04 Yz450F oil leak out of decompression screw hole?


8 replies to this topic
  • BulletRaG

Posted June 29, 2011 - 01:57 PM

#1

Hi, I noticed a small oil leak out of a screw hole on the right side of my engine. So I went to my service manual to see what that hole was and its for a after market decompression system if you choose to put one in. So my next question is can I just put a screw in the hole, or is there a bigger problem going on in my engine? Any Ideas?

Just on a side note i noticed the oil leak because I started to see smoke coming up from my rad so i looked and oil was dripping from that hole onto my header. But whats weird is i bought this bike a few weeks ago without a muffler and i started it up then and i never noticed smoke so i dont think it was leaking then, but when i got a new muffler I noticed it right away so would having the muffler on it and the oil leak be conected, im thinking something to do with the back pressure or something, idk. plz help.

Heres a picture, Its the hole right above the header coming out of the enginePosted Image

  • earthmx

Posted June 29, 2011 - 04:15 PM

#2

the muffler would add backpressure to the piston and valve seat area but that hole is above that area entirely.

my guess would be bad valve guides possibly,if oil is coming out it is because there is blow by forcing it out.

if you plug it there it will leak somewhere else,best to fix it right

  • todds924

Posted June 29, 2011 - 05:55 PM

#3

Did you take the bolt out of that hole? If memory serves me correctly, there is supposed to be a bolt WITH an aluminum washer in that hole.

Edited by todds924, June 29, 2011 - 06:15 PM.


  • BulletRaG

Posted June 29, 2011 - 07:04 PM

#4

Did you take the bolt out of that hole? If memory serves me correctly, there is supposed to be a bolt WITH an aluminum washer in that hole.

I didnt take the bolt out of that hole, it could of fell out or just not of been there when i bought it. but in my service manual it does show a screw w/ a washer going into that hole but it was under the subject of puting in a decompression lever. So i dont know if there was a screw there stock or the holes only there for the decompression kit. But should oil be there in the first place?idk

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  • Anssi

Posted June 29, 2011 - 08:59 PM

#5

Yes, there should be oil (I think the hole is open directly to the cams to facilitate the decomp system actually operating on the exhaust valve(s)).

I would suggest getting an aftermarket plug that you can bolt on like the decompression system. The plug that is there from the factory is just glued or pressed on and is prone to popping off.

  • todds924

Posted June 30, 2011 - 07:00 AM

#6

Yes, there should be oil (I think the hole is open directly to the cams to facilitate the decomp system actually operating on the exhaust valve(s)).

I would suggest getting an aftermarket plug that you can bolt on like the decompression system. The plug that is there from the factory is just glued or pressed on and is prone to popping off.

Exactly! Like the bitchen ones for 17 bucks in the TT store.

  • grayracer513

Posted June 30, 2011 - 08:16 AM

#7

the muffler would add backpressure to the piston and valve seat area but that hole is above that area entirely.

my guess would be bad valve guides possibly,if oil is coming out it is because there is blow by forcing it out.

The exhaust has nothing to do with it. It leaks because it goes into the cam box, and is exposed to crankcase pressure. :thumbsup:

Hi, I noticed a small oil leak out of a screw hole on the right side of my engine. So I went to my service manual to see what that hole was and its for a after market decompression system if you choose to put one in. So my next question is can I just put a screw in the hole, or is there a bigger problem going on in my engine? Any Ideas?

To answer your question, I need to know what's plugging the larger hole in the front of the head over the exhaust port. The Gen 1 YZ450's came with a black, rubber coated plastic plug that fit in the bore originally used for the manual decompression shaft. These plugs were known to blow out without much encouragement, so the aftermarket came up with a couple of aluminum replacements that were held in place by the same bolt used originally to anchor the decomp shaft (the bolt missing from yours).

If you have the rubber plug, or if someone has installed a steel or brass cup plug (freeze plug) in the bore, you can use pretty much any M6x1.0 bolt with a copper washer.

If you have one of the fancy aftermarket aluminum plugs, you need the original bolt (PN 90109-06418-00) and a copper washer. This bolt has a pin extending from the end of it that was intended to engage a groove in the decomp shaft in order to retain it in the bore while allowing it to rotate. The aftermarket plug will have a similar groove in it.

I should point out that the threads in the head here are easy to strip, and one sure way to do that is to fail to align the retaining groove in the plug with the bolt hole. Be careful to do that if your bike is equipped with the AM plug.

  • BulletRaG

Posted June 30, 2011 - 10:51 AM

#8

The exhaust has nothing to do with it. It leaks because it goes into the cam box, and is exposed to crankcase pressure. :thumbsup:

To answer your question, I need to know what's plugging the larger hole in the front of the head over the exhaust port. The Gen 1 YZ450's came with a black, rubber coated plastic plug that fit in the bore originally used for the manual decompression shaft. These plugs were known to blow out without much encouragement, so the aftermarket came up with a couple of aluminum replacements that were held in place by the same bolt used originally to anchor the decomp shaft (the bolt missing from yours).

If you have the rubber plug, or if someone has installed a steel or brass cup plug (freeze plug) in the bore, you can use pretty much any M6x1.0 bolt with a copper washer.

If you have one of the fancy aftermarket aluminum plugs, you need the original bolt (PN 90109-06418-00) and a copper washer. This bolt has a pin extending from the end of it that was intended to engage a groove in the decomp shaft in order to retain it in the bore while allowing it to rotate. The aftermarket plug will have a similar groove in it.

I should point out that the threads in the head here are easy to strip, and one sure way to do that is to fail to align the retaining groove in the plug with the bolt hole. Be careful to do that if your bike is equipped with the AM plug.

Thats very helpful, but how can i tell which plug i have. If i post a pic of the plug head on do you think you could maybe identify it?

  • grayracer513

Posted June 30, 2011 - 11:23 AM

#9

Possibly.





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