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Hi,

2 days ago I was ridin' my KDX, not a problem in the world.. a few minutes later it seized en then got loose again, offcourse with no compression at all

The thing I find kinda strange is that my cylinder has been plated a month ago with new piston and new gaskets from that company (Powerseal here in the Netherlands), I didn't ride it a lot the last weeks so I didn't even used a full tank of gas..

Here are some pics of my cylinder and piston, maybe you guys know why it seized?











Normaly the reason is quite clear for me but now i realy don't know...

The jetting is fine, even a bit rich.
I use Putoline MX7 motocross oil with a fuel oil ratio of 1:40 (25ml of oil in 1 litre of gas)
I was ridin it in so I didn't even ripp it that much
the radiators were a normal temperature and the bike didn't real feel hot like a normal seizure..(is this the correct word?)
I bought a new BR8es spark plug, same as one that was in there when I bought the bike.
crank shaft is 100%, no play on the bearings or on the bigend bearing.
no signes of detonation or something like that.
My cylinderhead wasn't leaking, no white smoke or dirty coolant (clear green)

so... can you guys figure this out?

Looks like the cylinder rings broke? At least that's how it appears to me from your first photo.

Could the plating have been applied unevenly on one side of the cylinder wall?

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amstel78 wrote:Looks like the cylinder rings broke? At least that's how it appears to me from your first photo.

Could the plating have been applied unevenly on one side of the cylinder wall?

Sent from my SGH-T989 using Tapatalk 2

the strange thing is that I looks like it seized in al 4 the 'corners' so on the intake, and exhaust side.. on both sides.

the rings did not broke, what you see on the picture is aluminum from the piston that slided over the rings, so the rings are still on the piston.

4 corner seizure is usually from improper warmup or too lean jetting.

Julien D wrote:4 corner seizure is usually from improper warmup or too lean jetting.

but if it was a improper warmup (which I don't think it was the reason) why would it seize after almost 3 hours of riding and not sooner?

Lean jetting can't be the reason, my spark plug is coloured darkish brown en it stotterd a bit before the powerband
here's a pic by the way :

though it is a bit light on the right side strangely enough?

edit : those 2 things on the left side of the pic are drups of coolant btw, and there is some small damage from a previous seizure but that was before I bought it.

Looks lean from the plug. My plug is usually black and a tad moist (not spooged) and not brown and dry which indicates a very lean condition.

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Julien D wrote:4 corner seizure is usually from improper warmup or too lean jetting.

Yup. Those are the only two things I know of that cause it.

How do you warm up your bike? Fresh top end, yes? What about the bottom end? How is the intake manifold?

improper ring gap (too large) can cause a seizure....pistons for the kdx are available in 3 or more sizes for a better fit depending on the bore & plating, did the machine shop who plated your motor also supply the piston? what make of piston do you have, the number marking should be stamped on the top A B or C.

amstel78 wrote:Looks lean from the plug. My plug is usually black and a tad moist (not spooged) and not brown and dry which indicates a very lean condition.

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I never had a moist plug as far as I can remember with anything (except for some mopeds when I was 13), and black indicates usualy way to rich..

But maybe you could be right.. but then the bike did run like a clockwork, perfekt with a hint of richness (a small stotter before the powerband)

Possible suspect at the moment is :
lean jetting

My main jet is btw 178
airbox mod
DG pipe
Boyesen reed valves.
further quite stock.

SS109 wrote:

Julien D wrote:4 corner seizure is usually from improper warmup or too lean jetting.

Yup. Those are the only two things I know of that cause it.

How do you warm up your bike? Fresh top end, yes? What about the bottom end? How is the intake manifold?

I kickstart my bike, let it run for a minute or two to put on my helmet and gloves, then I get on it and drive slowly away, meanwhile I'm feeling my radiator if its warm, when its warm I twist the throttle and start riding faster.

A thing that comes to mind right now is that I was riding in a muddy crappy piece of land but the bike didn't seem to mind.

cornishwrecker220 wrote:improper ring gap (too large) can cause a seizeure....pistons for the kdx are available in 3 or more sizes for a better fit depending on your bore & plating, did the shop who plated your motor also supply the piston?

Jep they did, and this was my first gues indeed but I ain't sure if the right piston was supplied with the cylinder.. I thought that it would be fine because it came frome the same company that plated it.

if you can remove the top ring then install it into the cylinder & measure it (dont know what the gap should be off hand) that may help...you have a lot of numbers on the top of your piston which ive never seen before?

If powerseal provided the cylinder, then it should have been fitted.

Piston is a standard wiseco, they were not available in A/B/C.

The plug does look a little dry. However, reading a plug by the color of the tip is, as they say, useless as tits on a boar hog.

Main jet is a 178???!! Are you sure?

cornishwrecker220 wrote:if you can remove the top ring then install it into the cylinder & measure it (dont know what the gap should be off hand) that may help...you have a lot of numbers on the top of your piston which ive never seen before?

Its a Wiseco piston, does yours doesn't have those numbers on it then? or don't you have a Wiseco piston?

I'll try to find out the gap.. but how can I measure it ? with a marking gauge (if this is the correct word)


I don't own more measuring tools, except for a rules but I don't think that would come in handy

@ juliend
my bad, a 172.

With a 172, I would suspect the plug to be dripping wet, oily, black, and fouling regularly. Stock would have been somewhere around 158, which would be pig rich for most locations. Is your carb not stock, by any chance?

Julien D wrote:With a 172, I would suspect the plug to be dripping wet, oily, black, and fouling regularly. Stock would have been somewhere around 158, which would be pig rich for most locations. Is your carb not stock, by any chance?

I'm 7 feet below seelevel but would that make such a diffrence?
My carb is bonestock, no mods what so ever on it.

Nope, not that much. I would expect stock jetting to be as rich as you would ever need. 172 is HUGE!

Julien D wrote:Nope, not that much. I would expect stock jetting to be as rich as you would ever need. 172 is HUGE!

I know, but on that size it runs the best (strangly enough)

If it runs best on a 172 then I would think the engine has got to be sucking air somewhere other than just the carb.

SS109 wrote:If it runs best on a 172 then I would think the engine has got to be sucking air somewhere other than just the carb.

Yeah a thing that comes to mind right now is the left crank seal.. perhaps that's the culporate

you can measure the gap with a simple set of feeler guages ( the kind used for measuring your spark plug ) i am running a `wossoner` piston in my 220 `B` size

172? something is not right. never heard of anyone running this fat.
u got an air leak somewhere. that's my vote anyway.