----------
From: David Hall[SMTP:dhall@vcd.hp.com]
Sent: Tuesday, March 04, 1997 4:28 PM
To: 'Robert Allen'
Cc: 'MGList'
Subject: RE: Vaccuume Advance - Rebuild with Hot Cam and Roller =
Rockers?
Robert..
Thanks for the detailed information! I would guess that the huffa-huffa =
is
coming partly from the cam, and partly from worn valve seats. Also, =
thinking
about it, the rocker shaft is probably worn pretty bad as well. I am
guessing this because there is a noisy vibration around 3K which =
smoothes out at
about 3.5 - 4K. Also, around 2K, the variation in the intake pressure =
seems
to not be as bad. (Hence the cam.)
Solution for now is to make a restrictor for the vaccuume line to the =
distributor
vaccuume advance. (And keep working on the rebuild!)
As far as the rebuild goes - I am debating the advantages / =
dis-advantages of
putting a hot street cam in it, as well as roller rockers. I've read =
through
Peter Burgess book - Power Tuning a MGB Engine. He seems more concerned =
with
balancing the engine and porting the head than the hot cam. He also =
feels that
the stock cam is quite good. Also, he does not like roller rockers. =
Personally,
it seems like the bearings in the roller rockers would last much longer =
than
the normal rockers busings. What do you think? (And all you other =
listers who
are following this...)
I will probably bore the engine out a bit, but not all the way to the =
larger piston.
Balancing all of the connecting rods, and having the block line bored =
both seem
very valuable. Smooth-balance =3D free revving.
Thanks again!
Dave Hall
http://www.pacifier.com/~dlhall
72 B GT
74 Midget
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Dave, the cam is indeed the source of the "huffa huffa" sound. Your =
compression figures are very even, if somewhat on the low side, possibly =
also because of the overlap on the cam. It is very likely that the =
drivability problem is because the engine doesn't get "on the cam" until =
3k revs. I think roller tipped rockers are a good idea, as long as they =
retain the bronze bearing on the rocker shaft to prevent "brinneling" of =
the shaft and for oil pressure control.
=20
Good Luck
Leigh Egbert=09
Leigh@AVFH.com
46 TC
48 TC
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