450 valve\decompressor Q's


14 replies to this topic
  • mx_racer32

Posted 07 January 2007 - 06:55 PM

#1

recently put a new head on my '05 450r. new oem head, oem valves, springs, retainers, ect. i noticed that my bike was hard to start when i kicked it hard, but when kicked slowly, it turned over (like the auto-decompression was malfunctioning) also there what seemed to me like excessive valve train noise.

i took it apart tonight and noticed that there seems to be lateral movement on my decompressor arm inside the the journal on the top of the cam holder assembly. i never noticed this before, but never paid much attention to it either. is this normal? could this be the source of my "excessive noise"? i searched and came up with this thread http://www.thumperta...compressor play but it doesnt really say anything.

I checked my timing, i thought possibly it was off a tooth but nope, its dead on. checked my valves, my intakes are spot on, but the exhaust side is tight. out of clearance for sure, but the decompression arm is within spec of the rocker. if the exhaust was tight then that means the engine isnt having problems expelling the exhaust thus meaning that it is not the source of my hard starting?

i know thats a lot to read, but to recap:

auto-decompressor arm wobble normal?
tight exhaust valves cause of hard starting\kickstarter hard to move @ TDC?
which of these (if any) do you think is the causes of my excessive valve train noise?

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  • skthom2320

Posted 07 January 2007 - 08:22 PM

#2

The lateral movement is probably normal. The arm will definitely move side-to-side when you are wiggling it.

Even if you have checked the timing, check it again or even go ahead and change it by a tooth and see what it is like when you (slowly) turn it over.

I went through this the 1st time I dinked with my cam. When it is a tooth off it will be hard as hell to kick right at TDC, but will ease through it with pressure.

Don't know the source of your valve train noise though. They will sound really bad (clickety-click!) with excessive clearance but your clearances are correct, right?

Did you verify the timing with the mark on the flywheel or the other side or both?

  • mx_racer32

Posted 07 January 2007 - 08:35 PM

#3

I went through this the 1st time I dinked with my cam. When it is a tooth off it will be hard as hell to kick right at TDC, but will ease through it with pressure.


sounds exactly like how mine is. eases through with constant pressure on the kickstarter but when trying a hard, full, swift kick i about break my ankle.

Don't know the source of your valve train noise though. They will sound really bad (clickety-click!) with excessive clearance but your clearances are correct, right?

Did you verify the timing with the mark on the flywheel or the other side or both?


my exhaust side is tight, out of spec tight, but the intakes are right on target (left dead on, right only .01 off so its well within tolerance) i verified my timing from the large allen head bolt in the side of the cases (gear with dot on it, as described in manual) in conjuction with the timing marks on the cam gear.

  • skthom2320

Posted 08 January 2007 - 01:19 PM

#4

sounds exactly like how mine is. eases through with constant pressure on the kickstarter but when trying a hard, full, swift kick i about break my ankle.


I am convinced your timing is off by a tooth.

You can pull the plug on the left side case (smaller than the one on the RH side) and you will see a timing mark on the flywheel (unless you have an aftermarket flywheel). This timing mark is more sensitive than the one on the gear on the other side.

When you say your exhaust is out of spec, what is the measurement? You can run those at 0.009" instead of the factory spec of 0.011" ...

  • jcsjr

Posted 08 January 2007 - 01:41 PM

#5

You are definitely one tooth off, mine did the exact same thing. My timing marks on the right side looked closer when it was off a tooth than it does now, use the mark on the flywheel.

  • mx_racer32

Posted 08 January 2007 - 03:33 PM

#6

you guys are definetly RIGHT. thanks skthom2320 and jcsjr. i will be using the flywheel side for all my timing\TDC needs. i wont get to change it until tommorow. odd though, the bike runs good, just starting is sometimes a pain. can i expect to see some good power gains from getting the timing back right? I also am guessing i shouldnt reshim my exhaust valves until i get the the timing correct and re-check, right? thanks fellas...

  • Shawn_Mc

Posted 08 January 2007 - 03:51 PM

#7

Id imagine that you got the timing one tooth retarded, because if it was advanced it'd been easier to kick.

But yes, you should feel a performance gain.

  • mx_racer32

Posted 08 January 2007 - 04:21 PM

#8

thanks guys, i'll fix it tommorow and report back. that way if someone else has this problem and actually uses the search feature, they might stumble on this thread and have some of their Q's answered.

  • mx_racer32

Posted 09 January 2007 - 08:53 PM

#9

well, fixed the timing, same thing is going on with the kickstarter though. i re-checked my valves and intakes are still good, exhaust are out of spec, they are .008"

also, i re-checked my decompression arm clearance. in my book it says that the exh clearance is .28mm, and the decompression arms should have .35mm, so if you do NOT have a feeler gauge in between the exhaust valve\rocker, your clearance on the decompression arm should be .63mm. mine was tighter then this, so i readjusted it to spec.

darn thing still hangs up right near TDC. i watched closely at the auto decomp. arm and it is functioning, but i have a bad feeling this the culprut. do these have a history of wearing out or having problems? ive got a decent amount of time on my bike, well over 100 hours. thoughts\ideas?

..i did crank it after checking everything, runs good as before (from what i can tell on the stand, too dark to ride) but still hanging up when kicking it...im seriously thinking about turning that adjuster on the decompression arm in far so that it engages the exh. valves sooner and farther, too see if this helps.

  • skthom2320

Posted 09 January 2007 - 10:30 PM

#10

If your exhaust clearance is at 0.008" (0.20mm), then your total decompressor clearance should be at 0.55mm (0.20mm+0.35mm) or less. The value of 0.63mm is the "ideal" value only if your exhaust is exactly at 0.28mm.

It's no problem to set the decomp clearance a little tighter than the spec for easier starting, especially if you have a hi-comp piston in it.

  • mx_racer32

Posted 10 January 2007 - 05:10 AM

#11

oem piston, i will reset the clearance and see what happens.

  • mx_racer32

Posted 10 January 2007 - 04:16 PM

#12

If your exhaust clearance is at 0.008" (0.20mm), then your total decompressor clearance should be at 0.55mm (0.20mm+0.35mm) or less. The value of 0.63mm is the "ideal" value only if your exhaust is exactly at 0.28mm.

It's no problem to set the decomp clearance a little tighter than the spec for easier starting, especially if you have a hi-comp piston in it.


i put it together with it at .53mm gap, same thing, then went to .4; same thing, then even more extreme to a .35.

same deal everytime.


????ideas???

  • skthom2320

Posted 10 January 2007 - 05:19 PM

#13

Something's just not right! If it is that hard to kick, then the decompressor is somehow not actuating at the right time.

You can put a straw in the spark plug hole or screwdriver and confirm that you are at TDC when all your marks are lined up.

Did you ever try moving the timing chain a tooth? I would also just try moving it a tooth and look at your marks again.

  • mx_racer32

Posted 10 January 2007 - 05:35 PM

#14

i will have to get pics tommorow night and post up. i used a 1\4" extension in the spark plug hole to confirm with my mark on the flywheel it was at TDC. the marks on the cam are not exact with the arrow, but darn close. if i move it a tooth either way it just gets farther off, BUT i did move it one tooth, in both directions just to be sure. i also inspected the acuator arm, seems to be functioning correctly. will get pics tommorw.

  • mx_racer32

Posted 13 January 2007 - 07:50 PM

#15

got it fixed. took an extra pair of eyes to see what was wrong. luckily, it was something small and stupid. the return spring that puts tension on the small arm of the decompression arm activator (the part that is bolted to the side of the cam that "swings") the spring was inproperly mounted causing it to wedge that flapper arm at certain RPMS. oh well, shes fixed! thanks for all the help guys!





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