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-   -   chain box alignment (http://forums.pelicanparts.com/911-engine-rebuilding-forum/526848-chain-box-alignment.html)

robmog 02-16-2010 04:56 PM

chain box alignment
 
whats an easy and accurate way to measure if the chain box is aligning properly with the cam housing? i can't fit my mic in there square. pencil dashes on paper seems too inaccurate. thanks

4sd911 02-16-2010 05:49 PM

Mock up the engine half (without any sealant) cylinder base gasket, cylinders, heads, cam tower and chain box, make sure the cams turn freely them install the cam cover and see if the cam is in correct position. This is where I'm at now, with a 1.0mm spacer under the cylinders the cam is close to the inside edge of the cam cover, about .50mm, if I go with 1.5mm spacers the cam is closer to the out side edge of the cam cover. Now this is with using the factory chain box cover gasket that measures about 0.50mm, the after market graphite gasket (which B. Anderson recommends) is about 1.0mm, with this gasket I'd need to use the 1.5mm spacers.

Not sure how all of this works in with the piston deck height, haven't checked that yet on my engine.

Walt Fricke 02-16-2010 05:53 PM

I confess I have never thought to measure this. You just use new gaskets and bolt things back up and all is well.

So have you altered something - longer rods, or shaved heads for higher CR? Is it the alignment of the cam holder/O ring seal to the chain box that is of concern?

I think that is handled by trial and error - slide a cam in and see how things line up. Put the aluminum round 3 bolt holder on without the O ring and measure. For that matter, you could use snap gauges to see how close to being centered the cam is. Then increase or decrease the gasket thickness, or shave something, etc.

Minor changes can be handled by the O ring, which can be squished a bit more on one side than the other.

robmog 02-16-2010 07:05 PM

measuring off the cam cover works well.
thanks

4sd911 02-16-2010 10:55 PM

In my case the heads are fly cut and the case cylinder face resurfaced. When I put this together 10 years ago I didn't test assemble for alignment and the cam did not line up with the box, the machine shop recommended shaving the chain box to align, this time I bought another set of boxes.


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