6.5 Engine Knocking

[jel1990]

I have a 93 K2500 with a 6.5TD. A couple weeks ago while driving to work, it began to knock slightly. I was only about a half mile from work, so i continued to drive it easily until I got there. I then hauled it home the next day. When it first started knocking, the knock would come and go, but once I got to work, it was knocking constantly.

My first instinct was a faulty injector. I have heard injectors causing a knock in the past, and this sounded exactly like what I had remembered. I tried loosening the injector lines and thought I could hear a slight difference when loosening the line on Cylinder #7. I knew it was due for some new injectors, so I ordered a new set. I installed the new set today, but it still has the knock. I know it's not a broken glow plug tip in the engine, because I checked each one when installing the injectors.

The truck has 216k miles, but 2 years ago at 191k miles, I installed all new rings, rod, main, & cam bearings, timing set, oil pump, & water pump.

I tried unplugging the shut-off solenoid & cranking the engine, but can't hear any knocks. I think next week I might remove the pan and check out the bottom end. Or could this be a valve-train problem?

Does anyone have any ideas of where I should start? All help is appreciated.
Thanks, Justin

[Robyn]

I am assuming that the oil pressure is OK ???

If the oil pressure is ok then its not likely a bearing (rod)
Possibly a cracked or broken piston, or a failed wrist pin bushing in a rod.

Another good possibility is a failed crank/serp pulley.

Remove the serp belt and check to see if the pulley "Rim" will slop back and forth.

These pulleys have a rubber mounted rim that is held with a bearing and 4 spokes.

If the rubber fails the pulleys spokes can slam back and forth and make a nasty noise.

Inspect the pulley and the damper.

These things would be the first stuff I looked at.

This is an easy thing to check for sure.

I would yank the top half of the fan shroud off right quick and have a peek at these things.

Good luck and keep us posted

Missy

[jel1990]

Yes, the oil pressure is good, & has stayed between 40psi @ idle and 45psi on the hwy. @ 1800-2000 rpm.

I forgot to mention, I pulled the belt off yesterday also and checked the damper pulley & started the engine to see if it was anything on the accessory drive, but it was still knocking.

Could it be a valve hitting a piston, or would it most likely be a failed piston or wrist pin? When I had the engine out 2 yrs. ago, I re-used the original pistons, wrist pins, & bushings, & never removed the rods from the pistons. At that time everything looked great.

Thanks,
Justin

[z28cp]

If it is maybe a tapping vs a knocking sound, I would look at the valvetrain. The plastic buttons that keep the rockers in line can break, and allow the rocker to move sideways, causing a tapping noise. Eventually, it will become a miss, once the rocker slides completely off of the valve stem.

Just a possibility...

[Robyn]

Justin

Is it a hard Knock that's running at crank speed, or more of a lighter metalic sound running at cam speed (1/2 crank)

I hate to say it, but I would make plans to yank that sucker out and have a peek at things.

If its a upper rod bushing, its gonna have to come apart.

It could be a crank that cracked and ready to go away too.

If its not accessory based then its inside.

Far easier to work on, when out of the rig.

Missy

[jel1990]

I'm pretty sure it's knocking at crank speed, but I would have to listen to it again, and maybe have someone who is a little more experienced listen to it before i'm completely sure.

I have a cousin who has worked on vehicles for years, and he told me he has seen several chevys, gas or diesel, that had a knock, and it was caused by a cracked flex plate. I'll check that first. If its not the flex plate, I'll pull the valve covers just to rule out any rocker arm issues, since that's pretty easy to do. If I can't find anything there, I'll pull the engine & check out everything inside. It's sounding like it's most likely an internal problem anyway.

I won't be getting back to it till Monday though, that starts my weekend.

I will keep you posted, thanks for all the help,
Justin

[JohnC]

Check the bolts holding the torque converter to the flex plate.

[jel1990]

I went out today and removed the inspection plate under the torque converter, and there it was, a loose bolt. I tightened it, rotated the engine & checked all the other bolts. I also found 2 other loose bolts. I checked the flywheel for cracks, but everything looked good. I put it back together, fired it up and no more knock!

I had no idea some loose torque converter bolts could cause such a terrible knock. But, then again, I didn't know an injector could cause a bad knock until I heard one. I'm just glad it wasn't an engine problem. I was already pricing engine parts :)

Thanks everyone for all the replies,
Justin

[JohnC]

I'm buying a lottery ticket tonight! ;)

[jel1990]

I'm buying a lottery ticket tonight! ;)

Sounds good, you're on a roll. ;)

[phantom309]

I'm buying a lottery ticket tonight! ;)
Aw c'mon,. just mail me the money,. then it'll be put to a good use,..

Nick