Messages

1

Technical / Troubleshooting 2nd seizure on KX 125

« on: October 15, 2012, 08:33:20 AM »

Hi Guys, had a better look at the power valves last night and your right, they are just managing to reach into the bore because the tips have worn down. So thats the mystery solved, feel a lot more confident now to rebuild the top end. Thanks for all the help.

@arnego2, interesting post on the remix ratios, I'll stick to 40:1 for a bit but will decrease the ratio as I start getting more out of the bike.

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Technical / Troubleshooting 2nd seizure on KX 125

« on: October 14, 2012, 11:12:45 AM »

@cnrcpla, sucks about that water pump! Agreed though 2 stroke is the way to go, simpler engine and loads of fun to ride

@arnego2, im using a premix of 40:1 with a fully synthetic oil, the manual suggests 32:1 but I ended up increasing the ratio because I was fouling plugs. A few experienced riders told me they run the same so I didnt think it would be a problem, maybe its time to get back to 32:1 and change the jetting.

@2strokerrevolution, the exhaust port looks good on the inside, it just has 2 indentations where the valve stops against the barrel, I have fiddled with the valves and there is no way they are able to reach into the barrel.
Unfortunately we only have 1 engineering shop here that can do the nikasil plating and they dont provide any parts, but I did measure the diameter which was right for the stock size.
Good question on the piston direction there might be something to that, on both seizures the piston is in the correct direction but for some reason on the original build the ring gap is facing the exhaust port. I know from the OEM piston I put in that the gap should be facing the intake because it has a ridge so you cant get it wrong. So this could be a reason for the 1st seizure, as the ring wore down it got caught in the exhaust port.

I ride trails and dont give the bike much abuse, I've heard of people getting 100hrs out of their engine but im not that brave lol, seizures are an expensive risk

Just to clear the screw thing up, it is not missing in the engine, it came lose from the reed valve assembly but was not able to move enough to escape into the engine.

3

Technical / Troubleshooting 2nd seizure on KX 125

« on: October 13, 2012, 04:49:14 PM »

Thanks for the reply cnrcpla, thats correct its the exhaust side, I did check the power valves when they were still lose but they dont seem to be able to reach into the barrel, they just stop against the outside of the barrel.

The screw had come lose before the 1st seize but it never made its way into the engine, it just allowed the petals to move out of place and break the tips off. I cant see any debris looking into the bottom end, but your right there will definetly be something there so I'll make sure its opened and checked, dont want to risk another seize

4

Technical / Troubleshooting 2nd seizure on KX 125

« on: October 13, 2012, 02:45:20 PM »

Hi guys, hoping to get some valuable advise here, my bike has seized twice recently and I?m trying to troubleshoot why.

The bike is a 2004 Kawasaki KX 125.

The first time it seized we had stopped for a break, when I started the bike it took a few extra kicks, made it around 25 meters of slow riding and it seized. The bike had done 33hr's since the original owner had done both the top and bottom end. The bike hadn?t been ridden hard but at the time the compression was getting low need a top end refresh.

I figured I'd do the top end rebuild myself because I have a semi decent amount of mechanical experience and enjoy working working on the bike, It?s like an adult version of legos

When I took apart the bike I found it hard to determine the cause because there were a few possibilities:

1) A screw had worked lose in the reed valve assembly, so chips of the carbon fiber petal tip had broken off and made its way through the barrel.
2) The piston head had a few pin holes which could have been made by sand, I do clean my filter after each ride and it was in good condition but you never know what might sneak through.
3) The compression was low so maybe the ring had worn too far and collapsed.
4) The bolts that hold the exhaust power valve assembly were lose and the valves and some play, I don?t see how this would have caused the issue but I feel it?s worth mentioning.

So I fixed the issues above, had the barrel re-plated (nikasil), and put in a new OEM top end kit, checked all clearance?s and ran the engine in by the book.

The bike was running 100% and never felt better, had about 1.5 hrs breaking the engine in and another hr riding. Then a bit of a disaster to cause the 2nd seizer or add some confusion to why the bike seized the first time. The road I needed to get through was flooded and deeper than I expected, ended up dropping into a 4x4 rut and water got sucked through the intake.

After that I drained the oil (which had about 25% water!) and remaining fuel in the carb, then left the engine open for a month to dry. Once it was all back together starting the bike was a mission, took about 30 minutes and I eventually got it started by taking out the plug and heating it up.

While warming it up I noticed that if I rev it up, while the revs would drop at a certain point I would feel a nock with my hand on the seat! I had never noticed this before and have a feeling this could be the cause of the 1st seizer and the next one to come, I rode the bike for a bit but it was occasionally bogging down with the throttle open. I figured I did a bad job at draining out the carbs the first time (instead of opening them to drain them I turned them upside down and drained what was in them till I thought they were empty) so I opened it up properly and cleaned it out, there was a small milky clump under the main jet.

Bike started better the next day and rode it for 5 mins to test, all seemed ok with no bogging but while I was idling to come to a stop it seized for the 2nd time.

When I compare the piston damage from both seizures they are almost identical so now im wondering if there is a common problem that caused both seizures. Flooding the engine before the 2nd seizure definitely adds some confusion because that could have also caused the 2nd seizure.

I know the obvious answer is to take the bike to a professional, and I might still do that. But first I want to see if there's anything obvious that I could identify and fix, I?m already knee deep in it and I like working on the bike as a hobby.

If anyone has any advice or can help me out with the following questions I'd be very grateful:

1) The pics of both pistons are abelow (1st seize on the left of the images), they've both broken by the exhaust port and in the identical place. Any ideas on what could have caused this type of damage? From my research online it looks like a possible coolant leak, but I haven?t lost any noticeable coolant and did use a new gasket & o-rings on the rebuild. I guess the 2nd seizure could be from water left in the fuel anyway.
2) The conrod has a lot of play left to right (but not up and down) on the main bearing. I?m not sure what the usual tolerances are here, could this be a problem?
3) If that "thump" while the revs drop is worrying is there anything I can test without opening the bottom end, if it comes down to that I might just send in the bottom to a professional.
4) Any idea other theories or things I can check will help point me in the right direction?







Thanks for taking the time to read through the post and provide any help.