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Re: MGB Camshaft Questions and brake realizations

To: mgs@autox.team.net
Subject: Re: MGB Camshaft Questions and brake realizations
From: Jim & Marilynne Mellander <jmel@netcom.com>
Date: Thu, 07 Nov 1996 20:05:42 -0800
At 05:16 PM 11/7/96 -0500, you wrote:
>
>       I learned a good lesson today. Don't buy rebuild kits until you've
>taken things apart.  I went ahead and ordered rebuild kits for my brake
>calipers and rear cylinders and THEN started reading the manuals which all
>said don't rebuild if there's any sign of wear, and THEN started taking the
>things apart and finding evidence of pitting and wear <sigh>.  I've
>occasionally done this sort of thing before, and just said, "ah, screw the
>manuals, what do they know anyway?" But this time that little voice in my
>head told me I'd probably rather lose the $60 or so in parts than a few
>limbs to a brake failure.
>
>       Now I can't work on my brakes cause I don't have any parts in, and
>I'm waiting for my hydraulic lines to come in, and I'm waiting on new paint
>for my dashboard, and I'm supposedly getting my engine back from the machine
>shop this week, but I'm sure you all know how that goes, and I don't want to
>take my transmission apart cause I'm still looking for an O/D.  Anyway, I've
>been getting anxious to do something.
>
>       So, I measured the lobes on both the new and old cams to see if they
>were the same (Hey, it's SOMETHING!).  Well, unless I measured wrong
>(Possible, I'm going to go take the measurements on the old cam again
>tomorrow with a more familiar micrometer) I got a lobe height of about 1.38"
>on all the lobes of the old cam, and 1.32" on the new cam.  Unfortunately
>the stats in the manuals don't give me lobe heights.  The closest thing I
>could find was valve lift.  Does anybody ever actually measure cam lobe
>height?  Do any of these numbers sound familiar? Does Anybody know how to go
>from valve lift to cam lobe height, or is it not that simple?
>
>       Anybody have any great suggestions on what I can work on while I
>can't work on anything? And don't anybody in the know say my Spit's engine,
>because I'm currently denying that the crankshaft is bad.  Hey, ~2 PSI oil
>pressure at 60 MPH isn't so bad, right? (And it only rattles when hit the
>gas :-) Besides, nobody on the MG list would tell me to work on a Tri***h
>now would they?
>
>----
>Jeremy DuBois                              jer@thlogic.com
>Manager, Info Systems                      http://www.thlogic.com/~jer/
>Thermalogic Corporation                    '60 TR3A, '74 MGB, '76 Spit
>
>

Unless I'm mistaken, every time a cam is ground, the lobe height would be
less (the diameter of the lobe decreases), the profile also decreasing.  I
assume it can be ground until the cam no longer meets the specs.  This would
indicate that your "new" cam has been ground more times than your "old" cam
- proving once again that 'new' & 'old' are relative terms, especially in
the LBC realm.

Jim Mellander


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