[DeTomaso] July POCA newsletter and distributor installation

[Thomas Tornblom]

2011-07-08 07:22, JDeRyke at aol.com skrev:
> In a message dated 7/7/11 6:01:43 PM, Thomas.Tornblom at hax.se writes:
>
>> The article mentions that the gear should have a 0.010" clearance to
>> the block boss and should never touch the block. This is just plain
>> wrong and will potentially destroy your distributor. The boss acts as
>> a thrust bearing, and it is what takes up the axial loads of the
>> distributor shaft from the load of the oil pump through the spiral gears.
>
>
> Thomas, I don't know what to tell you. Looking at the distributor boss
> on my OEM '72 block, the junk block in my photos and a third block I
> have in stock. none show any trace of contact between the boss and the
> distributor gear. I also have a 351-Windsor block that shows no trace of
> gear contact. So apparently 0.010" static clearance is very close to
> what's needed. Whether the gear then pulls down to kiss the block in
> operation, or whether there's still an oil film between, I don't know-
> but there's definitely been no metal to metal contact on these 4
> examples. All used standard oil pumps during their operation, so maybe
> the loads imparted were not high enough to pull the assembly into full
> metal-to-metal contact.

If you look at the bottom of the gear you'll see that the bottom surface 
is machined smooth, and the boss is block is also machined so that it 
works as a thrust bearing, given a suitable oil film in between.

As the oil pump is a major load on the shaft, the spiral cut gears pulls 
the distributor shaft and gear down towards that boss. That load would 
have had to be taken up internally in the distributor otherwise, and it 
is not designed to have any axial loads at all.

Rest assured that if Ford had intended that there should be a clearance 
between the boss and the gear, neither the bottom of the gear, nor the 
boss would have had any machining done after casting the block. You can 
just check the upper surface of a standard cast gear, is has no 
machining whatsoever.

The Ford document specifies a distributor endplay of .024" - .035". This 
should probably be split evenly up/down, so that you should be able to 
lift the distributor housing about .012" - .017" before the shaft starts 
moving, and you should also be able to lift the shaft the same amount 
with the housing firmly attached to the block. The distributor should 
only guide the shaft radially, there is no real axial bearing in any of 
the standard Ford distributors or cam sensors I have, and they are from 
various cleveland/windsor/v6:s.

Another piece from the Ford document:
---
ALTERNATIVE METHOD OF VERIFYING CORRECT DISTRIBUTOR GEAR INSTALLATION:
After STEP 7, install distributor assembly in the block you are using. 
Timing chain set and camshaft must be removed.
With the aluminum distributor housing fully seated against the block, 
verify that the distributor gear can be lifted off the
support in the block at least .005”. Next, pull the distributor gear 
down against the support in the block and hold it there.
Pull up on the aluminum distributor housing and verify you can lift it 
up at least .005” while holding the gear against the
support in the block. This procedure will confirm that the gear is not 
being forced down against the support and not being
held up off the support in the block. Then, continue with STEP 8.
---

This describes exactly what I mean.

> Bud Hower has brazed a bronze washer to the base of his gear on the
> example block that showed actual metal to metal contact, so after he
> gets some miles on the rebuilt motor, we can see how this works as an
> actual thrust bushing. Cheers- J Deryke

Cheers,
Thomas