After I took care of things at home I headed to the garage. First I moved the indicators to valves 1 & 2 from 7 & 8. I repeated all my checks (intake LCA and overlap angle). Just like my previous tests, I found the LCA was still at 109 ATDC and the overlap was still at 4 BTDC. That reassured me that nothing had moved and that my method was consistent.
Then I removed the new sprockets and chain and refitted the paint marked old parts. I did this two ways. First I just tightened the cam bolts with no chain tension, then I repeated my tests with the timing chain tensioned by turning the crank in the normal direction of rotation (to take out all the slop in the sprocket mounting holes). My findings are below.
Old timing parts with no chain tension when bolts tightened:
Intake LCA = 107 ATDC
Intake/Exhaust overlap = 6 BTDC
Old timing parts with chain under tension when bolts tightened:
Intake LCA = 108.5 ATDC
Intake/Exhaust overlap = 4 BTDC
Yesterday's readings...
New timing parts with no chain tension when bolts tightened:
Intake LCA = 109 ATDC
Intake/Exhaust overlap = 4 BTDC
So... I still cannot explain why the overlap is not occurring at TDC. However, I can say that if I fit the new timing components and set the timing by intake LCA, the overlap will occur at the same point it did/does with the old timing parts. Since the engine ran well with this timing before the rebuild I am comfortable taking this approach. I could retard the timing a degree or two so the overlap occurs closer to TDC and the LCA falls right at 110 degrees. However, then it will become more retarded as the chain stretches.
I'm still thinking about this but I am more comfortable now having measured the timing with the old parts.
Doug L.
--Previous Message--
: No it would be @ .040 tappet rise, in the
: case of this cam.
: "Assuming I do have a stock cam
: and that its real duration is about 256
: degrees, then the duration would have
: to have been checked/measured somewhere
: between the 0.010" and 0.015"
: of lift you mentioned."
:
: I do both event points and centerline,
: sometimes on more than 1 lobe.
: Some grinds are set by setting the
: crank angle at a specific point in
: lift. Some just split the overlap. The
: results should all be the same or very
: close.
: I can't add anything to what is in the
: Crane article, the applications are
: different but methods the same. I don't
: have any online references, all of my
: stuff is paper!
: Take 2 aspirin and post more in the
: morning!
: g.
:
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