WESCH

Hi
I dismanteled my 68 big block's point type distributor and found the main shaft and lower bushing worn near the drive gear.
ECKLERS offers a new tach drive type shaft for I think 60 $.
Can I use this one ? Does it fit both small and big block distributors ?
What else could I do ? Undersize the shaft ?
Anz ideas ?
Oh yes. I also noticed oil in the distributor cap area. I could not see any seal at the shaft ? Is the oil only sealed off by the bronze bearing bushing and shaft ?
Thanks and happy new year.
Gunther

jackson

Gunther:
As far as "fit" goes ... same shaft will "fit" both sbc & BBC. There is a small cam that is brazed to the very top of the shaft (I'm NOT referring to the cam that opens points ... the points cam does not come with new shaft ... you'll press off/on & reuse your old points cam). There were MANY tiny variations in the cam that operates in concert with the mechanical advance curve weights ... hence there were MANY different shafts. As far as I know, there are only one or two reproduction shafts being produced ... kinda universal, one-size fits all. So the advance cam on it may or may not be exactly, precisely, perfectly matched to your mechanical advance curve weights. IMHO, you'll never notice/realize any difference in cam. Get the Eckler's shaft ... or from another supplier.

Under the breaker point plate is a grease well that has a plastic retainer/washer and underneath that is a felt (fabric) washer. The well should be filled with a heavy hi-temp distributor grease ... then the felt washer replaced ... then the plastic washer. The grease well/felt/plastic serves as a "seal." Chances are the grease is gone or dried hard ... the oil is getting past it.

Consider replacing or retrofitting bushings ... have bushings sized to fit shaft (new or old shaft). Same goes for top ... although some have bushings ... and some don't.

If shaft/bushings has much wobble, it may've caused undue wear at distributor drive gear/cam gear ... and at tach drive gears. G'Luck!

WESCH

Hi jackson

Thanks.
My distributor's shaft is .494 "
SUMMIT offers a .006 oversized drive bronze gear. P/N = MSD-8472
Does this mean that the hole is smaller, so that I could machine the distributor shaft a bit down to .488". The wear is just above the gear and of course to insert it from top back into the distributor casting, it needs to be machined down also where it accepts the drive gear?
The top bushing seems to be tight. Also the tach drive gears are like new. The main drive gear shows slight wear, more like polished areas where it drives. Can't measure any wear as such.
My original drive gear is steel, can I use the bronze gear ?
I don't want to spend lots of money on this distributor as I might go with a new one later on. I just haven't decided jet.
Thanks a lot and again, have a happy new year ( wich is a celebartion year for CORVETTE, isn't it ? )
Gunther

Desertvette

Gunther,I had the same problem with my 67 S/B distributor. Lars gave me the advice I needed to straighten it out. You can find the post under Lars or Desertvette back in 8/25/02 in the search archives. I ended up replacinng the lower bushing and the shaft with pieces I ordered from http://www.tld-corvette.com the shaft was $45.
Along with imformation I got from SWC Duke to shim the dist shaft end play to .007 and use 32 once points ,Accell makes them,I'm now able to pull 6000 rpm easy. Also follow the advise given by jackson to clean the upper well out , regrease.and replace the plastic seal. Lol
Bob

Smokehouse69

Gunther,
My shaft was badly worn as well as the lower bushing. I ordered a new shaft and lower bushing from Paragon or Zip (I can't remember which) I got the old bushing out by filing a groove the length of it done each side of the inside of the bushing. It is fairly soft brass or bronze so it was no problem.
I cut a piece of my old distributor shaft and made a madrel out of it, and used it to guide the old bushing, while I drove it in place. I did put the bushing in the freezer for about 15 minutes and I heated the bottom of the distributor housing with a propane torch for a few seconds.
The new bushing slipped right in place with very little effort. The new bushing's inside bore was very tight even with the old worn shaft inside it, so it needed to be honed to fit the new shaft. I took some emery cloth and wrapped it around a drill bit and started honing, I used some light oil on the cloth and checked every few seconds using the old shaft to check with. After just a few tries the old shaft fit fine, I then tried the new shaft and it was pretty tight. So I honed some more and tried the new shaft again. After a couple of more tries the new shaft fit perfectly and spun in the housing like it was on glass.
I did not go into this blind, a few months before I had paid an AC/Delco repair shop to do the same job (of installing and honing the bushing) on another distributor. It took them all of 15 minutes and they charged me $25.00, to do it. So I did not think it was too much of a risk in me trying to do it myself, and it has worked out great and the distributor operates like a new one.
Here's a picture of my old shaft.



[Modified by Smokehouse69, 6:25 PM 12/26/2002]

jackson

Gunther:
The others' advice & methods & sources are very good ... exactly what I'd do ... go for it.

Not so sure on the hi-po32 oz. points ... everything's a give & take. Heavy springs on hi-po 32 oz will cause upper bushing & wear block to wear a bit more quickly ... and you'll have to reset points gap/dwell a bit more often. If you really need to rev way above 6K then you need hi performance 32 oz ... otherwise I'd stick with heavy duty 23 oz. Accel pn's for contacts only (not uniset) are:
23 oz heavy duty = 110127
32 oz hi-po = 110128

However, DO NOT use a bronze gear. Those are ONLY for billet steel roller cams (I don't think you have one since your steel dist gear's wear seems minimal). Since wear on your gear sounds minimal & typical ... just reuse your old steel gear ... but use a NEW roll pin. Bronze gears wear out very quickly ... you don't need one.

BTW, if I recall correctly, the 0.006" oversize is in the OUTSIDE DIAMETER of gear ... they use these in RACE CARS to keep ignition timing float minimal ... by very closely tightening gear lash. Again, you don't need nor want this.
G'Luck!


[Modified by jackson, 11:18 AM 12/28/2002]

WESCH

Hi
Thanks for all help.
OK, I will not use a bronze gear, thanks for the explanation regarding it's use.
Thanks for the address TLD. They do have all required parts at a better price than SUMMIT and more detailed.
They offer a hi perf shaft and STD perf shaft ? What's the difference ?
I guess, I need the hi perf one as this was a hi perf 396 CI Camaro engine.
So, I need following
lower bushing 8 $
shaft 40 $
shim kit 4 $
small parts kit 7 $
cap 10 $

This makes it 69 $ and my distributor should be as good as new after this.
Thanks again and happy new year.
Gunther :cheers:

Big Fish

Maybe you want to keep your 69 all original, but if that's not the case, why not put a later model HEI distributor in. They will out perform the points type units and no points to worry about. :cheers:

WESCH

Hi
No nead to keep my 68 original sinse the engine is a non numbers matching engine.
I don't want to spend a lot of money on this as I just modified to PETRONIX elctr ignition.
May be at a later date.
70 $ is not a problem to o/haul it.
I'm presently trying to get a distributor in apparently very good condition on E-bay. If I manage to get it and it's OK, I will use it .
Otherwise I will get the spare parts.
There was a post a little while ago to drill a hole through the distributor casting between the lower two support walls to pressure lubricate the lower bushing. Is this a good idea ? Will the oil pressure fill the distributor cap when doing this ?
Thanks for all the help and happy new year.
Gunther

jackson

Gunther:
Drill hole BETWEEN support bosses (as you suggested) is a good idea ... especially since it's already apart. It'll help a little bit ... because some oil will be thrown from lower end & cam and SPLASH into hole. If you drill between ... there will be no liquid pressurized oil into hole ... other than the crankcase vapor pressure that is already pushing into the bottom of distributor ... drill between & you'll be ok. The OE distributor support bosses are a loose fit into block ... so little-to-no liquid pressure there. Look at a MSD dist ... its bosses are o-ringed ... and it is drilled between the bosses. Some Accel & others are similar. The OE distributor doesn't have much of an upper seal ... IMHO, I believe if you pushed Pressurized Liquid oil into that hole, some would migrate into the plate & rotor.

You seem well-equipped to rebuild your distributor ... I'd rebuild your own. Unless the ebay dist goes for super small $ ... I'd let someone else worry with that one ... ya never know what you're getting. If rebuilding yours, now is a good time to check/replace its vacuum advance can.

With pertronix, our posts about HD vs HiPo points don't matter too much.

WESCH

Thanks jackson

I did not get the E-bay unit, got outbit.
Now, with the oil pressure between the lower 2 support bosse, is this not the pressure galery oil from the valve lifters ?
The previous post mentioned to drill a hole into the lower support boss to get oil onto the drive gear and a hole between them to get oil to the bearing bushing.
Above the 2nd support boss is a big hole in the casting. This should return the oil into the block, doesn't it.
Your right, no seal at the upper bearing bushing to shaft !
I guess this area should even have a slight vacuum due to the block being vented back into the carbs vacuum section, or ?
Would installing O-rings on the lower support bosse help ? This should be easy to mashine a grove.
Do you have any idea about the difference of the 2 mentioned shafts?
Hi or STD perf shaft ?
Thanks a lot.
Gunther

norvalwilhelm

I'm the guy who keeps posting about drilling a small 1/8th hole between the 2 lower supports on the distributor housing. This is pressurized oil. These 2 machined surfaces seal off the pressurized oil. Pressurized oil will flow through this 1/8th hole and lube the bushing. Above this in the housing of the distributor is a 3/8th hole that is used to mist the bushing but any pressurized oil will exit out this hole and never reach the top of the distibutor. I also file a .030 grove, that is a slight cut .030 wide and deep on the lower machined support and on the side facing the cam when the distributor is installed and timmed correctly. This sprays a little oil on the cam distributor gear..
I have used bronze gears on the street but don't recommend them because of quick wear problems.
I run a high volume high pressur pump with about 70-80 pounds of normal oil pressure and have never had a problem flooding my distributor with oil after these modifications.

WESCH

Thanks Norval

This modification , I will definately do as I'm also running a high volume pump.
The pressure is always at top ( 70 PSI ) gauge except when very hot in idle at 40 PSI, never lower.
Guess this might be part of the wear reason.

Happy new year. Gunther

jackson

Gunther:
I believe the small difference in two shafts is in the shape (“curve”) of the mechanical advance curve cam that is brazed onto very top of shaft ... but what does TLD say? Y'all please correct me if needed.

Shop currently has several sbc for seasonal freshening ... we rarely run BBC on circle tracks here so no BBC for me to check.

Last night, I verified distributor boss’ fit into three different sbc blocks using two different OE distributors. I did so with NO cams in blocks, so not to confuse any cam gear interference/lash with any distributor-to-block/bore interference/tightness. All the blocks were iron small blocks (not BBC), one distributor was an early (79?) aluminum HEI, another dist was an early (probably 71 sbc vette) iron tach drive. While the blocks’ dist bores & distributors’ bosses are machined surfaces ... they are not a press fit. I did not measure with bore gage & mike ... but did a wobble check. Each dist wobbled in each block. I ESTIMATE the clearance at approximately 0.005” - 0.015” . Both aluminum & iron dists yielded about same looseness of fit.

The machined surfaces do limit oil bypass ... NO doubt ... they have to or there would be no oil pressure in cam bearings. However, due to looseness of fit, IMHO they do not seal it. Again, this was done with sbc & NOT bbc ... I cannot be certain the results & implications are same for bbc.

The MSD’s have their bosses o-ringed .... but that design feature not intended to aid dist bushing oiling. As Norval says, there is liquid oil pressure fed into block’s space between the bosses. BUT ... since the bosses are a rather loose fit (~ 0.005” - 0.015”) into block ... the o-rings are intended to provide a better seal, thus aiding increased oil pressure through the camshaft bearings (again, I checked sbc only).

In addition to the HEI I used to check fit, I looked at several others ... including a brand new gm# 1104067 from a new ZZ4. None of the HEI had any holes nor grooves.

The iron tach drive distributor I used to check fit has two holes in it and a groove. Just as Norval says, there is a ~3/8” hole just above the upper boss ... about 1/2” from cl of hole to cl of upper boss. However, there is also another hole .... ~3/16” hole located about 1” below the dist gasket flange. Both holes are in same plane ... about 20 degrees from tach drive ... toward the vac can. The lower boss has a machine-cut groove in it. The groove is about 1/8” deep and about 1/4” wide. Groove is located about 180 degrees from the points wire hole in dist base. Both holes & groove appear to be OE & not modifications.

Of the ones I looked at, all HEI & the iron td had a chamfer cut into bottom of lower boss. All HEI had a two-piece serrated spacer-shim between main gear & lower boss.

IMHO, I also believe the HV op may put a bit more stress on lower dist bushing.

WESCH

Thanks.
That's exactly what my distributor housing has presently.
I like the idea of a hole to pressure lubricate the lower bearing bushing and also the small groove to pressure lubricate the gears.
My HV oil pump keeps the pressure so high even at idle, that this shouldn't harm any pressure or flow to the lifter valleys.
Anyway, I'm running solid lifters, so no worry on the amount of pressure.
TLD's answer to the distributor shaft is that the HI PERF shaft will fit all applications, so that's what I will order.
Oh jes, i can't feel any play when I insert the distributor into the BB.
It is a tight fit, no wobble at all ?
Thanks for all the help to guid me to the distributor overhaul.
Gunther :seeya