Rebuilt 400ex top end...wtf?

[matholland]

Alright guys...I have had a few bikes/quads apart...split the cases and such. This one kinda has thrown me for a bit of a loop. I just traded for it not long ago. It needed a clutch, so I put a clutch in it. It was smoking a bit and also leaking oil out of the head...gaskets were bad I figured, every gasket on the top end. So I pulled it apart and the piston was scored up a bit but not bad...cylinder was as well, again not bad. I honed it out, mic'd it, and it was a .020 over. I bought a new piston and a gasket kit, pulled it all apart, and put it back together. Adjusted the valves as well. It has a slip on exhaust. I decided to take the airlid off and rejet it as well. Went to a 42 pilot, and went up one on the main. Got it all back together, and ran damn good. Let my buddy ride it, and he had left the choke halfway on...said it was cutting out. I said you left the choke on. It was also getting low on gas, so I filled it up and it was still not acting right. I got on it, and came back down the rd. and noticed it wasn't running as good as it was when I rode it the first time. Didn't sound quite right either...even dad mentioned something to me about it when I walked in said it didn't sound like it was running as good as it was. I noticed that oil is pretty much pouring out of what looks to be the base gasket...on the passenger side ...thats where it looks like it is all coming from. I know I am going to have to pull it back apart...but I know everything went back together right..everything torqued down correctly as well. Thoughts/suggestions?

[matholland]

Well, I know of one problem...I didn't install the oring at the bottom of the cylinder...didn't have any idea to what the big oring was for, never had one apart that needed one lol...what the heck are the little green deals that are in the gasket kit also?

[Stickman400]

Stripped threads on the passenger side bolt/bolts? Or that big O ring on the base of the cylinder like matholland said. Don't know why else oil would be coming out of that side only.

[DragonGunner]

Stripped threads on the passenger side bolt/bolts? Or that big O ring on the base of the cylinder like matholland said. Don't know why else oil would be coming out of that side only.



Other than the oil leak.....I like inline gas filters, even though there is a screen in the gas tank. You might of got some stuff into the carb. How does your plug look, try a different plug.

[Zakradu398]

Before you go taking it all apart again. Make sure it isn't the cam chain tensioner gasket leaking. I had that problem and thought it was the base gasket, really wasn't..

[01boneless]

the little green things are valve seals.

[matholland]

Can I reuse the head gasket and the valve cover gasket you think. It has like 10.mins on the motor. I know I didn't put the o ring on that's why it is leaking

[Stickman400]

You can re-use the valve cover gasket, but I'd be alittle weary of re-using the head and base gasket. When you tighten them down they form to the metal to form a seal, when you take it apart and re-use it it won't want to re-form and seal again. You can try but you may have to take it apart again to install new ones.

[matholland]

I pulled it all back apart, installed the o-ring this time, installed a new base gasket, but reused the head gasket and valve cover gasket...seems like its running how it did when I first got it back together now...doesn't appear to be leaking oil now, and it runs how it did when I first rode it and put it back together...fingers crossed now lol.

[matholland]

UPDATE:

IDK what happened this time...got it all back together, went to go actually ride it today...got about 2 miles from my house...was at a stop sign, took off and I was in 4th gear cruising maybe 1/4 throttle and it lost power....I down shifted and i hit the gas, and it didn't want to pull..so I let off and it died...had my buddy come get me...pulled it apart, didn't jump time...pulled the cylinder off, and it scored the cylinder rear bad, scored the piston up very bad, and seized the piston where it wouldn't twist...it was a ***** getting the piston and wristpin off...had to take a grinder, cut piston and half, then got it out...scored up the inside of the rod a bit...took some emery cloth to it and stuck my old wristpin in it that originall came out and it doesn't seem like its dragging any...what the heck caused this? It act like it didn't get oil or something, but there was plenty of oil in it...wasnt' even running the quad hard.

[Stickman400]

What main did you have in it anyway? Sounds like it got hot and seized up.

[matholland]

I don't think that it ran long enough to get hot enough from jetting...spark plug looked fine, 142 main and a 42 pilot...bike is stock except for airlid removed as far as mods go...I think that the rod has a little too much side to side play..and now the rod is grooved from where the wristpin seized up...it really looks like it was starving for oil for some reason...it wasn't getting rode hard nor had it got very far from the house...it was a max of 2 miles...probably more like a mile and a half, and for most of that it was 2nd/3rd gear going slow through town just creeping.

[Blodg]

It sounds to me like the piston rings were possibly installed upside down. What was the piston-to-cylinder clearance?

Or there is actually a problem with the oil getting to the head like a problem with the oil pump or oil filter installed wrong?

[matholland]

I didn't realize that the rings on these went one way...but I had the markings facing up. I don't remember off the top of my head what the piston to cylinder clearance was, and the piston is kind of cut in half now lol. I only had a ride on the oil that was in it, and I threw a new piston in it and was going to change it after a tank of gas. Filter for sure was installed correctly. I had a few hours on the quad since I originally got it, so I find it pretty hard to believe that all of a suddon after I throw a new piston in then it locks up. The only thing that changed was the cylinder was honed and a new piston was put in...the old piston wasn't bad, and didn't have much scoring at all...the whole reason for tearing it down is because it was smoking a bit...I needed to change the gaskets because it was leaking a bit of oil so I went ahead and threw a new piston in it. Don't really understand what went wrong at all...like I said I had a few hours on it prior to the rebuild.

Whats the opinions on the crank thats in it...its grooved a bit at the bottom of the wristpin hole...I took some emery cloth and smoothed it out. My buddy said he thinks there is a little too much side to side play on the crank...the crank will teeter just a bit. I haven't replaced any cranks before without them being locked up, or having up and down play, so don't really know a whole lot on that subject.