Decompression Plug / Water Seal Replacement


4 replies to this topic
  • sCvHeaVenS

Posted November 17, 2011 - 08:31 AM

#1

Hi,

New member here, been browsing the forums for a couple of months now as a guest reading up on the threads, especially considering I bough a used 04 YZ450 and I about had a heart attack when it boiled over on me ! (one reason Im installing boyesen water pump kit)


I have done a ton of searching and I am still slightly confused on one thing...


how to do you check bearings in regards to the water pump seal replacement? Also to check the balancer shaft bearings do you insert the impeller shaft into it and try to wiggle it up and down?


As far as the decompression plug, do you simply unscrew bolt, remove old, use channel locks to press new one in and tighten bolt, or am I missing something?


Thank you!

  • sCvHeaVenS

Posted November 17, 2011 - 08:33 AM

#2

I also meant to mention, I took it to a shop to do leak down test / check valves after running it hot. Compression seems fine, I can kick over easily with one kick (maybe 2 if its cold and I'm being a sissy - already took kick start from another bike to leg and had to get stitches) after I ran hot (about 10 min / 2-3 miles of emtpy or almost empty coolant level)... Is there any other precautions anyone recommends?

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  • grayracer513

Posted November 17, 2011 - 10:29 AM

#3

I bough a used 04 YZ450 and I about had a heart attack when it boiled over on me ! (one reason Im installing boyesen water pump kit)


I have done a ton of searching and I am still slightly confused on one thing...


how to do you check bearings in regards to the water pump seal replacement? Also to check the balancer shaft bearings do you insert the impeller shaft into it and try to wiggle it up and down?


As far as the decompression plug, do you simply unscrew bolt, remove old, use channel locks to press new one in and tighten bolt, or am I missing something?


Looks like more than one thing.

Depending on the conditions under which it boiled, it could be normal, and the pump kit won't help much. A normal healthy YZ450 that stands at idle more than two minutes from a cold start in 70 degree weather might very well boil over. It will almost certainly do so if it's standing at idle for a minute after it's up to normal op temps. They are also prone to it if you're working through a long tight slow section on a hot day, where your speeds don't reach above a crawl for an extended period.

Boiling over isn't dangerous by itself, but running them low on coolant is, and they only hold about a quart and a quarter.

To check the bearings, You are looking for excesses of clearance and roughness. The WP bearing should only have .001-.002" clearance, and the balancer shaft maybe twice that or so. Any means of moving the shaft perpendicular to its axis will work.

Not sure what you are asking with regard to the plug. If it's the OEM plug (a black, rubber coated piece of sh, um, plastic), it's not anchored by the screw in the side of the head at all. These can be removed just by prying them out of place with a small screwdriver or pen knife blade (or by pinching the breather tube and riding the bike for ten minutes). If it's aluminum, like these:

https://shop.thumper...tCode=TR_376507

...Then it is anchored by the screw and would be removed by the means you describe. The seal will either be the same as for the '02 decomp shaft (like the ones in the link) or an O-ring on the cheap imitation. DON'T strip the screw by misaligning it with the groove in the plug on the way back together.

The OEM plug can also be replaced with an 18mm freeze plug, but those are hard to install with the radiator in the way.

Unless you have the OEM plug, or yours is leaking, there's no real reason to disturb it in most cases.

  • sCvHeaVenS

Posted November 18, 2011 - 04:25 AM

#4

Thanks alot! Yes It is leaking, not bad but enough for me to look up on these things... also my breather tube has rubber clips instead of metal, I am wondering if it has already blown in the past.... I already ordered the Boyesen so idk if they will allow me to cancel. I was under the assumption that most people running it noticed a huge difference when riding slow trails (which currently thats what I have been doing). Does it not also pump @ lower RPM so less speed is required to efficiently move the coolant?

I was confused on how to install it, I seen threads saying you have to drive it in, but I also seen a thread where you placed a picture showing it being pressed in with plyers using the head as support to squeeze.



how do you check for clearance exactly in the bearing?

  • grayracer513

Posted November 18, 2011 - 07:21 AM

#5

The rubber clips are an OEM upgrade they phased in at some point after '03.

The OEM bore plug just pushes in. The aftermarket plugs vary as to the force they need to be installed with.

Accurately checking bearing clearance is done with a dial gauge. "Eyeballing" works pretty well, though, if you have some experience.





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