Frank,
The "B" came with 155 SR 14 tires. Most were replaced after about 20K miles
with 165 SR 14 steel belted. The list recommends everything from that up to
about 195 70's, depends on who is talking. I've still got 165's on my B,
3rd set since the originals, don't know what I'll put on next.
My 72 B speedometer surges from time to time and when it gets to bothering
me, I pull out the cable and grease it up with Vaseline or whatever I have
handy such as lube grease. Some people recommend graphite lube for the
cable. I've never tried that.
As to oil, the general consensus as I read it, is to use 20 W 50, I have
been using 10 W 40 since new, but may change over to 20 W 50 in the summer
as my engine is getting on in miles and the extra heavy weight will probably
hold oil pressure better when it is hot out. My oil pressure only drops to
the 20-30lb range at idle after the engine has had a long run or is a little
low on oil, otherwise it pops back up to normal range on the gauge of 50 -
60 lbs. as soon as rpms increase (don't really pay attention unless it
drops).
As to rpm at 70 mph, I think mine reads around 3500. According to the
specs, the rpm / mph is 17.9 mph /1000 rpm which would read about 3911 at
70. If you have an overdrive the ratio is 22.3 mph / 1000 rpm which would
translate to 3139 rpm at 70 mph. When your tack bounces, it is probably
related to a poor connection at the coil or perhaps the points/condenser
need renewing. I am assuming that you have an electrical tach as I do in my
72, if it is mechanical, please disregard the electrical reference and
grease the cable. At to checking a tach, if you have a portable tach, dwell
meter, which is nice for setting points, you can compare the readings. I
don't think the tach is all that accurate in the B's anyway. If you are
within a couple of hundred rpm of actual, that's probably as good as it
gets. I would figure on a 10% maximum error, same with the speedometer.
Congratulations on your new B and for living another year. Us OF's
sometimes count the years. If you don't know what an OF is, wait 'til
you're over 50 and flatulent.
Dave 72 B
-----Original Message-----
From: Phillips, Frank <fwp@ufl.edu>
To: 'mgs@autox.team.net' <mgs@autox.team.net>
Date: Thursday, June 08, 2000 7:16 AM
Subject: 68B new with questions
>Listers,
>
>Yesterday I bought a 1968 MGB for my birthday. The car is in fair shape
>overall but has a few issues that lead to a few questions...
>
>First the good news, it has prefect compression across all cylinders ~160,
>little rust, and is very original... Note: I will be replacing all hoses
>ASAP, already have them, safety fast!!!
>
>Now the questions:
>
>1) What size tires did a 68B with disk wheels have? Any recommendations?
>2) The speedometer surges. At all speeds the needle jumps within a 10-15
MPH
>range and bounces back to what appears to be the true speed. Does the cable
>need a good lube? Bad gauge?
>3) The oil pressure was good but the gauge seems to stick some. Also, does
>oil viscosity play a role in oil pressure? As I drove, two hour drive home,
>the pressure dropped. After one hour it was around 25-30#. The current oil
>in the sump is 10W-30 NOT 20W-50 as most would run.
>4) RPMs seem high. At 70 MPH what should the RPMs be? Also, how do I
>diagnose the RPM gauge?
>
>Thanks in advance...
>
>
>Frank Phillips
>'68B
>'69B basket case
>Email: fwp@ufl.edu
>
>
>
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