decompression thing [Archive]

justin1022

07-30-2008, 09:49 PM

Originally posted by fastredrider44
Not sure if it would cause it to knock or not, but the "decompression thing" is a dowel pin on a spring that goes in a recessed hole in the head that rides on a seperate lobe on a stock cam. Highly doubt it would ever cause a knock. I'd start by adjusting your valves, but then again, they usually have more of a "tick" sound.

hey i got a hot cams stage 2 and lost that little spring wile doing a rebuild can i just pul that doul out and run without the decompression?

blue_ex_rider

07-30-2008, 10:10 PM

You can run it with out the decompressioner

justin1022

07-30-2008, 10:15 PM

Originally posted by blue_ex_rider
You can run it with out the decompressioner

ok thanks i was really scared about it and wasnt sure so its that little doul right and then there is a little spring under it right? if so i lost that little spring..

blue_ex_rider

07-30-2008, 10:20 PM

I DONT THINK HOTCAMS HAS THE DECOMPRESION RELEASE ON THE CAM

justin1022

07-30-2008, 10:35 PM

Originally posted by blue_ex_rider
I DONT THINK HOTCAMS HAS THE DECOMPRESION RELEASE ON THE CAM

ha now that you mension it it dosnt i remeber looking at that because the cams look very diffrent one it thin and the other one all placked up with junk

rideracelivemx7

07-31-2008, 12:10 AM

aftermarket cams dont use the decompression mechanism, you have to remove the pin and spring as instructed in the directions.

400exrider707

07-31-2008, 08:58 AM

Exactly the aftermarket cams do not use the mechanism on the stock cam. You can have it pressed off and pressed on the new cam, but there is no need. If you ever put the stock cam back in, you either need to press off that mechanism or if you do keep it on, you need that spring and dowel or it will never start.:blah:

justin1022

07-31-2008, 11:03 PM

Originally posted by 400exrider707
Exactly the aftermarket cams do not use the mechanism on the stock cam. You can have it pressed off and pressed on the new cam, but there is no need. If you ever put the stock cam back in, you either need to press off that mechanism or if you do keep it on, you need that spring and dowel or it will never start.:blah:

thanks i just wasnt sure because someone told me eve nwith the afteramrket cam it has to be in there or it wont close or somthing but if you really think if it that dont make much sence and i never read the instructions ha my freind put it in fast because we wanted t ogo rideing and i didnt no how to its crazy that was only about a month ago and now im already into the eingein and thats 10 tims harder then swaping a cam ha

TRX_450

08-17-2008, 10:43 AM

ive got a stage 2 hotcams and left mine in. do you have to remove it?

justin1022

08-17-2008, 05:14 PM

Originally posted by TRX_450
ive got a stage 2 hotcams and left mine in. do you have to remove it?

i tihnk you dont have to it wont get touched if you dont got the decomresion lop pressed on your cam.. i left mine in for like a month with my hot cams and it didnt do anything weird.

MtnEX

08-18-2008, 12:18 AM

Originally posted by 97WarriorRider
yes that "decompression thing can cause a knock/ticking. to see if thats what s causing it you can take your valve covers off and make sure your quad is at TDC on the compression stroke. Once you get this far try to wiggle the rockers. If the right exhaust valve doesnt move its more than likely the decompressor sticking.

I have this problem too... (singular sounding knock/tap)

Could you please be way more specific about the amount and type of "play" I should see in the rockers???

This was the one thing I had the most issue with when I checked my valves. The first time I lined up my timing mark, I could swear I had no movement at all in the right exhaust rocker.

I turned the motor over a few times, and I swear it seemed like I could only ease in one way to the timing mark. When I went to turn it over again, the engine would really spring on around a long ways.

Anyways, I got it lined up where all the rockers seemed to have a very small movement to them. I believe just the lash gap of .004 and .005. They were spot-on with the feeler guages... I didn't change a thing.

400exrider707

08-18-2008, 12:10 PM

Originally posted by TRX_450
ive got a stage 2 hotcams and left mine in. do you have to remove it?

You left the spring and the dowel in the head with a cam swap?

TAKE IT OUT NOW!!!

If you dont take it out, it will fall into the bottom end of the motor. I dont think I need to tell you how bad this is!

justin1022

08-18-2008, 01:58 PM

Originally posted by 400exrider707
You left the spring and the dowel in the head with a cam swap?

TAKE IT OUT NOW!!!

If you dont take it out, it will fall into the bottom end of the motor. I dont think I need to tell you how bad this is!

may i assk how it will fall down there? i am not saying your wrong or anything i am just wanting to learn somthing new. mine is out now. i dont no about the other guys though.

onebad440

08-18-2008, 02:33 PM

When I took my top end apart. The sping and pin was left in there with a stage 2 hot cam from the previous owner. I thought the same thing "Holly **** that would have been bad". But after I looked at it further, the pin can't come out because of the clearance to the cam. Dont know why it was left in there though!?!? Took mine out when it got put back together and havent had any problems.

MtnEX

08-18-2008, 04:42 PM

What does this noise "SOUND" like?

bugsy

08-18-2008, 05:05 PM

The noise is a loud knock from the top end of the motor. It seems worse at idle. When i give it some R.P.M.'s it seem to go away. Still haven't figured it out yet.

justin1022

08-18-2008, 05:13 PM

Originally posted by bugsy
The noise is a loud knock from the top end of the motor. It seems worse at idle. When i give it some R.P.M.'s it seem to go away. Still haven't figured it out yet.

if it wasnt described as a "knock" i would guess the valves are out of time a little bit or the decompression is sticking other thenthat i wouldnt have a clue.

MtnEX

08-19-2008, 04:38 PM

I did the wooden stethescope test on mine.

It's remarkable what you can hear that way.
But I still was not able to pinpoint the spot of the noise.

Pretty frustrating considering I could even hear fine details like the timing chain.

MtnEX

08-20-2008, 08:14 PM

How would the decompressor make this noise and not damage the engine?

I guess I really just don't understand how it works.

Would the noise come from the top right side?

justin1022

08-20-2008, 09:01 PM

Originally posted by MtnEX
How would the decompressor make this noise and not damage the engine?

I guess I really just don't understand how it works.

Would the noise come from the top right side?

i no about as much as you about the decompression. but i read in my book on my 400ex if you pull that cap to rotate the engine to tdc you can take the ratchet and go rapidly back and forth and it is suppost to break the decompression loose you should try this and if the knock goes away then you no what the problem is.

Mellow Yellow

08-21-2008, 09:09 AM

justin1022

08-21-2008, 10:22 AM

Originally posted by Mellow Yellow
Is this true??? I've read several times not to rotate clockwise. I've got a tap I'm trying to get rid of too!

i read that to but this isnt rotating its just kind of jerking ot back and forth you no.

bugsy

08-21-2008, 03:46 PM

My knock definitly seems to be on the top right side. I tried the setting to t.d.c. and then turning engine back and forth sharply but the knock is still there. Guess i'm going to have to pull the top off to see.

MtnEX

08-21-2008, 07:37 PM

Originally posted by bugsy
My knock definitly seems to be on the top right side. I tried the setting to t.d.c. and then turning engine back and forth sharply but the knock is still there. Guess i'm going to have to pull the top off to see.

I'm trying to figure out how to reset the cam chain tensioner and adjust it... if possible from outside. This would be worth trying before going in.

If you go in before then, do check the chain and tensioner.

I'm thinking it's possible the chain could be clacking from slack or clacking on something... like if the tensioner is plastic coated metal and the metal is worn away...

jeepthing07

08-21-2008, 07:48 PM

I hate to jack a thread but what exactly is the decompression for on the cam? Since aftermarket cams don't have it why did honda put it on?

On my Kawasaki bayou 300 it has a compression release lever so you can pull start it easier but i don't get the point of the EX having one.

Anyways im rebuilding my motor and i plan to break the rings in on the old cam then stick a stage 2 hotcam in it. So while its apart i removed the decompression lobe off the factory cam and toss it in the trash. Soooooooo now the spring and pin in the head is gone and i pressed the mechanism off the cam im good to go right?

MtnEX

08-22-2008, 02:08 AM

Originally posted by justin1022
i no about as much as you about the decompression. but i read in my book on my 400ex if you pull that cap to rotate the engine to tdc you can take the ratchet and go rapidly back and forth and it is suppost to break the decompression loose you should try this and if the knock goes away then you no what the problem is.

Originally posted by Mellow Yellow
Is this true??? I've read several times not to rotate clockwise. I've got a tap I'm trying to get rid of too!

Originally posted by bugsy
My knock definitly seems to be on the top right side. I tried the setting to t.d.c. and then turning engine back and forth sharply but the knock is still there. Guess i'm going to have to pull the top off to see.

Well boys... I'll be able to tell you the truth of the matter during daylight hours sometime later today.

I said the heck with it... I wanted to see if I could see any part of it working after extensive study of the top end disassembly/assembly.

Sooooo.... what I did was, with the spark plug out, I very slowly and carefully turned the motor over backwards and kept turning until I saw the decompressor clutch on the camshaft snap/lash. Then I turned the motor several revolutions in the proper direction. Then I repeated the whole process a second time.

With that said, as I was in deep thought with the diagrams I drifted back in thought to where this noise started for me... after an oil change.

If you have ever lifted your bike and stood it on it's rear bumper by yourself, you did it in gear.... I did it to remove my skid for an easy oil change.... but if you didn't switch to neutral or pull in the clutch to push the bike down.... well you have turned your engine over backwards already.... I have, so....

Anyways, in a few hours we'll see if this helped anything...

And if it was a really really bad thing to do, then I've been the village idot for everyone else.

justin1022

08-22-2008, 10:34 AM

Originally posted by MtnEX
Well boys... I'll be able to tell you the truth of the matter during daylight hours sometime later today.

I said the heck with it... I wanted to see if I could see any part of it working after extensive study of the top end disassembly/assembly.

Sooooo.... what I did was, with the spark plug out, I very slowly and carefully turned the motor over backwards and kept turning until I saw the decompressor clutch on the camshaft snap/lash. Then I turned the motor several revolutions in the proper direction. Then I repeated the whole process a second time.

With that said, as I was in deep thought with the diagrams I drifted back in thought to where this noise started for me... after an oil change.

If you have ever lifted your bike and stood it on it's rear bumper by yourself, you did it in gear.... I did it to remove my skid for an easy oil change.... but if you didn't switch to neutral or pull in the clutch to push the bike down.... well you have turned your engine over backwards already.... I have, so....

Anyways, in a few hours we'll see if this helped anything...

And if it was a really really bad thing to do, then I've been the village idot for everyone else.

no man i am sure you will be fine and if the decompression was stickin it shouldnt be now. because i read to do that in the service manual so im sure you didnt wreak anything. and its not liek you could jump timing. so you arnt going to screw anything up garentied.

MtnEX

08-22-2008, 02:51 PM

Well, for me it didn't hurt a thing...

Didn't help a thing either.

It's still going clack-clack-clack...

It's really hard telling what the noise is. With everything off I did the wooden stethescope test all over the engine, even dead on top.

You can hear so much like that and the engine is so noisy naturally that it's hard to tell. I wouldn't think so, but it is.

If it's coming from anywhere in the top end, it's gotta be the right side.

It could be the decompressor contact points or the timing chain.

But there is also always the slight chance it could be a wrist pin.
That might explain why the clack can't be pinpointed.

justin1022

08-23-2008, 02:03 AM

Originally posted by MtnEX
Well, for me it didn't hurt a thing...

Didn't help a thing either.

It's still going clack-clack-clack...

It's really hard telling what the noise is. With everything off I did the wooden stethescope test all over the engine, even dead on top.

You can hear so much like that and the engine is so noisy naturally that it's hard to tell. I wouldn't think so, but it is.

If it's coming from anywhere in the top end, it's gotta be the right side.

It could be the decompressor contact points or the timing chain.

But there is also always the slight chance it could be a wrist pin.
That might explain why the clack can't be pinpointed.

well if oyu tihnk it ould be a wrist pin i would jsut pull it apart. if that pin ever broke out it would screw your gears and imagine if that big pin fell out man would that be a mess. just pull your top end and check things out everything souhld be a steelgasket besides the base one but you can tell if a wrist pin is gon once yo usee the pistion try wiggleing it back and forth does it burn oil? i no mine wiggled and it was a wrist pin.

MtnEX

08-24-2008, 11:14 PM

Originally posted by justin1022
well if oyu tihnk it ould be a wrist pin i would jsut pull it apart. if that pin ever broke out it would screw your gears and imagine if that big pin fell out man would that be a mess. just pull your top end and check things out everything souhld be a steelgasket besides the base one but you can tell if a wrist pin is gon once yo usee the pistion try wiggleing it back and forth does it burn oil? i no mine wiggled and it was a wrist pin.

Well, I took a chance and tried something odd for the heck of it.

When I had my spark plug out, I happened to notice it was black in there... probably carbon and gunk... from someone elses crappy workmanship on my quad (jetting probably).

Anyways, I wanted to run some Seafoam through it to see if I could clean it out some.... and the idea formed...

I recalled having some lawn and garden engines hydro-lock on me over the years.... happens when you have a leaky needle and the engine stops low in the compression stroke... fills the cylinder with gas and locks the motor up if the rings and valves are making good seals...

Sooooo.... I took a trans funnel and filled my cylinder pretty good with Seafoam, put the plug back and let it soak a while. Then I took the side access plug off, stuck a socket and ratchet on it (breaker bar would have been better).

I tried cranking the engine over counter-clockwise, figuring I'd get no effect because of the decompressor... but it was worth a shot.

Turns out I couldn't crank it over by hand, no way. So then I tried some wiggling back and forth to see if I could hear anything out of the wristpin.

In summary....

I wasn't sure if I could get a hydro-lock due to the decompressor.
I expected the Seafoam to leak down past the rings anyways.
But it didn't leak down and I did get hydro-lock.

I also expected I might hear a faint wristpin clack... but I didn't.

I don't know what... if anything any of this means...
But those were my results nonetheless...

As a bonus, I also found another additional use for Seafoam.
It's a great way to test for exhaust leaks.
Mine has leaks at the pipe joints.

justin1022

08-25-2008, 07:30 PM

dude your really really really really smart.. i would of just ripped it apart as soon as someone told me my wrist pin is shot.. but hey man im out of ideas.. what do you think it could be? maybe try and retime your valves with a difrent fealer gauge. other then that i would take it to the dealer if you cant figure anything else out.

MtnEX

08-25-2008, 11:25 PM

It may well be the wristpin... I'm not sure.

I appreciate you saying I'm smart, but I'm not really that smart at these 400EX's. If I were, I know no doubt what the sound is... LOL.

At this point I think it is either nothing... just a lash sound from the decompressor at low RPM.... that sounds way worse than it is.

Or the new oil/filter I am using (Amsoil/Wix)

Or I think it is some sort of weird spark knock clatter.
This one I'll know more about tomorrow evening.
I have filled a can with 110 octane race gas.

Just not sure rather to drain and run it... or tame it down by mixing with the 93 in the tank.

Could be those dang "invigorate" additives or the new formulation of BP/Amoco 93.

justin1022

08-25-2008, 11:59 PM

i run 114 octaine gas but i got a 440. um does it go away after you give her gas or is it seriously a loud knock that wont go away?

MtnEX

08-26-2008, 12:13 AM

Sometimes yes... sometimes no... and it depends on how high or fast I rev. And sometimes it will go away after that... other times it will come right back.

It will generally go away though, and it does disappear after it warms up and gets into a ride.

That is what made me suspect the wristpin in the first place.

justin1022

08-26-2008, 01:27 PM

ya i would for sure say wrist pin maybe after you try the gas you shuould rip it apart and replace all that.

MtnEX

08-28-2008, 12:41 PM

Yeah, it wasn't any kind of wierd spark knock, and I didn't think it was going to be because it wasn't like any I'd heard before. I just wanted to try the race gas to rule that out entirely if possible.

I'm running straight 110 octane and it's there from the moment I start up.

Anyways, I've messed with this thing so much I've gotten really good at getting the noise to go away. I just put my thumb on the very tip of the throttle and give it a quick snap-slip.

So it's got to be something about the decompressor mechanism, or the timing chain & tensioner, or the wristpin.

justin1022

08-28-2008, 01:42 PM

if i was you i would take the decomression out. and see what happens check if your cam chain is tight. you shouldnt be able to move it on the sproket at all and if it still knocks then i would say replace the wrist pins.

MtnEX

08-28-2008, 04:21 PM

justin,

Did your tap all the time? Ever go away?

Mine stops once it gets hot, and I don't recall it returning after that.

bugsy

09-02-2008, 04:49 PM

I started this thread and really appreciate everything i read. So now its time to dive into it and see if can figure it out. I have been so busy lately i just haven't had the time but plan on making time soon. Again thanks for all the info.

MtnEX

09-14-2008, 08:12 AM

I out up a video of how mine actually sounds.
Go check it out... I'm curious if it is similar...

http://www.exriders.com/vbb/showthread.php?s=&threadid=364729

geezy

09-14-2008, 08:21 AM

it seams everybody has a tap or knock in their head, i got one to i cant pinpoint

MtnEX

09-14-2008, 08:29 AM

Yeah, I can't pinpoint mine either... not even with a sounding rod.
Strange... but maybe not likely the decompressor after all... since you have an aftermarket cam.

Flyin-Low

09-14-2008, 03:27 PM

Just curious, but why are you running high octane on stock 9.1:1 compression?

MtnEX

09-14-2008, 03:31 PM

Originally posted by Flyin-Low
Just curious, but why are you running high octane on stock 9.1:1 compression?

Dunno if you are asking me or not, but I will answer this because I have tried it...

I just did it to make sure the sound wasn't related to some ignition ping in some weird way....

MtnEX

08-22-2009, 12:22 AM

Originally posted by MtnEX
I out up a video of how mine actually sounds.
Go check it out... I'm curious if it is similar...

http://www.exriders.com/vbb/showthread.php?s=&threadid=364729

Well, I'm going around trying to UPDATE and I have now realized I'm going to pull a bunch of old threads up from the dead, and maybe even annoy some people in the process, but I feel it's worth doing...

The noise heard in that video is actually coming from the decompressor mechanism from the stock camshaft.

I have now had this professionally verified TWICE...

And after the second time around and also being in the process of carb work, I understand why.

What is happening is that... due to changing conditions.... atmospheric, and also things like fresh oil changes.... what is happening is that my engine RPM is fluctuating through a range that is getting my decompressor started clacking... That's why it comes and goes.

My carb has not been quite right since I had the work done on it, and I'm in the process of trying to correct that now.

If I can stabilize my idle, and then adjust it above this RPM range, I should never hear it again.

So nothing is wrong with my engine.... nothing is going bad or torn up.

And not only is that so... but it is obviously so.... because it has been doing it a YEAR now.

Ryanwolfe911

08-22-2009, 09:38 AM

Originally posted by 400exrider707
Exactly the aftermarket cams do not use the mechanism on the stock cam. You can have it pressed off and pressed on the new cam, but there is no need. If you ever put the stock cam back in, you either need to press off that mechanism or if you do keep it on, you need that spring and dowel or it will never start.:blah:

Oh, It'll start all right, but you'll have to unadjust the right exhaust valve all the way or you'll have no compression.

THe guy I got my 400 from rebuilt the top end and couldn't figure out why it wouldn't run without the valves unadjusted all the way. I knew what he did, but I didn't say anything, I told him that the timing wasn't set right and he bent the valves. So I got the bike for damn near nothing.

storms400ex

08-22-2009, 01:43 PM

so if you take it out, it won't start?? i would think it would start aslong as you have a strong battery

MtnEX

08-22-2009, 02:01 PM

Yall don't have to take it out...

Just get your carb in good shape and get your idle speed to stay above it's range...

Even if it makes noise, it's not hurting anything. Mine has done it off and on for a year. Worst thing I guess is that my decompressor has been used more than it should have been?

I just wanted you guys to know what it is for sure when it is "THIS" noise.

And I know it's scary sounding and hard to overlook, because it sounds like an engine internal is going to torpedo out of the engine.

storms400ex

08-22-2009, 06:34 PM

on the search thread i came up on a thread about the same noise i hear until mine warms up, they say you can take the decompresser out on a stock cam, you just have to have a machine shop press it off.

Exrider434

08-24-2009, 12:08 AM

ive been researching this noise lately and it turns out that most people have cured it with a cam chain, CRF cam chain is on its way! =]

MtnEX

08-24-2009, 12:27 AM

Originally posted by Exrider434
ive been researching this noise lately and it turns out that most people have cured it with a cam chain, CRF cam chain is on its way! =]

Well, it depends on what the noise actually is... what it sounds like, etc...

I just read yesterday where a guy did his and still had the noise. If it sounds like my video, it's the decompressor... and nothing is wrong with it...

Exrider434

08-25-2009, 07:43 AM

ah, i figured out my noise...

too much lash in the rockers caused it to make the slapping/ticking noise.

I believe i adjusted the valves on the exhaust stroke leaving them too loose on the compression stroke, it runs with very little noise except the usual 400ex valve tick.

MtnEX

08-25-2009, 10:30 AM

Yeah, that would do it and would make them way loose if you did not adjust them on the right stroke at the "T" mark.

To avoid this happening again, always check to see that all 4 are loose/free, you can wiggle them by hand.... if not, wrong stroke.

storms400ex

02-17-2010, 08:58 PM

Originally posted by MtnEX
Well, it depends on what the noise actually is... what it sounds like, etc...

I just read yesterday where a guy did his and still had the noise. If it sounds like my video, it's the decompressor... and nothing is wrong with it...

yours sounds just like mine

MtnEX

02-17-2010, 09:20 PM

Yep... still running strong....

storms400ex

03-26-2010, 07:34 PM

i took my cam out cause mine had a knocking sound, press off the decompressor thing, dowel and spring out the engine. its the quietest it has ever been, even the ticking is hardly noticeable. Before i took off i notice the one piece of the decompression stuff was just looser then crap witch probly when it started the knocking noise, but now it is quiet as hell!!!!!!!!!!!!!!

MtnEX

03-26-2010, 09:13 PM

I have thought about doing it to mine as well.

Do you notice any difference besides lack of noise?
Harder starting or anything?

How big of a deal was it to get the cam out?

What about getting the stuff off it?
What all is involved in that?

storms400ex

03-27-2010, 09:25 AM

starts up the same, all you do is remove the valve cover, then rotate the engine so the cam lobes are up, then undo the cam sprocket bolt, then rotate again so the lobes are facing down, (look on cam sprocket and line the two lines up with top of head) then zip tie cam sprocket to handle bars, then undo the last bolt on cam sproket, and slide the cam out and go get it pressed off at any place with a press, then remove that junk and press back on sprocket flange and your done, make sure you remove dowel pin and sping from head, i had to use a screw and put it down in there to get spring out. just remember the lobes face down when sliding cam back in.