Simply taking the slack out is not exactly what I was gettin at.  You lob off the underside of the head and now the cam centerline gets closer to the crank centerline.  The chain will go waaaay slack.  Cam timing will be retarded, and the slack side of the chain will have to move forward, toward the drive side of the chain.  At some point, it’s gonna start getting too close to the drive side of the chain.  If the slack side touches the drive side,   Oooooooo man that would be ugly.

Might be able to re-arch the rear chain guide such that more of the slack gets taken up at points closer to the cam sprocket, areas where there is more distance between the drive & slack sides of the chain.  That would probably require bucking up the rear guide with some sort of strong back to make sure it doesn’t flex.  I think that’s doable.  It’s certainly something I’ve been considering.  I really would like to tighten up that quench zone.

Just a thought ,but if your trying to rid yourself of extra cam chain slack ,rather than arch the rear guide ,it may be better to arch the front guide . For one thing it's fixed in place ,and it would have the advantage of advancing the cam timing,  rather than retarding it, if that's your need.

sparktfxr wrote on 10/03/18 at 04:28:37:


You may be completely accurate in your compression calculations.......the 10.5:1 often quoted is what Wiseco lists for the piston when fitted to a DR engine.  When installed in the Savage both the compression ration and deck height may be less than what would be ideal - but it is better than stock!

So....maybe we can start running 87 or 89 octane?

Mike  said he was multiplying the cam lobe lifts by a 1.38  advantage of the rocker arms . IF the Clymer manual is to be believed, it states that total valve lift is .330 for both the intake and exhaust(stock cam), yet the stated cam lobe lift for the stock cam is .254 /.244    . That would make the rocker arm ratios  1.299 for the intake, and 1.352 for the exhaust , That and the fact that manufacturing tolerances / and pivot shaft wear , of the rocker arms can be +/- .015  , can lead to false assumptions on total valve lift.

DragBikeMike , I fully agree that your actual measurements  are the way to go,  but for example the stock intake valve lift (.254  x 1.299 = .330 ) could range (do to the +/- .015  rocker arm tolerance)  from .310 to .349  , so that moving the same cam from one motor( Head) to another might see some difference in the actual total lift , strictly caused by the change in rocker arms. I would think in some cases it might pay to move the rocker arms with the cam.

Here is a shot of one cam lobe.

As you can see, all appears well.  I have pondered this oil hole issue and have decided to leave the cam as-is.  Although Dave has shown that drilling the holes is perfectly doable, I want to test the cam without the holes to see how it holds up.  Although there is some risk involved, I think we can all benefit from a good look at how it holds up over the long hall.  So far it seems to be holding up well.  There is no indication of any sort of adverse wear.  I might add, I am not a big fan of break-in procedures.  I know it's the prudent thing to do, but I'm an old drag racer.  You can't take your drag bike out for a 1000 mile break-in procedure.  You put it together with ample clearance and run the guts out of it. That's what this DR cam got.  I was WOT pretty much from day-one on this cam.  It held up good so I guess it can take it.   Surprise! Yes, the cam & rockers hold up well, but the main bearings don't.  Be careful, this is a trap.  The holes seem to be there to lubricate the cam, but IMO they are there to send additional oil down the head drains to provide lube to the main bearings.  I've got over 50K on the odo and the cam lobes and rockers still look great, but the left-hand main bearing, not so great.  Factory service manual says main bearings get lube from the head drains.  I shoulda drilled the holes.
DBM  7/13/23

Holymoly that is a clean top end. We usually only see them when there is a problem.