400 EX Rebuild Issues

[Hailstatedogs 0]

I’ve got a 2007 400 EX I purchased from an individual several years ago and have been slowly rebuilding it.  The engine was seized up when I bought it and I found out later that several of the gears were stripped out of the transmission.  Needless to say, the engine was completely dismantled.  Replaced three gears in the transmission and crank bearings in the bottom end.  Had the crank checked out and it was surprisingly in good shape.  Took the oil pump apart, cleaned it well and made sure it functioned as it should.  Of course the cylinder was bored and a new piston and rings installed.  The timing chain didn’t look bad but replaced it anyhow.  Got the head torqued down to spec in a cross pattern.  Got it set to TDC and placed the cam lobes down toward the head with the marks on the cam sprocket set correctly.  Torqued the valve cover to spec in a cross pattern and then proceeded to replace the tappet screws.  That’s when things went bad.  Set the gaps on the intake side with no problem and then the exhaust on the left side.  Then I got to the right side and the problem showed up.  There is absolutely no play even without a tappet screw.  I pulled out all the other tappets and removed the valve cover for an inspection.  From what I can see, everything looks fine and doesn’t appear to be bent.  As soon as I tried to put the valve cover back on, the right exhaust valve clearance was completely gone by the time the valve cover bolts were hand tight.  I can take a foreman engine apart from top to bottom with no problems and have rebuilt numerous ones, but this is my first time with an overhead cam and I have absolutely no idea what could be wrong.  Guess it doesn’t help that the engine was seized when I got it so I don’t have a good baseline of what I was dealing with to start with.  Don’t know if I screwed up or if it was already in that condition.  Any help would be greatly appreciated!

[jeepwm69 7,719]

Welcome aboard!   I'm better with the newer utility engines, but I'll be @shadetree can help you out.

[shadetree 5,969]

18 hours ago, Hailstatedogs said:

I’ve got a 2007 400 EX I purchased from an individual several years ago and have been slowly rebuilding it.  The engine was seized up when I bought it and I found out later that several of the gears were stripped out of the transmission.  Needless to say, the engine was completely dismantled.  Replaced three gears in the transmission and crank bearings in the bottom end.  Had the crank checked out and it was surprisingly in good shape.  Took the oil pump apart, cleaned it well and made sure it functioned as it should.  Of course the cylinder was bored and a new piston and rings installed.  The timing chain didn’t look bad but replaced it anyhow.  Got the head torqued down to spec in a cross pattern.  Got it set to TDC and placed the cam lobes down toward the head with the marks on the cam sprocket set correctly.  Torqued the valve cover to spec in a cross pattern and then proceeded to replace the tappet screws.  That’s when things went bad.  Set the gaps on the intake side with no problem and then the exhaust on the left side.  Then I got to the right side and the problem showed up.  There is absolutely no play even without a tappet screw.  I pulled out all the other tappets and removed the valve cover for an inspection.  From what I can see, everything looks fine and doesn’t appear to be bent.  As soon as I tried to put the valve cover back on, the right exhaust valve clearance was completely gone by the time the valve cover bolts were hand tight.  I can take a foreman engine apart from top to bottom with no problems and have rebuilt numerous ones, but this is my first time with an overhead cam and I have absolutely no idea what could be wrong.  Guess it doesn’t help that the engine was seized when I got it so I don’t have a good baseline of what I was dealing with to start with.  Don’t know if I screwed up or if it was already in that condition.  Any help would be greatly appreciated!

my first thought is..did you inspect the cam lobes for any odd wear ?. did you remove the valves..and see if any of them are bent ?. did you inspect for any wear in the cam journals in the head ?. rebuilding an engine takes more than just tossing parts at it ?, YOU MUST INSPECT EVERYTHING WHEN TAKING IT APART ?,,AND PUTTING IT BACK TOGETHER !. last but not least for now..did you insspect the rocker faces on the rockers for any wear ?. take a jump back into this, then get back to us.

[Hailstatedogs 0]

Shadetree, thank you very much for the guidance.  I should’ve mentioned the valves….not sure if they needed it, but I pulled each of them out after numbering them, inspected, cleaned off the carbon buildup, and lapped them.  Valves didn’t appear to be bent.  All the springs and collets went back where they came from.  I’m obviously far from an expert, but I feel the valve train is in good shape.  However, if you think I need to reinspect them, I’ll certainly make the effort. I generally try to look for worn parts or abnormalities during tear down so I know what I may have to order, but I know there are certainly several things I could’ve missed in my inexperience.  For what it’s worth, the dowels that recess in the head just outside the cam bearings were hard to put in….especially the one on the right side.  It’s going to be several weeks before I can get back to it, but I’ll follow up with you now that I know more what I should focus on.  Thank you again for your advice!

[SlammedRanger 1,559]

When you had the head removed did you make sure the plunger and spring went in the little hole under the cam? That is part of the auto decompression mechanism. If its missing the cam will spin that piece and try to lift that valve. Thats what it sounds like to me is missing. Hopefully not dropped into the bottom end. My .02

[SlammedRanger 1,559]

[Hailstatedogs 0]

Alright, guys.  I finally found my way back to the 400ex over the weekend.  As shadetree recommended, I stepped back and carefully evaluated the assembly, existing parts, and surfaces.  Took the motor back down to the cylinder.  Evaluated the head and removed the right exhaust valve.  No hints of bending.  One of the cam journals on the head looks to have a little wear, but not sure about that translating into a problem.  I’ve included a few pics for reference.  Also checked the decompression mechanism.  Thanks for that tip!  It was there but was stuck and I had to put quite the effort into removing it.  The spring came out with no issue, however.   Got them cleaned off, placed a good coating of assembly lube, and put them back.  It functions as it should now. Decided to try something to see if I could rule out potential problems.  Had the head off the motor, installed the cam in the TDC position, and bolted the valve cover to the head with the bolts that do not extend deeper into the motor.  Was able to place the tappet screw in the same location for the right exhaust valve as all the others and got the same clearance.  Repeated the process with the head on the engine, but only with the head bolts slightly more than hand tight.  Got the same result……feeling good about things!  Pulled the cam back out, torqued the head down, replaced the cam, and started to put the valve cover on.  Got all the bolts in place and slightly more than hand tight.  Right back where I started.  The right exhaust valve has zero clearance even if I back the tappet screw all the way out.  So everything works fine up until I torque the head down.  Any ideas? As mentioned before, the engine was seized when I bought it and several of the transmission gears were completely stripped down.  Had plenty of metal to clean out of the bottom end when I pulled it apart.  The oil plug had no crush washer on it and the head on the plug was disfigured.  Could tell there was evidence the engine had been leaking oil.  Just wondering if the motor came to an abrupt stop and maybe that has something to do what’s going on?  Thank you for the advice already received and whatever you can provide at this stage.