camshaft timing

masunari · Post by **masunari** » Sat Jun 02, 2012 5:21 am

I have reluctantly had to strip down my 1967 cb72 to try and find the cause of severe backfiring. This is severe enough to have caused the silencers to burst! Any ideas? I am reassembling the head with a new camchain. However, I am not too sure how to align the crankshaft/camshaft. In my cb160 there is a nice hole in the sprocket. Could any one give me the necessary information to get it right?
masunari

mike in idaho · Post by **mike in idaho** » Sat Jun 02, 2012 8:38 am

There should be a similar mark on your cam sprocket, it should be up with the right cylinder at TDC on the firing stroke.

masunari · Post by **masunari** » Thu Jun 07, 2012 1:47 am

Dear Mike,
Thanks for the info. here are two holes in the sproket but from what I can gather there is also a O mark which indicates the one to use.
Have you any tips about removing the right hand camshft? I have now noticed that the outer lobe is quite badly worn and maybe should be replaced. I have been trying to follow threads but there is no definitive thread on removing the camshaft.
Best Wishes
MAsunari

mike in idaho · Post by **mike in idaho** » Thu Jun 07, 2012 9:39 am

Start by pulling the cylinder head off ( the cylinder studs interfere with the rocker shaft removal) then remove the rocker shafts. There is a large nut on the side of the sprocket that needs to be slacked off to release the cam(some early models were left-hand threads). Work the camshaft out of the sprocket by tapping on it with a soft drift. It will be a snug fit in the splines so it will take a bit to get it out. There should be a reference mark on the points cam that lines up with the timing mark on the sprocket, it needs to go back together the same way or the ignition timing will be 180° out. The left hand camshaft is retained by an internal tapered bolt, loosen the nut on the end and tap on the end of the bolt to loosen the taper to remove the left cam.

Phil-UK · Post by **Phil-UK** » Fri Jun 08, 2012 4:43 am

Hi

Bill Silver's Restoration Guides give a lot of useful info but if you can find back issues of Classic Motorcycle Mechanics, Mark Haycock did a rebuild of a CB77 with lots of step-by-step photos in 2000/2001. I found the photos easier to understand.

The one that is most use is from Nov 2000 "Building Up the Camshaft" ... if you cannot find it contact me and I'll see if I can help.

You don't say if it had been running OK before it started backfiring or if its always done it. If its suddenly started is the cam sprocket loose on the centre piece ?

We've just got back from taking 3 CB72s to Coupes Moto Legendes in Dijon ( @1100 miles round trip ) with no problems other than a puncture. The only issue was restricted space for tent, sleeping bag etc., but the engines were fine.

good luck

Phil