Knock in engine

rdsar2k · Post by **rdsar2k** » Sun May 06, 2012 10:40 am

Went to my first convoy activity with my M170. ARMVPA Travelers in AR. It was a 100 mile route with a lot of stops and one of the most organized civilian outings I've ever seen. About 20 miles in I started hearing a knock in my engine that got louder the farther we went. Oil pressure was good temperature was good power was good though the knock got louder the higher the rpm and under acceleration. I made the route but rushed home and took off the covers hoping for a loose lifter. Nope. I fear the worse and suspect conn rod bearing seized/spun. So much for being done.

rdsar2k · Post by **rdsar2k** » Sun May 06, 2012 1:30 pm

Okay so I used a long screwdriver as a stethoscope and tried to identify this knock. The fuel pump is the noisiest at idle but it is not the same kind of knock more of a tappet kind of noise. The front of the engine by #1 cylinder plug has the pronounced noise resembling the knock but I do not have enough load on the engine to really bring it out. Oil pressure is 30 cold and 10 to 15 hot. Checked the valves twice and they are dead on. Oil has no signs of metal on the dip stick. Clean and bright. I would disconnect the spark plug wire as suggested here on other posts bit the noise is only under load so it would be difficult to tell while driving. Suggestions? Do I need to take the engine our and inspect at this point?

oilleaker1 · Post by **oilleaker1** » Sun May 06, 2012 4:33 pm

You don't need to drive it to test it with the plug wire disconnected. A rod will knock as you open the throttle from a idle. If it goes away with the wire removed, you found it. It still could be a weak spring on the fuel pump lever that contacts the cam. That would sound like a lifter ticking. A rod has a definate knock. A steady tick noise with all valves dead on could be the cam moving front to back because of too much end play and worn thrust washer behind the cam gear. A deep knock that never goes away, wires or not is main bearings. A broken piston skirt can knock just like a rod also. Same test with the wire off. You have to tear it down either way if the knock goes away with the wire off. They call it the school of hard knocks. All Jeep guys have been here at some time. John

rdsar2k · Post by **rdsar2k** » Sun May 06, 2012 7:46 pm

School of hard knocks.
I stripped this thing down and took it to the motor machine shop where they dipped the block, bored the cylinders. 030 fit all bearings. Matched all parts to each journal and put in new freeze plugs. New cam bearings. I set thrust and cleaned every port prior to assembly. Used assembly lube on everything and pumped oil in the system prior to starting. This is not the first engine I've overhauled bit it is the first I've had to take back out.

rdsar2k · Post by **rdsar2k** » Sun May 06, 2012 7:55 pm

It doesn't knock until it is under load driving. Won't do it reving up in neutral

oilleaker1 · Post by **oilleaker1** » Sun May 06, 2012 8:43 pm

All the bad rod bearings and pistons I've had and witnessed did the noise just coming off idle. This makes me think it's something else. I haven't a clue what unless it's in the drive train. Does making a turn under load make it louder?

John

rdsar2k · Post by **rdsar2k** » Sun May 06, 2012 8:58 pm

It is a predictable noise. It does sound like a rod though. Turns don't matter. When hot it the worst. Loaded hot it knocks pretty loud. Unloaded it isn't there definitely coming from the engine not a body part. I'll just have to take it out and take a look.

Post by **wesk** » Sun May 06, 2012 9:00 pm

Check end play on the crank.

jimbob · Post by **jimbob** » Mon May 07, 2012 7:46 am

Check for a loose flywheel bolts, I had that problem on my M38 sounded like a rod knock.

Jim

rdsar2k · Post by **rdsar2k** » Mon Oct 29, 2012 7:21 am

Update:

When I rebuilt this engine I did the static timing as I couldn't see the marks when the light was shined on it. I bought one of those timing pointers and this weekend installed it. When I shined the light on it, it was way off. Re-timed it and it is the miracle fix. Noise gone. Drove it all over to be sure. Funny thing is prior to this the engine would drip from the front and rear main seals after a drive and those drips are now gone also. What a relief! Feel like driving it to work now.

Post by **wesk** » Mon Oct 29, 2012 8:45 am

Now you know what Pinging from incorrect timing sounds like.

Beacher425 · Post by **Beacher425** » Fri Nov 02, 2012 8:41 am

I have a 24v 1955 M38A1 that has been converted to the electronic ignition per the instructions found elsewhere. If I set the timing up per protocol to the 5 degree BTDC mark it runs a little ruff. No backfiring at idle or reving, but trys to cut out and runs ruff. Turning the distributor to produce a timing of about 10-13 degrees BTDC smooths things out nicely. I have been driving it at this position for about 300 miles. Should I go back to the book timing of 5 degrees or stay at the ear timing of 10-13 degrees? Thanks for any input.

Post by **wesk** » Fri Nov 02, 2012 8:54 am

10 is fine for today's gas. You probably have a small error in the positioning of the Hall effect units. With the jeep in third gear at about 35 MPH when you stomp on it to accelerate if it pings then you'll need to reduce the advance a wee bit and test it again.

Beacher425 · Post by **Beacher425** » Fri Nov 02, 2012 9:23 am

Thanks!!

Knock in engine

Knock in engine

Knock in engine

Knocking engine

Engine knock

Knock

Rod knock/timing