What happens if your decompression return spring breaks!



8 replies to this topic
  • AZJeff_99WR400

Posted February 12, 2001 - 02:51 PM

#1

Greetings to the WR owners everywhere and thank you for all the great tech tips.

I have a rather sad story to relate. It's a bit long winded, sorry. Here goes.

Somehow during my last ride in the Arizona desert the decompression release return spring broke. I only discovered this after washing the bike for the next ride and attempting a restart. As I pulled the decompression lever in preparation for the pre-start "ritual" it felt like the cable had snapped and the engine kicked over way too easily. So, off came the tank - that's when I discovered the broken return spring. Pushing the decomp lever back to its normal position did nothing to restore the normal leg-busting compression. Hi-ho, hi-ho, off to the repair shop I go :)

The diagnosis? A basic leakdown test of the cylinder is pointing towards bad valve guides, possibly more :D I do not know the full extent of repairs and parts as I am writing this, but the shop suggested replacing the piston rings as long as they have to go into the motor that far.

Has anyone else ever heard of this type of part failure or know additional information?

Thanks,
Jeff

'99 WR400, YZ timing, no airbox lid, FMF oversized headpipe, Power Core IV-SA exhaust, Race Tech suspension, IMS YZ desert tank/seat combo, FMF 909 bars and grips, *Aluminum Bark Busters with big plastic UFO hand guards, *Moose skidplate, *Scotts rear disc guard, *Acerbis front disc guard (all *items a must in AZ!), Water-Wetter in radiator water. A Scotts steering damper is next...

[This message has been edited by AZJeff_99WR400 (edited 02-12-2001).]

  • Hick

Posted February 12, 2001 - 03:40 PM

#2

So, at some point the spring broke while the bike was running. When you tried to restart it later the compression stroke was effectively nonexistent. Now, I’m assuming, it won’t run at all. Hmm.

I don’t understand how your bike lost compression while you were washing it. Maybe the actuating rod is binding on something (part of the spring, the stop-tab on the head) that prevents the exhaust valve from closing completely. Did you try removing the shaft completely and then trying the leak down test? Did you tell the shop about the broken spring? I’m sure you did, but what bugs me is they didn’t investigate any damage this may have caused.

I’m working on the assumption that the broken spring and motor problems are related, if the broken spring allowed the release to actuate the bucket and valve while the bike was running for extended periods I’m sure you have done some valvetrain damage. Maybe this has damaged the exhaust valve bucket to the extent that the valve is now hanging open. I’m guessing if you inspect that exhaust valve, cam and bucket you will probably know why you have lost compression.

Sorry for your misfortune bud…

  • Boit

Posted February 12, 2001 - 03:51 PM

#3

This is a new one. It surprises me a little that the compression release shaft was able to stay in the position of holding down the exhaust valve......unless you pull the lever in completely. Is that what you are saying happened? ..and you only experienced low compression after washing and trying to restart? Have you checked your valve lash lately? I'm wondering if maybe there might be a valve or two that are a bit too tight and not closing enough to seal completely giving the low compression. I'm not sure how a leak down test will show bad valve guides?

  • AZJeff_99WR400

Posted February 12, 2001 - 04:00 PM

#4

Hey Hick.

Thanks for commenting on my dilemma.

I'm sure the spring broke while the bike was running and being ridden, it would pretty much have to don't you think? Funny thing is the bike restarted all that day without any problems AND the decompression lever seemed to feel OK and worked properly. Very strange indeed.

Regarding the internals of the motor, I trust all the SERIOUS thumper work to my performance mechanic. His shop knows the whole story about the broken spring and all.

I agree with you that if the broken spring allowed the release to actuate the bucket and valve while the bike was running, that would likely result in my current state of valvetrain damage.

Since I have not heard the final report from my mechanic, I can't comment as to the full extent of damage that occurred. The decompression return spring is apparently the bike's Achilles Heel.

It's been almost three weeks now since my last ride and I'm hating every non-thumping minute of it!

-Jeff

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • Ken

Posted February 12, 2001 - 06:00 PM

#5

Keep in mind that a warm engine would allow for increased clearance in the bucket bore (as compered to a cold engine). If the decomp cam has damaged the bucket and the engine cooled, potentially the bucket is now stuck (down) in the bore of the head. Just a thought.

Ken

  • AZJeff_99WR400

Posted February 12, 2001 - 07:57 PM

#6

Ken,

Thanks for the additional information. So far, all the comments you, Hick and Boit have made are open possibilities. I guess I will just have to sit tight for a few more days until my mechanic can provide the real story (and unfortunately, the bill $$$).

The AZ desert just chews up and spits out everything it encounters!

I'll post more news when I get something solid to report.

-Jeff

------------------
Phoenix, Arizona - home of the Arizona Trail Riders and the Desert Mountain Enduro Series. Visit ATR at <A HREF="http://www.arizonatrailriders.org).

'99" TARGET=_blank>www.arizonatrailriders.org.

'99</A> WR400, YZ timing, no airbox lid, throttle stop trimmed, FMF oversized headpipe, Power Core IV-SA exhaust, Race Tech suspension, IMS YZ desert tank/seat combo, FMF 909 bars and grips, *Aluminum Bark Busters with big plastic UFO hand guards, *Moose skidplate, *Scotts rear disc guard, *Acerbis front disc guard (all *items a must in AZ!), Water-Wetter in radiator water, Scotts steering damper is next...

[This message has been edited by AZJeff_99WR400 (edited 02-12-2001).]

  • Rich_in_Orlando

Posted February 12, 2001 - 08:18 PM

#7

Geez, not another thing to worry about!!! Is there anyone out there who hasn't had a major mechanical problem? I'm serious.

I'm beginning to think Yamaha designed the WR as a throwaway bike.

Rich

  • TheBOS

Posted February 15, 2001 - 04:22 AM

#8

Originally posted by Rich in Orlando:
Geez, not another thing to worry about!!! Is there anyone out there who hasn't had a major mechanical problem? I'm serious.

I'm beginning to think Yamaha designed the WR as a throwaway bike.

Rich



Keep in mind:

1)A lot of people post here ONLY if they have had a problem with the bike and are looking for advice on how to fix it. There's a large number of Yamaha 4stroke owners out there and if a fraction of them only post on this forum if there's a problem then it's going to appear as if the bike has lot's of problems. When in fact 99.9% of the riders out there are very content.

2)Just imagine if everyone posted their positive experiences after every problem-free ride they have had on a Yamaha 4stroke....I think it's fair to say these posts would greatly outnumber "problem" posts.

3)It's a dirtbike, if you ride it hard it's going to break, especially if you don't do preventive maintance (just like any dirtbike).

  • bonez34

Posted February 15, 2001 - 03:21 PM

#9

same goes for me. i have had my bike for over a year with zero problems other than the normal parts that wear out-brakes, fork seals, etc.. i have never owned anything that can take the punishment i give to a dirt bike like the WR. two strokes are a maintenance nightmare without working on them after every ride and dumping hundreds of dollars in them every month. my dollar to ride ratio is higher on this than i could ever expect out of any other bike of this performance category. in my opinion the wr has written itself a new category of super performance, ridability, and price. if you want problems, go over to the drz forum, they got some :)!!

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DRZ400E: Where's the power on this thing?




 
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