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tantric33

Torque procedure for 426f head bolts (why not use angle torque method))

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Grayracer513,

I will be reassembling my 426 very soon (waiting for the head to get back from seat cut) and have a few questions about torquing the head bolts.

You suggested to another TT member that he stick to the torque procedure in the owners manual for the 426 (32 foot-pounds in two stages) and of course that is a sensible suggestion, but I can't help but think that the YZ450 method (angle torque) may be suitable and perhaps more accurate so I wanted to get your thoughts on this.

Here's what I'm thinking that leads me to believe that the angle torque would work:

1. I believe the 450 and the 426 use the same bolts

2. Looking at it in a VERY GENERAL sense I would think the two heads and the cylinders are so alike in size, weight etc. that the angle torque procedure must be just another way to get to 32 foot-pounds. I mean we're trying to accomplish generally the same thing with either method (that is, crush an MLS gasket and a rubber base gasket between two metal parts of the same general size weight hardness and thickness)

3. The angle torque procedure wants the bolts to 14 foot-pounds and then two 90 degree rotations. Again, this seems like it's most likely 32 foot-pounds (I know what assumptions can get you though).

Another thing that concerns me about using the 426 method is this:

Recently my cylinder base gasket began to leak out the left side around where the timing chain passes through. I noticed on the new OEM gasket that I purchased it appears that they have built up that area with a bead of some sort of dry sealant applied to the gasket. This bead is tall enough that when you lay the cylinder down on the case you can visually see the cylinder sitting up higher on that side. I would think that the side with the sealant bead is not going to crush/set the same as the other side giving an uneven/incorrect clamping force (which, again, makes me think about the angle torque procedure and how it "sets" the gasket).

Then you throw in the fact that a lot of torque wrenches are just not that accurate and angle torquing really starts to look like the way to go.

Are you aware of any issues that shops were having with the 426 leaking gaskets after rebuild using the 32 foot-pounds method? Are the 426 and 450 head that much different in design?

It even looks like the CRF's are using 32 foot-pounds torque as well, so again we're in the same ball-park with the torque specs regardless of the head/ cylinder design.

How about a mxture of the two torque methods (i.e. set the gasket a little. back off then got to 32 foot-pounds)?

Ha ha, phew. I guess I'm an "over thinker".

Thanks

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You are on the WR thread but the question can still be answered here.

I would use whatever the factory service manual recommends for torque spec on your bike.

Heres why; In 2003, Yamaha made some significant changes in their manufacturing technology used in casting engine cases and other cast parts. The Aluminum alloy used is different and the average sectional thickness is thinner on the '03+ bikes (to save weight). These factors were used to determine the cylinder head torque procedure. All of the material properties and how they react to certain loads has to be taken into consideration when the engineering staff design an assembly procedure.

I would guess that the angle-torque method would work fine on earlier bikes but I would be hesitant about using the straight 32 lb/ft torque on any 450 '03 and later.

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You are on the WR thread but the question can still be answered here.

I would use whatever the factory service manual recommends for torque spec on your bike.

Heres why; In 2003, Yamaha made some significant changes in their manufacturing technology used in casting engine cases and other cast parts. The Aluminum alloy used is different and the average sectional thickness is thinner on the '03+ bikes (to save weight). These factors were used to determine the cylinder head torque procedure. All of the material properties and how they react to certain loads has to be taken into consideration when the engineering staff design an assembly procedure.

I would guess that the angle-torque method would work fine on earlier bikes but I would be hesitant about using the straight 32 lb/ft torque on any 450 '03 and later.

Thank for the reply.

Those do sound like significant changes that would affect torque (thinner, lighter, softer, harder).

Thanks again, great info!

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