Triumph Repair: Triumph Timing Marks - again, wooden dowel, cam lobe

Question
QUESTION: Hello,

I see that your expertise is in the TRs and Spitfires, but my question is about a Spitfire with a GT-6 conversion - does that count as a Spitfire question?  I have the same question that you answered about timing marks for the Spitfire four, but need to know how to time my six in the same way.  Please help if you can.  

Best regards and thanks,

JC

ANSWER: Hi JC,
Which prior question are you talking about? And are you talking about ignition timing or cam timing? Let me know.
Howard

---------- FOLLOW-UP ----------

QUESTION: Hello again,

I apologize for the generalization.  My problem is with cam timing.  The car that I have is a 79 spitfire with a 73 Gt-6 engine.  It came with a few bent pushrods and a bent #4 valve. I tried setting #1 to TDC, then rotating the cam halfway between the intake valve closing and the exhaust valve opening to "guess" the correct cam position.  It provides me with good compression on five cylinders, but #4 is dead because of the valve which I am about to replace.  I want to get this right after I pull the head, but i fear that I'll do the same dumb thing that the previous owner did.  He speculated that the cam lobe was ground incorrectly on #4, and I thought that was foolish, but after my unorthodox timing attempt, I wonder if he's right.  Using a wooden dowel, the #4 piston is at TDC when the valves are opening, so either the cam is in the wrong position, or it was made wrong.  My gut says the former is correct.  If you can help this backyard engine hack, please do.  Thanks for your time and consideration.  This could be a very nice roadster if I can get it to run right.  I'm ready to buy a new cam and timing set if someone makes some that have timing marks.  So far, nothing.

Thanks again,

JC

Answer
Hi JC,
Your method is close to correct and is commonly called "Splitting Overlap". I doubt the cam has one set of lobes out of time.
The GT-6 had some sprockets marked with a line on the cam sprocket and on the crank sprocket. If they are there, they point directly toward each other on a line between the center of the crank and the cam.
With no marks this is what Triumph says,
Temporarily attach the cam sprocket and turn the cam until #12 push rod has has reached it's highest lift point. In this position adjust #1 rocker clearance to .040"
Repeat the procedure with #11 push rod and adjust #2 rocker to the same as #1 rocker.
Turn the cam until #1 and #2 have reached a point of balance. (when one valve is about to open and the other is about to close. At that point the crank should be set with #1 and #6 piston at TDC.
If the cam is not exactly correct, you can adjust the cam by a half tooth of the chain by removing the cam sprocket and flipping it over. This is why Triumph has four mounting holes and only two mounting bolts. The holes are slightly off so you can reposition the sprocket and flip it over for a closer adjustment.
Be SURE to use the special hardened bolts and a lock tab. Grade 5 bolts must not be used in this position. After you finish set the #1 piston at exactly TDC and the #1 & #2 valves should have the same clearance. Then reset the valve clearance to .010" on in. and ex.
Howard