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Jeff Wolf

kawasaki bayou 400 piston

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Bought a nonrunning 1996 bayou 400. Tore down engine and found major problems. Piston is damaged and cylinder liner needs replacing. Looks like cause was a broken oil pump gear.

 

Question is can a piston from a prairie 400 be used? Is it the same engine? I assume the liner is replaceable?

 

 

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Welcome to quad crazy. The piston would probably fit but it’s not worth using it. There are two ways to go about it. You can bore the cylinder out and go with a bigger piston and rings and maybe have to re-jet the  carb. 

Or you can buy a used one from eBay but I would buy a new piston since it’s all torn down.  I just looked and found a used jug in great condition for $166. I rebuilt one of the same bikes about a year ago. Water cooled bike was super strong.  I think I paid $45 bucks for a full gasket kit on amazon. I would also do the valve seals while your in there.  

But this all depends on the condition of the bike and if it’s worthwhile. Also are you sure the oil pump gear was the problem? Because here’s my question.  The oil pump brings oil to the head to oil the top end valves, cams etc not the cylinder walls.  That’s done by the oil that’s in the lower end.  The piston could have just blown because it was beat on or the bike was ran out of oil.  

 

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When we took off the right side cover, the plastic oil pump gear was deformed and not attached to the keyed shaft that drives the oil pump, so that for sure needs to be replaced. Could have been run without oil though because the roller bearings on the connecting rod at crank are totally shot, with some of them in the bottom of engine.

The bottom of the piston sleeve has a chunk of metal out of it, half moon about .5 inch.  Piston is all busted up. One valve looks like it might need to be redone.

Trying to get the flywheel off now. We don't have the special puller. Does it take a 33mm puller? Tried the pry out with screwdriver and tap on slightly undone center bolt with no luck so far.

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Yes you will need a wheel puller to get that off. I’m honestly feeling like the engine is blown and may be beyond repair.  You really have to take a good look and see what happened.  The engine could have locked up and came to a complete stop and broke that oil pump gear.  Best bet is to take it all apart and see what the main bearing looks like.  Worst case is you lost time.  

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got it all apart. Bearings look good... in fact everything in bottom end look good except for connecting rod and bearings. There is a chunk out of rod and bearings blew up.

So... we have a used crank with connecting rod, and used cylinder and piston on the way. Also a used oil pump gear.

Plan on cleaning everything up real well and reassemble. 

Will get some new seals for valves and clean up head well and reassemble. Also some new seals for side panels.  So far it has been a fun project for my son and I.

Any suggestions on what I may be missing?

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Awesome stuff.  I would recommend changing the water pump while your in there.  That bike was fun to work on. The valve cover bolts 8mm  there are quite a few different lengths that go on that cover so be sure about the way they go back.   Be super careful with the water temp sensor wire, they break off easy.  Use a lot of grease on the parts, cam, lobes etc  prior to start up and crank the engine without the spark plug in for a few seconds each time so you pump oil up to the head.  Other then that I think your  right on par.  

Good luck. 

Post some dam pics I love pics!!!!

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Worked on quad some more this weekend. I've included pics of damaged piston, jug, and connecting rod. Also a bent valve.

Have the case back together with replacement crank and connection ng rod in. Put crank in freezer for 4 hours and propane torch on case (225f) and it slipped right in. Pretty cool. 

New valves should be here thursday and it will be back together.

Plan on turning it over by hand a few times before installing plug or spark.

Next will be electrical evaluation.

20190611_071059.jpg

20190611_071116.jpg

20190611_071141.jpg

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I know right? Crazy damage... still not sure how it all happened.

Drive shaft and transmission gears look great and parts not strapped in engine look like they are new. Who knows.

Hopefully electrical stuff will work.

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Probably...I'm surprised these machines dont have low oil alert lights...(maybe they do and I dont see it yet). Would have prevented a lot of damage.

Picked up some cheap 10/40 oil for when we get finished.. was thinking run it a couple of hrs then change oil and filter just in case?

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Yes for sure. Always a good idea to do a secondary oil change after a job like that.   Plus I like to add grease to the lobes of the cam and valve rockers etc and run my finger around the cylinder with a little grease as well. This will relieve some initial start up friction. 

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When the ignition key is on and transmission is in neutral the "neutral " light should come on whether the engine on/off switch is in either position right?

Need to find a wiring diagram I guess... anyone know if the bayou 300 wiring is the same?

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If so take the light green wire coming from the harness not from the wires coming out of the switch and add a ground to it and see if the bike cracks and the light comes on. If so there’s a problem within the neutral safety switch or contact point on the reverse cam. 

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You are the MAN! After grounding the green the neutral light came on.. also with the starter disconnected we could hear the starter relay clicking on and off when pressing the start button.... so now to re-evaluate that switch... see how expensive to replace.

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Ok so what’s bad most likely is the reverse cam, not the neutral safety switch.  

Ive attached pics of the reverse cam.  On that revers cam there is a small pin that’s spring loaded. That spring loaded pin is what touches the electrical tab on the neutral safety switch.  Over time the spring collapses and does not make contact. 

Good news: it’s cheap to fix parts wise 

bad news: the bevel gear housing that covers that switch can only be removed with the engine raised up off of the frame or the engine pulled.  

 

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Ok... after further inspection the neutral light came on when lifting shifter lever. Sensor was removed again and rotated slightly and functions properly again..whew!

 

Now just waiting for valves to arrive and top end can go back on.

Getting closer....

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That’s good but It will work intermittently so be sure it’s good.  That spring loaded pin inside the reverse cam gets week over time and it gets lazy and will only work sometimes.  It would suck if you did all this work just to have to pull the motor again.  

One of my recent posts on my bayou I had to change the reverse cam. There were some good progress photos of the old and new reverse cam differences with regard to the spring.  

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Got it back together....turned over by hand fine then by starter.

We are getting spark. Now we are cleaning carb in hope of firing this thing up.

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