B-81 starter update

[Old Blue]

I have a B-81 and I'm looking to get rid of the 6 volt battery's and update the stater to a Delco Remy 39mt 12volt. This is a first for me so any advice or tips would be awesome. 

[eddeere]

There have been a number of articles here on this . If you look them up I think you will find anything you need.  Pictures of your truck would be great.

Edited January 12, 2017 by eddeere
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[Freightrain]

I just hit my local starter shop years back and bought a 12v starter.   Don't have part numbers, but it should not be hard to get the right starter and electrical for it.

I used a standard Ford solenoid mounted where the original s/p switch was at.  I used my existing starter wire to kick that solenoid to engage the starter.  Has worked flawless for 14 yrs.

[Old Blue]

Anyone have a part # for a series parallel/magnetic switch combination, and where I could get one. 

[41chevy]

Going with a set of 900 to 1100 CCA 12 volt batteries and a choice of a standard 12 volt starter or a 12 volt reduction starter there is absolutely no need for a series / parallel switch. Wire in the pair of batteries in Parallel. You are doubling the capacity (amp hours) of the battery while maintaining the voltage of one of the individual batteries.  Use a jumper wire between the positives of both batteries and another jumper wire between the negatives of both batteries. Connect your positive and negative wires to the same battery to run to your unit.

Follow Freightrain (Larry's ) advise on the solenoid.

[Rob]

You will need a pair of group "31" top post batteries, a pair of "Flag" terminals, (sometimes referred to a "Tee" terminals, and couple lengths of at least 2/0 welding cable, (SOOW series) an intermittent duty magnetic switch, (starter solenoid) and some minor interconnecting wiring and terminal ends. As mentioned interconnect the batteries in a parallel configuration, ( + to +, and - to -). The starter motor itself is not polarity sensitive but the starter solenoid mounted to either a 40MT, 42MT, or 39MT series is. They are readily available in either polarity. If retaining your original generator the system should be positive ground and unless you want a bit more work, I'd leave it that way but it's easy enough to change to negative ground for modern convenience items also.

Do not skip installing a second magnetic switch to pull the main starter solenoid in which is physically mounted to the starter motor as the push button in the cab is not designed to handle the current needed. Also, I've seen not one, but two replacement 39MT starters go defective on a hobby truck from lack of use over winter months. Both of these were Chinese "knock offs" of Remy branded starters of which I've never really seen problems from. They weigh about 1/2 of what a good 40MT starter does but the 40MT has been around for many a year and are very much worth rebuild. A 39MT is not and is a replacement item when it goes bad. Just experience talking, not bias.

If it were me, I'd acquire a fresh 40MT starter with an 11 tooth drive gear, a good pair of 950CCA starting batteries, necessary cables and interconnecting terminations, change to negative ground swapping out the generator with a later model alternator from a large truck, (Delco-Remy 25SI series are cheap, reliable, and rugged) and be done with it.  You'll never look back.

Rob

[Rob]

Probably should mention if converting a starting system from the 12/24VDC series parallel system to a straight 12VDC starting system, you need a "counterclockwise" rotation starter, (CCW). They will be available in both CCW, and CW rotation but if the starter mounts on the lower right side of the engine, (facing the flywheel from the rear) the starter rotation needed is CCW. If the starter mounts to the lower left side of the engine, (facing the flywheel from the rear) the starter needs to be CW rotation. Both scenarios are for an engine that normally rotates to the left when running, a.k.a. standard rotation.

Normally I would just state driver's and passenger sides of the truck but we do have Aussie friends on the board so will be more "correct" in analogy as per "Momma's" suggestions, or more rightly yet, "threats of bodily harm" if I don't straighten up. 

Mack engines only use an 11 tooth starter drive gear no matter the clutch size I've seen through the years on the B, and R model series. 

Rob

[Old Blue]

Thanks for the information.  It's greatly appreciated, I've never done this before and every bit of advice helps.  

[Old Blue]

Had time today to install the new starter.  After many years of sitting she runs again.   I had already gone threw the injection pump so that's  seems to be good but it looks like one or two injectors may be bad.