JMW
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| posted on 7/12/20 at 10:37 PM |
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BCF2 camshaft, or is it?
Can anyone help me identify this camshaft that I pulled out of a crossflow years ago? It is marked (crudely) BCF2. I can't upload a photo
unfortunately, I wish I could.
The reason I am querying whether it is a genuine BCF2 is that the cam lift measurements don't correspond to the 6.62mm cam lift specified in the
Kent Cams catalogue.
The numbers I get using a decent vernier, but with an inexpert hand are (all in mm):
6.27
6.30
6.31
6.24
6.25
6.27
6.23
6.15
[I got these numbers by taking the lobe to base circle distance and deducted the base circle.]
And the lobes don't look worn to me.
Have I got rogue cam?
Or does BCF2 indicate the profile more than the specific lift? It doesn't sound plausible to me.
Haas the BCF2 changed over time?
Am I missing something obvious? Or have I made some elementary error?
Any help appreciated.
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Bluemoon
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| posted on 8/12/20 at 10:30 AM |
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Are the rockers 1:1? No experience but mechanical advantage might be part of the equation?
[Edited on 8/12/20 by Bluemoon]
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JMW
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| posted on 8/12/20 at 11:07 AM |
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Cam lift is not affected by rocker ratio.
Valve lift is. Valve lift is also influenced by clearance which is why Kent quote one figure for both inlet and exhaust cam lift, but different
figures for valve lift as the clearance is different between inlet and exhaust.
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rusty nuts
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| posted on 8/12/20 at 06:53 PM |
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quote:
Originally posted by JMW
Cam lift is not affected by rocker ratio.
Valve lift is. Valve lift is also influenced by clearance which is why Kent quote one figure for both inlet and exhaust cam lift, but different
figures for valve lift as the clearance is different between inlet and exhaust.
Valve clearances are inlet 0.014”exhaust 0.018” for BCF2 cams inlet and exhaust are NOT the same
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Deckman001
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| posted on 8/12/20 at 07:10 PM |
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Could it depend on how the cam is ground in the first place, so each lobe may be slightly different diameters so the cam lobe is then ground to suit
the top height?
Jason
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mccsp
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| posted on 8/12/20 at 10:30 PM |
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I think the standard rocker ratio is 1.54:1. Using your measured data ties up with the valve lift on the Kent cams website. I wonder if the cam lift
is a typo. Might be worth giving them a call
Why do it the easy way, when I can do things my way!
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steve m
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| posted on 8/12/20 at 10:49 PM |
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If, i am reading this correctly, then the cam size has nothing to do with cam lift, as when the cam on a crossfliow hits the valve head, as long as
the gap between the valve head, and the cam, is a constent in either exhaust 15 thou or inlet 13 thou , then the "lift"! will always be
the same, assuming all the clearances were the same.
Im sorry to say, and ive built many many Xflows, but the tolerances on a Xflow. are not rocket science and you can swap bits from many many engines,
and ive done so, and would never detect a problem, its only when your pushing around 150 Bhp from a 1700 does this come in to play
We are talking about an engine, that was designed in the late 1950's (pre crossflow but same bottom end) its an extremely basic engine for use
today
steve
Thats was probably spelt wrong, or had some grammer, that the "grammer police have to have a moan at
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