So, I have almost all the new parts to take the engine head to the machine shop, but here's another question I have.
Since I purchased a 'step up' camshaft (stage 2 camshaft from MSA), do I need thicker lash pads or can I use new stock lash pads? And yes, I am getting new rocker arms and pivots.

The details on the new camshaft are: Lift(In/Ex): .480/.480 Duration(In/Ex): 274/274

I called MSA and they suggested I ask the guys at the machine shop to run a 'wipe pattern check' to make sure I have the right lash pads for this camshaft.

I'd like to hear from you guys, since I'm getting a bit confused about this.

 

you need thicker lash pads if the cam uses a smaller base circle. The lash pads need to make up for the fact that the cam will actually sit further away now. As far as I know the MSA cams do use a smaller base circle to allow the higher lift.

and "wide pattern check" should be "wipe pattern check" And thats to make sure the cam isn't wiping off the side of the pad.

 

Oops, mispelled that word there.

Well, when I called MSA to order the 'correct' lash pads for this camshaft, they suggested that I get a wipe pattern check so that I can get the right measurements for the lash pads. I don't know if one has to do the other one.

 

yeah...well the machine shop has to determine how thick of a pad to install. They perform the wipe check to see where the cam wipes the pad. If it's too far off in either direction then they'll install a thinner or thicker lash pad depeding on which direction its off in. If the cam is wiping off the side of the pad then it can cause premature wear and even destroy the cam lobes and/or lash pads.

 

If the cam were the only part that changed, you could just order lash pads that were thicker than stock by the amount the base circle changed. But if you had valve/seat work done, then the valves are slightly higher, unless the machinist had to take much off to get them all in the same level straight line. Or maybe you got new valves, and they're longer, or different keepers, and... That's just too many what-ifs to get the right lash pad thickness on the first shot.

Ideally, whoever sets up the cam should have a variety of the different thicknesses, get the right one figured out by trial-and-error with the wipe pattern test, and then order a whole set of that thickness. Each one still has to be checked with a wipe pattern test during the final setup, just to be sure. They're supposed to be centered, but there is some adjustment for lift vs. noise. Just don't get the pattern too close to the end of the pad, like j said. 0.010-0.015 inches is the closest you want to get (and that still makes me nervous, I like a little more). You can save a little time and screwing around by using your stock pads and some pieces of a gap gauge to make shims to create an effective thickness that you can then order.

The only catch is that if your machinist didn't straight-edge the ends of the valves when assembled, to be sure they're all in a straight line parallel to the axis of the camshaft, then you would have to custom-determine the right lash pad thickness for each valve. Not fun.

Dave

 

Ok, it's starting to make more sense.

I'm getting new rocker arms, rocker pivots, springs and spring retainers by next week. Not to mention the other parts I have. I'll take the head to the machine shop when I get the rocker arms.

Thanks for the help J.

 

I haven't taken the head to the shop yet; I was waiting to get all the parts ready before I did that, but thanks the for heads up.

I'll come back with more questions once I'm ready for the engine block.