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Firemack-Need Your Help Again


gmbelt
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My 1962 B-85F semi-open cab pumper with a Mack Thermodyne ENF-707C gasoline engine is need of a major tune-up. My mechanic tells me that it could use new plugs, plug wires, points, condensors, maybe new distributor caps, etc. He also said I would need to find a "dual" timing light because of the dual ignition on the engine. He also noted that one of the distributor caps was sitting on top of a device a little bit larger than a soda can; no idea what it is.

In any event, I'm looking for a source for these parts and would greatly appreciate some advice as to where to turn. I can provide any photographs that might help. I have the maintenance manual for the truck which was sent to me by the Mack Museum.

Many thanks in advance for your help.

Gary M. Belt

Manassas, VA

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Gary,

Sounds like you need another mechanic, there is no such animal as a dual timing light. I just finished tuning a 707C in a 1960 B95. You might want to consider changing over to electronic ignition to improve the performance and remove any chance of the points and condensor causing any problems. I used a Pertronix electronic ignition module for a 12 volt positive ground system. The parts are still available at NAPA but I like the quality of the parts from Brillman Company- he uses all brass fittings etc. I still purchased plugs from NAPA- AC R45. The points, condensor, (or electronic ignition module), cap, rotor and wires, I purchased from Brillman Company in Mt Jackson VA. Contact John Brillman at 540-477-4112, he is a nice guy, and you may see him a the VA truck meet as he has an old Autocar tractor.

Once you install the ignition parts you will need a regular timing light attached the positive (red lead) and negative (black lead) of the battery (and the timing lead connected to number one spark plug wire on one of the distributors at a time). The timing light does not need to reversed for positive ground and will most likely ruin the timing light if not correctly connected. You can use a engine dwell tach or engine analyzer with the red lead connected to the primary wire of the distributor (Ground) and the black lead connected to the ignition hot at the coil. This can then be used to set the dwell (if you decide to use points and condensor) or to monitor the engine rpm to set the idle mixture and idle speed. Timing on a 707C is done on the flywheel under the truck not on the front pulley. You set the dwell and then set the timing. Do one distributor at a time and it makes it easy to get the truck started (on the one you have not changed) and then adjust the timing on the one you just updated. After setting the dwell and timing on both then set the idle mixture for the highest idle speed, then reset the idle speed. I usually set the idle at about 600 rpm but can be set as low as 350 if you like it there.

If you mark the wires and send them to John Brillman he makes the original style (Packard 440) wire sets in the exact size of the wire set you send him and is reasonably priced (a little more than Napa). This way you have an exact replacement wire set and not some mix and match from a parts catalog.

The B95 pumper now runs great and just went to it's first show in 18 years.

Good Luck,

Firemack

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  • 10 years later...

Firemack, how do you physically adjust the timing?  Should I be able to turn the distributors or is there another method to do this?  I've got a 1951 with a 707A and the distributors feel loose when I loosen the hold-downs but won't rotate.  

Thanks in advance,

FireMech307

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  • 2 years later...

I’m wondering that too.my truck has a hesitation and stumbles a bit. Did fuel system, carb pump already. I’m not sure how old my ignition stuff is or if it was ever installed properly so I’m doing plugs, wires, codensor points cap and rotor on my 52 L85 707b. How do you time this thing I’m lost. Anyone that can help?

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You need to borrow a timing light haha im I’m Not sure about that does not have a working timing advance. A lot of times the vacuum leaks will do that hesitation. but you guys usually hear them … Bob

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I didn’t find any vacuum leaks so far. The distributors don’t appear to have weighted advances or vacuum lines going to them. That’s what confuses me. How the heck is the ignition advancing 

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sorry bud just checked my manual...nothing about gas jobs,,,surprised  me because its from 1980 and then there was still alot of them in use...theres is a lotta guys on here with them,,,dont know why nobodys answering 

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