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1. 03:38 PM - Lycoming Camshaft Question (J. Mcculley)
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| Subject: | Lycoming Camshaft Question |
In Lycoming 4 cylinder engines there are only 6 cam lobes. If I have
deduced it correctly, the four exhaust valves are each driven from their
individual cam lobes, but the intake valves share cam lobes as follows:
Cylinders #1 & #2 share the same lobe and #3 & #4 share another lobe.
This arrangement results in only 6 total cam lobes being necessary.
(BTW, in the 6 cylinder models, there are 9 lobes for the same reasons)
My questions are the following:
1) For those of you with considerable experience in tear-down of these
engines for problem analysis or overhaul have you noted any correlation
in observed cam lobe wear of the lobes that drive the intake valves
versus those lobes driving exhaust valves? Since the intake lobes make
twice the number of follower contacts per crankshaft revolution the rate
of wear would seem to be greater, if all other variables are constant.
2) Assuming that one of the lobes driving a pair of intake valves does
wear significantly, what engine operating symptoms would be a clue to
this event?
3) How would this symptom differ from that of an exhaust valve lobe
wearing to a similar degree?
4) Which situation, if not detected by oil analysis and cutting open oil
filters, would be easiest to recognize via engine performance degradation?
Jim McCulley
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