Knocking at top end when warms up get louder-noise speeds up with rpm

[CJB4POWERBILL]

When start up cold engine I notice small tap on top end. After high idle kicks off after bout 10 minutes the tap ahas became much louder. Loud at idle, but if I rev it up it speeds up and quite down a little. But when return to idle it gets louder. Just put new main bearings in it bout two weeks ago and have test drove several times and all is well there. I seem to think the noise is coming from the valve train area. BUT IT FOR SURE GETS LOUDER AS THE ENGINE GETS HOTTER ! Anyone have a quick check list or procedure to start the process of elimination and try to narrow this down. Any thoughts will be gladly accepted.

 

[Torxhead]

Go get one of those automobile stethescopes and play doctor to try and locate the source of the noise.

 

[CJB4POWERBILL]

I heard of doing that , but hek a knock from a specific area can still be 1 of 10 things lol. I have read to while running unplug each plug wire to eliminate specific cyclinder related problems on lower end and see if knocking stops ? Then to pull valve cover and do visual inspect followed by running with cover off to inspect ? Finally take a hammer handle and press down on the valve spring side of rocker arm and if noise stops than i have found the problem. ? Does all this sound like good attack plan and whats your alls thoughts. Jeep runs fine, Jest cant stand the knocking, sounds horrible

 

[grozam]

How's the oil pressure?

 

[CJB4POWERBILL]

well when i start it up the oil pressure is bout 40-50 but after engine gets hot the oil pressure idles at bout 5, if rev it up it goes up to bout 20 and will drop back to 5 at idle. but with all the low oil pressure problems i have read about on this AMC 258 i6 / 4.2l stock engine i havent really worried about it. this is the factory gauge im referring to. mabey i should put a mechanical gauge on it and check it? i put new oil pump when i replace main bearings. Whats your thought brother.

 

[Petescj]

My CJ7 Limited project sounds alot like what your describing. When its cold its pretty quiet but as it warms up it gets a little louder. The previous owner said oil pressure would drop to around 5 p.s.i. on trips over 50 miles. Since you replaced the bearings already Id be looking into putting in a new pump. Thats what Im gonna try and its relatively easy and cheap as well.

 

[CJB4POWERBILL]

Its got a new oil pump . I think this old electrical oil pressure gauge is incorrect...im getting a sunpro mechanical gauge from store when i get off tonight and will put on tonight and let u know if result differ from the factory gauge

 

[Petescj]

Its got a new oil pump . I think this old electrical oil pressure gauge is incorrect...im getting a sunpro mechanical gauge from store when i get off tonight and will put on tonight and let u know if result differ from the factory gauge

Ok thatll work. Grab a good old mechanical gauge.

 

[Old Dog]

Sounds to me like you have a bad lifter.

 

[DHugg]

When start up cold engine I notice small tap on top end. After high idle kicks off after bout 10 minutes the tap ahas became much louder. Loud at idle, but if I rev it up it speeds up and quite down a little. But when return to idle it gets louder. Just put new main bearings in it bout two weeks ago and have test drove several times and all is well there. I seem to think the noise is coming from the valve train area. BUT IT FOR SURE GETS LOUDER AS THE ENGINE GETS HOTTER ! Anyone have a quick check list or procedure to start the process of elimination and try to narrow this down. Any thoughts will be gladly accepted.

My Dad used to use a small-diameter vacuum hose, one end in your ear and the other end snooping around where you think the noise might be. I've done the same, and can find even small grinding noise or a vibrating hum this way.

RATS! I wish I had paid more attention to what he was trying to teach me!

 

[CJB4POWERBILL]

How to I spot a bad lifter

 

[Old Dog]

try to listen and see if it's coming from the valvecover area. If so do the "take the valvecover off and push on the rocker arm while it's running" thing you talked about earlier. Or with the cover off you should be able to listen and tell which one it is.
If you have a bad one all you can do is replace them.
A bad lifter will be a tick not a knock.

 

[Petescj]

Sounds to me like you have a bad lifter.

I understand that from the noise standpoint. Does that mean we're just left with a bad gauge for the fluctuation on oil pressure? Mines consistent , meaning it drops everytime it gets warm. If the gauge was screwed I dont think it would be the same all the time.

 

[Petescj]

try to listen and see if it's coming from the valvecover area. If so do the "take the valvecover off and push on the rocker arm while it's running" thing you talked about earlier. Or with the cover off you should be able to listen and tell which one it is.
If you have a bad one all you can do is replace them.
A bad lifter will be a tick not a knock.

Now Im intrigued a bit. Im gonna start mine up in the garage and listen a little more.

 

[Old Dog]

I understand that from the noise standpoint. Does that mean we're just left with a bad gauge for the fluctuation on oil pressure? Mines consistent , meaning it drops everytime it gets warm. If the gauge was screwed I dont think it would be the same all the time.

Your right, if the gauge was bad it probably wouldn't act the same all the time. Any engine will loose some oil pressure when it gets warm,(oil gets thiner) but 5lb is pretty low. It's usually a bad pump, or bearings going bad.

 

[grozam]

well when i start it up the oil pressure is bout 40-50 but after engine gets hot the oil pressure idles at bout 5, if rev it up it goes up to bout 20 and will drop back to 5 at idle. but with all the low oil pressure problems i have read about on this AMC 258 i6 / 4.2l stock engine i havent really worried about it. this is the factory gauge im referring to. mabey i should put a mechanical gauge on it and check it? i put new oil pump when i replace main bearings. Whats your thought brother.

I was thinking weak oil pump, but I see you say it's new so whatever is making noise is not getting enough oil. 5 at idle to 20 is not enough oil pressure. You are looseing it somewhere. Mabey a lifter is making noise from the lack of it.

 

[CJB4POWERBILL]

I follow what your saying on the oil pressure gauge is true everytime the same thing , so why should it be bad. Im fishin here but mabey it could be since its electric and all, that its reading correctly when cold and oil is thick ( shows bout 40-50) but if something on the inards of gauge is bad it may not read correctly at lower pressures. But with new bearings and oil pump i just dont think it should be low as 5 at idle....im kinda weary about an electric gauge anyway cause i aint got nothin electrical from 1983 laying around that works to well lol. Kinda same concept that i dont like push button 4x4...i just lean towards the older ways. i will feel safer with a good old mechanical oil pressure gauge with actual oil running to it showing me what i got rather than trusting a electric gauge that i cant tell u how it work, probally with ohms , amps, and resistors and all that confusing stuff.......ill let yall know tonight

 

[CJB4POWERBILL]

And why yall jest thinking on this one check out my other thread on water spray out exhaust and drop me answer on it .

 

[Old Dog]

I agree, I run a mechaical gauge myself.
Why did you change the main bearings and not the rod bearings too?
Was there a bunch of sludge in the engine when you had it apart?
Just searching for info here.

 

[tinhorn]

Sounds to me like you have a bad lifter.

Yup, I agree. When my Mazda does this it's either low on oil or it's time to change it.

i just lean towards the older ways. i will feel safer with a good old mechanical oil pressure gauge with actual oil running to it showing me what i got rather than trusting a electric gauge that i cant tell u how it work, probally with ohms , amps, and resistors and all that confusing stuff...

Yup, that's why I bought a 40-year-old Jeep.