Beware of Auto decomp damage



108 replies to this topic
  • Frostbite

Posted March 09, 2009 - 05:41 PM

#1

There was a thread a few weeks ago regarding dents in the top of a valve bucket. I had my 450 apart at the time and took a look and sure enough I had 1 bucket that looked like it had been hammered, all the rest perfect. The initial poster and I discovered that the same bucket was damaged, and then someone else pointed out that was the bucket that the auto decomp pin hits.

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The general feeling was that the dents aren't in the area where the cam lobe contacts, so it shouldn't be a problem. I was getting ready to install my cams this evening and took a little closer look at my exhaust cam and can't believe I didn't notice this before - the lobe beside the pin is sharpened to a point. Looking straight down at the lobe (which I did when replying to the initial post) the lobe looks fine, nice and shiny and no scratches. Looking from the end is a different story.

Posted Image

Oher exhaust lobe

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So I re-looked at the bucket and now things make more sense. There are 3 rings on the face of the bucket. There's a center circle that's dented up, then a middle ring that's fairly smooth, and then an outer ring that's dented up.

The center circle is not contacted by the pin whatsoever, only the cam lobe strikes here. The middle ring is where the pin strikes the bucket. The outer ring is contacted by the cam lobe and the pin.

Posted Image

As the cam lobe starts to contact the bucket, it first makes contact near the very outer edge as it starts to push the bucket down. So the cam lobe appears to wipe across the entire surface of the bucket and all the way around, as the marks appear to indicate that the bucket is spinning.

The dents in the outer ring of the bucket appear to be caused by the pin as it starts to make contact. The sides of my pin are fairly sharp, so it’s no problem to believe that they are causing the dents. The middle ring appears to be smooth, but I think it is worn smooth by the cam, eventually wearing down the dents.

One intriguing question is “why doesn’t the cam wear down the center part of the bucket?” I looked at the other 4 buckets, and although they are not beat up, there is a center ring on them that appears not to be worn.

Posted Image


Maybe the momentum of the valve opening takes the pressure off the cam lobe at it’s peak – ie. maybe the valve is thrown down fast enough that the peak of the valve barely touches the bucket as it passes, resulting in reduced wear.

Most likely it’s got something to do with the little pimple on the underside of the bucket. The non wear area on the top of the bucket looks to be the same size as the pimple underneath. Maybe the extra metal causes that spot to be slightly concave, or maybe when it get’s hot the thickness of the metal causes it to warp slightly, again making it a bit concave .

I checked my decomp stuff and it appears to be working freely. I’ve heard a few different RPM’s that the pin is supposed to engage at, so I stuck a variable speed drill in the end of the cam and started winding it up. The counterweight swung out at a very, very low RPM. I was trying to count the bumps as the lobe bounced off my finger, but it was hard to be accurate. I’ll guess 2 or 3 bumps per second, so that would be 120-180 RPM. Pretty damn low and hard to believe that the engine would stay running at such a low speed. That leads me away from the “lugging the engine” theory. I’m now leaning more towards the damage being caused at startup or shut down.

To sum things up, my bucket is beat up and my cam lobe is sharpened to a point. The center of the bucket is only contacted by the cam lobe, so either the lobe is dragging bits of metal to the center, or the lobe itself is doing the damage as it disintegrates. The lobe looks smooth and shiny, not chewed up the way I would have expected. Bottom line is I need a new cam and bucket. The question is “WHY?”

  • JSanfilippo

Posted March 09, 2009 - 08:57 PM

#2

Bottom line is I need a new cam and bucket. The question is “WHY?”


The '07+ WRs are hard to kick because of the lack of valve overlap...apparently to appease the tree hugging bark pokers.

My theory is that because of that extra compression its basically taking more force to open the valve during starting than say, an YZ 450f. That force is chewing up the bucket. Again, this is what I think is going on.

I'm gonna open her up in about 400 miles (if I ever get this suspenesion sorted) to check the valves again and I'll pay special attention to the cam lobes.

This may be an incentive to go to at least a YZ exhaust cam.:p

  • Birdy426

Posted March 09, 2009 - 09:25 PM

#3

Cam lobe wear like that is typically a result of one of three things: Initial start up after assembly...didn't put the bad boy together with assembly lube, didn't prime the pump, or didn't "run in" the camshaft. If you've never dorked with the cams, that would be a Yamaha build issue. Second, oiling issues, either a plugged oil passage or something like that...frostbite, with the cold temps you operate in, I assume you're using 5Wsomething multi-grade oil, and I think I remember a burnt bike from a block heater, so I'm not sure how likely that is, and Third, excessive contact pressures, eihter due to geometry (in this case, something would have to be mis-assembled) or high spring forces. Oh...a fourth possibility (and probably most likely) might be a bad heat treat on the cam. As long as you are installing new parts anyway, you might want to send your camshaft and some photos to Yamaha to see if they will help you out with parts cost, or at least send 'em to a failure lab to see if it's heat treat. I, too would be concerned about putting the beast back together until you understand why it did what it did...

  • SXP

Posted March 09, 2009 - 09:34 PM

#4

The '07+ WRs are hard to kick because of the lack of valve overlap...apparently to appease the tree hugging bark pokers.

My theory is that because of that extra compression its basically taking more force to open the valve during starting than say, an YZ 450f. That force is chewing up the bucket. Again, this is what I think is going on.

I'm gonna open her up in about 400 miles (if I ever get this suspenesion sorted) to check the valves again and I'll pay special attention to the cam lobes.

This may be an incentive to go to at least a YZ exhaust cam.:p


Yeah, but the first poster (TAKSX) who reported this wear has an 04 so it's not limited to the 07+...:ride:

  • Frostbite

Posted March 10, 2009 - 02:39 AM

#5

The '07+ WRs are hard to kick because of the lack of valve overlap...apparently to appease the tree hugging bark pokers.

My theory is that because of that extra compression its basically taking more force to open the valve during starting than say, an YZ 450f. That force is chewing up the bucket. Again, this is what I think is going on.

I'm gonna open her up in about 400 miles (if I ever get this suspenesion sorted) to check the valves again and I'll pay special attention to the cam lobes.

This may be an incentive to go to at least a YZ exhaust cam.:p


So the YZ exhaust cam will drop in and has different geometry than the WR cam? I'm surprised that the end of the pin isn't more rounded, the edge of it is fairly sharp and explains the little hatchet marks in the top of the bucket.

Cam lobe wear like that is typically a result of one of three things: Initial start up after assembly...didn't put the bad boy together with assembly lube, didn't prime the pump, or didn't "run in" the camshaft. If you've never dorked with the cams, that would be a Yamaha build issue. Second, oiling issues, either a plugged oil passage or something like that...frostbite, with the cold temps you operate in, I assume you're using 5Wsomething multi-grade oil, and I think I remember a burnt bike from a block heater, so I'm not sure how likely that is, and Third, excessive contact pressures, eihter due to geometry (in this case, something would have to be mis-assembled) or high spring forces. Oh...a fourth possibility (and probably most likely) might be a bad heat treat on the cam. As long as you are installing new parts anyway, you might want to send your camshaft and some photos to Yamaha to see if they will help you out with parts cost, or at least send 'em to a failure lab to see if it's heat treat. I, too would be concerned about putting the beast back together until you understand why it did what it did...


This is the first time I've opened the engine in the 450, except to replece the valve cover. I run synthetic 0W40 and a block heater, and never had a problem with the old 400. Lack of oiling was aproblem with my bike, as the reason I took it apart was to put a new crank in, the bottom end bearing went. I'm blaming this on the 2 times my valve cover gasket 1/2 moon blew out and I was forced to ride home low on oil. However, only the decomp bucket is damaged, the other 4 buckets are perfect, and it looks like the pin is doing the initial damage.
Birdy, don't you think #1 would be the cam lobe wearing prematurely against the rough surface of the bucket? If lack of asembly lube would wear down the cam even with a smooth bucket, then it would make sense that a chewed up bucket would eat the cam.
I will contact Yamaha and send the cam and bucket if they allow.

Yeah, but the first poster (TAKSX) who reported this wear has an 04 so it's not limited to the 07+...:ride:


Good point SXP. I wonder how hard it would be to convert to manual decomp?

  • grayracer513

Posted March 10, 2009 - 06:38 AM

#6

The wear in this case is almost certainly caused by the decomp pin, shaped as it is in the picture here. The YZ pins are rounded to a half-ball point, and I've never seen any damage such as this to a YZF lifter. Given the angle at which the pin must initially contact the bucket, I don't see any way this would have been able to pass inspection by any thinking engineer, and if there are in fact a number of WR's produced this way, I think it's a problem. I wouldn't think it had any chance of working over the long term as it appears here.

One thing that occurs to me is the possibility that the pin once had a hardened cap that was friction welded to the end, and has now broken off. An owner of a low mileage WR would be able to verify that by seeing what shape the end of the pin is in his bike.

The cam lobe wear is the result of the cam having lost its hardened outer face. Cams are surface hardened, and wear like that once the surface is worn through. As you noted, the cam wipes across the face of the lifter as it engages it, but the first contact is actually right in the area contacted by the decomp pin. The flank of the lobe rolls down onto the bucket, and the contact patch then rolls out toward, but never over, the edge (the need to avoid edge contact is one of the limiting factors for how aggressive lobe profiles can be without roller lifters). At low speeds, peak pressure on the cam/lifter is obviously at peak lift, but in a dynamic sense, peak pressure occurs as contact is made, and the valve accelerated off its seat. The valve is decelerating as it nears peak lift, and the velocity of the cam lobe surface running across the lifter is quite high, with well established hydrodynamic planing on the oil film. Lifters on passenger cars often do wear more in the center, high speed engines often do not.

Valve timing and overlap won't really have an effect on how hard the engine is to kick over, but the decomp timing will. Since the exhaust valve is lifted prior to the beginning of the compression stroke while the intake is still closing, compression has no effect on the load on the pin. The time at which the valve reseats during the compression stroke is where the resistance or lack of it in the kick crank comes from, and this is a function of the length of the pin and the angle of the bore in the cam. Remember that the purpose of the decomp mechanism is to shorten the compression stroke, not eliminate it. And you are right about the speed at whichit operats being rather low. It is supposed to disengage at around 700 rpm, which would be 350 rpm camshaft speed. It won't ever be active while the engine is running.

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.

So anyway, it looks to me as if the pin hacked up the lifter, the lifter damaged the cam, which then cam back and wore down the lifter. I think it needs to be discovered whether the pin normally looks like that first, and if it does, I'd change the cam in a bike of my own.

  • taksx

Posted March 10, 2009 - 07:44 AM

#7

My lobe did not look anything like frostbite. Its still a nice oval rounded shape. But now that this is brought up I'm going to open her back up and double check it again.

I have a 2005 and I believe that's when Yamaha moved over to auto decompression.

  • grayracer513

Posted March 10, 2009 - 07:52 AM

#8

I have a 2005 and I believe that's when Yamaha moved over to auto decompression.

Auto decompression was introduced in 2003 along with the electric starter. An e-start would have been impossible without it.

  • taksx

Posted March 10, 2009 - 07:58 AM

#9

Auto decompression was introduced in 2003 along with the electric starter. An e-start would have been impossible without it.


I stand corrected. Thank You :p

  • Charles De Mar

Posted March 10, 2009 - 08:03 AM

#10

Frosty could your subzero lifestyle have any impact on this?

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  • Frostbite

Posted March 10, 2009 - 11:22 AM

#11

Thanks Grayracer, your knowledge and insight is always appreciated, and is very confidence inspiring. :p

I like the theory that a rounded end may have broken off of the pin, at least that would take pressure off of Yamaha engineering. Looking at the length of the pin though, I’d be surprised if it could be much longer. In it’s current condition it opens the valve for quite a few degrees of duration. In the picture showing the pin, it is actually making contact with the bucket, and it is near the edge of the bucket. A longer rounded pin may not open it much earlier, but would open the valve a lot more. This morning I ordered a new stock WR cam, so it’ll be interesting to see what the new pin looks like.

Frosty could your subzero lifestyle have any impact on this?


Charles, I am thinking that cold may be a factor, but Taksx has an identical bucket, and he’s listed in Jamaica, so I don’t think cold caused his problem. This could be the same effect from 2 different problems, so I’m not so quick to say his and mine have or do not have the same cause.

Generally the first causes I look for are cold related. 1 thing I thought of is that the decomp weight may be sticking in cold oil. Even though I use 0W40 synthetic and a block heater, there are times when I’m out on the tundra with no electricity, and start the engine cold. Even the 0W is a bit gooey at -40.

This led me to think of a more probable reason for the weight to stick – frost. There is a lot of moisture inside a hot engine. My crankcase vent hose has plugged solid with ice 2ce, causing the valve cover gasket half moon to blow out under pressure (which is probably why I had to replace the crank).

On my 400, I had problems with frost building up on the valve stems or faces after the engine was shut down. After a perfect ride and shutdown, the engine would have zero compression after sitting overnight. This happened a few times, and I was baffled, and brought the bike into a heated space to work on it. Usually I’d bring it inside and let it sit for a few hours so the ice and snow would melt. Then when I returned to see what the trouble was, there was none. Full compression and the engine fired right away.

I noticed that I only had this problem occasionally, which seemed odd, but then I clued in that it only seemed to happen when I let the engine die in gear instead of shutting it down with the killswitch. After this I always set the engine to TDC when I shut down so the valves would all be closed.I never had the problem again, since even if the valves frosted shut, the cam could pop them open, but the valve spring didn’t have the power to pull them closed.

I guess it’s possible that frost can form on the cam sprocket, and may lock up the decomp weight until it gets hot enough to melt. The decomp pin seems to ride on a type of worm drive, as the weight can move the pin, but the pin can’t move the weight.

The only other possibility I can think of where the engine would turn over a lot very slowly is jump starting, and that may be something Taksx and I have in common. A couple of times, until I got a few cold bugs worked out, my 450 was very hard to start in extreme cold. Once in a while I had to be towed by a snowmobile to get restarted, and sometimes that took a few minutes of towing. Trying to bumpstart the 450 on a slippery snowmobile trail is tricky without a manual decomp, so I’d start out in 5th gear, ease the clutch out until the engine is spinning, and then gradually gear down to get the engine RPM up enough so it would start. This would be an occasion where the engine is definitely spinning over slow enough for the decomp pin to be hitting the bucket every time by.

So, to see if our the causes of our problems could be related, I have a question for Taksx – have you had to jump start your engine?

  • taksx

Posted March 10, 2009 - 11:46 AM

#12

Taksx has an identical bucket, and he’s listed in Jamaica

I'm in southern california, sorry for the confusion. its still warm here though 70ish year round...sorry :ride:

I have a question for Taksx – have you had to jump start your engine?

Yes, I race the hell out of this bike and I tend to kill or stall the engine on nasty rock down hills out here in the california desert.

I think where getting somewhere :p

Eddie

  • Frostbite

Posted March 10, 2009 - 11:51 AM

#13

I'm in southern california, sorry for the confusion. its still warm here though 70ish year round...sorry :moon:


Yes, I race the hell out of this bike and I tend to kill or stall the engine on nasty rock down hills out here in the california desert.

I think where getting somewhere :p

Eddie


Kool. :ride: So when you stall on the downhills, do you bumpstart to re-fire, and/or is the engine still turning over as you roll downhill after stalling?

  • grayracer513

Posted March 10, 2009 - 11:56 AM

#14

I like the theory that a rounded end may have broken off of the pin, at least that would take pressure off of Yamaha engineering. Looking at the length of the pin though, I’d be surprised if it could be much longer. In it’s current condition it opens the valve for quite a few degrees of duration. In the picture showing the pin, it is actually making contact with the bucket, and it is near the edge of the bucket. A longer rounded pin may not open it much earlier, but would open the valve a lot more. This morning I ordered a new stock WR cam, so it’ll be interesting to see what the new pin looks like.

It will be interesting. One of the things I do know for certain is that the difference between the '03-5 YZ450 e-cam (5TA-12180-00-00) and the one in the WR's of those years (5TJ-12180-10-00) is timing. The camshaft itself is identical; the gear is simply indexed differently. It's actually been like that ever since 1998, and up 'til '03, all you had to do to retime a WR to behave like a YZ was to retard the exhaust cam 1 tooth. Even the part numbers for the '06 and '07 cams (5TJ-12180-20-00 and 5TJ-12180-30-00) indicate that they may be only minor revisions of the same part.

But remember we said the cam itself is identical. That means that if you retard or advance the cam, you also advance or retard the operation of the decomp pin as to the point at which the exhaust valve reseats. If the YZ cam were to be advanced, the decomp pin would loose contact with the lifter too early, and the relieved compression stroke will be longer than it should, and teh engine too hard to turn over. The way Yamaha dealt with this was to use a longer pin in the WR camshaft assemblies so that the pin takes longer to roll away from the bucket.

If you look, you can find references to this in threads here where some will advocate the grinding of the pin to allow retiming the engine using the WR cam. I don't recommend it, BTW.

  • taksx

Posted March 10, 2009 - 12:12 PM

#15

Kool. :p So when you stall on the downhills, do you bumpstart to re-fire, and/or is the engine still turning over as you roll downhill after stalling?


Sorry that wasn't a very detail answer.

After I loose the engine on technical down hills I will grip the clutch in all the way down to the bottom of the hill, just before I come to a stop I will bounce on the seat and jump start the engine. Some times I hit the magic button, but I would say seven out of ten times I bump start the bike.

Now this has happens here and there but not very frequent. I will loose total control of the bike, I let go of every thing and the bike does roll on the engine for a little bit right before it locks up the rear wheel.

  • Frostbite

Posted March 10, 2009 - 12:22 PM

#16

If you look, you can find references to this in threads here where some will advocate the grinding of the pin to allow retiming the engine using the WR cam. I don't recommend it, BTW.


It is possible that the fellow I bought the bike from may have had the cam set to YZ timing (it did have some of the usual mods done). This seems to be a popular thing and is sort of common knowledge to folks who don't know a lot about bikes. Maybe he had the timing changed, which is very simple, but didn't do anything with the pin, which would be much more difficult to mod.

I thought maybe I was on to something here - maybe the changed timing could be the cause. As I'm writing this, though, I realize that even if the valve timing is different, that wouldn't have any affect on the way the pin hits the bucket, so it shouldn't cause the pin to beat on the bucket.

I don't know if my cam timing was YZ'd or not, but I plan to install the new WR cam to WR timing. I ordered 2 new buckets and plan to open the top up regularly to monitor things. If the bucket starts to get dinged up, I can swap it out, hopefully before it eats the new cam.

  • Frostbite

Posted March 10, 2009 - 12:32 PM

#17

Sorry that wasn't a very detail answer.

After I loose the engine on technical down hills I will grip the clutch in all the way down to the bottom of the hill, just before I come to a stop I will bounce on the seat and jump start the engine. Some times I hit the magic button, but I would say seven out of ten times I bump start the bike.

Now this has happens here and there but not very frequent. I will loose total control of the bike, I let go of every thing and the bike does roll on the engine for a little bit right before it locks up the rear wheel.


Well, that means that we do have some bump starting in common, but the more I think about it, the more I think that shouldn't be a problem. The pin is designed to be hitting the bucket at low RPM, so bumpstarting for a few hundred feet should only be equivalent to e starting a few hundred times.

It must have something to do with the pin hitting the bucket at high RPM, something it was not designed to do, or as Grayracer mentioned, maybe the rounded tip broke off.

Our buckets have nearly identical marks beat into them, so if my pin tip broke, i'd guess that yours did too. The little crescent moon looking divots in the face of the bucket must be getting made by the edge of the pin.

Do you remember what your pin looked like? If you do open up the top end to check the cam, have a look and maybe take a pic of the pin. Let's see if our pins look the same.

  • grayracer513

Posted March 10, 2009 - 12:43 PM

#18

It is possible that the fellow I bought the bike from may have had the cam set to YZ timing...Maybe he had the timing changed, which is very simple, but didn't do anything with the pin, which would be much more difficult to mod.

Going from WR to YZ, the pin HAS to be modded, or the cam replaced, because leaving it as is and retarding the cam a tooth would result in there being too little cranking compression for the engine to start at all.

But, maybe he just ground it off flat because he was, oh, what's the word...STUPID. :p

  • Frostbite

Posted March 10, 2009 - 12:48 PM

#19

But, maybe he just ground it off flat because he was, oh, what's the word...STUPID. :ride:


That is always a strong possibility. For anyone just joining us, I'd like to point out that Grayracer is referring to the previous owner of my bike, not me. (Haha) :p

  • GCannon

Posted March 10, 2009 - 12:50 PM

#20

Very Interesting Tread!:p

I am considering going Auto Decomp in the old beast. But really what I want is smooth power delivery for technical riding.

I have tried both WR and YZ timing with the stock cam. I find the YZ timing makes me more tired at the end of a long day of technical riding mostly from hanging on and working harder at throttle control over rough trails.

I was hoping to install the WR decomp cam.

This thread is causing me to reconsider. However there seems to be only
two incidents in all the WR's on the forum.

Per Grays' and Frosty's description it seems the YZ cam sprocket timing has been advanced for the WR power delivery charictaristics. I believe this is where the problem is since the YZ's do not seem to be having this problem. Since the decomp system my have been designed for the YZ and merely adapted for WR use (for economic reasons). I believe this is the case since the decomp pin seems to be striking the lifter at a less than desirable angle based on what I see here.

My Questions are:

Am I worried about nothing?

Is there another cam I should be considering, From what I have read hear the Hot Cam has decomp problems in addition to the OEM problems (I have no E-start)?

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




 
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