# Broken Eccentric



## TinIndian67 (Feb 11, 2017)

Evening All:

I wanted months to get my 461 stroker in the GTO, and after 300+ miles on gently driving her to break her in, I broke down. Thought it was the fuel pump at first, so I replaced it, and still no fuel pressure. No way it was two mechanical fuel pumps. Stuck a camera behind the timing chain cover and confirmed the eccentric was loose. Pulled everything off, and the bolt was backed out. The only reason it was not all the way out was because it was hitting the back of the timing chain cover. Looks like there is some loctite on the bolt threads, so odd that it backed out. Also, the tooth on the eccentric was broken where it seats. It is probably sitting in the oil pan now, so I will have to get it out.

I ordered a new eccentric from Butler, but before I put this all back together, any thoughts on why this would happen other than just a defective eccentric? I want to make sure it was a fluke, and there are no possible underlying causes.























Thanks all in advance.


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## 67ventwindow (Mar 3, 2020)

Was it just the bolt rubbing on the timing cover? There no marks from the eccentric making contact? Is the bolt sloppy I have bolts in the head of my Mercury that are sloppy till they run out threads. The eccentric could have been defective. I couldn't telling zooming in, if there looks to be an existing crack before it broke. Hope it doesn't keep you off the road long. I think its been a long winter for everyone. Time to have a little fun,


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## BearGFR (Aug 25, 2008)

TinIndian67 said:


> .. and the bolt was backed out. ...


That's a >big< bolt. Don't be afraid to torque that sucker down tight. (I had one back out on me too - once.)

Bear


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## PontiacJim (Dec 29, 2012)

Put the Locktite on clean threads. Then make sure you have a quality torque wrench and double check your settings and torque it down. I got a torque wrench from an auto store that allowed the handle to loosen up which was part of how it torqued. Good thing I caught it as I was torquing rod bolts down. Threw the wrench away and bought another better one. Went back and found the torque on the rod bolts were certainly off and would have cost an engine if I had not noticed.


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## Old Man Taylor (May 9, 2011)

My best guess is that the builder accidentally forgot to torque that bolt. That happened to me one time. Don't torque bolts when you have someone looking over your shoulder.


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## TinIndian67 (Feb 11, 2017)

Thanks guys - makes me feel a little better. When you spend all that $$ and something like this happens especially after a painful year, just gets you down. I will loctite and torque the hell out of her.


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## Old Man Taylor (May 9, 2011)

As I recall that bolt gets 45 ft-lbs.


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## BLK69JUDGE (Jun 10, 2010)

I would dump a gallon of deisel down the front and wash any debris out of the pan

I have seen broken ones also ...
seems there is 3 different size tabs on different years of motors...
some tabs are big and fill the hole and some are almost 1/2 the size of the larger tabs

bummer 

Scott


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## TinIndian67 (Feb 11, 2017)

Getting ready to throw the eccentric on finally. I did read a post from BearGFR a week or so ago that the cam gear should be sticking out past the face of the timing chain gear. If you look at my first picture above, mine is flush. Not sure if that is something I should be concerned about and look into before I put this all back together or not. What's you guys' thoughts on that?

Again, thank you all for your time and input.


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## PontiacJim (Dec 29, 2012)

TinIndian67 said:


> Getting ready to throw the eccentric on finally. I did read a post from BearGFR a week or so ago that the cam gear should be sticking out past the face of the timing chain gear. If you look at my first picture above, mine is flush. Not sure if that is something I should be concerned about and look into before I put this all back together or not. What's you guys' thoughts on that?
> 
> Again, thank you all for your time and input.


I don't think it was face of the timing chain gear seeing the teeth are set into the chain. What I believe you read was the timing gear should stick out past the face of the block? On the Pontiac engines, the cam is pulled backward due to the reverse rotation of the distributor - as I recall reading. This is why you don't see aftermarket "cam buttons" placed on the front of the cam to rest up against the timing cover like you do on Chevies. The thrust plate retains any forward motion.

The back of the block has a freeze-type plug at the rear of the cam. I know if it is sunk too deep or wrong plug used, the cam can hit it and wear on it and create problems. With the correct plug, it gets recessed .300" below the block surface.

In Rocky Rotella's book, he says you should be able to push the camshaft in towards the back of the block and the machined surface of the cam snout should be slightly past the block surface if the cam bearing plug at the rear of the block has been installed correctly and has enough clearance. If you had any doubt, you could use a dial indicator, but since you did not have any problems before, you are probably OK. With the lifters/distributor in place, not sure if this test could be done as it was for a cam install prior to the rest of the engine assembly.

Bear uses a roller cam and am not sure if he used one of the small roller needle-bearings that go behind the cam's thrust plate? Here is an article on it, but it does not show the roller bearing plate, but does explain it.









Pontiac V8 Roller Camshaft Retainer - High Performance Pontiac Magazine


Check out this in-depth look at this Pontiac V8 Roller Camshaft Retainer. Read more only at www.highperformancepontiac.com, the official website for High Performance Pontiac Magazine!




www.hotrod.com





I think what Bear may be pointing out is that you need some clearance between the cam gear and block surface. Never had an issue, but it could be something related to off-shore parts made almost correct, but not correct. So, just check it.

From the '68 Service Manual:

Cam Trust Bolts - 20 ft lbs
Eccentric Bolt - 40 ft lbs
Timing Cover-to-block bolts/nuts - 30 ft lbs
Pan-to-cover - 12 ft lbs
Harmonic Balancer Bolt - 160 ft lbs


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## TinIndian67 (Feb 11, 2017)

PontiacJim said:


> I don't think it was face of the timing chain gear seeing the teeth are set into the chain. What I believe you read was the timing gear should stick out past the face of the block? On the Pontiac engines, the cam is pulled backward due to the reverse rotation of the distributor - as I recall reading. This is why you don't see aftermarket "cam buttons" placed on the front of the cam to rest up against the timing cover like you do on Chevies. The thrust plate retains any forward motion.
> 
> The back of the block has a freeze-type plug at the rear of the cam. I know if it is sunk too deep or wrong plug used, the cam can hit it and wear on it and create problems. With the correct plug, it gets recessed .300" below the block surface.
> 
> ...


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## TinIndian67 (Feb 11, 2017)

Thanks, Jim. It was actually both of those things I read about, which you echoed above. I found the actual picture I was talking about, and attached to this reply. I guess the cam gear sticking out a tiny bit helps center the eccentric when the shoulder fits around it. Mine is flush, but I really paid attention to getting it center. Maybe that's why it broke in the first place - who knows.


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## PontiacJim (Dec 29, 2012)

TinIndian67 said:


> Thanks, Jim. It was actually both of those things I read about, which you echoed above. I found the actual picture I was talking about, and attached to this reply. I guess the cam gear sticking out a tiny bit helps center the eccentric when the shoulder fits around it. Mine is flush, but I really paid attention to getting it center. Maybe that's why it broke in the first place - who knows.


Stop right there. The eccentric does need to go over the cam snout stick-out, it should not be flush. That is what does keep the eccentric centered and held centered. Without that fit, my guess is it could spin off as only the tang is holding it in place should the bolt back off.

You have to figure out what is going on. Is the cam simply sunk in because of its position due to the lifters/distributor gear drawing it in? Can you install the eccentric backwards so the larger cup side fits over the cam snout and seats on the cam gear and then insert the cam bolt and tighten it down a bit to see if it will pull the cam snout out past the cam gear - sorta like using large washers bigger than the crank snout and set on the gear so you can tighten the bolt while keeping the cam gear in place and drawing forward the cam with that bolt. Might be that simple.

If not, I'd be looking at 2 things. Cam Thrust Plate behind the cam gear may have been replaced and is too thick - holding the gear too far forward on the cam snout? Or, the cam timing gear may be machined incorrectly or is defective on the back side where it rides on the thrust plate and is placing the cam gear too far forward and even with the cam snout.

If you cannot get the cam to pull forward enough, with the thrust plate installed, then I would first get a new thrust plate. If that did not achieve the cam snout stick out, then I'd go for a new timing set, gears and matching chain.

In any case, I would get that addressed before buttoning up and having another issue.

Check out this video. No need to watch the whole video, move the time slider right to 24:55 and watch it from there as he installs the eccentric. Look at the cam stick-out.


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## TinIndian67 (Feb 11, 2017)

Jim & all:

Thanks for the help and suggestions. I did watch a bunch of that guy's videos - he is the man. I did torque the bolt at the eccentric while sticking shims to the side on the block, and the cam actually slightly pulled outward. Eccentric installed, and she is up and running again. Consider this one closed, and I am about to post some questions in another topic to try and figure out an ongoing issue.


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