Wednesday, September 22, 2010

1974 CB 360

CB360 cam adapted for needle rollers
Part of the rebuild for the CB360 engine at the shop included converting the cam to a needle roller setup, this involved having a friend machine the head to accept 28mm bearings, modifying the oil holes for the old bearings, and creating a new oil passage to the center bearing.  After riding a few miles, oil started coming out of the left oil seal and I found that the cam didn't have enough of a shim on the left side and was pushing out the oil seal, so I split the difference with the 1mm shim on the right side, and used two .5mm shims, one on each side.  After 300 miles, the engine was again pulled due to another issue, turns out one of the tappet locknuts came loose and backed out with the tappet, got stuck in a valve spring and siezed the cam, the camchain slipped over the sprocket and the pistons nailed the intake valves.  Because I had the engine apart, I inspected the cam and also found spalling on the bearings where they rode on the needle rollers.  Turns out the chill hardened cast iron of the cam isn't hard enough to run on needles, so the solution became machining some stainless sleeves to the original OD of the cam bearing, machining down the cam bearing to the ID of the sleeve, and heat fitting the sleeves over the original bearing areas.  After a few tests, it was found the stainless has much better wear properties and should last indefinitely.
machining the cb360 head allows for a larger
shim on the left and right sides of the cam,
this is better for the longevity of the shim

the installed cam without bearing shows
the machined stainless steel sleeve that
will allow the cam to ride on needle
bearings without causing damage
to the soft cast iron of the cam
I found that the head can be machined about .090" on each bearing side, to make it even with the valve cover sides, making it easier to install a thicker shim which should last longer.

After machining the head, the replacement intake valves were lapped into the seats and tested for sealing.  I used a method of installing the valve with spring and retainer, then resting the head on it's side and filling the intake ports with paint thinner, after letting this setup sit for 15 minutes, any tiny leaks will be apparent, as the thinner has a way of seeping through the smallest of pores.  A little condensation around the seat is normal, and can be seen if you dab at the seat with the edge of a paper towel, but any actual runs of thinner indicate a less than adequate seal.

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