Necessary to use timing marks when adjusting valves?

2024-01-29 Kz1300 Cam Lobe Position and Valve Adjustment

Last time I adjusted valves, did it 'by the book'. Removed RHS alternator cover, matched timing marks, did work.Had small oil leak at valve cover rubber cap, off comes the cover. Hmmm, let's QC my previous work and measure valves again. 

The bike has approx 30 minutes run time now since valve adjustment....but don't really want to remove the RHS alternator cover. It's difficult to keep drip free, and she's sealed up good right now. (RHS cover has alternator wire grommet at bottom, LHS sub alternator the grommet is higher up, less likely to leak)

Rather, since I have to inspect the starter motor clutch, pull that cover, rotate crankshft on that side...But what about the timing marks? What would happen if one simply pointed the lobe to top side, at same angle as valve stem?In other words, position cam 'heel' at bottom. Is that a legit process?

I think yes.

Starting position. Clearance measured as .203 mm.

Ending position. All points between start and end measured .203mm which matches exactly to my As Left measurement 
after valve adjustment.

I repeated this test on 5 more valves, intake and exhaust, same result. Indicates to me that 1979 kz1300 A1 cam shafts have symmetrical 'heels' and using timing marks is not required.

Called a bud who's been a tech since dirt asked the same question. He replied that most Japanese bikes this technique is valid.

But not all. Honda CBX is an example where this won't work.

It's a bit of a math thing. The advertised duration of the valves is 270 duration inlet and 280 degrees duration exhaust. that means the camshaft is active for 135 deg inlet and 140 degrees exhaust. You can add about 10 degrees either side of that for opening / closing ramps so we add 20 degrees to 135 + 20 = 155 degrees and 140 + 2- = 160 degrees and we now have the "active degrees of the cam lobes.4
That leaves 205 degrees intake and 200 degrees exhaust of inactive camshaft lobes i.e. the "base circle" where you can measure the valve clearance.
since the engine fires every 120 degrees, you can appreciate that there's also 1 inlet valve and 1 exhaust valve that could also be measured if you have the one active valve at exactly on the timing mark, but if you choose to do the lobes one at a time and position the lobe point up from the valve stem, then not a problem. Just don't expect to do the other optional valves unless you use the timing mark.

As far as the CBX, they may have extended the ramps at the ends of the lift portion of the lobes and maybe to get a "true" valve clearance, you have to go to lobes pointed straight up. But even a wild duration like 310 degrees would only have 155 (plus 20 degrees for ramps) = 175 degrees of active lobes so there would still be 185 degrees of base circle to take measurements at.
 

An interesting question. I’ve wondered about this before when working on engines. Thanks for the insight, Kawboy.

On a couple of my old Hondas, the cams run directly in the head with enough clearance that the cam rotation is a bit 'sloppy'.  So depending on how other cylinders are positioned (and how their cam lobes are pushing down on other buckets) the clearance on the 'base circle' of the clearance being measured will vary.  So, the importance of using the timing marks as a reference when measuring clearance is to ensure the clearance is repeatedly measured at the same spot (and all the other cam lobes in the same spot).   Not as big of an issue for cams that don't wobble as much, I guess?

Surely, unless badly worn, there shouldn’t be that much clearance in the cam bearings to make the difference you mention. 

'Wobbly cams' were perfectly normal on the Hondas in question (CB900F/CB1100F - not sure about the 750F).  I believe the notion, among the 'F community', is that the block flexes under load just (at least partially due to the OEM fibre base gasket) enough that, to avoid problems, the cams needed to ride in 'looser' journals.  Apparently there are high speed videos showing the block flex under load (but I've never seen it).

Performance rebuilders go to great lengths to reduce the flex by using a specific later model year crankcase (which had additional reinforcement near the block), using copper (or other metal) head and base gaskets - which make the engine more rigid and allows the cams to be 'tightened up' by refacing the cam caps ever so slightly (reducing the clearance - and wobbling).