10 BTDC is more advanced than 5 BTDC ( spark occurring 10 in advance of
the piston reaching TDC). If your dwell angle and timing remain pretty
steady, you probably don't have much distributor shaft wear to worry about.
Seeing as how you are setting your timing with a light, I'd say you are
trying to set it too retarded by the numbers you're quoting. 10 BTDC would
be close to right ( book) if you are idling at 500 rpm with the vacuum
advance disconnected and plugged ( I believe you have a '66 right?). If
your idle rpm is higher (1000-1200), you will probably need to set the
timing more in the neighborhood of 20 for it to run right, because of the
advance being cranked in by the weights in the distributor.
From: Skye Poier <firstname.lastname@example.org>
To: REwald9535@aol.com <REwald9535@aol.com>
Cc: MG Nuts <email@example.com>
Date: Sunday, January 03, 1999 1:33 AM
Subject: Re: Points Gap and Timing (2Q)
>Word on the street is that REwald9535@aol.com said:
>> 2. Wait a minute here, 5 degrees is retarded from 10 degrees. The full
>> statement is 10 degrees before top dead center (BTDC). Top dead center
>> when #1 is at the absolute top of it stroke. The ten degrees refers to
>> many crankshaft degrees (before or sometimes after) TDC the spark fires.
>> degrees BTDC would be less advanced than 10 degrees BTDC.
>But aren't the degrees for BTDC measured BACK from TDC, hence a spark
>at 10 degrees BTDC would occurr *before* a spark at 5 degrees BTDC,
>5 deg is more advanced (along the stroke) than 10 deg BTDC.
>> If after you have adjusted the dwell correctly if the timing is out too
>> then the distributor needs to be loosened and turned until all the marks
>OK. I'll try and turn it more, but it sure seems like its at a 'limit'.
>> I suspect that your dist. has a lot of play in the shaft and when you set
>> dwell with a meter instead of a feeler gauge it moves past the amount
>> can adjust with the "dizzy"
>I was worried about a worn distributor shaft as well, but the timing marks
>are rock solid with the strobe, as is the dwell angle.
>1966 MGB GHN3L-70307 __,__\__ Finger for
>The MGB Experience http://www.mgb.bc.ca/ (_o____o_) PGP key