Question about cam timing - Am I dumb?

[flightlead404]

Its been 24 years since I've done this so bear with me. Timing LHS cam, Dougherty SC cams on '86 930. Yes, I have the LHS cam in the left cam tower

Crank at Z1 (the second of the two close together pulley marks when rotating clockwise to pass the TDC notch). Set the cam with dot and Woodruff key at the top, "930" at the bottom. Pin in sprocket, idler arm and chain tight, intake #1 in and adjusted. Verified nothing moved. Checked at dozen times, I'm at Z1, cam aligned as described above, rocker foot adjusted right, dial gauge on the valve retainer lip.

Now, Wayne's book says it s/b starting to open not long after I start turning the crank, but I have to go almost 360 degrees before there is any movement. Valve doesn't start to move until about 5 BTDC or 355 degrees of rotation. At TDC I'm at 0.0737mm or 0.0029" Is this right?

Then, I reach 1.8mm or 0.0709" of lift at about 25 ATDC. That is, almost exactly the same distance the BTDC mark is before the Z1, except after Z1. Way, way before I'm at TDC again.

My maximum lift is 11.303mm or 0.445" at about Z1 + 125 or 25 ATDC cylinder 6/3.

I'm very confused. What am I not understanding or doing correctly.

[flightlead404]

Chris from Turbokraft called me while I was still in the shop, on a Saturday night no less (must have the same social life I do lol) and walked me through my thinking.

I'm keeping the thread going in the rebuilding forum which I think is the best place. I still have a question there about what is acceptable difference between LHS and RHS.

[jpnovak]

Sounds like you are doing it correctly but your cam is about 25 deg retarded. This is because you reach your desired lift (presumably 1.8mm as specifically called out) at 25 deg ATDC.

So, Engine at Z1 TDC (rocker is loose due to valve lash)
rotate engine 360 deg to put cam at overlap.
rotate cam (not crank) until dial gauge reads your desired lift.
insert pin
torque nut/bolt (depending on year)
rotate engine 720 deg (2 turns) and verify you are at correct overlap lift.

Then move on to Cylinder #4.

[flightlead404]

Originally Posted by jpnovak

Sounds like you are doing it correctly but your cam is about 25 deg retarded. This is because you reach your desired lift (presumably 1.8mm as specifically called out) at 25 deg ATDC.

So, Engine at Z1 TDC (rocker is loose due to valve lash)
rotate engine 360 deg to put cam at overlap.
rotate cam (not crank) until dial gauge reads your desired lift.
insert pin
torque nut/bolt (depending on year)
rotate engine 720 deg (2 turns) and verify you are at correct overlap lift.

Then move on to Cylinder #4.

Thanks Jamie. I got it completed. You're correct what was throwing me was that the initial setting was so far off that I didn't get the behavior I was expecting.

[jpnovak]

Great. What cam is it? 1.8 should be close to 993SS.

[flightlead404]

SC+ from DRC. Their recommend was 1.8mm