MG MGB and MGB GT Tech Talk
I removed my camshaft and crank as part of my rebuild today. The cam doesn't look to bad, but where would one look for markings on it to see what type/brand it is. Did the original ones have any identifiers on them? Do any camshafts have identifiers on them? Is there a way to measure the lobes to identify lift /duration or could a machine shop figure that out?
Most cam grinders have their own markings. Some put the duration of the intake and exhaust (270/260) in degrees and others have their own code. If you don't know who the cam grinder was, you may never know what any markings mean. I'm unaware of any factory markings.
In order to measure lift, just set the cam in a set of V blocks And then put a dial indicator on the base circle of a lobe then rotate the camshaft 180 degrees and measure the cam lift at its peak. Subtract one reading from the other and you'll know the lift at the cam. Then subtract the amount of valve lash you set your valves at (.012" - .014" ) and then multiply the remaining difference by the ratio of your rockers - I think the stock rocker is 1.4375 : 1. That will tell you the total lift at the valve. Duration is harder to measure. Again with the camshaft in a set of V blocks, put a dial indicator on the base circle of a lobe. Attach a degree wheel to the camshaft just like you were degreeing your camshaft. Turn the camshaft slowly until the dial indicator says that you have reached .050" of lift. Set your degree wheel to zero and use a pointer/indicator stylus (an old piece of coathanger works as a pointer) to mark zero. Then rotate the camshaft over the top of the lobe and around to the base circle again. Then back up until you are at .050" of lift on the other side of the cam lobe. Read the degree wheel. The number of degrees from .050" off the base circle until .050" before returning to the base circle is the duration measured in degrees. Be sure to degree and measure lift on both an exhaust lobe and an intake lobe - frequently they're different. But before going to the expense of re-grinding your cam, factor in that a new camshaft with the stock MGB grind on it will only cost $167. Best of luck. Basil
Most aftermarket manufactures have markings stamped or etched in-between the lobes on the cam or on one of the ends of the cam. I don't recall if the stock ones have any markings. Crane blanks had copper between the lobes, but they are not as common as the Indian blanks which are bare.
Thanks all. I'll clean it some more tomorrow. The ends didn't have any markings, so I'll check between the lobes and the edges of the lobes. All the lower end bearings looked really good to but since I'm there they're all being changed. I had 60-70 lbs of pressure when running so oil was flowing in there just fine. Even the thrust washers looked good along with the crank.