Hi All,

Well, I was happily driving my Dart home last night when the horror happened again...my camshaft drive gear failed and shredded the plastic dizzy gear. Sounded like a shotgun when that fuel detonated at the wrong time, nearly blew my exhaust system apart. Below is a link to the cam gear damage and the dizzy gear. As you can see, one side of the dizzy gear is in pretty decent shape while the other side is shredded.

http://s785.photobucket.com/user/67dart ... sort=3&o=0

http://s785.photobucket.com/user/67dart ... sort=3&o=1

http://s785.photobucket.com/user/67dart ... sort=3&o=0

This exact thing happened in my last rebuild. It was the same camshaft, a "380-252 CAM" or "Performance 254S Grind" from S&J Engines. I don't know if they harden those gears, but the oil pump gear is unharmed, like last time. I have a DD oil pump on there so I believe it was getting plenty of oil. I have 2.76 gears, and was going about 75 mph (2200 rpm) when she failed. The engine was running beautifully both times this happened, and I was going about 75 mph both times (last time was 3.23 gears, so likely higher rpms (incidentally both times happened within a few miles of each other - scary)).

I know there are threads on this site about similar gear failures, has anyone had this happen recently? Do they harden the camshaft drive gear typically and/or can this be done? Anyone have a particular camshaft type/vendor that is reliable? I thought the first time was a fluke, but I believe it is the camshaft itself, as I now have two data points.

Thanks all,

Brian

ugh...

_________________
https://tinyurl.com/yynpj4v2

Usually the failures you read about on here are oil pump gear failures and the cam gear. Usually the distributor is along for the ride and has very little load on it's gear. That is why the plastic survives so long. Did you see any burrs on the camshaft gear that could be tearing up the plastic gear?

_________________
2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

The cam gear was perfect at installation, and the engagement of the oil pump gear and cam gear seemed OK.

The cam gear is now shredded, sharp bits of metal and as you can see from the pic, the teeth are bent/warped from something. I think it's failure under heat stress or something, but it appeared to be oiling OK. My oil pump gear is hardened, like last time it appears unscathed.

brian

_________________
https://tinyurl.com/yynpj4v2

I half expected that the dizzy gear had failed and the cam drive gear would be OK, but it got torn up somehow. My system is clean, there was nothing in the oil system that could have jammed in there, so I'm guessing it's a flaw in the cam gears...as you said the dizzy gear destruction is just an artifact of the cam gear failing. I pulled the valve cover, I don't see any bent pushrods or anything, but boy that bang was LOUD! Last time the bang was in the manifolds, under the hood, this time it was way back a the muffler, late detonation of built up fuel in the exhaust system. Must have scared the guy behind me...

_________________
https://tinyurl.com/yynpj4v2

Is there front to back play in the slant camshaft? I thought I saw some strings on this board where people put something to take out any such play in the camshaft, is that true or am I dreaming? I didn't do any such modifications nor did I check for play before installing the engine. I didn't do the rebuild, I had S&J do it. I just went from long block onward as far as installation, broke it in, etc.

brian

_________________
https://tinyurl.com/yynpj4v2

if the oil pump gear is fine and only the dizzy gear is getting torn up..did you check the distributor gear to cam gear engagement?

* is maybe the distributor not seating all the way in?
a burr on the OD of the housing or the wrong distributor o rings ?
** c clip missing from the inside of the distributor allowing the shaft to rise up?
***how much end play are you seeing between the top of the gear and the base of the housing
**** maybe a bent distributor shaft or worn distributor housing causing the shaft to run out or bind..

I think I would be trying a different distributor,,

I rebuilt the distributor and it has very little play up and down, the gaskets allowed it to seat fully and it was engaged well, I made sure of that. I ran it this way for about a year with no issues. I had played with another distributor and there was no wear on that gear when I pulled it. Also, I had pulled this super six dizzy a couple times to check for wear and there was none, like after 5000 miles.

Is there any chance it's just the plastic of these gears fails? Then when the timing is off and it backfires the hardened oil pump gear shreds the softer cam gear? Does anyone use the metal dizzy gear for this reason?

I'm considering a DD oil spray tube for extra oiling next time, thoughts?

Brian

_________________
https://tinyurl.com/yynpj4v2

Looking at the dark distributor gear, it looks like the worst 'chewing' was at one concentrated at point in particular; same thing on the white gear. That would suggest that the distributor shaft might be wanting to hang up or is not running concentic on the shaft. If the gear was out, I would expect the same wear all around the gear and that does not show up on the white gear pix.

Same distributor internals? Rotor button whacking the cap at one point?

Checked the distributor and cap, shaft seems fine, no indication of wobble or eccentric behavior, it's a nice tight tolerances, easy spinning fit.

Besides, the last time this happened, different motor, different dizzy, different cam (but same model/grind) the dizzy gear was shredded evenly all the way around.

I'm beginning to believe this is the plastic failing. If the plastic gear fails it'll be out of time, fire at the wrong time and shred the cam gear against the hardened oil pump gear.

I think the way to test this is to use the metal dizzy gear; I don't trust the plastic ones any longer. I'll add a DD spray tube so it gets even more oil.

I've always told folks how the slant six is indestructible, but this is the weak link. Whatever the cause, I have to figure it out. I can't keep doing rebuilds every other year - though it is fun to swap out everything...

Maybe this time, I'll send my distributor to one of you guys and have you evaluate it before I install it. As far as I can tell, I'm doing everything correctly distributor wise. The car ran great for thousands of miles before this happened and I don't see anything to indicate the dizzy is eccentric or has too much vertical play in the shaft.

I'm not going to tell you that I don't run her hard, sustained 80 mph on the highway sometimes, but the slant should take that easily.

brian

_________________
https://tinyurl.com/yynpj4v2

I read the stream about the Pentastar bronze gear, but it wasn't clear whether that'll fit an American dizzy.

Does anyone know if that'll fit, do I have to drill it out to fit the American shaft?

thanks,

Brian

_________________
https://tinyurl.com/yynpj4v2

Don't introduce more variables. Billions of miles have been put on plastic distributor gears, both original and aftermarket.

I don't see how any misfires or ignition issues will "shred the cam gear against the hardened oil pump gear". The oil pump is just along for the ride. If the pump or cam gear breaks, that can chew up the plastic, but not the other way around. The comparatively soft nylon will just get shredded.

What Pierre said, I would look into adding a cam button in case the cam walked a bit and put stress on the assembly when it took up all the remaining tolerances and a bit more.

The Bronze gear would be a boon for a billet cam where you need something harder than plastic with the better steel cam...the down side is, if that gear wears or shreds an oil pan magnet won't keep the particles from going through the oiling system and galling something up...for the racer, if it goes, it's a shut down and tear down anyway...

I'd look at all the variables, when I build the engine I put it all together and roll the rotating masses and inspect the pattern before I put an oil pan on it...since I have a distributor machine I put the cap on the dizzy and make sure nothing "snags" at any rpm....

I'm thinking you have a little bit of everything, cam walk, wear on the cam from the oil gear (especially if your cam is a new softer blank, not an OEM cam that was reground), and maybe a snag on the cap when the assembly got briefly tweaked...

Great advice.

Is there a link to the cam button install?

I'm just "gun shy" because this happened twice and I thought I was being very careful and meticulous with everything.

On your note about the softer cam vs a regrind or whatever you said, is there a procedure to harden the cam drive gear and is that worth it? Seems like I'm having bad luck with this weak point...otherwise my slants have run beautifully, tons of power and run really smoothly. I checked the cam gear/oil pump gear engagement prior to closing the long block up, and they seemed to be evenly engaged. As for distributor engagement, I didn't check that before closing, I'll be sure to do so next time. That said, as I mentioned, I pulled this dizzy at 5k miles and there was no wear whatsoever the nylon gear looked perfect. I'm stumped unless it is an oil flow issue or the "perfect storm" of cam play as you mention. I'll most likely fab a DD oil spray tube next time and the cam button. I suppose the bronze gear is overkill, perhaps dangerous as you said...non-magnetic. What about the older steel gears?

brian

_________________
https://tinyurl.com/yynpj4v2

Here are some pics of my dear dart in the garage...started breaking down the engine today....

I recently rattle-canned her with black rust inhibitor

http://s785.photobucket.com/user/67dart ... sort=3&o=3

engine bay: you can see I ran my tranny lines on the passenger side...

http://s785.photobucket.com/user/67dart ... sort=3&o=2

Check out my custom made horn button for a Grant steering wheel...I took an original '67 horn button and modified it to fit the Grant wheel. Also I mounted a small VDO tach in the dash (in the only place it would fit, but it's easy to see through the wheel).

http://s785.photobucket.com/user/67dart ... sort=3&o=0


Brian

_________________
https://tinyurl.com/yynpj4v2

Seems like from what you're all saying is that the likely solution is a more robust cam shaft and a cam button, take the play out and don't use a soft cam...

_________________
https://tinyurl.com/yynpj4v2