Beware of Auto decomp damage



108 replies to this topic
  • Demo_Slug

Posted March 10, 2009 - 01:04 PM

#21

shouldn't the pin only touch the bucket when the engine is starting? seems like a lot of dings on the bucket. is it possible that the pin got stuck?

  • Frostbite

Posted March 10, 2009 - 01:04 PM

#22

I am curious to see what the fix for this is. Is it converting to a YZ Cam?


I prefer the manual decomp. If I thought my 450 would start (kicking, not e start) without the pin, I'd take it out and eliminate the possibility of the problem returning.

There may only be 2 threads regarding the problem, but it is possible that some just don't know about it yet. I took my engine apart to replace the crank. I didn't even consider that there was a problem with the cam, and the engine ran perfectly, just the crank was knocking.

At a glance my cam and bucket appeared fine. Looking straight down at the lobe, it was perfectly smooth and shiny, not pitted as I would expect a bad lobe to look. the only way to get a good look at the bucket is to remove the cam and clean the oil from the bucket face.

I just happened to see Taksx's post asking about the bucket, so I checked mine so I could give him some information, since my engine was already apart. At first all buckets looked the same, but the film of oil was kind of filling in the dents. once I wiped the oil away I could see damage, but had to take a close up pic to really see some detail. I actually told Taksx that my cam lobe was fine. It wasn't until last night that I looked at my cam from the end as I was installing it, and noticed the pointy lobe.

I would say that it is very possible that there are other WR owners out there with the same damage, but just don't know it since there are no symptoms. An easy way to tell is to remove the valve cover (OK, not so easy on the aluminum WR's) and look at the cam lobe from the end. If it's pointy, then you've got a problem.

  • Frostbite

Posted March 10, 2009 - 01:11 PM

#23

shouldn't the pin only touch the bucket when the engine is starting? seems like a lot of dings on the bucket. is it possible that the pin got stuck?


No, the pin touches first, but the cam lobe is much higher than the pin, so the lobe takes over pretty quickly. The pin opens the valve before the lobe, and holds it open a bit after the lobe has passed.

The dings in the center circle of my bucket could not have been made by the pin, as the pin can't touch this spot. Maybe the pin dug up some shrapnel which then got squashed into the bucket by the cam lobe. The near perfect ring of dents near the center of my bucket tell me that they were probably made by the same object. Since only the cam lobe touches here, it must've been a chunk coming off of the cam, or a piece of shrapnel stuck in the cam lobe long enough to pop all those dents before it got spit out.

  • grayracer513

Posted March 10, 2009 - 02:14 PM

#24

Maybe the pin dug up some shrapnel which then got squashed into the bucket by the cam lobe.

The material that was on the cam lobe went somewhere, and while it was leaving the cam, it was between the cam and lifter.

Pending finding out that the pin is not normally square on the end, I'd say this is a fairly isolated occurrence, but with two at the same time, 3 years apart, one that you should watch for via regular inspections.

  • Frostbite

Posted March 10, 2009 - 06:40 PM

#25

The material that was on the cam lobe went somewhere, and while it was leaving the cam, it was between the cam and lifter.

Pending finding out that the pin is not normally square on the end, I'd say this is a fairly isolated occurrence, but with two at the same time, 3 years apart, one that you should watch for via regular inspections.


I took some close up shots this evening. The pin looks factory, doesn't show signs of grinding or a broken weld.

Posted Image

There is a slight convex in the face of the pin, but it's not far from being flat, and it does look like it was manufactured this way. There is a bevel around the outside edge which would help a bit. In this pic you can see the bevel, and see how the edge that contacts the bucket is discolored and worn away. The opposite side of the pin looks identical, so both of the edges that contact the bucket are worn away. The pin can't spin around but can rotate about 5 degrees, so the same edges always hit the bucket. Looking at the height of the pin when it is retracted, it couldn't be any longer or it would stick out farther than the neutral part of the cam, and constantly hold the valve open.

Posted Image

In this picture, you can see that the pin hits at a fairly nasty looking angle.

Posted Image

I did a closeup of the other 4 buckets, and they all looked like this.

Posted Image

You can see that the cam lobe wipes across almost the entire surface of the bucket. There is a slight bevel at the edge of the bucket, and the wear marks go right to the edge, so they're not wasting any material here.

Here's a closer look at the bad bucket.

Posted Image

The really chewed up outer portion is where the pin strikes.

After looking at close ups of all of the components, here is my conclusion:

The decomp pin caused initial damage to the bucket face. looking at the way it strikes, I'd say that it would probably dent the face. If the face is heat treated like the cam, once damaged it would get worse fast.

Around the dent, there are likely raised ridges in the metal. the cam lobe would be wiping across the rough surface and that would start to degrade the surface of the cam lobe.

The edges of the bad cam lobe are jagged. As the material on the face was wearing away, the lobe may have been mushrooming a bit, similiar to the way the metal looks around the decomp pin in the close up photo above. Since the dings near the center of the bucket are very uniform, I'll guess that they were made by a jagged edge on the cam as it was coming apart. Those little dings line up perfectly with the edge of the cam lobe.

Because the contact edges of the decomp pin are so worn down (probably only 1500 miles on the bike) and possibly look discolored, maybe due to heat, I'd say that the pin was hitting the bucket face steadily at speed for more than a few seconds that it takes to start the engine.

I'm going with the theory that the pin stuck somehow. all the little gizmos that interact to move the pin in and out are very small and light and have close tolerances. Thick oil or frost could hang up the weight itself or the little shaft that runs through the center of the cam. When the engine is off the pin is extended, so this is the position it would freeze in. Since the pin can't work backwards and move the weight, you could beat on it all day and it wouldn't help to free up the stuck shaft or weight. Until the weight frees up, the pin stays out.

I have seen frost on the underside of my valve cover on my 400, so I know it's in my engines on cold days. This may have only happened one time, one unlucky cold morning, but once the bucket was dinged, the wear would continue every time the engine was running, simply from the cam wiping across the bucket.

When starting cold, I don't rev the engine when it first starts. I let it idle to warm up, probably like most of you, and take it easy for the first bit of riding. Maybe this is a bad thing if the decomp weight is sticking. Maybe a good crack of the throttle right away would free up the sticky pin, where the idle speed may not be enough to do the trick. What I need is a clear half moon in my valve cover gasket so I can see what the heck is going on with the weight instead of all this guessing. That may not be a bad idea, drill in a little view port.

Maybe I'll use one of the stick on block heaters (that burnt my 400) to preheat the valve cover before I start, but that won't help me when I shut down on a trail ride. I think I'm going to have to remove the decomp altogether, or maybe reverse the spring so it holds the pin in, and then drill in a little manual lever that will flick the weight as it passes by, like a locking differential in a 4 X 4.

  • Frostbite

Posted March 10, 2009 - 07:02 PM

#26

shouldn't the pin only touch the bucket when the engine is starting? seems like a lot of dings on the bucket. is it possible that the pin got stuck?



Sorry DS, I reread your post and think i may have misinterpreted.

I read "shouldn't the pin only touch" but translated it as "shouldn't the 'PIN ONLY' touch" as in "only the pin". You're correct. The pin should only touch when the engine is starting, and I do think that mine stuck.

  • mlynn450

Posted March 10, 2009 - 07:36 PM

#27

My 07 wr450's pin looks like the pictures , but without the dent in the edge. The bucket has the dings about 3mm in from the edge only and is not nearly as bad as the picture. I have about 220 hours on this bike. The pin looks the same as it did when it was new.

  • Frostbite

Posted March 11, 2009 - 02:26 AM

#28

My 07 wr450's pin looks like the pictures , but without the dent in the edge. The bucket has the dings about 3mm in from the edge only and is not nearly as bad as the picture. I have about 220 hours on this bike. The pin looks the same as it did when it was new.



Thanks for the info Mlynn. Now I know that my pin is normal and that a 3rd person has dings in the bucket.

I think most would agree that any dings in the face of the bucket are a problem. The surfaces of the cab lobe and bucket should be perfectly smooth. Surely Yamaha wouldn't have designed this knowing that the bucket would get banged up.

  • Frostbite

Posted March 11, 2009 - 04:45 AM

#29

Conversion to manual decomp is possible on '06 and earlier engines by using Yamaha's kit, PN 5TA-W1228-00-00, or the individual parts, but you would no longer be able to use the e-starter without AD. It's impractical on the '07+, since the bore in the head for the decomp shaft was eliminated.


I ordered the manual decomp kit this morning, thanks for the part # Grayracer. Best case scenario would be if I can reverse the spring on the auto decomp so it holds the weight in the off position, and adapt the manual kit to flick the weight to the on position for starting. That'll allow me to continue to use the E start, which I have become fond of.

If that's too impossible, I'll try to drill and tap the head so the manual kit can be installed the way it was intended, and go back to kick starting, which I have had plenty of practice with from my 400. Maybe the E start will be able to spin the engine over once that 1st compression stroke is released, you never know.

  • grayracer513

Posted March 11, 2009 - 06:32 AM

#30

I ordered the manual decomp kit this morning, thanks for the part # Grayracer. Best case scenario would be if I can reverse the spring on the auto decomp so it holds the weight in the off position, and adapt the manual kit to flick the weight to the on position for starting. That'll allow me to continue to use the E start, which I have become fond of.

If that's too impossible, I'll try to drill and tap the head so the manual kit can be installed the way it was intended, and go back to kick starting, which I have had plenty of practice with from my 400. Maybe the E start will be able to spin the engine over once that 1st compression stroke is released, you never know.

I hate to be the one to tell you this, but you'll recall I said this kit will not fit an '07 because it lacks the bore in the head. You will not be able to duplicate that machine work without removing the head and setting it up in a mill. It has to be precisely placed, and has 3 steps in it.

If you did have the kit in place, reversing the spring would also prove to be impractical. Your simplest solution would be to grind the pin down to the point where it was no longer effective. Removing the entire mechanism is fairly simple, but would likely require rebalancing the cam; it does spin up to 5000 rpm, after all.

A better approach, IMO, would be to carefully radius and polish the contact edge of the pin and use the setup as is.

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  • broccoli2

Posted March 11, 2009 - 07:59 AM

#31

Holy Christ... You guys know way to much about your bikes.. I what to be just like you when I'm all growed up... Shiiiiiat i am all growed up.. And I am a Photographer and them there are some nice pic's Frostbite. Great lighting and love the shallow focus. I'd put a couple of those on my wall, would make great conversation piece, and are just plane cool looking.. I might have to take my bike apart just to take some photos, Crap, but than I'd never get it back together, well i could but I don't think it would run for long...

  • Charles De Mar

Posted March 11, 2009 - 08:41 AM

#32

Frosty run it till it blows:p hopefully that won't be 30 miles from the nearest heat and out on the arctic ice.

  • erickdj

Posted March 11, 2009 - 09:01 AM

#33

I haven't seen anyone in the yz forum bringing this issue up, not that it doesn't happen and nobody has noticed. But, if it doesn't happen to the yz's, then you'd benefit from installing a yz exhaust cam and a new bucket. That way, the problem is eliminated and you pick up a good boost in performance at the same time. I recently installed a set of 06 yz cams to my 07 wr450f, the e-start still works. For what it's worth, I don't remember seeing any kind of wear on the valve buckets, I'm pretty sure they all looked smooth and shiny like new.

  • Frostbite

Posted March 11, 2009 - 09:11 AM

#34

I hate to be the one to tell you this, but you'll recall I said this kit will not fit an '07 because it lacks the bore in the head. You will not be able to duplicate that machine work without removing the head and setting it up in a mill. It has to be precisely placed, and has 3 steps in it.


Haha, I did read that you said it wouldn’t bolt onto the 07, but I thought I could drill it myself. The head is off so I’ll see if it looks possible. I don’t have a mill but can do wonders with a drill press.

If you did have the kit in place, reversing the spring would also prove to be impractical.


My thought here was to have the decomp default to pin in, so if it did stick there would be no damage, just hard to start. I was planning to see if it would be possible to tap into the valve cover so the weight could be activated manually during starting. I know this is waaay out in left field, but it’s a thought.

Your simplest solution would be to grind the pin down to the point where it was no longer effective. Removing the entire mechanism is fairly simple, but would likely require rebalancing the cam; it does spin up to 5000 rpm, after all.

A better approach, IMO, would be to carefully radius and polish the contact edge of the pin and use the setup as is.


If I did round off the pin, wouldn’t that reduce it’s effectiveness quite a bit. It would significantly decrease the duration that the valve is held open, but maybe it would help. If the surface of the pin is hardened, and I ground it, I’d be in trouble.
I never thought about rebalancing the cam. Normal cams don’t seem to have counterbalance balance weight to compensate for the lobes, or is the weight incorporated so you don’t really notice it. I don’t think it should be a problem to leave the weight in place and just remove the pin. I can practice with the old cam before I mess with the new one.

Holy Christ... You guys have know way to much about your bikes.. I what to be just like you when I'm all growed up... Shiiiiiat i am all growed up.. And I am a Photographer and them there are some nice pic's Frostbite. Great lighting and love the shallow focus. I put a couple of those on my wall, would make great conversation piece, and a just plane cool looking.. I might have to take my bike apart just to take some photos, Crap, but than I'd never get it back together, well i could but I don't think it would run for long...


Hey Broccoli, I do enjoy that you think I’m a good photographer, but I’m not. Those pics were taken with a cheap digital camera, set to macro, and the lighting is from a tiny 1.5 volt led light. I shot the pics with the lens pushed in tight to my lighted loupe. I played around with the distance between the loupe and the cam to get the focus close.

Frosty run it till it blows:p hopefully that won't be 30 miles from the nearest heat and out on the arctic ice.


That’s my whole reasoning behind eliminating the decomp pin altogether. I regularly ride far out of town, alone, in extreme cold. I got stranded overnight once and don’t want to go through that again. Just knowing that the pin could cause problems would have me worried. Since it’s -30 here most of the time, it’s impractical to remove the valve cover regularly to check for damage. The hoses and cables are so cold that they won’t bend enough to allow removal of the cover. To get it off I have to bring the bike inside, usually my livingroom. Not only does it take a while to thaw out, I have to lay plywood down to protect my floor from the spikes, so it comes in only when absolutely necessary.

  • Frostbite

Posted March 11, 2009 - 09:13 AM

#35

I haven't seen anyone in the yz forum bringing this issue up, not that it doesn't happen and nobody has noticed. But, if it doesn't happen to the yz's, then you'd benefit from installing a yz exhaust cam and a new bucket. That way, the problem is eliminated and you pick up a good boost in performance at the same time. I recently installed a set of 06 yz cams to my 07 wr450f, the e-start still works. For what it's worth, I don't remember seeing any kind of wear on the valve buckets, I'm pretty sure they all looked smooth and shiny like new.


Is the YZ cam a direct drop in for the WR? If it is, then maybe I will get the YZ unit. The shop I ordered from doesn't place their Yamaha orders until Thursday, (tomorrow) so I have time to change it.

  • erickdj

Posted March 11, 2009 - 09:25 AM

#36

Is the YZ cam a direct drop in for the WR? If it is, then maybe I will get the YZ unit. The shop I ordered from doesn't place their Yamaha orders until Thursday, (tomorrow) so I have time to change it.


Yes, direct plug 'n play. Same timing marks, etc... The 06 and 07 yz cams fit, but the word is that the 06 cams give the best power boost. I used both intake and exhaust cams from 06 and the power is quite nice.

  • grayracer513

Posted March 11, 2009 - 09:27 AM

#37

If I did round off the pin, wouldn’t that reduce it’s effectiveness quite a bit(?) It would significantly decrease the duration that the valve is held open, but maybe it would help. If the surface of the pin is hardened, and I ground it, I’d be in trouble.

It would reduce the duration of the pin's lift of the tappet slightly, but I doubt it would be so much as to have a significant negative effect on the operation of the unit. That is to say, radiusing the pin will in fact cause the exhaust valve to be reseated earlier than it otherwise would, but only by a few degrees, and I think the compression stroke would still be adequately reduced so that normal starter operation could occur.

I have a feeling that the pin is fairly hard clear through, as there are some who have ground it down quite a bit more than what I'm talking about doing here in order to reset their timing to YZ specs, as I mentioned earlier. The key is the finish you put on it. You could even practice on your old cam. Anyone even considering attempting precise machine work with a drill press should hardly be intimidated by this.

Again, the YZ450 does not appear to have this problem, and the decomp pins in those are ground to a half-round shape.

  • Frostbite

Posted March 11, 2009 - 11:13 AM

#38

Anyone even considering attempting precise machine work with a drill press should hardly be intimidated by this.


Point well taken.

Again, the YZ450 does not appear to have this problem, and the decomp pins in those are ground to a half-round shape.


Yes, direct plug 'n play. Same timing marks, etc... The 06 and 07 yz cams fit, but the word is that the 06 cams give the best power boost. I used both intake and exhaust cams from 06 and the power is quite nice.


Thanks guys, these points also well taken. I just called and cancelled the manual decomp kit, and changed the cam from 07 WR to 06 YZ. I appreciate the advice.:)

  • erickdj

Posted March 11, 2009 - 11:21 AM

#39

Thanks guys, these points also well taken. I just called and cancelled the manual decomp kit, and changed the cam from 07 WR to 06 YZ. I appreciate the advice.:)


Let us know how you like the extra power with the yz cam.:banghead:

  • Frostbite

Posted March 11, 2009 - 11:23 AM

#40

Let us know how you like the extra power with the yz cam.:)


I'm also installing an athena big bore kit, so there should be a nice bit of extra power. I'll let you know if I over rotate my first wheelie.:banghead:




 
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