Tom's challenge of the Butcher (Part III) - an answer?

[Tom Wells]

Today we think we know more than we knew yesterday. When I picked up the engine from the builder, he handed me the Ford distributor which he had taken apart, i.e., pressed out the shaft.

There was clear evidence that the distributor shaft was being galled by the bushing inside the distributor housing!

At last we have a relatively clear suspect in the distributor gear / cam gear failure!

THEORY:

The distributor shaft binds in its bushing, causing overload on the drive gears, which fail after 812 miles.

Other evidence includes the following:

1) there is considerable scuffing or galling on the distributor shaft itself. The bushing appears to be more than an inch in height (along the direction of the shaft axis), giving it plenty of area to "grab" the shaft and try to slow it down. Kind of like a miniature Prony brake (remember the things that used to be used in dynos in the Dark Ages to load up an engine?).

2) There is a scattering of baked and blackened grease on the shaft itself and inside the distributor housing.

3) And last, but most ominous, is the dreaded stamp "REMFG" on the housing of the distributor, which marking was not noticed until after the failure. This is the very distributor that Ford supplied with this crate motor.

CORRECTIONS APPLIED:

We installed new cam, distributor drive gear, a new MSD distributor (this one has a BALL BEARING, not a bushing) and a new Melling oil pump.

The old oil pump didn't seem harmed but putting a new one in was felt to be a safety factor.

All of the dimensions invloved were checked and double checked. The depth of the distributor mounting surfaces (must be 4.000" in this engine) and the distributor drive gear mounting location.

By the way, check your MSD distributor! The gear location on the one I got (new) was off by more than 0.010" which could definitely contribute to a failure.

WHAT'S AHEAD:

Where from here? Well, the engine may go back in as early as today. If the new trans is ready tomorrow (another story, sigh) it will go in tomorrow. The new torque converter from Edge Racing arrived yesterday to replace the TCI unit which may be part or all of the cause of THAT failure.

Also, I will notify Ford, send them parts as they deem fit, and request some pecuniary salve - I want some money back for this failure!

In the meantime, the distributor will be plucked out early and often to check its condition. Once burned...

I'll report back on progress on all fronts if and as anything of any significance happens.

Driving the car is too much fun to let anything like these problems stand in the way,

Tom

[jdean]

Tom,

It was good to meet you at DVSFII.

If the average Cobra owner has 2-3 major problems over a 3-5 year period, you are not due for any more for a long time. I hope you have now gotten many years worth of glitches out of the way early.

You definitely belong in the "we don't give up easy" club.

Anyway, could you get me the name of the AFR guage company you are using?

Please give us the latest report after you get back behind the wheel.

Good news is there is still a lot of driving season left!

John

[Tom Wells]

Hello John,

We enjoyed talking with you guys too! That was some kind of GOOD box lunch at the church.

Here's the data on the air /fuel ratio gauge:

MFR: Westberg Mfg. Inc.
3400 Westach Way
Sonoma CA 95476
800-400-7024, 707-938-2121

GAUGE: Westach Cat # 2C5-56, lighting kit option is kit # 186-12A2L.

As my oldest says "we're still in the drum roll" about getting the car back. The best would be having it back on the road by tomorrow night or sometime Friday.

Regards,

Tom

[Andy Dunn]

Hey Tom

I have a question on the MSD gear location. How do you measure this and where? Would you maybe have a picture? I have seen it referenced on a couple occasions and want to check mine to be safe. Are you looking in the front of the engine where the cam thrust plate covers? How do you determine the .010? What is the range you seek? And how do you correct it if things are wrong.

hope you are back on the road shortly. I am half way through my rebuild and having a lot of fun learning.


Andy

[Mike Braddock]

Great update Tom. Seems you are on the home stretch. Good luck buttoning it back up and please let us know how everything turns out.

Mike

[SFfiredog]

The distributor gear mounting length (for a 429/460) is measured from the face of the base of where the distributor mounts in the block to the end of the base of the gear (not just the teeth). The spec is between 3.996" and 4.005", 4.000 being perfect.
HTH,
Mike

[niles]

I second Andy's question. Will some gear experts PLEASE!!! come forward and tell us how to set the gear mesh?

I just reviewed my "Dudley" gear handbook while eating lunch and it reminded me of many things.
All this folk lore about can/t use steel with iron, bronze must be used with steel is an old wifes tale. Steel can be used with steel, iron or bronze; just the correct tolerances/lubes must be applied.

For the touters of can't use steel on steel; think for a minute what your rear ring and pinion are made off? What about the transmission, ie, all hardened steel on steel.
The distributor gear is hypoid or cross helical and are very sensitive to base circle matching. Scanning the tables of tolerances in base circle and backlash they are in the range of .001 to .005 in.
I recall reading about a yr ago that you had to set and shim the depth of the distri. engagement to less than .010 in. tolerance. I can't find that tech article anywhere. Someone have it? This squares with everthing in the handbook.

What I think is happening is that all the manufactures are machining with a -o/ +oox toleracnce so that there parts won't be too "short". Both the distributor people and the block both take this "proper" tolerancing strategy. The problem occures when both are at the +.005 x 2 and you get a +.010 in "too deep" mesh. When the base circles are off by this amount the tooth tip can't clear the base cirlce and it quickly machines the clearance itself. This self machining distroys the surface smoothness and rapid wear insues. This is probably happening much more frequently because of the frequent use of different manufacture's products; detroit blocks, mallery, MSD, Ford disti, etc. The chance of being off .005 to .010 in is greatly increased

This problem is analgous to setting up ring and pinions. I have tech manuals that show how you dial indicator it close; then put "dycom blue"? on the gears and run them for 15 minutes and then inspect the contact pattern. It even shows pictures of the contact patchs and the resulting shims need to bring the contact patch to the center of the pitch circle. The cam/distributor gears sensitivity and setup needs the same care and careful control of the tooth/engagement depth.

I'm about 80% sure that proper shimming under the distri. housing to insure the proper depth will correct the rash of gear failures. Can somefind those/articles or know the " correct-measure-shim" procedures please inlighten the masses. For all those that are eating gears ever 500 mi, a fifth would be appropriate for a fix.




grover niles

[niles]

SFFIREDOG;

Do you have the dem's for a 351C, 351W, etc.
thanks
gn

[Tom Wells]

Hi Andy,

You are mah heero!

Seriously, I found myself wondering what you'd do in these situations and how you'd recover. It gave me some of the backbone to continue with only minimal use of the four-letter-word.

Actually I am so hooked on driving the car it HAS to get fixed!

I have uploaded a scan of the addendum sheet that came with my MSD 8580 distributor, which MSD says fits the 460 and 351C. Look in my gallery to see it and let me know if it isn't legible.

Interestingly it says "Ford" not just 460 / 351C so it may apply to other engines. It does give a different measurement for the FE engines. You can and should CHECK THE BLOCK by measuring the distance between where the indicated distributor and gear surfaces contact the block itself.

The fascinating part of all this is that the new MSD distributor came with a gear on it, and it was located more than 0.010" off - clearly out of spec! Check 'em!

The builder installed the Crane steel gear correctly after removing the MSD-supplied gear.

I used steel because this is primarily a street car and is similar in setup to the zillions of 302s that came with roller hydraulic cams and steel distrbutor gears. Some recommended a bronze gear, but it would need to be checked periodically as they are touted to last less than 10,000 miles.

Needless to say, this one will probably be checked every 50 feet until it goes over 10,000 miles .

The builder also verified the block's matching surfaces were 4.000" apart.

SFfiredog's length is correct for this unit.

Hi Niles,

A quick read of the Crane literature for the cam I use says "8620 STEEL ROLLER CAMS ... WE HIGHLY RECOMMEND THE USE OF AN ALUMINUM BRONZE GEAR OR A SPECIALLY PROCESSED IRON OR STEEL GEAR SPECIALLY MANUFACTURED FOR STEEL CAMSHAFTS, ON THE DISTRIBUTOR" (the caps are theirs ).

Crane's heavy inference here appears to not only be geometry, but also lubrication and compatibility of materials. I don't have a clue what they mean by "specially manufactured" and "specially processed". We are now using the Crane gear, where previously we used the Ford gear.

To All,

I spoke with Jeff at Ford Racing's tech line a little bit ago. He said my request for reimbursement was not unreasonable; they'd like to see the parts before they agree or disagree which I took as a reasonable request.

So I'll bundle up the parts, write a note describing the problem and my requirements and send it off. There'll probably be a few weeks delay (well I DO have to go diving, don't I? ).

So I'll leave this on an optimistic note -

Later,

Tom

[cobrashoch]

Tom - On your recomended suggestion I checked my distrib. gear and its clearance. I got a surprise. First, the gear checked good but now for the supprise. There was a thin shim that fit under the MSD dristib. between the block and the distrib. !!!!!! I haven't paid any attention to this prior to this post and I LUCKED OUT that it was set to the correct 4 inches with the shim. Now that I think about it a bit, the factory block milling specks have to be all over the place on a block from the factory just because 385's being what thay are. Thanks, I've now found ANOTHER thing to look out for!!!! Hope you get everything glued back together soon
and thanks for the heads up.
cobrashoch

[millennium200]

You might have your engine builder check the cam shaft end play. If the cam can move back and forth in the block too much, you will get the distributor gear to fail no matter what it is made of.

[cobrashoch]

millenium200 has got a good point. I know most custom engine builders as well as my engine guy also, uses thrust plates on the cam. Does Ford SVT crate engines have them? I don't know. Cam walk indeed IS a problem on roller equiped engines for sure.
Cobrashoch

[Double Venom]

Niles,

I like your post, but I think you are on a lost cause proclaiming the type of gears used is a "wives tale". Crane, MSD and even SVO claim a "matching" gear must be used. Then, throwing everything else out, if different materials are not needed, why do they make three different gears?

We've never had a gear failure using the recommended gear ??

I love threads like this! I will continue to use the recommended gear, but now I will also "mic" out every distributor we use.

Thanks Bill for the tips!

DV

[Tom Wells]

Hello All,

Just a quick note to say the car is back on the road!

Would you believe we had to cut a hole in the hood for the distributor? The MSD unit is that much taller than the stock Ford piece. Education is never free

Defective/destroyed parts will go to Ford next week with a request for reimbursement - stay tuned for chapter IV...

Back in three weeks - gotta go diving now!

Regards,

Tom

[niles]

DV:

As usual these thing are a lot more complex that mets the eye: I still stand by the gear handbook that says any material in ok as long as the hardnesses are compatible. Normally you don't want two very smooth steel gears of the "same" hardness cause they tend to develope atomic attractions to each other like Jo block's do.
You dispense with this my different surface finishes or harnesses.

Cranes own manual down plays the material with there own words:

A quick read of the Crane literature for the cam I use says "8620 STEEL ROLLER CAMS ... WE HIGHLY RECOMMEND THE USE OF AN ALUMINUM BRONZE GEAR OR A SPECIALLY PROCESSED IRON OR STEEL GEAR SPECIALLY MANUFACTURED FOR STEEL CAMSHAFTS, ON THE DISTRIBUTOR" (the caps are theirs ).

this strongly implies that many different combo are compatible.

Two things are going on here in my opinion: 1. Crane wants you to buy Crane gears; not real concerned which type.
2. Crane, or any other manufacature for that matter, may have tooth profiles that are unique to there gear hob machines and "sets" from them are more compatible.

The selection of gear material from an engineering viewpoint is driven by what do you want to wear; hard always wears less than soft. So if you want all the wear to occur on the distributor gear use bronze. If you long wearing but have "some came protection, use iron. The longest of all would be steel; the down side is that the cam may actually wear out first. Never simple; always many layers before you get the bottom.

gn

[Double Venom]

Niles,

I, Sir am ready for metallurgy class 101!


DV

[cobrashoch]

Ed- I think the confusion on gear types revolves around the distributor that you use and not so much the gear itself. Anything that rotates (in this case a distrib.) will have harmonics and the bearings and such vary in quality. So you want to use a gear that is the most forgiving for the distrib. that you use. A MSD is a example of a high quality piece that has little slop and as such will take anything you put on the shaft as long as it is hardened. On the low end is factory stuff with lots of stock production slop so in this case the soft bronze gear is the right thing. I've allways used bronze, as I stated above, even on high quality distribs. knowing full well that they wear out quick.
The hardend gears sold will last longer for sure, but I don't think they are very good for "loose" distributors. It's about choices and knowing what you want to do. The reasoning I use is the MSD distrib. that I use has less harmonics(tighter) than most stuff out there and this helps the bronze gear last longer to! Anyhow, I am reading Toms post as a distrib. failure.
I think the reason the cam folks are so ambiguous is they don't know what distrib. you are using or the shape its in, so they tend to give a lot of lead-way.
cobrashoch

[Rick Parker]

This thread raises an important area that can easily be taken for granted. Evidently few have given it much thought. Regardless of which basic Ford engine we employ 289, 302, 351W, 351C, 427, 429, 460 etc; there is one design element that I have thought about for some time but never seen addressed in any engine article printed. The length of the distributor shaft that extends below the distributor gear and engages onto the oil pump drive passes through a machined hole in the block and creates a thrust surface for the gear and the fit/clearance of these parts provides stability for the bottom of the distributor and hence the gear itself. It would seem some improvement could be had with a bearing of some sort, granted this is out of the question for a production engine application but the shaft in a Ford distributor
(OEM or Aftermarket) has a significant amout of side to side movement and could be reduced with a better fit in this area.

Any opinions
Rick

[cobrashoch]

Rick - I think you are correct about about the shaft issue. Bottom end play will also wear out a distributor faster to. But the real answer I suspect is the given reality that the stock stuff, no matter how bad it is, seems to last well past 100K miles. With that in mind your proposal may help a distrib. last for over say, 200K miles. I suspect the extra costs involved may not warrant the higher cost when you buy it, even for a high end piece. Its about money I would think.
cobrashock

[niles]

DV;
I'll lighten it up.
I was just trying keeping the thread alive; while awaiting the original query:
What is the corret dimension and procedure for setting the distri gear mesh?
gn