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View Full Version : 400ex timing, valve adjustment, and decompression clutch questions



02CR500Rex
09-16-2007, 07:41 PM
Alright, I've got my engine back together after a rebuild...been having some problems, but I've now got it to fire, but it won't start. I got it to *kinda* hit one time with ether, but no start.

I'm going to ask some 3 quick questions, for those who don't feel like reading a lot. For those who do, I've got an explaination for each question below.

1.) do the timing marks on the the cam gear have to be EXACTLY parallel with the head? Or can one be a hair below and one be a hair above?

2.) if the decompressor pin would happen to "fall" out of the head (onto a towel I had laying underneath the head) is it possible that the spring would stay inside the head? When I moved the head I immediately saw the pin laying there, but no spring.

3.) Hypothetically speaking, if the cam timing marks don't have to be EXACTLY parallel with the head, and the spring would have happened to stay in the head, what's the proper procedure for setting valve clearance? I have a Haynes manual and followed it pretty well, but it's not very clear.

here are some things I'm going to note, and wondering if any of these could be my problem.

1.) I put the piston to TDC with the "T" mark lined up with the lower timing mark. I installed the camshaft pulley, but the timing marks wouldn't EXACTLY line up with the head. They were pretty close, but the left mark was slightly below the head and the right mark was slightly higher. Left > _ I _ < Right. I know you guys aren't dumb, but I'm just letting you know which way I was looking at the cam gear. Anyway, rotate the above image approx. 2 degrees counterclockwise and you'll see how it looked. I tried a tooth forward and it was WAY out of time. Anyway, I figured those marks were just for a close reference as it looked like the head was actually slanted and the marks were running level.

ok 2.) I had the head upside down cleaning the carbon out of the chamber and when I flipped it over, I saw a little pin looking thing. I stuck it back down where I'd seen it before, below the decompression piece on the cam. I didn't know what it was at the time, but I do now. There was no spring laying with it...if there had been I would have known to stick it in below this pin, but I just thought it was an oil passage or something. Also, the decompressor "thing" on the cam had wore a groove into the head...it didn't turn backward or anything and I didn't see where it was going to hurt anything, so I stuck it back together. I figured that it was a decompressor, but also figured it was inoperable, like maybe Honda continued to use the same cam that the kickstart 400's and the motorcycles used. Anyway, hindsight is 20/20.

3.) I put the valve cover back on, and checked the valve clearance. the 2 intake valves seemed to be good. I used a .005 i believe, but the feeler gauges were straight...flimsy enough that I thought they could accurately measure the clearance, but I'm not sure. I had a little trouble getting the .004 into the exhaust valves...had to bend the feeler gauge to approx. a 35 degree angle...broke it twice, but finally got it to stay bent and I believe it to be able to accurately read the clearance. The left exhaust valve (looking at the engine from the back) had very little play in it. It hung up the feeler gauge. I adjusted it out and checked the right exhaust valve. It seemed to be alright in my opinion. This was the first time I had ever attempted to adjust valves.



Guess all that's left to do is remove the decompressor pin and the decompressor clutch from the cam, try to fix the timing, and adjust the valves once again. Just trying to figure out if I MIGHT possibly be able to get away with only adjusting the valves.

Thanks ahead of time for any advice or help.

Paul

dariusld
09-16-2007, 07:54 PM
Sorry if you said this, but is it the stock cam?

02CR500Rex
09-16-2007, 07:56 PM
yep, it's the stocker?

zrpilot
09-16-2007, 08:02 PM
Originally posted by 02CR500Rex
[B]



1.) do the timing marks on the the cam gear have to be EXACTLY parallel with the head? Or can one be a hair below and one be a hair above?

1.) I put the piston to TDC with the "T" mark lined up with the lower timing mark. I installed the camshaft pulley, but the timing marks wouldn't EXACTLY line up with the head. They were pretty close, but the left mark was slightly below the head and the right mark was slightly higher. Left > _ I _ < Right. I know you guys aren't dumb, but I'm just letting you know which way I was looking at the cam gear. Anyway, rotate the above image approx. 2 degrees counterclockwise and you'll see how it looked. I tried a tooth forward and it was WAY out of time. Anyway, I figured those marks were just for a close reference as it looked like the head was actually slanted and the marks were running level.


I don't think this is a problem, but it is hard to verify without being there.



Originally posted by 02CR500Rex

2.) if the decompressor pin would happen to "fall" out of the head (onto a towel I had laying underneath the head) is it possible that the spring would stay inside the head? When I moved the head I immediately saw the pin laying there, but no spring.
2.) I had the head upside down cleaning the carbon out of the chamber and when I flipped it over, I saw a little pin looking thing. I stuck it back down where I'd seen it before, below the decompression piece on the cam. I didn't know what it was at the time, but I do now. There was no spring laying with it...if there had been I would have known to stick it in below this pin, but I just thought it was an oil passage or something. Also, the decompressor "thing" on the cam had wore a groove into the head...it didn't turn backward or anything and I didn't see where it was going to hurt anything, so I stuck it back together. I figured that it was a decompressor, but also figured it was inoperable, like maybe Honda continued to use the same cam that the kickstart 400's and the motorcycles used. Anyway, hindsight is 20/20.




Guess all that's left to do is remove the decompressor pin and the decompressor clutch from the cam, try to fix the timing, and adjust the valves once again. Just trying to figure out if I MIGHT possibly be able to get away with only adjusting the valves.


This is Exactly what I would do!

Go back and check everything over.

02CR500Rex
09-16-2007, 08:09 PM
Originally posted by zrpilot
[B]

I don't think this is a problem, but it is hard to verify without being there.




This is Exactly what I would do!

Go back and check everything over.


Well, I really didn't want to hear that but lol just kidding. It's not that big of a deal, I just want to be done with this bike already! it's been down for a month. I've been working on it for 2 weeks (ordering parts, waiting, working on it, etc.) Just want the nightmare to end :( lol thanks for the replies. Hopefully I'll get it running tomorrow.

Any suggestions on adjusting the valve clearance? I use to have a set of feelers with bent ends, but no more. Only straight ones. Can I accurately adjust the valves this way?

Also, I don't have the exhaust on it yet, and when it's cranking over it sounds like...well kinda like a drop of water every time the exhaust valves open. Is this normal?

zrpilot
09-16-2007, 08:42 PM
I had to cut and bend my feeler gauges until I bought a set of Motion Pro gauges.

Did you try to run this thing with the exhaust system on? Cause if not, that would make a difference.

zrpilot
09-16-2007, 08:47 PM
Originally posted by zrpilot
Motion Pro gauges.

GPracer2500
09-16-2007, 09:12 PM
When you put the decomp plunger back in the hole in the head do you recall if it felt like there was a spring down there? Did the plunger just drop in with a clunk or ? If that spring isn't behind the plunger then that's likely why your engine won't start. That plunger is actually part of the reverse decomp function. The decomp mechanism actually does two things: 1) It holds one of the exhaust valves open (just a smidgen) until about 600rpm to aid starting AND 2) there is a separate lobe that works with the one way bearing in the mechanism to open that same exhaust valve if the engine spins backwards. This second function is a vestigial remnant from when this engine was used in the kickstarting XR400R.

If that plunger isn't being held up by the spring then there's nothing to prevent the reverse decomp lobe from spinning freely with the cam. Normally the plunger stops it and the reverse decomp lobe will only spin with the cam when it's spinning in the wrong direction (because of the one way bearing).

Kind of confusing, I know. But the point is without that spring and plunger doing it's job like it's suppose to, the engine will behave just like you described. It will spin over freely and act like it wants to start. But it never will because the reverse decomp lobe keeps knocking an exhaust valve open when it should be shut. The strange sound your hearing coming out of the exhaust port is related to this, I'd bet.


It's not unusual for the cam sprocket marks to not line up exactly. They should be very close but don't worry if they are off a smidge.


Pretty sure there's a how-to around here somewhere with pictures and text describing how to adjust the valves. The short version is:

1) Set piston at TDC on the compression stroke. You'll know your on the compression stroke TDC and not exhaust stroke TDC because all the valves will be completely closed on the compression stroke. Only spin the engine counterclockwise. Spinning it the other direction won't cause damage but it will activate that pesky reverse decomp cam. If you miss your mark, go all the way back around twice to get back to the same stroke you were on before.

2) Slide feeler gauge between the adjusting screw and sub-rocker arm. Adjust the screw by loosening the locknut, turning the screw, and retightening the locknut. Check the clearance again to confirm it's where you want it.

As mentioned, you have to bend the ends of most feeler gauge sets to get them to fit.

02CR500Rex
09-16-2007, 10:56 PM
zrpilot, I think I'm gonna hack up the set I have for now, but I'm gonna definitely invest in a set of those gauges for the next adjustment.

GPRacer, thanks for the detailed explaination. And to answer your question, no, it didn't feel like there was a spring in it at all; the plunger just dropped into place. but when I took the cam out of it in the first place, it didn't seem like there was a spring in it? The plunger stayed in the head...flush with the head for over a week of me moving it around. Should it have sprung up once the cam was removed? I tackled the bottom end first, and when I finally got around to pulling the valves to put new seals in and clean up the chamber...I had the head upside down and the plunger fell out. When I went to flip it back over, I noticed the plunger and no spring? And, I'm wondering why the decompressor wore a groove in the head...hmmm.. I dunno...but I searched the site for "decompressor" and I saw a couple posts that said I can remove it...might as well do that rather than order a new spring from honda eh? I mean the aftermarket cams don't have one anyway and I don't believe my crank will be rotating backwards...unless I park it on a steep hill in 5th or something.

If it won't hurt anything, I'm going to remove the decompressor and pin tomorrow? Then adjust the valves and hopefully that cures my problem.

Oh, and thanks again for the explaination of how this mechanism works...and for the clarification on the timing marks...and the quick write-up on valve adjustment. I'll post back and let ya guys know if she runs tomorrow.

Paul

GPracer2500
09-16-2007, 11:21 PM
With the spring in place the plunger should stick out of the hole. Without the spring it won't.

Removing the decomp mechanism is one way to go. The 400EX starting system is robust and I've never heard a peep of complaint from anyone who runs a cam without one (LOTS of folks).

02CR500Rex
09-17-2007, 04:22 PM
Well, my damn crap luck. I pulled the valve cover, pulled the cam, sure enough no spring below the plunger, so I remove it. Call a friend, get a ride to the machine shop (because my license is suspended and the 400 is my means of transportation). Well, I show the redneck machinist my cam...he says he thinks the ears might break off the hub...I tell him to go for it. He does...I remove all the stuff from the cam and put it in a zip lock baggy. He proceeds to press the hub back onto the end of the cam, charges me $5, and I head home. I get there, my buddy leaves, I look at the cam...the hub is pressed on one tooth back. One of the small teeth on the hub dug a groove in the wide tooth on the cam, and the small groove beside it had a blank groove (where the wide groove was supposed to be sitting).

Well I had no way back to the machine shop tonight, so I scope the cam, looks like if I turn the cam gear 1 tooth clockwise it will be where it needs to be...I do so, adjust the valves, try to start it, it kinda fires but won't start. Shot some ether to it, starts and runs til the ether is gone with the throttle almost wide open...I tried choking, etc.

I guess I'm gonna just have to take the cam back and have him re-do his mess up. I was thinking possibly I could make up for it by adjusting the valves, but I'd say it's a little too far out...I mean it's not bad, but, it's not right either. Oh well...maybe tomorrow

gojk
09-17-2007, 11:42 PM
Just a little more info.

When the cam marks didn't line up exactly with the head on mine, it was because the cam chain was stretched too far and the cam chain adjuster was bottomed out. You may want to verify that the cam chain adjuster does indeed tighten the cam chain when you release it, and that is also has a little more to go on the adjuster before it bottoms out.

02CR500Rex
09-18-2007, 09:00 AM
Originally posted by gojk
Just a little more info.

When the cam marks didn't line up exactly with the head on mine, it was because the cam chain was stretched too far and the cam chain adjuster was bottomed out. You may want to verify that the cam chain adjuster does indeed tighten the cam chain when you release it, and that is also has a little more to go on the adjuster before it bottoms out.

Hey, thanks for the info. That's how it was when I put the engine back together. I pulled it apart yesterday to remove the cam and the cam marks lined up. I think I accidentally tightened the chain tensioner. I let it go until it quit turning on it's own and gave it an extra twist.