I didn't chop it up before determining that it would fit. It works like a champ, both on Rusty and Dad's, as it requires only one bolt hole on the head. But the other bracket requires two holes on the heads, which Dad's heads apparently have, but neither Rusty's heads nor the Trick Flow heads have both holes drilled.

Yes, it is very possible Rusty's heads are of a different vintage than Dads.

 

That is strange Bill. I wonder maybe one of the motors has Cleveland heads on it?? That would be a nice surprise.

 

Could be, or the earlier engines probably did have different heads, if I remember correctly, the 400 was introduced in 1971 when Ford was still using higher compression (GM dropped compression across the board in 1971, Ford didn't until 1972 and Chrysler dropped in low performance engines in 1971, high performance in 1972). I don't know if the casting numbers are visible without some disassembly. Cleveland heads would probably carry a D0 or D1 number as the 4 barrel came out in 1970, 2 barrel in 1971.

 

Well, the good news is that I found the alternator/AIR pump bracket that had gone missing. It was hiding in plain sight. So, I mounted it to the mock engine and played with the pulley arrangement a bit. And, I'm sure it is going to work.

First, here's a shot of the two pulleys. On the left is the pulley from the automatic tensioner that Bill sent me, and on the right is the v-belt pulley from the stock tensioner. Bill's was from a 460 with the serpentine belt so that pulley is flat with lips to retain the belt, which is perfect to take the back of the v-belt.



The ID and thickness of the bearings in both pulleys are identical, so the pulleys swap by just unbolting - with one minor exception. The flat pulley has a hat-shaped washer that needs to be bored out a bit to allow the shank of the bolt to pass. Here are all of the pieces:




Then I had to take about .070" off the retaining bolt so it didn't protrude through the back of the bracket:




And, here's the "finished" idler pulley - although I'll replace the pulley itself so I have a new bearing. But, you get the idea.




And, you may ask, how does it fit?



I think it is going to work quite well. Obviously I need to get a longer belt, but that will have to wait until I get the 3G and find out exactly how long it needs to be. But, the span in this arrangement is 10" as opposed to the 11" the old routing for A/C belt had, so I'm confident there won't be too much belt whip.

Next up is finding a crank pulley with the front two grooves the same size. And maybe a bit of surgery on the alternator/AIR pump bracket?

 

Gary, if you move the idler up a bit, it will shorten the run even more. I would try for a belt that will just go on new, so there is lots of adjustment as it stretches.

 

I like that A/C belt routing, since it increases the contact radius on the pulley. More surface area to drive the pulley, less chance of belt slippage.

As for the belt "flopping" around, dad's 390 has a second idler pulley between the A/C and crank, on the "downstream" side of the A/C. Not sure if it's factory, or his method of reducing the belt flop.......

 

So Gary, if the balance pulley doesn't have identical radius dimensions will it cause the belt to slip on the pulley?

 

Yes. The belts will be travelling at different speeds, due to the differing diameters of the drive pulley, so there will be some slippage at the alt (common pulley).

 

Bill - Where the idler is sitting is as far as it can go counterclockwise due to the slot the clamp bolt runs in. So it will be further clockwise, which I think is equal to your "up". My plan is just what you said - just get the new belt on with the idler fully clockwise and then bring it in tighter as the belt stretches.

RW - I don't think the belt will flop much with the fairly short span it'll have, so doubt I'll need another idler. Sure hope not.

Bruno - If the grooves aren't the same size it'll cause all sorts of wear and probably squealing. It would be the same as having 3.50 rear gears and 3.00 front gears and running in 4wd on the highway. Lots of bind.

 

Just for reference, the added idler on dad's 390, is about where (what I assume is) the PS pivot is on your bracket. It only adds about 5 degrees of belt deflection, just enough to tame the floppy tendancies of older Ford A/C belts. They tend to get quite floppy on the trip from the comp back down to the crank......

 

That's a pretty crammed area due to the P/S pump sitting there and the three-piece bracket arrangement. (What is it with Ford and their brackets? Do the engineers get paid for the complexity?)

On a different topic than this idler pulley, but quite related, what would be the advantage of using the later style round A/C compressor? I don't know if it is possible but I do have the 351W brackets and a compressor so could figure out if it is possible if there is enough advantage in it. However, that'll mean I'll have to start over on the idler and 2nd belt.

 

The later compressors have less drag, and are better suited to use 134A. Both can be rather desireable with the way things are today, gas and R12 related. I doubt either will ever get any cheaper, or more plentiful......

 

I wonder what the chances of the holes in the heads for the accessory brackets being in the same place are?

 

Dunno on that, but there are places that offer a later style comp designed to fit on the older style brackets. Look thru the 73-79 section, and I'm sure you'll find several links to them.

 

As my son says, we shall see. Probably no chance, but I might as well check since I have the W brackets.