Eliminate Cam decompressor

[Viktor_trx400]

Is it possible to eliminate the cam decompressor? Thanks

[Honda#4]

Are you putting in a Hotcam? if so just remove the spring and plunger. If its the stock cam idk if you can remove the decomp

[Viktor_trx400]

I have installed a WB cam with stock decompressor. Can I eliminate it?

[NacsMXer]

Originally posted by Viktor_trx400
I have installed a WB cam with stock decompressor. Can I eliminate it?

You should be able to. You need to press the cam sprocket flange off the cam, then the decompressor assembly will slide right off. Then you press the sprocket flange back on. Keep in mind it is very important to also weld the 2 oil holes in the cam shut where the decomp used to be. If you don't weld them shut you will starve the rest of the cam of oil and trash it.

This website has a couple of pictures on removing the stock decomp mechanism: http://www.4strokes.com/tech/honda/xr4engwk/

[Honda#4]

Agreed with Nacs reply.

[Viktor_trx400]

How can I weld the oil holes?spot weld? thanks

[JOHNDOE83]

xr400 has a cam decompressor i know it the same as 400ex but from what ive heard and had experience with the 400ex does not have 1. i installed a stage 2 hot cam and in the paper work it said remove cam decompressor only for xr400 models 400ex is not needed cause it doesn not have 1. look into it, i could be wrong but i dont think so.

[F-16Guy]

What would the benefit be? Just curious.

[NacsMXer]

Originally posted by Viktor_trx400
How can I weld the oil holes?spot weld? thanks

You can MIG weld it, but you will have to be careful not to get weld spatter on the cam lobes. Having it TIG welded is better, as it is very precise and produces less heat. The holes aren't very big, so it's not a major job for someone who knows their way around a welder.

[NacsMXer]

Originally posted by JOHNDOE83
xr400 has a cam decompressor i know it the same as 400ex but from what ive heard and had experience with the 400ex does not have 1. i installed a stage 2 hot cam and in the paper work it said remove cam decompressor only for xr400 models 400ex is not needed cause it doesn not have 1. look into it, i could be wrong but i dont think so.

XR400 and 400EX stock cams come with a decompressor assembly on the camshaft. 95% of aftermarket cams don't reuse the decompressor assembly though.

[NacsMXer]

Originally posted by F-16Guy
What would the benefit be? Just curious.

The main benefit IMO is to eliminate excess ticking/clicking in the valvetrain. This mod is done religiously by the XR400 guys with stock cams. Many claimed to have a noisy topend, but immediately after eliminating the decomp the motor was quiet as can be.

If you ever handled a cam with the decomp assembly on it you might notice how much slop there is in the decompressor lobe. I believe that slop may or may not be the source of the metallic ticking sound.

It is also extremely rare, but has happened for the decomp assembly to wear out and scatter its parts inside the motor. Not likely, but i've heard of this happening on some extremely high mile XR's.

I've also seen people shortcutting this mod by cutting the lobe off of the rocker arm that rides on the decomp assembly of the cam. I've heard this eliminates the noise as well. But I think it's better to just strip the whole thing off the cam in the long run...kinda pointless to have those extra parts spinning on the cam doing nothing.

[F-16Guy]

Interesting. I was thinking friction or something along those lines. Seems like a lot of work on a stock cam. I actually wish the HotCams would accept the mechanism. When my quad is hot, it can give the starter a run for it's money once in a while.

[Viktor_trx400]

Originally posted by NacsMXer
You can MIG weld it, but you will have to be careful not to get weld spatter on the cam lobes. Having it TIG welded is better, as it is very precise and produces less heat. The holes aren't very big, so it's not a major job for someone who knows their way around a welder.

ok, thanks

[NacsMXer]

Originally posted by Viktor_trx400
ok, thanks

No prob ;)

Here's a picture of the two oil holes that need to be welded...it is obvious once you remove the decompressor from the cam. One is superficial, the other is recessed in a deeper hole. I had these TIG welded.
http://i656.photobucket.com/albums/uu289/nacsmxer/Rebuild/DSC_0650.jpg

[Viktor_trx400]

thanks again, it is a good pic. And, what can i do with this?

[NacsMXer]

Good eye. Those are just 2 pins that are pressed into the cam....they "locate" the decompressor on the cam so it doesn't spin.

I've heard that you can just leave them alone since they are pressed in. I didn't know that, and since I took that picture I had those 2 pins lightly tacked in place with a TIG welder to make sure they wouldn't come out. But again, I found out you can just leave those 2 pins alone.

[v0lcom13sn0w]

Originally posted by JOHNDOE83
xr400 has a cam decompressor i know it the same as 400ex but from what ive heard and had experience with the 400ex does not have 1. i installed a stage 2 hot cam and in the paper work it said remove cam decompressor only for xr400 models 400ex is not needed cause it doesn not have 1. look into it, i could be wrong but i dont think so.

400ex has a decompressor... ha i know this because a buddy rebuilt his bike and his decompressor fell out and he didnt notice it or even know it had one and the thing would not run at all... we found this out once we got to the dunes and had to take it to the honda shop in florence and luckily the guy had a spare one layin around he gave to us for free.

[Viktor_trx400]

Originally posted by NacsMXer
Good eye. Those are just 2 pins that are pressed into the cam....they "locate" the decompressor on the cam so it doesn't spin.

I've heard that you can just leave them alone since they are pressed in. I didn't know that, and since I took that picture I had those 2 pins lightly tacked in place with a TIG welder to make sure they wouldn't come out. But again, I found out you can just leave those 2 pins alone.

i will do the cam´s mod and install it. Thank you very much