6.2 w/engine knock?

[mark g]

i just bought a military k30 w/6.2 diesel. it has a knock that i cant identify. oil pressure is good. no blow by. no cooling system pressure. i thought the noise was on top of the valve covers, i pulled both and watched them with engine running. everything looks good. sounds like metal hitting something inside but the engine runs great. anybody have a clue before i tear this down? could it be flex plate hitting something? the engine has 39k miles, but with 4.56 gears who knows what happened. any guess??? :mad: :mad:
thanks for any help. btw im not a paid member, maybe i should be!! thanks, mark

[john8662]

Knocking... Thats a tough one thats not easily solved w/o listening to it. If you suspect that the flexplate is hitting something you can remove the dust cover (4x4's are a big aluminum cast cover) and take a look. There have been some on here that have had the flexplate crack at either the bolt holes holding it to the crank or on the bolts holding it to the torque convertor. Sure is something to look for, because this will make a metallic noise.

Other things to consider are bad injectors. A bad injector (so I'm told, not witnessed) can make a nasty knock sound. You can diagnose this by having the engine running and then loosening one injector line nut at a time enough to bleed pressure to cause that injector causing it NOT to fire. This is similar to taking plug wires off on a gasser. Anyways, if the knock quits at a preticular injector, that could be the cause.

[aloharovers]

How about power, etc from the engine?
Also is this your first 6.2?

I don't know if its the different intake or the fact that they run JP-8 for fuel, but I have always found the Military 6.2/6.5 to be louder then the civilian counterpart. This is standing outside the vehicle.

Pete

[mark g]

thanks for all replys. i did kill all the cylinders one at a time with no change in the noise. with a stethascope the noise is loudest on top of the pass. side valve cover. im at a loss :confused: :confused:
i guess ill pull the trans and check the flywheel.

ive owned more 6.2s than i can remember

this motor runs so good, whatever the noise it doesnt seem to affect anything :mad: :mad: riding down the road you dont here it at all!!

[Lightyear]

What kind of a noise are you hearing? My '88 Burb (6.2 with a Banks Sidewinder, 260K) has an odd noise also. Sounds like a metallic 'chug', audible from both sides, you can hear it in the truck as well. Doesn't seem to have affected driveability, but I might be a pound down on boost. But that could be the weather here in ATL. I just had the balancer replaced, so it idles like a fine watch, but still has this odd noise. Let me know what other steps you take; I'll try to duplicate. Thanks!

[lmocibob]

i had a 82 6.2l with engine knock up high (valve cover)
turned out to be cyl. # 6 shattered piston skirt broke off laying in the bottom of the oil pan.

[mark g]

so i guess i need to pull the pan and look for some big metal chunks :eek: :eek:

my noise sounds like its up high also, thanks

[twaddle]

Hi Markg,
It may be a hydraulic cam follower that is not operating correctly causing excessive valve clearence.
This would sound noisy at the top end although it can also sound noisy when listening from under the engine.

good luck

Jim Twaddle
Biggar, Scotland.

[mark g]

ive had both valve covers off and checked valve train , even put the lines on and watched the engine run with the covers off, didnt see anything out of the ordinary.



after reading the latest post about noise i think ill check my flex-plate. ill let you know :mad:

[NH2112]

I'd do 2 things before disassembling anything. 1) Drain a quart of oil and add a quart of ATF or Marvel Mystery Oil, the detergent properties of which should free up a sticking lifter. Don't load the engine or hit highway speeds while it's in there, just do normal around-town driving. Drain it in a few hundred miles. 2) Remove the air cleaner cover and with the engine running around 1200-1500rpm, mist water from a spray bottle into the intake. This will turn to steam in the cylinders and soften any carbon deposits.

[mark g]

i have decided to put another motor in this truck. i pulled the converter cover and all looks well. the noise sounds like something on top of a piston.

i bought a 91 c30 van from the feds. 6.2 that runs great, has the aluminum box on the back.
question? the pan on this 6.2 looks different than any others ive messed with. its a j code motor but the pan has a funny shape to it.

overdrive transmission, is it 700 or 4l80??? truck built early 91. has a semi-float 14 bolt rear. has a gear reduction starter.

im going to put this in my military truck.

[john8662]

91, probably a 4L80E, worth hanging onto, but it's for a 2WD being a van.

I need some Van parts, if you're wanting to sell some by the way...

[mark g]

what parts do you need? this is a cutaway van with the aftermarket box on the back, side door and 2 back doors that swing out. military bought lots of them from 86-91, all diesel

what about the funky looking oil pan on this truck? new style? when did they change? thanks

[john8662]

I don't need much, other than the breather assembly. What I'm looking for is the part of the air intake that attaches to the radiator core support, it's a piece of plastic that makes a 90* and bolts to the core support. This piece then connects to the resonator going into the air cleaner. I need the little 90* piece, and it's not easy to find.

I don't know what to say on the oil pan, perhaps you can shoot us some pictures? The van I'm driving is an 83 and as far as I'm aware it's got the same pan as a truck, but I don't plan on finding out any time soon though...

[mark g]

john,send me an email, thanks. n0tx@sbcglobal.net

the truck has a 700 transmission, i drove it yesterday to make sure it shifts. runs out good.

[mark g]

i got the motor out of the truck and im fixing to get it out of the van. had to pull the front off the van to get access.
john, with regards to this transmission, it has no tv cable or vacumn. has a big electric plug on the drivers side towards the back. also has a tag on the top that says gm goodwrench remanufactured. 4L80 or 700?? or can you tell? got your parts yet?

[john8662]

Mark,

Sounds suspiciously like a 4L80E to me. It's no surprise that it's been rebuilt either, because the first versions of this transmissions had lots of problems.

I got the snorkel pieces, they were exactly what I needed for the ol van. THANK YOU! You've really helped out, it was becomming really hard to find just that piece. I'll be getting it installed tonight and go for a test drive and see if it helps the power/smoke issue with the rig.

[GregV]

Hi -
I'm new to the forum, but I have some info for you. I've had the same 6.2 fail on me twice. The second time it was a engine knock, which grew louder, very loud in just a few miles. Anyway, it turned out to be two badly scuffed pistons, with a third piston beginning to scuff. The worst piston had the top ring groove badly worn and that was probably the one which caused piston slap in the cylinder. Needless to say, two cylinders are badly scored and will need to be re-bored or sleeved.
It's not good news, but I hope it helps you to diagnose your engine noise.

[mark g]

i got the motor in the military truck and it runs great. im still trying to decide what to do with the old engine since i want to use it. the bottom end looked new. i guess ill pull the heads and see whats up. nothing was in the pan. thanks, mark