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MG TD TF 1500 - Dwell Angle Measurement

My MG TF will not pull on the hills so I think it is time for a good tune up. It is a 1250 eng with the symmetric or asymmetric cam. I have checked the manual and have found all the specs except the dwell angle measurement HELP Thanks in advance Bill
Bill Mason

Bill, according to Chip Old's excellent information in the NEMGTR T-Type Restoration Handbook (Back to Basics #8 --Distributors) the specs are:

Symmetric: gap=.010 - .012 in. Dwell angle=41 - 49 deg.
Asymmetric: gap=.010 - .012 in. Dwell angle=45 - 53 deg.
High Lift: gap=.014 - .016 in. Dwell angle=57 - 63 deg.
Bud Krueger

Bill - Are you sure that you have the symmetric or asymmetric cam? The TF should have the high lift. The cifference between the symmetric and the high lift cams is not just the profile of the cam (hard to distinguish), but also the position of the rotor locating slot (see illustration C.20 in the shop manual) If you don't have a shop manual with this illustration in it, e-mail me and I'll send you a copy of the picture. Also be aware that if you are using a 3 wire dwell meter and your car is still positive ground, the meter may read the compliment of the angle (33 - 27). Good luck - Dave_
David DuBois

First Thanks to Bud & David

My dizzy is Nr. D2A 40367B
and below that DA 41 with an arrow 351

As per the manual page C1 this indicates a high lift cam without the letter B On page C12 it shows that any letter prior to E is either symmetric or asymmetric. Am I reading something wrong ? My cam does look like the high lift but I am confused. Not the first time. Thanks Bill
Bill Mason

Bill - After all these years you can have any cam in there up to and including one from a chevy V8 (just kidding on the V8, but it is almost that bad). Try setting the dwell at 57 - 63 and see how the car performs. Remember, if you are using a 3 wire dwell meter on a positive ground car, you will probably read the complement of the angle (27 - 33). Good luck - Dave
David DuBois

I hate to plead ignorance but how do you know if you have a three wire dwell meter? I have tried to use mine but I could never get a dwell of around 60 so I figured it just did not work on our cars.

John
John Progess

Doesn't the 351 indicate the distributor was made in March of 51? Which if the cam hasn't been changed (as Dave says who knows) would suggest you might have the earlier cam profile.
Dennis
D F Sexton

John - When I refered to a "three wire" dwell meter I was refering to one like the gunson (that's just one example) that has two wires for power and a third wire that goes to the distributor points connection. Because the positive powere lead of the meter is going to ground, and the negative lead (which is normally the ground lead on a negative ground vehicle) goes the positive side of the battery, the dwell reading winds up being the complement of the angle. Cheers - Dave
David DuBois

This thread was discussed between 06/07/2005 and 13/07/2005

MG TD TF 1500 index

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