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Author Topic: Checking camshaft/crank timing on '78 cb750  (Read 6039 times)

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Offline restforyoursouls

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Checking camshaft/crank timing on '78 cb750
« on: February 17, 2011, 05:17:39 PM »

Bike:  '78 cb750 supersport

Is there a way to check the timing between the camshaft and crankshaft without the motor being taken out of the frame?  I want to verify that my friend's cam chain has not skipped a tooth due to the tensioner being loose.

any help is greatly appreciated.  I'm familiar with working on my own vintage bikes but I've never worked on a 750 but i told my buddy i would try my best to help get his bike back on the road.  Thanks!
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.a slow bike that runs great is a lot less frustrating than a fast one that doesn't.

'72 CB450 twin...leavin' it stock
'75 CB550 four....shoulda left it stock :)
'71 CT70
'75 CT70

Offline BrianAdair

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Re: Checking camshaft/crank timing on '78 cb750
« Reply #1 on: February 17, 2011, 05:36:21 PM »
The only way I know, is pull the valve cover.
 In a stock frame, that hasn't been modified to remove the lower tubes under the main backbone tube, you can't get the cover off.
The cam has a notch that is perpendicular to 2 parallel marks on the end of it, remove the points cover and turn the crank to the T mark on 1 & 4. On the cam, the notch is at 12 O-clock or 6 O-clock  and the marks will line up horizontally with the seam where the cam tower cap meets the lower part of the cam tower.
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Offline restforyoursouls

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Re: Checking camshaft/crank timing on '78 cb750
« Reply #2 on: February 17, 2011, 05:43:12 PM »
I suppose I'm pulling the motor unless someone else has a trick for it....
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.a slow bike that runs great is a lot less frustrating than a fast one that doesn't.

'72 CB450 twin...leavin' it stock
'75 CB550 four....shoulda left it stock :)
'71 CT70
'75 CT70

Offline SOHC Digger

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Re: Checking camshaft/crank timing on '78 cb750
« Reply #3 on: February 17, 2011, 05:44:48 PM »
You can get a close approximation of Top Dead Center by watching the valves on #4.  When #1 is at TDC, #4 will be in between exhaust and compression and will have valve overlap.  Both the intake and exhaust rocker on #4 should have tension when you position the crank at TDC.  If only the exhaust has tension, the cam may be off.
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Offline SOHC Digger

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Re: Checking camshaft/crank timing on '78 cb750
« Reply #4 on: February 17, 2011, 05:46:47 PM »
And if you have a dial indicator, you can put the intake to zero lash and put the indicator on the rocker.  This will let you know exactly when the valve starts to open.  I am not sure exactly how many degrees before TDC this occurs, but I am sure you could find that information easily.  You can then reference when it's supposed to occur and when it IS occuring.
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Offline Gordon

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Re: Checking camshaft/crank timing on '78 cb750
« Reply #5 on: February 17, 2011, 10:57:30 PM »
You can lift the valve cover off the head a little bit without pulling the engine.  Might possibly be enough to shine a light in there to see the cam shaft notch.  If not you can pull the engine mount bolts and drop it in the frame so you can lift the valve cover a little more. 

Keep in mind that if it's been a while since the valve cover gasket was changed it will likely tear when doing this and need to be replaced.  Some have successfully done this with the engine in the frame, but if the old gasket is adhered to the mating surfaces you'll need to scrape it off, which won't be easy. 
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