Engine help - possible rod problem

[JWW]

Last weekend my son was riding his KX100 when it appeared to have seized. He was between 3/4 and full throttle when it bogged down and died. I rotated the kick-starter with my hand and heard what sounded like metal on metal grinding.

I pulled the cylinder and the piston and rings appear to be fine. The only exception is the top edge of the piston has a small rolled edge. It looks as if someone took a small hammer and dented the edge. The cylinder is absolutely clean and smooth. It shows no sign of the rolled edge hitting it.

If I grab the rod and move it left to right it seems to have an excessive amount of play. The top end of the rod moves a little over 1/8" overall side to side. If I look down into the crank nothing appears to be cracked or broken.

What is the actual procedure for checking the connecting rod play at the bottom?

Is it possible that the rolled edge caused the problem?

I’m tempted to put the new piston and rings and give it a shot. My only concern is turning a minor bottom end problem into a major one.

Any tips, thoughts or advice?

Thanks

 

[rooster51]

if you could move the kickstarter with your hand the angine isnt seized.

 

[rooster51]

engine* typo

 

[a454elk]

Yeah it probably didn't seize, but it sounds like your piston had a problem. Look at the area where the piston had damage and line it up to the cyclinder wall and see what it looks like. There is usually play in the rod, there was on both of my bikes. It did move side to side too. Once the piston is all the way in the cylinder, it usually won't move other than up and down. It may have just lost compression which caused it to bog down, trust me, I know this! Anyway, I'd take a good look in the cylinder and see why and where it hit. A majority of the time that I've seen this problem, it's near the exhaust port. If the rings are in good shape, then it may have just overheated, not sure. Good luck

 

[JWW]

You are correct. The mark in the piston is next to the exhaust port. I could not find any marks on the cylinder at all.

I will slap it all back together and see what happens.


Thanks

 

[SULLY]

Ooer...hang on, if you are 100% sure you heard metal to metal grinding, then you can be 100% sure there is something wrong. Personally, I would not run the engine again until I knew what it was. Take a real good look with a good torch into the bottom end. Look in the gaps between the crank lobes and the crank case, between the crank lobes and the con rod, and also in the oil slit in the big end of the con rod where you can see the big end bearing. Also look below the crank into the bottom of the crank case. What are you looking for?....anything that doesn't look right- any signs of heat blueing, particles of metal or burnt bits (I have had the thrust washers either side of the big end bearing break down on KX100's). Turn the engine over with the cylinder off, and listen to the bottom end, if you hear any any screeching, tight spots or greating then don't mess about, take it to bits and you will be glad you did.

That's my humble opinion, but learnt through experience!

 

[SULLY]

PS. For 2 stroke engine purposes, the phrase 'seizure' does not mean the engine has locked solid (total seizure), but rather that there has been a coming together of two moving metal surfaces, without either sufficient clearance, or lubrication or both.

To say that because you can turn the engine over by hand means it has not suffered a seizure is nonsense. Consider this- the engine gets hot parts expand and seize, then it cools parts contract, and the engine will turn fine by hand.

 

[a454elk]

Sully is right, I'd probably drain the oil and makes sure there is nothing in it as well. The exhaust valve may have slipped further into the chamber, which could cause the hit. Check that it is tightened and not loose as to let it slip too far in. Then check the bottom end real good like Sully stated.

 

[Ol'89r]

Jeff.

While the top end is off, bring the rod up to tdc and grab it with both hands. Try pushing and pulling the rod directly up and down. If you feel any movement the big end may be bad.

There will be a little side to side movement but, should be no up and down movement. Like Sully said, check the thrust washers for wear or heat. Also, check the big end of the rod for heat, blueing, discoloration.

Terry.

 

[a454elk]

He said grab the rod. BWUAHAHAHAHAHAHAHA!!!

 

[JWW]

PS. For 2 stroke engine purposes, the phrase 'seizure' does not mean the engine has locked solid (total seizure), but rather that there has been a coming together of two moving metal surfaces, without either sufficient clearance, or lubrication or both.

To say that because you can turn the engine over by hand means it has not suffered a seizure is nonsense. Consider this- the engine gets hot parts expand and seize, then it cools parts contract, and the engine will turn fine by hand.

Thats what I was thinking.

Based on the pison marks it looks like the exhaust valve might have hit it.

Even though Im taking it down to a professional tomorrow I think Im gonna go home and tug the rod. :thumb:

Thanks for the info

 

[Chili]

Right after a fresh rebuild we had the pin that holds the kips valve in place snap on my son's KX80. Took a chunk out of the piston and destroyed the cylinder. From what I've been told this is a very common failure in the Kawi mini's. Just something else to take a peek at.

 

[JWW]

Right after a fresh rebuild we had the pin that holds the kips valve in place snap on my son's KX80. Took a chunk out of the piston and destroyed the cylinder. From what I've been told this is a very common failure in the Kawi mini's. Just something else to take a peek at.

It just so happens that the two screws holding the cover on are frozen. Seems that these mini KX's require quite a bit of attention.

 

[SULLY]

YEs I has one screw stuck on a KX85. If the cross heads are still in good order then try an impact driver, if they are nadgered then cut a fresh slot with a hacksaw and use on impact, or with a sharp chisel cut a nick in the head and hammer it undone.

 

[JWW]

I had it checked out today and its not good.

At some point the motor seized and also toasted the bottom. Im not sure of the details but its not pretty.

Thanks for all the advice. :thumb:

 

[sunnyboy]

sunnyboy

STOP--and let me clear this up for you--your bike is a 2-stroke looking at the oil will only tell you what is going on with your trans,you have no valves to bang on your piston.you are right it sounds like you have to much play in the rod this means your crank bearing is bad.the manual will give you the acepttable clearance(side to side)the marks on your piston tell me that somthing has come lose in the bottom end traveled up through the transfer ports banged around on the piston and left through your exhaust port.you did sieze it but it is your crank not the piston.you need to split the cases and check out all the bearings,as this is a 100 i would replace all the bearings conrod piston and so on,these small bore bikes rev like crazy and are hard on bearings bringing the motor back to 0 time is in order. putting it back together and trying it the way it is is a waist of time and money(always use all new gaskets)and you can do more damage that can cost big bucks.also let me add while you have the cases split you want to get a seal kit and replace them all,i also always replace all the bearing crank and trans. thier is nothing like splitting cases and a few mounths later the one bearing you didnt replace goes out and you are back sliting cases again ive had it happen once.i learned.do it right and you will have a great bike that will last a long time :thumb:

 

[Chili]

you have no valves to bang on your piston

So I guess the KIPS EXHAUST VALVE on my son's KX80 is mythical and doesn't exist? Dang sure would like to know what broke that hunk off the top corner of the piston at the exhaust valve side then :think:

 

[sunnyboy]

i have never seen a power valve hit a piston and have seen lots of pistons damaged by debri kicked out of the bottomend and lot of times they hang around the exhaust port trying to get out,the valve comment came from another replay if my memory is correct so calm down.i read your reply and do not belive this to be his problem as this would be quite aparent during the teardown but slop in the rod tells a lot.have a good day and always make sure you put thing together write the first time as things dont just go snap in less somthing is wrong to begin with.see ya on the trail