[Sun Tuned]

So for awhile now I've not really been active on the board here for around a year. Some have their "ideas" about that, which I can assure you are dead wrong.

A man ran into me in town who owns a company who restores/services classic cars for clients, currently they have 186 in the house. I started doing tune up work on a case by case deal for them at his request. This got serious about 5 months ago. I'm still around here for those who need anything but as far as across town... I'm heavily slammed, but staying at pace with them with no sign of slowing down there anytime in next 2-3 years.

Which brings me to my reason for this post.

A man posted a question about some distributor endplay issues, which was answered, and a slight discrepancy followed. Hence the sole reason for this post.

It will be rather lengthy over its course. I hope to address answers to questions that haven't been asked and even some questions people have as to why some members of this board are absent for lengths of time. Mainly that reason is because they are damn good at what they do and they are BURIED trying to satisfy the customer base at the level of quality folks have come to expect over the years from these individuals.

In a manner I didn't use to possess I would have retorted in a post and effectively wrecked the original posters post. We aren't doing that, so I'll start one here.


Let's ask a question...


WHY DiD THE FACTORY ENGINEERS LEAVE THE ENDPLAY AS WIDE AS THEY DiD AND WHO CAME UP WITH THE IDEA TO SHRINK IT AND WHY???

[STEELCITYFIREBIRD]

I'll take a shot at why, because aluminum alloys expand linearly at approximately 2x the rate of most steel alloys.
Who and why shrink it from production #, I don't know, but I first read about the end play # of 0.010" in one of the HO Racing books.

http://www.amesweb.info/Materials/Li...nt-Metals.aspx

[Tom Vaught]

https://www.engineeringtoolbox.com/t...als-d_859.html

1) Believe the majority of the old distributor housings were "grey cast iron" with a thermal expansion rate of 5.8 (from 32 to 212 degrees F temperature), not steel.

Did not know of any Pontiac Housings made of steel. But the shafts were steel. Did not see cast iron material in your link.

2) Aluminum (using same web site above) say the expansion rate for aluminum is 13.1, so basically slightly more than 2x the expansion rate of the cast iron housings.

Either way as the cast iron housing expands, the steel shaft expands you get a clearance number.

Same deal with your numbers, aluminum housing expands, steel shaft expands you get a clearance number.

So if the 'as received' clearance on the cast iron housing/steel shaft & gear is .015" and you read a aluminum housing/steel shaft & gear at .030", the engineers did it for a reason. Not sure if HO Racing was aware of that, assume they were, but I have always run a cast iron housing with their recommended clearance.

Have several MSD/"Hot Rod" aluminum distributors bought over the years and have never run them. Points and cast iron housings worked fine for me.

Tom V.

[STEELCITYFIREBIRD]

I postulated this, based on a problem I had with wheel bearings on an aluminum axle tube quickchange rearend on the circle track car.
So.... am I on with my proposed theory?
I bet my HEI was easily 0.125"+.... stock.

[Scarebird]

The cam, hence the distributor only turn in one direction - so why box in manufacturing with tolerances that serve no purpose?

[Blued and Painted]

End play reduction is an attempt to accurize the ignition system. Even though the shaft is thrust upward while running. Any one who owns a feeler gauge won't like the idea of .125 endplay or clearance anywhere on the vehicle. Except for maybe water pump impeller clearance or a clutch pack.

[ponchjoe]

Originally Posted by Blued and Painted

End play reduction is an attempt to accurize the ignition system. Even though the shaft is thrust upward while running. Any one who owns a feeler gauge won't like the idea of .125 endplay or clearance anywhere on the vehicle. Except for maybe water pump impeller clearance or a clutch pack.

And I believe this is the problem for most DIYers, .125 seems sloppy when you remove a dist.

That and the aftermarket conversions taking about shimming if the air Gap is not correct like pertronix.

http://www.pertronix.com/docs/instru...eets/91181.pdf

So to Suntunes point, listen to the engineers, they knew what they were doing...

[Tom Vaught]

Originally Posted by Blued and Painted

End play reduction is an attempt to accurize the ignition system. Even though the shaft is thrust upward while running. Any one who owns a feeler gauge won't like the idea of .125 endplay or clearance anywhere on the vehicle. Except for maybe water pump impeller clearance or a clutch pack.

Another comment is: The oil pump is applying a load on the distributor intermediate shaft which in turn is loosely attached to the distributor drive shaft so there is always several "players in motion" here. Distributor Gear is trying to move in one direction. Intermediate shaft is fluxuating back and forth, and the oil pump gears are seeing a drive force vs the oil pumped to the engine. Doing all of that "Old Engineering" vs the new simple stuff where the oil pump is driven off of the crankshaft nose took a lot more thinking.

Tom V.

ps the HO Guys tried to eliminate a bunch of that on their race engine with the very long oil pump/distributor drive shaft sliding into the drive gear on the pump. (No intermediate shaft).

[Formulajones]

Originally Posted by ponchjoe

And I believe this is the problem for most DIYers, .125 seems sloppy when you remove a dist.

That and the aftermarket conversions taking about shimming if the air Gap is not correct like pertronix.

http://www.pertronix.com/docs/instru...eets/91181.pdf

So to Suntunes point, listen to the engineers, they knew what they were doing...

Pertronix isn't the only one. The BOP Polymer gear from Butlers also comes with instructions to shim the gear with a specific clearance. I have that paper here somewhere, pretty sure it wants .012" or something really tight like that.

[Rocky Rotella]

Let’s not forget that the lower bushing is lubricated by oil mist.

[Will]

This is not meant to refute what Sun Tuned is saying as he clearly knows his stuff and when looking at a distributor I more often than not scratch my head and drool a little...

However using "engineers did things for a reason" as an explanation for everything that was done on these engines misses the mark.

Remember, these are mass production pieces. A lot of what was done served the purposes of easing manufacturing and keeping costs down. Other things served other purposes that didn't necessarily coincide with attaining maximum performance - such as lowering compression ratios when emissions began to be a thing or using cams with low lifts to make the valvetrains more durable at less costs, etc. These engines were only warrantied for one year/ 12K miles back then. Why bother with close tolerance machining or assembly if whatever clearance happens to be there once the parts are assembled serves the purpose and doesn't create a bunch of warranty problems?

The factory very clearly did not blueprint these engines. One could just as easily defend out-of-square blocks and off-index cranks (which we all know are VERY common) by saying "engineers do things for a reason" when it really wasn't the engineers that did it, it was simply the fact they were churning these things out as fast as they could and some dimensions simply weren't that critical for a mass produced piece that only had to live a year.

As enthusiasts who have the luxury of time and the willingness to spend money to correct the deficiencies in the mass production process in service to the goal of squeezing all the performance we can out of these engines we often modify what the factory did. Everything from clearancing the water pump impellers to the divider plates to gasket matching ports to possibly modifying the distributor shaft endplay.

Now, all that said, I'm eagerly awaiting Sun Tuned's explanation of why the shaft endplay is what it is. I'll be perfectly happy to not screw around with shimming distributor shafts from here on out if it's just a waste of time.

[Tom Vaught]

Originally Posted by Will

The factory very clearly did not blueprint these engines. One could just as easily defend out-of-square blocks and off-index cranks (which we all know are VERY common) by saying "engineers do things for a reason" when it really wasn't the engineers that did it, it was simply the fact they were churning these things out as fast as they could and some dimensions simply weren't that critical for a mass produced piece that only had to live a year.

As enthusiasts who have the luxury of time and the willingness to spend money to correct the deficiencies in the mass production process in service to the goal of squeezing all the performance we can out of these engines we often modify what the factory did. Everything from clearancing the water pump impellers to the divider plates to gasket matching ports to possibly modifying the distributor shaft endplay.

I would disagree with you will on this one. Everything an Engineer does is for a reason. Maybe the first year of production he gets to make it the way he wants but then each successive year the bean counters and management are after him to REDUCE the cost, increase the line speed to install the part, open up the operating specs to allow more parts to be accepted (vs rejected) from the vendors, etc.

Many do not understand that an engine design is a "dump truck full of compromises".

I remember a story about how GM Engineers (Mark Donahue's Book) built the 'perfect engine' as far as parts being exactly to the engineering specs they considered best for performance and when GM got the engine back, many of the clearances, etc had been
modified based on some Engine Expert's opinions. The engine never did make the power that the GM Engineers dynoed it at with their specs. Course everyone knows more than the Engineer who designed the parts in the first place. Just like in Suntuned post where the clearance on the distributor is modded many times based on something read in a magazine, etc. Point being people can't leave stuff alone and have to put their signature on it as they are always smarter vs the engineer.

Tom V.

[Sirrotica]

A friend of mine built a 383 SBC for his dirt track car and the guy that he bought his parts from "did him a favor" and built him a distributor, as he had a Sun distributor machine. Upon firing the engine up for the first dyno pull they warmed it up and then did the first pull. The distributor seized up and spun far enough that the plug wires all pulled out of the cap.

My friend was sooooo mad I thought he was going to hit the guy that had done him this "big" favor by blueprinting the distributor. The guy offered to fix the distributor and my friend said, "No FFFFing way it was ever going back into that engine, just order me a new one". And he then threw it on the concrete floor hard enough that there was no salvaging it.

The funny thing is he had just driven back about 40 minutes from the location they were dynoing the engine at, so he either stewed about it on the drive back, or he had time to calm down, and was much worse 40 minutes earlier....................

So taking too much clearance out of the end play in a distributor can have a bad outcome.

BTW, my friend had about every penny he had, invested in that engine, so it was pretty traumatic for him. He thought it had scattered when it shut off so abruptly under load.

[Tom Vaught]

I saw a chebby guy break a camshaft (Factory L-88 part) on a concrete floor after he installed the cam 3 teeth off and killed the valvetrain. Bent every pushrod in the engine.
Cam was probably still good. Several bent valves. He went thru 3 crate L-88 Engines from GM, (GM Employee) due to his stupidity before he got it right. I sold him the L-88 camshaft and lifters. How was that GM's fault or the Engineers fault?

Tom V.

[Scarebird]

Originally Posted by Tom Vaught

I would disagree with you will on this one. Everything an Engineer does is for a reason...

Tom V.

not so sure of that, Tom, as anybody that has fitted up a 70-73 Firebird front bumper would love to query the assembly engineer WTF he was thinking/smoking...

[dataway]

I'm no engineer or expert ... but I'm going to venture a guess that any factory clearance over what is necessary to compensate for expansion is to allow oil to get to the lower bushing .... like another has mentioned .... tight up that clearance too much and it's possible very little oil could get to that bushing.

Also ... am I wrong in thinking that if the clearance is too tight, and things expand, it would put downward pressure on the oil pump gears? Increasing wear on the bottom plate of the oil pump?

[tom s]

And 69 firebirds!Tom

[Sirrotica]

Originally Posted by Tom Vaught

I saw a chebby guy break a camshaft (Factory L-88 part) on a concrete floor after he installed the cam 3 teeth off and killed the valvetrain. Bent every pushrod in the engine.
Cam was probably still good. Several bent valves. He went thru 3 crate L-88 Engines from GM, (GM Employee) due to his stupidity before he got it right. I sold him the L-88 camshaft and lifters. How was that GM's fault or the Engineers fault?

Tom V.

Tom, FYI, just dropping a cast camshaft from 5-6 feet on a concrete floor will break one. We used to do it with flat lobed cams all the time after we had removed them for replacement. The casting is so hard and brittle, it shatters when dropped from any major height, you don't even have to throw it. Try it sometime with any GM cam, you'll be amazed at how easily they snap off.

[Tom Vaught]

Originally Posted by Sirrotica

Tom, FYI, just dropping a cast camshaft from 5-6 feet on a concrete floor will break one. We used to do it with flat lobed cams all the time after we had removed them for replacement. The casting is so hard and brittle, it shatters when dropped from any major height, you don't even have to throw it. Try it sometime with any GM cam, you'll be amazed at how easily they snap off.

Agree, My point is I was standing right beside him when He (in a rage) THREW IT DOWN on the floor. He did not drop it by accident. But agree totally that if you drop one it will most likely break like glass too.

Tom V.

[Kenth]

Same answer as in "the other" distributor post:

There IS no endplay with engine running due to the helical drive/driven gears and the force from oil-pump drive shaft.

Totally waste of time and effort shimming to .010" with the risk of getting glitter in oil from oil-pump bottom plate and excessive wear on distributor/cam gears located too far down.

I have several NOS Pontiac distributors having ,40"-.60" "endplay".

And as for lubricating the lower bearing "endplay" is NO issue since there is a space between wear shim and distributor housing on alu housings and a hole in distributor body just above bearing on cast iron housings.