When I had Colt Cams grind my custom cam for my car I had a similar
problem they recommended installing it in the advanced position rather
than the retarded position so that would be 109 ATDC. Which
coincidentally is what I ended up with for peak lift on my cam when I
degreed my cam and plotted the cam lift and timing in an Excel chart,
mine should have been at 110 degrees. Recording the lift every 5 degrees
and entering it in a spread sheet and then converting it into a chart
really helped make sense out of the cam timing . Just out of curiosity
what are the lobe centers on your cam? Oh and don't feel bad about 5
hours time in, by the time I took my laptop down to the garage and
plotted both intake and exhaust curves I must have spent 8 or more hours
at it but I'm much better educated on the subject now than before I
started. I also now know the exact rocker arm ratio for each rocker arm
and the lift/timing at each lobe on the cam. I did get a little carried
away documenting the blueprinting of my engine.
Doug Hamilton
1960 Triumph TR3A
1963 Fiat Cabriolet
>Date: Wed, 12 Jun 2002 11:41:43 -0400
>From: Rob Christopher <robc@cisco.com>
>Subject: TR6: Indexing the Piper270 cam, part 2
>
>Hi again everyone,
>
>Based on the responses from my first question on this topic (thanks to
>everyone Hugh, Randall, Bob) I had another shot at the cam last night
>using 'Method 1', crankshaft to 112 ATDC, find max intake lift on #1 and
>chain together.
>
>Now, the question is how close is close enough. I am using the original
>cam sprocket so I have the 1/2 tooth adjustability using the two sets of
>holes, and there is some slop in the bolts holes on the sprocket so
>there is a little adjustment there as well.
>
>Using the 'centreline' method in the cranecams.com document Hugh pointed
>me to, I get the following results:
>
>1st set of holes, moving the cam within the slop of these holes, I can
>achieve 104 to 109 ATDC for max lift on #1 intake.
>2ns set of holes, moving the cam within the slop of these holes, I can
>achieve 114 to 117 ATDC for max lift on #1 intake.
>
>Note, neither of these gives me the 112 ATDC the spec calls for. So,
>which of these two would be the better choice? 109 ATDC or 114 ATDC? I
>think as the chain stretches, the 109 would slowly become 110, 111...
>
>Should I just drill a new set of holes 1/4 tooth away from the others?
>Create a little more slop in the current holes? Or stiffle my
>engineering gene that won't allow me to accept 'close enough' and bolt
>it up at 109 or 114?
>
>Rob
>74.5 TR6 CF28217UO (now on the 5th hour of indexing the camshaft....)
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