4.2l engine knocking

mbalbritton said:
Pulled the pan and....

youtube.com

258 bottom end check

4.2l Jeep runs smooth and quiet at idle. Runs and drives fine, but at 1500-2000rpm a knock becomes audible. I pulled the oil pan and this is what I found.
youtube.com youtube.com


How the HELL could this thing idle so smooth and quiet and run like it did?
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mbalbritton said:
I don't know. Could the loose timing chain sound like a knock or be the culprit of the knock, or just another worn out part out of many things in there. I'm halfway tempted to replace the oil pump and timing chain and see what she does. But my gut says the knock would still be there. First I'll rotate the crank and check everything as good as I can. If I don't find anything I may go that route first. those are parts that would need to be replaced anyway.
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Timing chain controls timing. At idle, its going slow enough that nothing happens. At higher rpms, the additional sling of the chain is creating a different tension that is advancing or retarding the cam to the point that it is kahnocking.
 
jeepinmatt said:
Timing chain controls timing. At idle, its going slow enough that nothing happens. At higher rpms, the additional sling of the chain is creating a different tension that is advancing or retarding the cam to the point that it is kahnocking.
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Interesting, so adv/ret. of Cam can have a kahnocking symptom?
 
Alright, so I spun the crank around, checking the piston skirts, checking the play in the rod bearings, visually inspecting the cam, checked the flexplate. All appears to be in good condition considering the age. no cracks or broken skirts. they all feel snug. Cylinder walls looked good from what I could see. The rod bearings had just an ever so slight play that seemed normal from my Youtube research :D. The cam is probably the worst part of what I saw., but nothing I'd run from. I did not Pull the rod caps as suggested. I prefer to leave things undisturbed when I can, and like I said, they felt fine.

I think I'm gonna go for it on the timing chain replacement and see how it goes.

Ordered the following:
Complete engine gasket kit, cheaper than individual parts and who knows when I'll need any of the other pieces anyway.
Plan to do Front and Rear main seals, oil pan, timing cover... dry this thing up a bit on the outside.
Oil Pump
Timing chain and both Sprockets
Oil and Filter

Should I consider anything else while I'm down there?
 
mbalbritton said:
Alright, so I spun the crank around, checking the piston skirts, checking the play in the rod bearings, visually inspecting the cam, checked the flexplate. All appears to be in good condition considering the age. no cracks or broken skirts. they all feel snug. Cylinder walls looked good from what I could see. The rod bearings had just an ever so slight play that seemed normal from my Youtube research :D. The cam is probably the worst part of what I saw., but nothing I'd run from. I did not Pull the rod caps as suggested. I prefer to leave things undisturbed when I can, and like I said, they felt fine.

I think I'm gonna go for it on the timing chain replacement and see how it goes.

Ordered the following:
Complete engine gasket kit, cheaper than individual parts and who knows when I'll need any of the other pieces anyway.
Plan to do Front and Rear main seals, oil pan, timing cover... dry this thing up a bit on the outside.
Oil Pump
Timing chain and both Sprockets
Oil and Filter

Should I consider anything else while I'm down there?
Click to expand...
Don't forget to install the gasket between the block and the oil pump.
That's a mistake you make only once.
 
mbalbritton said:
Alright, so I spun the crank around, checking the piston skirts, checking the play in the rod bearings, visually inspecting the cam, checked the flexplate. All appears to be in good condition considering the age. no cracks or broken skirts. they all feel snug. Cylinder walls looked good from what I could see. The rod bearings had just an ever so slight play that seemed normal from my Youtube research :D. The cam is probably the worst part of what I saw., but nothing I'd run from. I did not Pull the rod caps as suggested. I prefer to leave things undisturbed when I can, and like I said, they felt fine.

I think I'm gonna go for it on the timing chain replacement and see how it goes.

Ordered the following:
Complete engine gasket kit, cheaper than individual parts and who knows when I'll need any of the other pieces anyway.
Plan to do Front and Rear main seals, oil pan, timing cover... dry this thing up a bit on the outside.
Oil Pump
Timing chain and both Sprockets
Oil and Filter

Should I consider anything else while I'm down there?
Click to expand...
High volume oil pump, will help with those worn cam bearings.
 
I'm going to go out on a limb here and say that low oil pressure, in and of itself, isn't a big deal for a AMC straight six. You can run a thicker oil, high volume pump, etc, but so long as you're getting flow to the top of the motor and the lifters are staying full, there isn't anything else that needs a certain amount of pressure (cam tensioners, etc) in order to function correctly.

Waiting patiently for @Jody Treadway to point out the error of my ways.
 
shawn said:
I'm going to go out on a limb here and say that low oil pressure, in and of itself, isn't a big deal for a AMC straight six. You can run a thicker oil, high volume pump, etc, but so long as you're getting flow to the top of the motor and the lifters are staying full, there isn't anything else that needs a certain amount of pressure (cam tensioners, etc) in order to function correctly.

Waiting patiently for @Jody Treadway to point out the error of my ways.
Click to expand...
Back 20-25 years ago, my parents had a 1990 XJ with a 4.0, and at one point, it got to where oil pressure would drop to zero then come back as you were starting/stopping/turning. I figured it might be the gauge, but after a few days (or maybe weeks) of this behavior, I decided to check the oil, and it didn't even show on the dipstick. A hair under 5 quarts later, back to good oil pressure, and never missed a beat. It holds 6 quarts :laughing:
 
safe oil psi is 10 psi for every 1K rpm. hot.
 
Alright, update.

Installed new timing chain and sprockets after checking things. I was a bit suspect of #5 from a bottom end inspection. Seemed like excessive play in the rod. Buttoned it all back up and fired it up and sure enough, still knocking. Honestly didn’t expect anything else.

FFWD to today. Fired it up cold and no knock. Waited for it to warm up, still no knock. Drove it, there it is knocking.

Pulled it in the garage, idling with no knock. Pulled spark plugs one by one and #5 starts knocking when I pull the plug. I think I found it. I’m thinking Wrist pin on #5.
 
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I have some here as well. Lemme know if you want me to snag one with the rod attached and snail mail it over.
(I grab 258s for the crank and scrap the rest).
 
Don’t care what you all think or say about @Jody Treadway . He’s ok in my book THANKS MAN!
IMG_0192.jpeg
 
And the Saga continues...

I had another carb thread going, but I'm going to continue this entire story in this thread. Started having a flooding issue, and rebuilt the carb. This did not fix the flooding issue, so I bought another carb figuring the old one was just flat worn out.

Got that installed this morning and no fuel dumping all over the place outside of the carb, but seems to be still flooding. just down into the venturis. While installing the carb I did notice that there was coolant seepage around the bypass hose on both ends when there hasn't ever been before. I continued working and tried firing the jeep up. it started to run and stumbled, then wouldn't fire. Looking for fuyel leaks, I notice more wetness around the bypass hose. I pulled the relief valve on the radiator and it was pressurised..... Noooooo, no no no no...

Pulled the cap off and cranked the engine again. coolant starts rising and coming out the radiator. FAWK!!!

Started pulling plug. These are brand new plugs, maybe just a few minutes of run time on them. 1,2,3 slight bit of soot and wet, I assume with gas. 4,5,6 look brand new, but wet. Unfortunately after Covid, my sniffer is AFU and I can't tell from the smell.

Seeing as I've been suspect of #5, I'm wondering about a blown head gasket.

So many different things going on here, Non start, flooding/carb issues, pressurised cold coolant system, knocking...

I was already planning to pull the head and open it up to swap the #5 piston out in an attempt to get a little more life out of it while I source and determine what exactly I want to do for an engine swap. Just a bit discouraged right now.
 
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