Sensor Question (and the usefulness of cam sensors)

[efi_student]

My dad builds circle track engines and relayed a story to me that might
shed some light here.  He built 2 SBCs for different competitors, and
they were nearly identical.  At the end of the season he got them back
for freshen up.  One had the timing chain and sprockets nearly beaten to
death, the other was practically brand new.  His investigation showed
only one difference between the two engines worth noting.  They had
different main bearing in them.  One set had an abrupt stop to the
center groove on the top bearing where the top bearing met the lower
shell.  The other had a smooth ramp from full depth on the groove to the
height of the lower shell.  He surmised, and I agree, that the abrupt
transition was causing a hydraulic shock in the oiling system.  Of
course, the oil pump is driven by the cam, so this shock was being
loaded into the timing chain and causing it to stutter and whiplash.  He
has since abandoned that style of bearings and has not had the problem
since.  Something like that could certainly cause the conditions that
Clayb described.

Lance

-----Original Message-----
From: owner-diy_efi at diy-efi.org [mailto:owner-diy_efi at diy-efi.org] On
Behalf Of Jon Davis
Sent: Friday, December 14, 2001 11:54 PM
To: diy_efi at diy-efi.org
Subject: Re: Sensor Question (and the usefulness of cam sensors)


clayb wrote:

> That said, I've found that cam triggering of ignition is definitely 
> inferior, especially when a timing chain is involved. With a 
> distributor firing my turbo 454, timing would bounce at least 5 
> degrees, while the distributorless ignition stays rock steady.

You must have had a bad timing chain or something... was it one of those
GMs with the phenolic gear on the cam? I have a DOHC 4 with a optical
pickup on the cam and a mile long single-row timing chain and I have
never seen any ignition bounce.

Jon Davis


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