[EliteEX]

Ive got a problem with my 400ex and need some professional advise. Sorry about the long post but there is a lot of small details that may give more hints on what the problems may be.

I bought it with a head gasket leak so i tore it down to replace it. When i had it apart i noticed some abnormal wear on the piston and slight scoring on the cylinder(figured the previous owner ran it low in oil). So i honed the cylinder and replace piston, pin, and rings with new oem. While i had it apart i also cleaned out the screens in the oil cooler and in the bottom of the engine. I then replace oil filter and filled with honda oem oil(It did seem to take slightly more oil than normal but i didnt think much of it since i had the oil cooler and side case off to clean out the screens).

Started it up and it ran great. Did about 8 heat cycles and some mild riding on it and then checked the compression which was around 120. Then i rode it fairly hard for a while till i noticed some smoke coming from the pipe and a very slight abnormal knock/ping while under load (the smoke continued seep out of the pipe for a while after i shut it off. It was a used pipe i just bought and put on, maybe it had some oil residue inside and was just burning out).

After it cooled off i removed the valve cover with intentions of getting a look at the cylinder but then decided to do another compression test before tearing down. So put the valve cover back on and tightened a few of the 6m bolts, did the compression test and at around 50 psi the engine seized. Took the cover off the side case and tried to spin the engine backwards, and it broke loose fairly easily. I tried to continue spinning it counter clockwise, and after a bit it got tight again. I pulled the valve cover off and the found the timing chain was tight all the way around (with tentioner in). Then i pulled the tenioner out and whenever the engine would get tight the timing chain work get tense the entire way around. (Tentioner seems to be working correctly)

Ended up pulling the head and cylinder off and found some fresh scores in the cylinder(much worse than the previous scores). The top of the piston also had a thin layer of black residue in the center.

At this point im stuck and need some professional input on whats wrong. If your feeling extra helpful and dont want the confusion of commenting below please send me a pm ...thx

 

[EliteEX]

Im by no means a professional. I took small engine classes in high school, but that only teaches so much. Your right i never took the cylinder to a machine shop, although now im wishing i would have.... I did take measurements of the cylinder and I thought it met all the specs i found in the manual, but again im not a professional. What would have cause the engine to seize during the most recent compression test and not at any other time?

 

[EliteEX]

So any ideas on what to do for the rebuild? I want something fairly budget friendly, but at the same time while im doing it i want to put something that makes good power in it. Ive heard bad things about 440 kits and heard better things about stroker kits but know very little about them.

 

[EliteEX]

Did you scrub the cylinder in hot, soapy water after honing it? Really work at it scrubbing and scrubbing...?[/QUOTE]

I cleaned it up in my parts cleaner....figured that would be just as good....?

 

[EliteEX]

Did you scrub the cylinder in hot, soapy water after honing it? Really work at it scrubbing and scrubbing...?

I cleaned it up in my parts cleaner....figured that would be just as good....?

Nope, not much difference than if you didn't clean it out at all. After machining and honing the bore is loaded with grit. The amount of grit in there that the bore holds can amaze you... You have to use HOT, Soapy water and scrub until you can't stand it anymore. Then rinse, dry with cloth and test your work with a clean white paper towel or cotton cloth with a bit of fresh motor oil on it. Rub the oil in really good then look at your wipe. If that wipe is not PERFECTLY clean you gotta mix up some more fresh HOT, Soapy water and scrub it some more! Oil it well once it is clean.

The amount of grit in there that the bore can hold after machining can truly amaze you... Failure to get it all out = early or immediate topend failure. This cannot be underestimated...

Thats good to know, i thought i cleaned it pretty well, but im usually one to go the second mile.

 

[EliteEX]

Im still having a hard time trouble shooting all this stuff...I dont want to just go and put a 416 kit in it when there could be other causes or problems. Im getting a measurement of 85.00 and 84.95 at the base of the cylinder. Shouldn't the piston made a fairly noticeable knock if the cylinder was bad enough to cause damage?

 

[EliteEX]

Also should the piston be able to rock side to side on the connecting rod? I cant feel any up and down play, but side to side seems kinda odd. Im wondering if maybe the oil pump is weak causing poor lubrication....?

 

[EliteEX]

You said earlier that the motor turns over freely for a bit then gets tight. You mentioned the chain getting tight all the way around the sprockets when the motor became tight. Did you put a new chain in the motor recently? On the old sprockets? At this point I would want to know whether the oil pump is working or not too... maybe you can get to it? Any chance you put the oil filter in backwards?

I haven't replaced the t-chain and as far as i know it never has been. Im 99.9% sure i put the filter in correctly, although even after dozens of oil changes im sure i could make a mistake at some point

 

[EliteEX]

I just re-read this thread and you mentioned having the side cover off to clean screens etc. Was there a reason for that? Crankcase have junk in it? Someone sink the motor? When you put the side cover back on, did anything get left out of there or did anything fall out of place (an o-ring, washer, oil pipe etc) as you were working? For some reason I have a sneaking suspicion that your motor wasn't getting any oil pressure...

The only reason i had the cover off was to check that screen. Figured while i had it apart for the piston i would check and clean both of the screens. They did have a nice collection of (im assuming) clutch material caught in them..... I keep my work bench as clean as possible so i should have noticed if any thing fell out while i had the cover off.

 

[EliteEX]

Heres a picture of the piston, thought maybe it might help....?

 

[EliteEX]

That piston hasn't been in there very long... and its getting chewed up. A few questions if I may...?

Was the top end under the rocker cover looking like it was getting lots of clean oil when you took it apart this time? Any discoloration on the cam or rockers from friction or heat? Any scratches on the cam lobes?

Is there any discoloration of the steel connecting rod at either end of it where it meets the wrist pin and lower bearing? No signs of high heat there?

How much wear is their left in the timing chain? Push the tensioner against the guide where it belongs and note the gap distance between the tensioner and cylinder.

Can you take a photo of the piston from the side so that we can see the ring set? Also a photo of the piston crown and combustion chamber?

Measure the piston-to-cylinder clearance and tell us what it is. Slide feeler gauges carefully between the piston skirt at its largest point (90 degrees from the end of the wrist pin) and the cylinder bore, while the piston is halfway down its normal stroke distance from the top. Start with a narrow feeler gauge and work your way up to thicker sizes until the fit feels snug and looks tight.

Careful, don't drop anything... fragile stuff.

Thanks,

Heres most of the pictures you asked for. The cylinder is currently apart so i cant get some of the specs and I dont have the time or space to assemble it tonight. Two things i noticed that i thought was odd while taking the pictures.... In the one picture it shows the rings with the gaps lined up, Im sure i had them spread out correctly... i guess they could have gotten spun since the disassembly. The other thing i noticed...i dont recall the weights on the crank being that blue the last time i had it apart.

 

[EliteEX]

Here some of them

 

[EliteEX]

And some more

 

[EliteEX]

And some more...

 

[EliteEX]

And some more....

 

[EliteEX]

Last one....

 

[EliteEX]

Yikes! Those rocker arms dont look healthy! I think you topend isnt getting oiled properly. The cam bearing journals look completely normal. Could explain your topend seizure. I would be pulling that oil pump and measuring and inspecting everything!

As soon as i have time ill pull the oil pump and update you guys. Which part do you think caused the seize? Considering it only seized at certain points of rotation....after turning the crankshaft about half turn either way it would get tight.

 

[EliteEX]

I had a hunch that putting the valve cover back without having it set at tdc caused the seizure. What would cause the timing chain to get tight the whole way around whenever the the engine got tight (even after taking the tentioner our)? I thought only only the side of the chain that was holding the load would get tight.
Ill try and get some specs as soon as i finish up some other projects and make space to work.
Thanks for everyones help so far.

 

[EliteEX]

A thought i just had..... Would a weak oil pump cause oil in the motor to transfer over to the oil tank at a slower rate? If so that would explain why after adding 2.5 quarts of oil over a period of time and doing the run, sit, and check method for checking oil, the oil still didn't seem to show up on the dipstick.

 

[EliteEX]

Well now it makes sense why it locked up! Pull the bottom end out of the frame tonight and found this little guy sitting in the bottom of the engine next to the timing chain.... Must have fallen out when i pulled the valve cover and i never noticed it! Finally some progress.... :icon_ banana: