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#8 hitting the head

8K views 27 replies 11 participants last post by  iautounlimited 
#1 ·
need some help my #8 piston is hitting the head. has anyone had this happen? what should i don?
 
#2 ·
How have you determined it is hitting the head ??
 
#4 ·
I highly doubt that (barring any abnormal use) your piston is hitting your head. its ver very unlikely. While the distances are INCREDIBLY close by human standards (less than a human hair thinkness), they are NOT touching. You would know it if it was hitting the head, because your engine would be destroyed. There are only a few ways this happens, all of which result in catastrophic engine failure. Unless you are a qualified mechanic, or at the very least, well versed in the Internal Combustion Engine and its workings, you are not gonna know where your tapping/knocking is coming from.

That being said, the ONLY way I could see you having a piston hitting the head and your engine isnt toast, is if your timing chain is stretched causing your timing to be ever so slightly off (happens after hundreds of thousands of miles of heavy use), or your piston connecting rod has stretched slightly, causing your piston to come high up on the exhaust stroke than tolerances allow. With tolerances we are talking Microns, not Milimeters, so theoretically, it is possible. Just incredibly unlikely. I have been wrenching since I was 15, and I have only seen it happen 1 time, and the engine had 420k on it (1990 Lexus LS400).
 
#5 ·
ill have to get pics. the reason i say that is the motor is takin apart the heads are off. the pistons are all black. but on #8 there is a moon shape shine, and in that same spot the head is dull, and looks as it has been beat on. i took the motor apart because it was knocking found out the timing chin tencheners was busted. also found out that the person who owned it b4 i used block sealer on it. i will get pics of it and post later to day.
 
#6 ·
What you have is valve to piston contact on the intake valves. The 4.7 tolerances are very tight and being just one tooth off on the valve timing will cause the intake valve to hit the piston and bend the valves. If the head isn't damaged, you can install new valves and reuse it.
 
#7 ·
Okay, now it makes sense.... I didn't know you had it torn apart. LOL

I'm with RamTech on this. He has likely forgotten more about the 4.7 in the last day than I've even known about it.


Good luck with your repairs, and keep us posted. :smileup:
 
#10 ·
Interwesting, wery wery interwesting. It'd have to be one of three things, creep in the connecting rod, deformed crankshaft, or you have play in the crank bearings. most likely is the connecting rod, less likely is the crank or bearings as you'd have more issues with vibration.

Now would be a good time for a stroker kit :LOL: No, I don't believe they make one for the 4.7L, but it's a fun thought.
 
#14 ·
IF i had an engine torn down

that engine would soon be in another vehicle, on its way to a engine rebuilders, to have them finish
stripping it
engine & heads would be going into the HOT tank
it would be Magnafluxed, Decked, Shaved, & Honed
new Mains, Inserts, Valve job
assembed & Painted
pay the shop $1500 - 2000
& you could be driving it next weekend, if all went well

BUT, that is just me
 
#15 ·
Have you opened the bottom to check the connecting rod's connection to the crank? I'm wondering if it's something as simple as loose or missing bolt. Or nasty like a deformed cap or crank damage or serious wrist pin wear or a combination of many of the above.

Although at this point, it is likely the rod has been damaged and will need replacing.

Have to say, this is not something you see every day. :Wow1:
 
#17 ·
If you rebuild the one you have, at least you will 'know' what you have. :smileup:
 
#23 ·
Dude, I just had a wild idea. The tranny's for the PowerTech and the Hemi are the same, right? Motor Swap FTW! Since you have a broken 4.7, why not upgrade? Should be minimal mount fabbing nessecary. Computer, Wiring, Cooling system and Motor and you are pretty much good to go! Suspension, steering and driveline should be the same (minus gearing...3.55 in 4.7 and I think 3.72 is standard in the Hemi).
 
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