Motor ticking noise...cam decompressor?

[NacsMXer]

Hey guys, my motor has been ticking for some time now. I had Laz at GT Thunder build the motor for me a couple years ago, so it has been professionally built so to speak. New valves, new rockers, new HD cam chain, and a new HRC cam with the factory auto decompression mechanism.

I've adjusted the valves a million times to no avail. If I go to start the motor from a cold start, it will start up and be absolutely quiet. Letting it idle and warm up, there is a louder ticking in the valve cover (right side of motor) that comes out of nowhere 2-3 minutes after the cold start. I can reproduce this, it always starts 2-3 minutes after the cold start.

The fact that the ticking comes out of nowhere tells me that it's not a loose rocker, valves out of adjustment, or a bad cam chain. All those things would make the motor tick all the time. This noise sort of just "kicks on" out of nowhere....so I am thinking it may be the cam decompressor.

I've been doing some reading on thumpertalk with the XR400's, and i've read some guys having similar issues. Once they pressed the decomp mechanism off the cam, the ticking instantly went away. They said the mechanism was loose and was slapping back and forth on the cam creating the loud tick sound.

Has anybody had this problem and removed the decomp from the cam? I've had a Webcam in it before with no decomp and it ran fine, but I am wondering if I can remove it from the HRC cam just the same?

Here's a walkaround video of it. It was supposed to be an exhaust clip vid, but you can still hear the ticking. You can hear it best at 0:20-0:24.
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[dalejiw25]

The Decompressor was designed for the kick-start motor that the 400 originally was. Why a knowledgeable engine builder would put it back in a rebuild of an electric start is beyond me.

[VTredneckgames]

so why would any 400ex have it?

[dalejiw25]

The decompressor is a spring loaded dowell that rides on a seperate lobe of the stock cams only. most aftermarket cams do not have this extra lobe so it cannot be reinstalled anyways. If your cam has that lobe on it, It must be used or it won't start. If you go with an aftermarket cam without the lobe you don't need it. Just make sure you remove the spring and cam so they don't end up in your motor.

[VTredneckgames]

well will someone explain to me how the decompressor works?

To me it seems like it would always be decompressing since it works off the cam. And how does just a spring and dowel make it lose compression?

[dalejiw25]

It holds the right exhaust valve slightly open to ease starting. If it kicks back during starting, the decompressor opens the right exhaust valve to stop it. Not needed with electric start. If you've ever experienced kick back while kick-starting a bike without a decompressor you'll Appreciate what it does.

[killer400ex]

honestly mine does the same thing and i have a stage 2 hotcam, im not positive what it is but as long as i dont notice any problems or performance losses im not going to worry about it, fact is that 400ex make a stupid ammount of noise after they have been tweaked a little bit, but as long as your not noticing anything different other than the noise i wouldnt stress about it

[gtt416ex]

mine ticks like that, maybe just a little louder too. i have a stg2 hotcam and it's loud when you're on the bike. Mine has new valves, springs, guides, everything and it still ticks. i wouldn't worry about unless it gets worse;)

here's what mine sound like
<embed width="600" height="361" type="application/x-shockwave-flash" allowFullscreen="true" allowNetworking="all" wmode="transparent" src="http://static.photobucket.com/player.swf?file=http://vid276.photobucket.com/albums/kk34/crg10493/100_1239.flv">

[TRXRacer1]

Originally posted by dalejiw25
The decompressor is a spring loaded dowell that rides on a seperate lobe of the stock cams only. most aftermarket cams do not have this extra lobe so it cannot be reinstalled anyways. If your cam has that lobe on it, It must be used or it won't start. Care to try again? lol


Originally posted by NacsMXer

Has anybody had this problem and removed the decomp from the cam? I've had a Webcam in it before with no decomp and it ran fine, but I am wondering if I can remove it from the HRC cam just the same? you can remove it from the cam. Don't forget to remove the spring and plunger too. I'm with the other dude that wonders why a builder would even install it. You don't need it at all.

[NacsMXer]

Originally posted by TRXRacer1
Care to try again? lol

you can remove it from the cam. Don't forget to remove the spring and plunger too. I'm with the other dude that wonders why a builder would even install it. You don't need it at all.

Thanks for the replies everyone.

Are you positive I can just press this thing off my cam? I've also heard that you have to epoxy the oil hole in the cam shut after you do this...not sure why though. I'm don't why Laz installed it, but I hope that he installed it because it is a Honda cam and was designed to be used with the decomp and not because it is absolutely necessary with this cam.

[TRXRacer1]

I have a stripped cam in my 400 and there was no oil passage you wanted to block. The HRC cam is pretty mild. The wild cams don't use the decomp, you'll be fine. Like you said, he probably installed it because he could.

[NacsMXer]

Cool, thanks man. Looks like i'm going to be taking it off. I've been doing some more reading about this on Thumper talk. Lots of people who have had a noisy tick like this were able to make it go away completely just by removing the auto decompression off the cam. Sounds promising.

May I ask how you pressed off/on the sprocket flange off the cam in order to get the mechanism off?

[TRXRacer1]

Got a big press at work. Blocked the hub and pushed the cam out with a slug of steel. flipped it around and drove it back in after everything was gutted. There's some good info over at TT. There's some older engines over with tricks we're just needing over here.

[MtnEX]

Check mine out... and let me know what you think...


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[NacsMXer]

Originally posted by MtnEX
Check mine out... and let me know what you think...


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Oh i've heard yours, I remember back when you first posted the problem you had with it. I kinda hoped you might reply when I made this thread lol.

Did you ever get yours figured out? I'm definitely removing the junk off the cam to see if it makes a difference...I don't have anything to loose really.

[MtnEX]

Mine is the decompressor mechanism for sure.

It's been indicated by several top shelf engine pros.

And they have to be right because it started almost a year and a half ago... and it's still going fine.

My idle is a hair unstable, which is why you hear mine come and go. The RPM level fluctuates.

Fire it up and get it to clacking... then mess with your idle screw. It's engine RPM related.


You can also take the cap off the case like you would to adjust the valves and very slowly turn the engine over backwards until you hear the decompressor snap... just to make sure it's not stuck or anything.

If I keep mine, it's getting a hotcam.
No more decompressor.

[red_rider_069]

same problem here on my 400ex... i actually had a problem starting because i forgot to put the spring in behind the plunger for the decompressor
i actually put itback together last after about 4 months of research off and on, i even changed my vlaves thinking it was bent, valve guide aswell not fun costo ver 80 bucks.. any who
so when iwas swapping out he guide i saw the plunger fall out, had no idea waht it was never paid attention too it, asked my instructor at school about what the problem could be and he told me he had seen it before due to no decompressor spring, and since i makes your exhaust valve stick mine was always sticking and messing up my screw and lock nut adjustment out of spec, i went and bought a battery today happy as heck, and loud tick, started right up like a spark,, literally one touch, and i got flames coming coming out of my exhaust lol, i forgot to turn in my fuel screw and its running really rich :O.. so ima try n fix this **** tomarrow :S










Originally posted by NacsMXer
Hey guys, my motor has been ticking for some time now. I had Laz at GT Thunder build the motor for me a couple years ago, so it has been professionally built so to speak. New valves, new rockers, new HD cam chain, and a new HRC cam with the factory auto decompression mechanism.

I've adjusted the valves a million times to no avail. If I go to start the motor from a cold start, it will start up and be absolutely quiet. Letting it idle and warm up, there is a louder ticking in the valve cover (right side of motor) that comes out of nowhere 2-3 minutes after the cold start. I can reproduce this, it always starts 2-3 minutes after the cold start.

The fact that the ticking comes out of nowhere tells me that it's not a loose rocker, valves out of adjustment, or a bad cam chain. All those things would make the motor tick all the time. This noise sort of just "kicks on" out of nowhere....so I am thinking it may be the cam decompressor.

I've been doing some reading on thumpertalk with the XR400's, and i've read some guys having similar issues. Once they pressed the decomp mechanism off the cam, the ticking instantly went away. They said the mechanism was loose and was slapping back and forth on the cam creating the loud tick sound.

Has anybody had this problem and removed the decomp from the cam? I've had a Webcam in it before with no decomp and it ran fine, but I am wondering if I can remove it from the HRC cam just the same?

Here's a walkaround video of it. It was supposed to be an exhaust clip vid, but you can still hear the ticking. You can hear it best at 0:20-0:24.
<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/qfN6ZbCBUDo&hl=en&fs=1&"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/qfN6ZbCBUDo&hl=en&fs=1&" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="425" height="344"></embed></object>

[red_rider_069]

i have the same exact noise, and you know i noticed it after the first time i ever took the cams off my bike, and re-installed, and in that video you have posted i have the same "EXACT" noise you do, but only mines contant it does not go away .. and its anoying,,



HAS ANY ONE RODE THERE BIKE WITH SUCH A LOUD TICK? RUNNING GOOD AND ALL??? LITTLE INFO PLEASE :(








Originally posted by MtnEX
Check mine out... and let me know what you think...


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[red_rider_069]

HEY NACMXER.. you should try to get a sticky for taking off the decomp on the cam, with pros/cons of taking it off.. i'd help ya, and i am thinking about taking it off as well

[MtnEX]

Originally posted by red_rider_069
i have the same exact noise, and you know i noticed it after the first time i ever took the cams off my bike, and re-installed, and in that video you have posted i have the same "EXACT" noise you do, but only mines contant it does not go away .. and its anoying,,



HAS ANY ONE RODE THERE BIKE WITH SUCH A LOUD TICK? RUNNING GOOD AND ALL??? LITTLE INFO PLEASE :(

Been riding mine that way for over a year.
Nothing has happened.

If I get my idle right, I don't hear it.
But I need carb work to stabilize better.

See if you can adjust it away with the idle screw.

[red_rider_069]

Originally posted by MtnEX
Been riding mine that way for over a year.
Nothing has happened.

If I get my idle right, I don't hear it.
But I need carb work to stabilize better.

See if you can adjust it away with the idle screw.

hmm i'll try that tomarrow
IM A MMI STUDENT HERE IN PHOENIX AZ
so yea

[MtnEX]

Originally posted by red_rider_069
same problem here on my 400ex... i actually had a problem starting because i forgot to put the spring in behind the plunger for the decompressor
i actually put itback together last after about 4 months of research off and on, i even changed my vlaves thinking it was bent, valve guide aswell not fun costo ver 80 bucks.. any who
so when iwas swapping out he guide i saw the plunger fall out, had no idea waht it was never paid attention too it, asked my instructor at school about what the problem could be and he told me he had seen it before due to no decompressor spring, and since i makes your exhaust valve stick mine was always sticking and messing up my screw and lock nut adjustment out of spec, i went and bought a battery today happy as heck, and loud tick, started right up like a spark,, literally one touch, and i got flames coming coming out of my exhaust lol, i forgot to turn in my fuel screw and its running really rich :O.. so ima try n fix this **** tomarrow :S

If I could understand "HOW" this thing works mechanically.... well then I could rationalize what would cause it to make noise.


Could you shed some light on that?


Or what conditions would cause this NOISE?

[red_rider_069]

Originally posted by MtnEX
If I could understand "HOW" this thing works mechanically.... well then I could rationalize what would cause it to make noise.


Could you shed some light on that?


Or what conditions would cause this NOISE?
well im not sure how it works lol i jsut know what it does, so since i didnt have the spring behind the plunger it made the decompressor on the cam always spin, with the plunger un-engaged the decompressor is constantly working, so this caused my right exaust valve to continuiosly be jumping to decompress.. get it? the plunger stops the so called "decompressor" lobe from spinning, if it spins it works as a second lobe on that valve? im not sure if i explained my self enough

[MtnEX]

Humm...

So if it's making the noise, it's lifting the valve?

[red_rider_069]

Originally posted by MtnEX
Humm...

So if it's making the noise, it's lifting the valve?
yup it causes you valve to float and tick, but the thing is that doesn't mean that this is the exact reason why its ticking.. the ticking could be somthing else, i jsut have a really loud tick like yours

only reason i found out it was that valve was because i could see that valve floating, i took off tank and caps and ran it with aux fuel bottle.. umm i drew a picture of how it works let me post it here really quick

[red_rider_069]

Ok look, when the plunger is riding on the cam it keeps the decompressor from spinning,

when the plunger is off the cam it spins acting as a secondary lobe which temporarily hold open the exhaust valve, when the engine reaching certain RPM it engages again and keeps the lobe from spinning, heres a pic i made with a sharpie check it out

http://i281.photobucket.com/albums/kk220/red_rider_069/spring.jpg

[MtnEX]

Ahhh... and that is why it is idle speed sensitive then huh?

[red_rider_069]

Originally posted by MtnEX
Ahhh... and that is why it is idle speed sensitive then huh? ehh well the thing is i dont know exacly why it would be speed sensitive, like i said all i know is what it does, i dont know how it trips the plunger to go down and let it spin free.. but some how it does


does my drawing make any sence?

[MtnEX]

Originally posted by red_rider_069
ehh well the thing is i dont know exacly why it would be speed sensitive, like i said all i know is what it does, i dont know how it trips the plunger to go down and let it spin free.. but some how it does


does my drawing make any sence?

Yes it sure does.

THANKS.

[red_rider_069]

Originally posted by MtnEX
Yes it sure does.

THANKS.
glad i could help

[dubee]

How do you keep it in time when you go to press it back together?? is it splinned? or maybe a key?? i dunno.

[08ex4]

your ticking isn't near as bad as some i've heard honestly i wouldnt worry about it. as far as the decompression plunger you dont need it even with the stock cam. my 08 doesnt have it in there cause i lost it but its starts every time i did notice that it works the starter a little harder but it is what it is. if that plunger is what is making the noise just take it out its easy.

[NacsMXer]

Originally posted by dubee
How do you keep it in time when you go to press it back together?? is it splinned? or maybe a key?? i dunno.

The camshaft sprocket flange and the cam can only go back together one way due to the splines on the cam. There's like one spline on the top that is wider than all the rest. Pretty much dummy-proof.

And 08ex4, I agree the ticking isn't that bad, but it still bothers me lol. On a cold start my engine is all nice and quiet then about 2-3 minutes in, the ticking starts out of nowhere and really bugs me. It can actually get quite loud after a hard day of riding too.

I'm going to open up the motor soon and get the cam out so I can get at it. Just haven't had the time lately.

[dubee]

My 07 ex was ticking like that too,but i didnt have a press or want to give a weekend up of riding. So i just grinded the extra nub off the right side exhaust rocker arm and i have no more loud ticking at all.