Beware of Auto decomp damage

[Frostbite]

holy smokes! That bike is going to rip with that stuff.... Which exhaust are you using?

Here is the sweet sound of that pipe on my 400.?

[taksx]

Here is the sweet sound of that pipe on my 400.?

Haha that was cool, I like your snow cone:lol:

[pablo83]

My 99 YZ400F has steal intake valves, but a magnet will not stick to the exhaust valves. I thought the 400's had all steal valves. Are the exhaust valves stainless? Is there an easy way to tell the difference between stainless and Ti without pulling them out and weighting them?

Also, I'm guessing the Ti valve bikes have a higher rev limiter than the steal valved ones. Is this true?

[grayracer513]

I thought the 400's had all steal valves. Are the exhaust valves stainless?

Yes, they're stainless. That's why a magnet doesn't stick. The only way you'd have Ti valves is if someone took the engine apart and put valves from an '01 426 in it. Not very likely.

[pablo83]

I took down my head today on my WR426. One of the PO's has installed an auto decomp cam on it. I was told it is from a YZ. The bucket has damaged, but it is minimal. I'll post a pic later. How can I tell what cam this is? Does anyone know the distance the YZ decomp pin sticks out vs the WR pin?

Also, it has a big bore kit in it. Stock bore is 95mm, mine is 97mm and the piston is gold colored. Does anyone know what brand it is?

Thanks

[Frostbite]

I took down my head today on my WR426. One of the PO's has installed an auto decomp cam on it. I was told it is from a YZ. The bucket has damaged, but it is minimal. I'll post a pic later. How can I tell what cam this is? Does anyone know the distance the YZ decomp pin sticks out vs the WR pin?

Also, it has a big bore kit in it. Stock bore is 95mm, mine is 97mm and the piston is gold colored. Does anyone know what brand it is?

Thanks

Someone mentioned that the YZ pin is rounded on the end like half an orange. My WR pin was flat looking on the end.

How does the cam lobe look? The surface of my cam lobe looks perfect, but looking at it from the end you can see that it's completely re-shaped.

[pablo83]

The pin on my cam is only slightly rounded.

The cam does not appear mis-shapen. The lobe height is correct, but you can see and feel a bit of a lip on the edge.

This pic makes the marks look slightly worse than they are.

[Birdy426]

I’m still using the White Bros E pipe from my 400.

Anybody want to take a guess at the jetting? 478cc, open pipe and -30C.

When I went big bore on my 426 (from 426 to 444), I actually didn't change jetting at all...

[Frostbite]

The pin on my cam is only slightly rounded.

The cam does not appear mis-shapen. The lobe height is correct, but you can see and feel a bit of a lip on the edge.

This pic makes the marks look slightly worse than they are.

Are you sure the lobe height is the same as the other? The decomp lobe looks “flatter” than the other lobe, which is the opposite of how mine wore. That lip is a good indication that there is abnormal wear

As for the bucket photo, think of it as if it were the wall of your cylinder, any marks are not good. There are 2 machined surfaces running against each other. Any irregularities in the surface can cause problems. It looks like you do have a problem, but the wear hasn’t gotten too bad yet. As Grayracer said, once the hardened surface of the cam wears away, it can wear much quicker.

When I went big bore on my 426 (from 426 to 444), I actually didn't change jetting at all...

Another vote for leaving the jetting alone. Thanks Birdy. I am going to roll it out the door without touching the carb..... as soon as my cam and bucket arrives.

[pablo83]

cam height:

non-decomp lobe: 1.221"

decomp lobe center: 1.221"

decomp lobe near edge with lip: 1.220"

I don't know how these numbers compare to the cam specs because I don't know what cam this is. (PO installed it).

The height from the cam shaft to the top of the pin is 0.078"

I know the lip on the edge of the lobe indicates wear, but I'm starting to think this is something I'll have to live with and monitor if I want to be able to kick the bike over easily. I have extra cam buckets, so I'll just replace them every time I pull the head and keep an eye on the lobe height.

[89TRX350RX]

Here is the sweet sound of that pipe on my 400.?

Holy "Survivorman"!!! Les Stroud would be impressed with the camera work... For you Yanks... Les Stroud is the Canadian version:canada: of your Bear Grills:usa: , but he actually does it all alone without a camera crew and help... As in all by hisself... in the middle of nowhere, with only his cameras, no film crew, nobody there and he stays out for around 6-7 days surviving on bugs and whatever he can get his dirty hands on...

Anyway Frosty, I just subscribed to '40BelowBiker" on Youtube so I can get all the rest of your awesome vids... Thanks, Jamie

[pablo83]

Frost, did you get your new cam in? If so, did you happen to note how long the YZ decomp pin is?

[Frostbite]

Frost, did you get your new cam in? If so, did you happen to note how long the YZ decomp pin is?

My new cam just arrived today. I ordered an 06 YZ cam, and I can see why there is a difference in power. The lobes on the new cam are at least 1mm taller and are wider.

I can't tell by eyeballing if the pins are indeed in different locations. The YZ pin has a much more rounded tip than my WR pin, but I still don't know if the WR pin is factory or if a piece broke off. I measured the heights of the 2 pins with a caliper (sorry, no mic) and they are identical. This leads me to believe that my WR pin is factory and does not have a broken tip.

Here are a few comparison pics.

Side by side, WR cam on top. The WR shaft has 2 grooves machined it it near the bearing, and the YZ has 1.

The gear ends look the same.

Lobe difference. This is the good lobe on my WR cam, matched up to the new YZ cam.

The non-business ends of the decomp pin are different.

Here's the WR

and here's the YZ

The sprocket teeth are also a little different - WR

YZ

And now for the pins themselves:

WR pin

YZ pin

So, the older YZ decomp pin is very much more rounded than my WR cam, but the heights of the 2 pins appears to be identical.

I bought 2 buckets, so I'd have a spare, but they're surprisingly pricey at $50 each.

Now I am wondering, how do I set the cam timing with the YZ exhaust and the WR intake?

[pablo83]

thanks for sharing. would you mind measuring the lobe height on the YZ cam?

[Frostbite]

thanks for sharing. would you mind measuring the lobe height on the YZ cam?

No problem. It looks like 31mm bang on, and the WR cam looks like 30.1mm.

[bloodline]

I'm new here and new to the WR. I just rebuilt one. Same damage on the bucket. No damage on the cam lobe. I reused the bucket. Time will tell...

Bike had 890 miles on it. '04 model.

[Frostbite]

I'm new here and new to the WR. I just rebuilt one. Same damage on the bucket. No damage on the cam lobe. I reused the bucket. Time will tell...

Bike had 890 miles on it. '04 model.

Welcome to TT Bloodline.

A word of caution on the cam issue - I thought there was no damage to my cam either, and was actually re-installing it when I saw the problem. The lobe surface looked perfect, nice and shiny like all the other lobes. Looking at the cam from the end, I noticed that the lobe by the pin was carved to a sharp point, not nice and rounded like the other lobe. You may want to have another peek.

Also, the lobe wipes across every square millimeter of the bucket, so any damage at all could lead to cam trouble.

[grayracer513]

As to the timing question, line the marks up, same as stock.

[camel toe]

My new favorite thread.

[Frostbite]

As to the timing question, line the marks up, same as stock.

Thanks Grayracer.?