Xr 400 noise...Decompressor and Cam chain?

I just pulled my 400 apart yesterday. Its sounded horable. The big end bearing is fine, the piston looks good (being changed anyways) the valves look straight.

The timing chain is stretched bad (its an 01 with no maintance ever) but I am worried that the auto decompressor is bad. The bike had little compression while kicking, which made me think I had a bent valve. It ran fine but sounded bad and smoked.

The decommpressor cam just flops back and forth on the cam. I am going to press the deal apart and make sure the little spring is there. Is that what the pin and spring in the head are for as well?

I have a manual but it doesn't discuss how the actuator works with the one way clutch. Anyone?

Is most of my noise from the spent cam chain?:worthy:

You will need a service manual to easily and sucessfully wrench on your XR400. There are downloads available for as little as $20, do a search. When the auto decompressor is working properly, you will most of the time feel very little compression when kicking. The cam chain will make a loud clattering/knocking noise when it is worn to the point that the chain tensioner runs out of travel, that is most likely what you are hearing.

Yea, I have a manual. The valves are good and the decompressor is fine. I pressed everything apart since this post. I think its all chain noise stuff now. We will see.

Yea, I have a manual. .

I overlooked your statement in your initial post that you have a manual, my apologies. If you can get hold of a service manual for an XR600R, '88 and later, the decompressor mechanism is shown in detail.

I just did the exact same thing! My XR400 started making a loud TICK TICK TICK sound from the front right exhaust valve. I figured it was just a loose valve, but after adjusting it a couple times, the noise persisted. I ripped out the cam and the little cam lobe that engages the system was just slapping back and forth on the cam. Lots of slop. Fast forward 1 week and I just installed my stage 1 Hotcam and NO MORE NOISE. All there is now the the normal/usual engine noises. My XR4 is dual sported and the auto decomp doesnt like sustained high rpms. Install a Hotcam, lose the auto decompressor, its just one more thing to go wrong. Kicking it over is slightly harder (not much) and it seems to start in fewer kicks now (was 3-6 kicks cold, now 1-3 kicks).

YEa I thought about that too. How much was your Hot Cam? Did you have to run a high compression piston?


Can I just remove the decompressor junk off the stock cam?

I payed $135 for my Hotcam, shipped from Ebay. The rest of my motor is stock. You can remove the junk, but I think it is a fairly complicated procedure (needs a press, heat, heard something about machining a collar?, etc...) I looked at it, but figured a aftermarket cam would both fix my problem AND give me more power, so I went that way.

Stage 1 HotCam is definitely noisier than stock (tick, tick, tick). You will have to learn the technique to start your bike, the manual decompression lever will be your new best friend.

Stage 1 HotCam is definitely noisier than stock (tick, tick, tick). You will have to learn the technique to start your bike, the manual decompression lever will be your new best friend.

Ya, its a tad louder. I have tried the decompression technique, but I cant get it to start that way (turning to TDC, pulling lever, kick just past TDC, then kick normal), it just wont fire. I just start it with full compression, it starts almost instantly and only requires just a bit more effort.

Well I could leave the oneway clutch on the cam as a stop for the cam gear. But I don't think I would need it either. The gear carrier is prety stout and there is a line on the cam to show where it is supposed to stop.

Ok. I have some follow up. I pressed all the Decomp junk off the cam and put everything back together.


Still smokes because the stock piston oil rings are shot. I can now do the whole deal in about an hour and a half. I am now going to buy a Namura piston kit off of Ebay and bolt is all back together.

The bike has alot of compression now and alot more juice!

The auto decomp is easily taken off the stock cam without using a commercial press; a few strategicly placed pieces of metal tubing in a large bench vice works just peachy. Some folk do not bother with plugging up the oil-feeder hole that is exposed, but I just fashioned up a collar by drilling out a small piece of the original steel handlebars (that I had left over when I put Renthal bars on). I cut a notch in the collar to allow the locator pin on the camshaft to fit.

You may still have a ticking noise though. Probably the timing chain (which is not always a rattling sound).

The manual explains the 'proper' way to replace the timing chain, but it is waaaaay easier to break the old and new chains then atttach the new to the old and use the old chain to pull the new one into the bike. Then just re-join the new chain and burr over the pressed-out rivet with a small hammer. You can buy micro chain breakers or use a c-clamp with a suitably sized torque bit (or similar).

Meat (Boer maak die plan) bomb......

I didn't bother and expect no reprocutions. The After market cam is a no fuss deal and the stocker minus the parts is the same deal. The Chain is a non issue as it sounds solid now.

that decompressor really sounds bad when the little,tiny spring is too weak.. i took it off my cam.. we do it on our XR250's and 400's here in the philippines.. i use a hammer with a soft hit.. but it got me a hour and a half before i pull it out.. pushing back in the cam sprocket attachment is so quick.. you just need that same hammer

Just make sure you don't mushroom the cam end. Happy trails.

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