400ex decompression mechanism

hondaguy · #1 09-05-2011, 09:36 PM

Hello. This is my first post to this forum. I got a 2000 TRX 400EX from a friend. It was in 5 gallon buckets. I found wear on the cylinder so bored .040 over and new piston/rings. Put it back together and it ran!

Now one of the exhaust valves is clattering. When I have it broke down and looking at the timing marks this particular exhaust valve has about 1/8" play on every other stroke while the intake valves are down.

Once again. every other stroke while intake valves are in travel down and until they close. Does that sound right? It's in spec at TDC.
Sitting on the bike it is the rightside exhaust valve. Please assist.

hondaguy · #2 09-05-2011, 09:38 PM

woe. hold on. not every other stroke. every other cycle

Here 2 help · #3 09-06-2011, 04:25 PM

This is a common situation that can be solved by following the directions in the service manual and having the engine in the correct position for adjusting the valves.

The RH valve is held open a bit by an automatic decompressor mechanism built into the camshaft during the first rotation of the camshaft. Rotate the crankshaft (using the flywheel bolt on the LH side of the engine) counterclockwise while watching the intake valves. When the intake valves are pressed down by the rocker arms, then come back up, continue to rotate the crankshaft counterclockwise until the "T" mark appears in the timing inspection hole. At this point, check the valve clearence. DO NOT TURN THE CRANKSHAFT CLOCKWISE AS THIS WILL CAUSE THE AUTO-DECOMPRESSOR TO HOLD THE RH EXHAUST VALVE OPEN. If done correctly there will be clearence between each rocker arm and it's valve or at least the valve clearence can be properly adjusted.
NOTE: (from the service manual) "If all the valves are closed except the the right exhaust valve, this may indicate a jammed decompressor unit. A jammed decompressor will also cause a steady ticking sound when the engine is running. To release the decompressor, move the wrench fitted to the crankshaft bolt quickly back and forth. The quick changes in crankshaft direction should release the decompressor from the valve."

hondaguy · #4 09-09-2011, 11:44 PM

Man. Thanks a ton H2H.
It sounds like the Decompressor mechanism could be my culprit.
It also sounds like the instructions are to move the flywheel clockwise and counterclockwise in a jiggling motion. Is that your interpretation? if so, how many clockwise rotations do you think I should perform afterwards, you know, to offset the clockwise movement?
Also, do you know where I can get a service manual on disk, CHEAP?
OEM Parts Honda TRX400EX (TRX400EX) 2001 CAMSHAFT - VALVE - Cheap Cycle Parts
uh, oh. I dont remember seeing spring part number 5 when I was in there, looks like the valve cover is coming back off.
thanks again Mr. H2H

Here 2 help · #5 09-10-2011, 02:54 AM

Download one at tradebit.com

Rotate the crank at least 2 full turns counterclockwise after the jiggling

hondaguy · #6 09-10-2011, 11:30 AM

5.00 USD! thats what Im talkin about.
H2H>rock

hondaguy · #7 09-10-2011, 02:05 PM

dang. jiggle fail. valve cover is back off. download service manual in process.

The Auto-Decomp is spinning freely in one direction, and keyed to the A-D clutch. it has no type of recoil at all (is that right?). it all seems to be solid and tight.

There is just a little play in one piece (Plate). The piece of the assembly closest to the asssociated lobe.

If I buy a Hotcam will it come with this assembly?

H2H. you seam to be the only one willing to step up on this. props.

joeylowthers450R · #8 09-12-2011, 02:33 PM

hot cams do not come with decomp assembly.
the decomp assembly is not used with hc
so i guess if this is your problem, a hot cam will could be your fix

hondaguy · #9 09-18-2011, 02:04 PM

Thanks Joey!
I just got the HC Stage 2 in the mail and I aim to put it on today.
At this point I believe the Spring and Plunger were not included with the bike I got. I really feel like they re not gonna be in there today.
But I'm not looking back on the HC invest! I'm stoked. Its my first go at this.

? do you have to have the HR stroker kit installed to go with the stage 3 HC?

joeylowthers450R · #10 09-19-2011, 02:37 PM

nope! i have run hc stg 3 in the 400s with stock stroke.

they both work great. stg 2 is a mid to top end cam and the stg 3 is a bottem end to mid cam.

they both make great power, just in diff rpm range.
stg 2 hp peak around 9500 rpm
stg 3 hp peak around 7500 rpm

i prefered the the stg 2 better because i never liked having to shift at low rpm to stay in the power range with the stg 3. just my $0.02