I found the source. It wasn't the service notices. It was John Brookes.
In the section on cylinder heads (P 49 of his latest edition) he has a note 1 that says there was a shortage of the cam cap bolts during early production of the Z1B, from engine S/N 46751 to 53907. They subbed with parkerized (black) bolts P/N 92003-177, using 2/3 of the recommended torque for normal bolts. John says they reverted back to the original bolts with 53908 but I suspect it might have been a little later. One of my Z1B's has engine S/N 55471, and while I don't remember that being the source of my collection I can't think of any other possibility.
73Z1...this is consistent with what you said about the early Z1B.
Edited to add....the lower torque on the parkerized bolts suggests you can go lower on standard bolts as well. What's good for the goose is good for the gander.
I have several restored bikes along with a 2006 Goldwing with a sidecar. My wife has a 2019 Suzuki DR 650 for on and off road.
Last edit: 01 Jun 2021 17:08 by hardrockminer.
The following user(s) said Thank You: slmjim+Z1BEBE
Edited to add....the lower torque on the parkerized bolts suggests you can go lower on standard bolts as well. What's good for the goose is good for the gander.
I’m not an engineer and a didn’t stay at a holiday inn but Would the diameter of the washer head on the Parkerized bolt allow for lower torque spec.
They have the same head size. But the parkerized bolt has a brittle surface due to the chemical process that turned it black. Higher torque means more tension on the shaft, which brings it closer to its failure stress. I don't know what that stress would be but some engineer at KHI would have done the calcs to come up with the revised spec. The probably failure mode is from vibration fatigue.
I have several restored bikes along with a 2006 Goldwing with a sidecar. My wife has a 2019 Suzuki DR 650 for on and off road.
They have the same head size. But the parkerized bolt has a brittle surface due to the chemical process that turned it black. Higher torque means more tension on the shaft, which brings it closer to its failure stress. I don't know what that stress would be but some engineer at KHI would have done the calcs to come up with the revised spec. The probably failure mode is from vibration fatigue.
Then a lower torque could be used on the chrome bolts. Spec is 7-9 ft lbs. 2/3 would be around 5ft lbs. could save from stripped threads.
Every 900/1000 I ever assembled I have always used 96 inch pounds/8 foot pounds on my cam caps using the 92003-092 chrome bolts.
I have never stripped the threads out of any cam cap since back in '74 when I started working on Z1/Kz900/1000 motors.
A Snap On inch pound clicker torque wrench is the only type of torque wrench I have ever used. Every few years I would send it back to Snap On for a check up!!!
1972 H2 750 Cafe Racer built in 1974.
1976 KH400 Production Road Racer.
1979 Kz1000 MK. II Old AMA/WERA Superbike.
1986 RG500G 2 stroke terror.
1986 GSXR750RG The one with the clutch that rattles!
A Snap On inch pound clicker torque wrench is the only type of torque wrench I have ever used. Every few years I would send it back to Snap On for a check up!!!
Theres a key point. Good equipment, the knowledge to use them correctly, and the maintenance of them.
