....and the magnet part, too.

Point is, that will tell what kind of metal it is, and thus, where it came from.

Re: 'top end looked like new.'

Please expand on that. Presuming the piston is out of the cylinder and no scuffs or tears are to be found on the piston/cylinder may be an incorrect presumption.......

Did the trans have the correct amout of oil it in? I mean...something came out of the drain hole?

Got Pics?

Re: 'top end looked like new.'

Please expand on that. Presuming the piston is out of the cylinder and no scuffs or tears are to be found on the piston/cylinder may be an incorrect presumption.......

Did the trans have the correct amout of oil it in? I mean...something came out of the drain hole?

The engine is out of the bike, top end is tore down and everything looks like new, clean piston and rings and the cylinder is not scratched up. I removed all the KIPS parts from the cylinder, all parts were there and in good working condition other than a little carbon build up. The reeds and cage were also in great condition.

When I drained the oil it seemed to be the proper amount for the lower end. It looked very clean other than some metal dust in it. My nephew was there and told me he had used synthetic oil in the bike all the time and had just changed it one short ride prior to it seizing

Did the 'stickage' happen under power? A 'locked up rear wheel screeching' stop?

Yes this is exactly what happened.


I have no experience in splitting the cases so pics would really be of no use.

I guess what I'm really looking for...is this bike really worth sending out to have rebuilt or will it wind up costing me a whole lot more than it's worth?

He gave me his KDX

you can't beat that...

is this bike really worth sending out to have rebuilt or will it wind up costing me a whole lot more than it's worth

So my personal answer would be: YES it is worth it (assuming the rest of the bike is in decent shape...)
PLEASE help save another green little monster! YOU WILL NOT REGRET IT

Sounds good for you so far!!!

With the transmission in neutral does the rod/crank assemble smoothly cycle when you move it by hand? If it does, then engage the different gears and cycle the rod by hand - don't worry about not having oil in the transmission. Does the countershaft turn? Does the rotating/cycling feel smooth? (you will have some drag due to the gears being engaged but should still be able to cycle the engine transmission without much effort.)

If this all appears to be functional then I would be flushing the lower case (area where the crankshaft and rod are located) just put a pint or so of kerosene or diesel fuel in the lower end- slosh it around and pore it out into a clean pan/tray/metal bowl or something similar. Check for debris. The first flush should take out most of the 2-cycle residual oil located in this area. A second flush should come out much cleaner. I've filtered the flush fluid and just reused the second or third flush a number of times looking for more metal debris.

If you are finding metal debris in this area you will need to determine the source of the debris. Assuming you find metal debris it appears you have eliminated all parts related to the top end, and reed cage so that only leaves what?

mechanical screeching on a dirt bike is usually a metal to metal occurence - e.g. spun bearing/ frozen bearing/piston-cylinder running dry and lean/ brakes overheating and locking up due to drag or overfilled MC/ etc.

I'm still thinking main bearing but this is not normally how they fail based upon my experiences and if the crank turns smooth and with no in/out play - I seriously doubt main bearing - but what else is there?

Any maintenance recently performed on the motor other than the oil change one ride ago? Anything stuffed into the carb or air filter area during any recent maintenance which could have contributed to something getting into the lower end? If answers are no - maybe splitting the case is in order. Should not be very costly if you pay to have it done - maybe .5 hour job to split case for a shop to take a look see.

Thanks for all the tips. I will check all of the above items in your post as soon as i get time.

The Top end had been rebuilt two months prior to it seizing,(about ten rides) but I would think if anythig was left in the carb or air filter area it would have reared its ugly head alot sooner...but who knows!

I'll keep Y'all updated as I'm sure there will be many more questions.

With the moral support I've already received from this site it looks as though this KDX will be a keeper.

THANK YOU
Jim

Siezed main bearing! The engine is in the shop, I was told it should be done by Friday.

That's kinda rare.... did they give you a reason this happened?

No, but I'll ask for thier professional opinion. At this point it's all speculation anyway.

"thier professional opinion"

Now i don't know this particular shop, but you might not want to stick too much value on their opinion - just my experience

My experience is that some bearing designs (or perhaps production runs) have weaker cages, and they just tend to go without any definable cause. I forget what era I had such problems but I think it was in the early nineties, and spanned more than one brand of bike. Wasn't just me who had such issues at the time.

Bottom Line - A bike which is reportedly in great shape for the cost of replacing the main crank bearings = Excellent Deal.

Think you should buy the nephew a brew or two provided he is old enough to indulge.