Strange but true, larger journals are not automatically good for cams.
They run on a film of oil with a load that pulses and tries to push the
oil out. I've never understood why (you'd think the higher bearing surface
speed would help) but little journals are sometimes better. I know it
sounds weird, but this used to be a problem with bikes. The manufacturers
would increase journal size to cut cam bearing wear and ease the load on
the cam chains, and it would make both worse. Big journals had a lot more
drag and would exhibit wear much sooner. Making them way smaller fixed
the problem.
-----Original Message-----
From: Bob Bownes [mailto:bownes@seiri.com]
Sent: Thursday, September 11, 2003 6:44 AM
To: Brad Kahler
Cc: fot@autox.team.net
Subject: Re: grinding cam journals
I'd be more inclined to have the blocks bored out. Larger journal = more
bearing surface = less wear.
What do you go through more of, blocks or cams?
Would also guess the cam journals are hardened along w the rest of the
surface of the cam, while the blocks are not...
iii
Brad Kahler wrote:
> Amici,
>
> While looking through our pile of good cam cores for Susan's spitfire
> we have found we have a lot of the large journal cams that were used in
the mk1/2 and 1500 spitfires.
>
> I know it is technically feasible to turn the journals down. We have
> a Paeco cam in the box that was originally a mk1 cam that has had the
> journals turned to match the small journal cam. However since its a
> Paeco cam we aren't going to use it.
>
> Susan talked with Iskey yesterday and they said they could do it but
> apparently they have had very few requests to do so.
>
> Myself, I can't see any technical reason not to turn cam journals
> down. However I'd feel more comfortable doing so knowing that others
> have done it or would recommend it.
>
> Thanks
>
> Brad
> 1957 TR3 vintage racer
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