stihl460

I would agree with the knock being in the valvetrain. It is possible it is a rod knock though. I picked up my 89 with a 3vz cheap because it had a knock. The truck had been run low on oil and chewed up one of the lifters and the camshaft. It ended up burning the exhaust valve in the no.5 cylinder. Needless to say im in the middle of rebuilding a 3.4 for the swap. Id start by running a compression test to see if any valvetrain damage has occured then go from there.

dntsdad

Sounds exactly like mine did when it spun a rod bearing. Chewed it to nothing.

https://www.yotatech.com/forums/f116...ooking-186183/

I said F it and got rid of the 3.0 for the 3.4. Best decision I have made thus far concerning vehicles.

jkdunbar

But a Rod Bearing would leave traces of metal filings in the oil.

I'm going to remove the plug wire from each cylinder first then do a compression check.

I will come back when I have the results, but any more suggestions will be helpful.

Kevin

vital22re

iTrader: (2)

pull the belts off the front and see if the noise is still there.

jkdunbar

Update:

Removed plug wires one at a time, still heard knocking sound.

Started to test compression in each cylinder:

1 - 120 psi
3 - 120 psi
5 - 150 psi
2 - 120 psi
4 & 6 - Not done yet. Have to remove air intake.

I even removed the main wire on the distributor cap and ran through 5-7 cycles, and there was no knocking.

I will complete 4&6 on Thursday and give another update.

The compression seems kinds low... must not have let it run thru enough cycles. Maybe I will retest them on Thursday...

dntsdad

mine still knocked like hell with the wire removed. WOuldnt knock at startup till about 1500 rpms usually and then I could find a sweet spot where it wouldnt. Did you did through the sludge in your pan for shavings?

b4wheeler

iTrader: (1)

My guess is it is not a knock...

Mine was making a similar sound and I found out that the A/C clutch was bad......

If it was a rod knock.. it would not clear up like that and then come back.. it also seems inconsistent at times...

Do as vital2re suggests and remove the accessory belts...

jkdunbar

Hey B4,

I don't have AC on mine so it cannot be the clutch...

I'm getting back into it today as it's not raining today here in NB.

Thanks for all the comments...

jkdunbar

Both belts are off and the knock is still there...

jkdunbar

Compressions is as follows:

1 (130), 2 (130), 3 (130), 4 (130), 5 (140), 6 (140)

Compression seems low but consistent.

Just to retell everyone:

I was driving along, when I started to hear a hammer noise in the engine. It shut down on it's own like it flooded. 30 minutes later it started ok and I was able to drive it until the noise came back, and now I'm afraid to drive it.

It runs smooth, except for the knock. I took the wires off one by one and the knock stayed. Compression test is ok and I removed the belts, and still the knock is there. No metal shavings in the oil, but I have yet to drop the pan.

Any ideas?

allkindsa

My '93 just started the same noise, but I haven't checked anything yet. Did you ever determine the culprit of your knocking problem?

thook

If you're having problems telling exactly where the noise is coming from, you should buy a stethoscope. They're real cheap at autozone. Otherwise, a long screwdriver or rod will work okay. Scopes are the bomb, though.

jkdunbar......are you sure you ran the test correctly? What instructions did you follow?

Is this how you ran the testing?

http://personal.utulsa.edu/~nathan-b...66compress.pdf

And, did you try running the test again with oil in the cylinders?

allkindsa

I would have to say that mine sounds & acts just like shown in jkdunbars youtube video in this thread.

dasrunner

EXACT same problem on my 95 runner, right now im at a loss but now i think im gonna go pull the 87 out and do some checkin as i have ac then after im gonna pull some belts and i guess check my valves if i come to nothing

allkindsa

I do most of my own work, but have a great mechanic (MPG Automotive, Raleigh NC) who does diagnosis if I'm at a loss. MPG's Mike says it's not valvetrain because it gets louder and tone even changes with increased RPMs and also because it gives a rattle if throttle pushed and quickly let off. He assures me it's a journal or rod bearing as I told him the oil got real low at highway speed. This oil starvation likely caused bearing failure. He said I'll be lucky if I don't have to replace crankshaft since only original bearings can be bought therefore almost disallowing any machining to crankshaft.

dasrunner, I hope you're more fortunate. But, hey, Mike could be wrong!

jkdunbar

I never got the real cause of the knock. I had a spare 3.0 engine that I picked up from an 88 and i'm in the process of changing it over. I might sell my old 3.0 to someone to rebuild for 150.00...

I started another thread about what sensors to swap from the 91 to the 88...

thook

If you haven't started tearing things apart just yet, you might check the EGR operation.

dasrunner

well i got my bottom end pulled out and am looking it over. from what i could see there was a bit of sludge buildup in the pan but when it came to the rods they all felt normal and had sufficient end play. gonna pull the #2 rod bearing cap tomorrow as thats where it sounded like it was coming from. by the way mine pretty much always had low oil pressure after it warmed up but ive had it over a year and it never gave me any problems. this all started about three weeks ago when we did some off roading and killed it in a good size mud hole.

allkindsa

Mine was just plain low oil level (needed 3 qts to show on stick!). I feel like the parent who who doesn't check to see if their kid is playing with a knife. There's not an obvious bad leak or smoke, so the low oil must have happened over a 5/6 week period since last change.

Andy A

Had a situation a number of years ago where one of the traces went bad in the distributer cap (#1) which caused a bad knocking noise. Basically the cylinder was just not firing and washing the cylinder with fuel.