A fellow UK Vette owner has a '69 vert (which is VERY nice) fitted with a Mallory distributor. There's no vacuum pipes to it, so I guess that it's just mechanical advance, & it has an optical trigger. His problem is that he hasn't got a clue as to what to set the timing to. Currently it's set to 8BTDC at idle & there's no hint of pinging, but he doubts that it's correct. Is anybody familiar with these upgrades? If so, is there any electrical auto advance built in (as somebody told him), or is it just like any other dist for timing purposes ie advance in steps until it pings & then back it off 2 deg?
I haven't had a close look at it, but is there any way to find out exactly what model/type it is just by looking? Sorry this is so vague!

p.s. If anybody comes up with an answer I might treat you all to a pic of a bunch of English Vettes parked up in a Square in the historic town of Brugge in Belgium (including a couple of the C5 forum members, Ha!).

 

Do you or should I say the person in question have a dial adjustable timing light?

You need to figure out the total mechanical advance of the dist. Lets just say that it has 24 degrees of advance at 3000 rpm. You would want to set your initial at @14 advance + the 24 for a total of 38 degrees.

 

should be a plate on it
its bolted on the same screw that the holders to the distributor cap are

 

Ther is no electrical advance to it.....purely mechanical. It may have an optical trigger, but that is where the electricity ends. It is like any other distributor but with no vacuum advance. If memory serves, I think there is 26 degrees of mechanical advance in the distributor if nobody has modified it. That equals whatever your initial setting plus that 26 degrees. You can go to mallory's web site at www.mrgasket.com and find more info.

 

Yea I got the exact same one, it's just a mechanical dizzy with the points replaced by the optical unit, no real black magic going on.

You need the degree key to set max mech. advance easily (it can be done without it but you need to check what you set it at and do it by trial and error), if you or your buddy doesn't have one, I think you can get them seperate from mallory, if not you can borrow mine

 

Thanks for all the replies. So, all we've got here is a common or garden mechanical advance unit, but with no points to wear, bounce, arc? I've given him a link to this post, so just need a couple of things made clearer
To figure out the total mechanical advance of the unit (MAA-558), all that he needs to do is use his dial adjustable timing light to read the advance figure at idle, then increase engine rpms to the point where no more advance is added & read the advance at that figure. The difference between the two readings is the total mechanical advance (I'm assuming that the distributor won't be adding any at idle?). What these 2 figures actually are is of no interest at all, it's the difference between them that is the crucial info.
Subtract this difference from 38 to give the value for the required timing setting at idle ie. the distributer needs to be rotated in the manifold to give a timing value of this when at idle.

Or, could he not dial in 38deg on his strobe, run the engine just above 3000rpm (or whatever point no more advance is added) & just set the timing that way (line up 0deg with the pointer)?
At the moment he just wants to get it right. It seems that it's been done correctly in the past as it's had an HEI advance curve kit fitted & used to run OK. Somebody has since adjusted the timing & it's not running as well as it did (it had run on & he found the timing had been set to 2BTDC at idle). Once it's set as it should be (38BTDC at full advance) we can then worry about when all the advance is in by & try to optimise it for best performance.
TIA

Hi Marck,
I've never had a close look at one of these distributors, but from your post would I be right in thinking that the amount of advance given by them is adjustable? And a degree key is used to set it?

 

You don't really need the key, the key is just to make it easy. The key gets wider in steps, each step has the advance setting for it printed on it, so you just pick the advance you want, loosen the arm, stick in the key to the desired postion, tighten the lockscrew and presto, max advance set. If you don't have the key you just set it somewhere, check total advance with your timing light and readjust from there.

 

I have a tuned BB engine and 36max 16idle right now and works fine. before it was 36-6 and did not work att all. Actually 36-18 or 36-20 might be best but my distributor can not be worked further. I have no vacuum canister at all.

 

Marck & Vesa,
Thanks for the replies. OK, the key is just used to set a known advance range without having to mess about adjusting, measuring, adjusting, etc until it's correct. I guess what we need to do first is find out what the mechanical advance figure is.

 

A word of advise - keep an extra pickup unit with you at all times!

I have one of those distributors that I had in service for about 8 years and the pickup failed on me twice! I always had a spare after the first time. Otherwise, I did like the distributor.