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I own a 2012 Challenger SRT8 with manual transmission that I bought used in 2014 with just 6k miles. I've put 40k miles on the car since. The previous owner had installed long tube headers and a cold air intake, but otherwise the power train is stock. It has always had noisy valves, but a few weeks ago a new tick started coming from the driver side of the engine.

I had just replaced the catalytic converters a few days ago because they had been rattling, so I took it back to the muffler shop that installed them to have the cats checked for leaks. They found none.

Then it started misfiring badly. I immediately had it towed to a shop. They pulled a code, it was a misfire on cylinder 5. They did a compression test, and cylinder 5 was only at 25 PSI. They also found that one of the spark plugs in cylinder 5 had almost no gap at all. Huh... They advised that I had a bent valve that needed to be replaced. I needed more time to assess what was going on, so I had the car towed to my garage and I've been trying to figure out what exactly happened before I start buying parts to repair it.

I pulled the heads and sure enough, the intake valve on cylinder 5 was bent so bad you could shine a flashlight through it. I took both the heads to a machine shop and they found a second bent intake valve. I found damage on the pistons too, there are little crescent dents on the pockets of pistons 5 and 8. The shop also told me the valve guides were a little loose but weren't out of spec. Other than the bent valves, they haven't found any other issues with anything else in the heads. The mating surfaces are flawless and they don't have to be resurfaced.

The intake rockers had some uneven wear on the surface that mates with the top of the valve. The exhaust rockers looked fine.

To the best of my knowledge, all the pushrods seem okay. I rolled each pushrod across a table and they all rolled freely. I haven't measured them yet, but I will once I pick up long enough calipers.

Next, I checked the lifters. The wear marks on the intake lifters weren't evenly worn across the surface of the lifter, and there was some scoring on a good number of them. The exhaust lifters had even wear across the roller surface.

The cam looked even worse. The heat treated surface on both lobes for cylinder 8 had been worn through. The cam bearing closest to the front of the motor had some wear marks on the lower half of the bearing, but I can't see any copper colors on it so it might be normal wear.

I just pulled the motor last weekend and I'm going to take it in to the machine shop. Now that I've pulled the motor down to the short block I might as well have it checked.

I've been trying to determine what the root cause for the bent valves were, but I can't figure it out. I've never overrevved the car and I've religiously changed the oil. I've checked the timing chain, and it was correctly timed. It's possible that the previous owner could have overrevved the motor while downshifting, but I feel like I would have noticed the misfire a lot sooner.

Any diagnosis and advice would be extremely appreciated. I've dreamed of owning this exact car ever since I saw it and I want to see this repair through.

Thank you for your time.
 

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I used a bore scope on my#5 cyl. It looks clean, top of piston. No unusual making. I think thre intake valve seat might ne braking out of its place causing valve to stay open. I haven't removed head yet so can't say if there are any seized lifters.
 

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The Bacon Hauler (‘12 Cop Charger)
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My best guess would be your engine fell victim to the “seized lifter eats Hemi cam” problem that has afflicted many a Hemi owner the last few years. There is an alarming number of reported incidents that can be found by searching the internet, but sadly no one can agree what the root cause is.

That’s the good news. The bad news is that you can replace the broken parts (including cam and lifters) with factory OEM parts and be just as susceptible to it happening again. The odds are not great it will happen again, but they aren’t 0.00% either.

But I don’t want to sound like I’m anti-Hemi or anti-OE parts, I’m not. My Hemi ate the cam at 90K miles, got a replacement OE cam and lifters, and has been running great ever since - 88K miles so far.
 

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Do you know if the previous owner had the engine tuned for the headers? Loose/rattling cats sounds like the engine may have been running lean. Also, problem with manual trans cars is you can make the engine rev passed redline but I have not read of anyone having valves hit because of it.
 

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What about aftermarket cams and lifters? Seems like somebody should be making these with no compromises for cost. I have a light tick under certain circumstances, I guess I'll send in an oil sample and see if it has more metal in it than normal.
 

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What about aftermarket cams and lifters? Seems like somebody should be making these with no compromises for cost. I have a light tick under certain circumstances, I guess I'll send in an oil sample and see if it has more metal in it than normal.
While you send the sample in you can also crack open the oil filter and look for any signs of metal shavings.
 

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While you send the sample in you can also crack open the oil filter and look for any signs of metal shavings.
Yeah, good call. I will do that this weekend if I have a filter and oil around. I did not notice any metal in the last oil change and I expect I would have if there was much.
 

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I don't know about anyone else's, but my m6 will not overspeed, at least in gear. It rev limits around 6000.
 

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I don't know about anyone else's, but my m6 will not overspeed, at least in gear. It rev limits around 6000.
if someone downshifted at speed, it could over-rev the engine. or if someone modified the tune and moved the rev limiter out of the range. 5.7s are 5.8K limited and 392s are 6.4K limited
 

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Good points, I'm horrified imagining a downshift @ redline. Mine seems to be running out of powerband just before the rev limit. I don't spend a ton of time north of 5,000 rpm so I could be misinterpreting fuel cutout near redline. Are people pushing more than 6,400 in stock form? Is there more power in that rpm range? I'd be pretty nervous at those speeds without some upgrades.
 

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Good points, I'm horrified imagining a downshift @ redline. Mine seems to be running out of powerband just before the rev limit. I don't spend a ton of time north of 5,000 rpm so I could be misinterpreting fuel cutout near redline. Are people pushing more than 6,400 in stock form? Is there more power in that rpm range? I'd be pretty nervous at those speeds without some upgrades.
a stock 5.7 peaks @ 5.25k rpm - for stock, the power falls off beyond that. redline is 5.8k

stock 6.1 peak @ 6.2K rpm redline is 6.4k

stock 392 peak @ 6.1K rpm redline is 6.4k
 
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