The 496 Is Down Again............

[MOPARHOUND!]

Been too sick over the deal to post about it.  About 3 weeks ago coming home from a local cruise I ran the Charger through 1st and part of 2nd (ran strong, pulled hard  ), then slowed down to not get in trouble on the boulevard. 

Went another 1/8th mile and it started running rough and clattering from what sounded like one of the valve covers.  Limped/coasted the remaining 1/2 mile to the driveway.  The clattering had stopped, and then shortly thereafter the engine died.

Pulled the valve covers, thinking I'd find a broken aluminum rocker arm, or hopefully, not another flat cam lobe.  All the rocker arms looked good.  Bumped the starter a little at a time, and the valve train was snug all around, so no bad cam lobe.  Didn't get an up close look at the valve springs, don't know if one of them broke.  Put the harmonic balancer at TDC, and the rotor on the distributor was where I thought it should be, so I don't think the timing chain jumped.  The car will start, but won't rev up, and backfires repeatedly through the carburetor.  The engine is not clattering or making any unusual noise now when it is started.

The Eddy heads have about 4000 miles on them.  I have heard of them having "tight" valve guide issues.  But mine were dis-assembled and given some minor port work, and had the valves back-cut with a 5-angle valve job, so they would have been checked by my builder then.

One thing that did happen a month or so ago was during a high RPM blast (for me anyway) at the National Charger Meet in Jefferson City, MO, the valves floated prematurely, which got me to thinking maybe the Eddy valve springs were getting weak.  Cam is the Comp 292H, 244 @ .050", .501" lift, with the 1.6 rockers lift is .536".

My next step is a compression tester, to see if the back-firing through the carb is maybe a bent exhaust valve.  The clattering I heard might have been a valve hitting a piston??  Will keep you posted.

Any advice appreciated.

-HOUND

[firefighter3931]

Sorry to hear that....you've had your issues with this motor, no doubt !  Those springs are fine for the Comp 292 hydraulic, even with a 1.6:1 rocker. Mine has a custom .580 lift (agressive) solid with lots of 6500 dyno pulls, and the springs held up fine. Lots of guys use those springs with the MP590 cam with no issues. The lobes on those Magnum grinds are relatively slow & gentle, compared to the newer fast rate profiles. I doubt if the timing chain jumped either....it would have to be very loose to skip over on the gear.

The next step is a leakdown and compression tests. That  will tell you what you want to know at this point, inmo. It could very well be a bent valve from what you're describing. I guess the question is whether or not the guides were in fact checked at the time the other machinework was done. 


Ron

[68chargerboy]

i would bet it to be a bad valve guide inmo.

[MOPARHOUND!]

Well, after 3 months, finally tinkered with the 496 enough finding the problem.

Could only access 5 of the cylinders to do compression tests, but the 5 did check out okay, 155-170 lbs.

Put a new distributor cap and rotor on, and moved the timing back 4-5 degrees.  Would fire but not start.  Moved it ahead 4-5 degrees from where it was originally and it started and idled. 

Had the valve covers off, watching the driver side valve train action, all looked good.  Engine stumbled and died as it was still cold on a 50 degree day.  Fired it back up and ran around to the passenger side rockers to check things out, all okay.  Idle actually sounded normal, without the backfiring through the carb.

Blipped the throttle, revved right up, but could hear clattering around the timing chain cover.  Shut it off, and moved my valve covers that were off the engine, but in the engine bay.  Wanted to make sure they weren't rocking with the engine vibration against something making noise.

Cranked the engine again and no fire.  Hmmmmm.........  Cranked it again, and nticed my valvetrain wasn't moving, but my pulleys, belts and fan were.  Knew what that meant.......timing chain or timing gear problem..........time to take the front of the engine apart.

The cam gear bolt backed off (more on why in a post to come), allowing the dowel in the end of the cam to disengage from it's slot in the cam gear.  As you can imagine things were in a heck of a bind, with the cam's dowel scraping along the back side of the cam gear, until it revolved back to the slot in the cam gear.  It eventually chipped/wore about half of the dowel off and a chunk out of the dowel's slot in the cam gear.  Between the parts wear, and the more the cam bolt backed off, the cam gear finally "free wheeled" on the end of the cam, not turning the cam and thus the valve train. 

Pic's of the damage cam gear attached.  First pic is the good side, showing the dowel's slot on the cam gear in about the 2:30-3:00 o'clock position.  Second pic is of the bad side that faced the cam, can clearly see a chunk missing from the slot:

[67_Dodge_Charger]

I guess that would explained the rattle after a strong rev.  Hmm.  I guess a lesson learned.

good luck

Robert

[firefighter3931]

Dang, i stand corrected ! I'm assuming you locktited the cam bolt on and used the proper (beveled) washer ? Hopefully there was no piston to valve contact. I'd be pulling the heads for a look see and maybe have the guide clearance checked just to be safe. I've seen this happen a few times but never with my own stuff. I wonder whay all cams don't come with a 3 bolt upper gear....just seems like a better way to go, inmo


Ron

[Just 6T9 CHGR]

Damn that sucks!  Looks like we have the same timing chain as well.

When I built my engine, I too should have specified a 3 bolt cam....looks to be stronger IMHO

I had to use an offset bushing to degree my cam properly...it was a bitch trying to drill the hole in that "slot".  A lot of other chains I have seen have a regular hole there.  I guess this chain is a universal type that will fit many cam/engine configurations.

Sadly this has nothing to do with your problem but when I saw your chain pic, I remembered the greif I had with mine....

[694spdRT]

Sorry to hear about your problem. 

I used a 3 bolt cam on my last 440 but was considering just using a 1 bolt on my next one....I think that will not happen now.

[MOPARHOUND!]

The cam gear bolt backed off (more on why in a post to come), allowing the dowel in the end of the cam to disengage from it's slot in the cam gear.

IIRC, hemi68charger here on the board also had a cam bolt failure.

The why of this cam bolt failure is mostly my fault.   At the risk of embarrassing    myself, I would rather someone learn from my mistakes. 

1050 miles ago, I installed this Comp Cam 292H, used only on the dyno previously in my 496, in place of a Comp Cams 305H that had a lobe go flat.  This was my first cam swap on my own, with the other being as a teenager 20 some years ago with some buddies.

When I began installing the bolt for the cam gear to the 292H, I noticed the bolt threads in the cam were like a 1/4-size to big.  Kinda like screwing a standard bolt into a metric nut, or vice versa.  It was odd enough to make me check it on the 305H cam I had just removed - fit like a glove.  Why the size difference I can only speculate.  Possibility Comp somehow tapped it wrong at their facility (I doubt).  Or, the original engine builder overtorqued or used an impact to install the cam gear when this cam was first installed in my engine at 0 miles stretching the threads.  Or, the original engine builder undertorqued the cam gear and it wobbled around during break-in on the dyno, and during the subsequent 8-10 pulls, damaging the threads.  (Long story, but engine then went directly to my current builder, this 292H was removed being deemed too small (not quality issues), and the 305H installed that would later have the cam go flat 9800 miles later.)   Irregardless of why the threads weren't right in the 292H, I should have done something different.

The correct beveled washer was used.  I remember thinking about putting lock-tite on the bolt like I do the torque converter bolts, but don't recall doing it.  Rather than buy another cam, and wait another week without the Charger running, I told myself if it torqued down okay (which it did), things would be fine.     

Now, the next move is choosing and spending $$$ for another cam and timing gear set.     Yep, it will have a 3-bolt setup.  Also will be doing a leak down test at my current builders to see if any valves are bent.  If it's like the compression test I did, it will be a major pain, as there is little room between the passenger side inner fender, the header tube, and the head.

[firefighter3931]

Thanks for the explanation Hound. No shame in admitting mistakes....we've all made many.  At least the cam isn't wiped and caused major bearing/cylinder wall carnage in the shortblock...i suppose that is the silver lining in this otherwise dark cloud. 


Ron

[Chryco Psycho]

ok so do you have any bent valves ?? with the crank turning & the cam stopped something Had to give
I always try to spec 3 bolt cams when ordering , it doesn't cost any extra in most cases

[MOPARHOUND!]

ok so do you have any bent valves ?? with the crank turning & the cam stopped something Had to give

Will be checking for bent valves.

Also will be doing a leak down test at my current builders to see if any valves are bent.