Loud Tapping/knocking

[CT9A]

'83 4wd 3ac

It's coming from the cylinder head (I think, 99% sure) and it sounds like a valve tap, but 1000000 times louder. All cylinders have good compression, 120 psi +/- 5, I adjusted the valves to factory spec.

I took the top timing belt cover off and still see nothing. I'm at a loss. I'm thinking about pulling the valve cover again and checking the cam towers to make sure one didn't come loose? The cam pulley did look like there was an ever so slight wobble to it, but I'm not sure about that.

Please help!

[takza]

If you just redid the valves...I'd get the cover off and check again. fuel pump?

[CT9A]

I'm going to pull the cover again today, but I don't think the valve lashing is the problem. The sound started prior to me doing the valves, doing them was an attempt by me to eliminate the sound.

[Neu]

I'm ganna chime in and say wrist pin.

[Petros]

Is it possible the engine swallowed a screw or other hard object that is now embedded in a piton top? Not likely the cam bearings are causing this kind of noise. It is possible a broken/bent rocker or valve spring could cause it.

Use a long screw driver and press it against your ear with the other end on various parts of the engine, like a stethoscope. this will help you isolate the source of the noise. They also make automotive stethoscopes for this purpose, I got mine at Harbor Freight tools for only like $8. Then if it sound like it is coming from the piston, take the spark plug out and with that cylinder at top-dead-center, use a strong flash light, and see if you can see anything on top of the piston that might be striking the head.

Good luck.

[CT9A]

I'm ganna chime in and say wrist pin.

Anyway to check this without opening the motor up?

[CT9A]

Is it possible the engine swallowed a screw or other hard object that is now embedded in a piton top? No likely the cam bearings are causing this kind of noise. It is possible a broken/bent rocker or valve spring could cause it.

Use a long screw driver and press it against your ear with the other end on various parts of the engine, like a stethoscope. this will help you isolate the source of the noise. They also make automotive stethoscopes for this purpose, I got mine at Harbor Freight tools for only like $8. Then if it sound like it is coming from the piston, take the spark plug out and with that cylinder at top-dead-center, use a strong flash light, and see if you can see anything on top of the piston that might be striking the head.

Good luck.

At this point, I'm thinking that anything is possible. The noise started out of no where on the highway last week.

If it's a broken rocker or valve spring, wouldn't it have been evident during the valve adjustments?

I did try the screwdriver to the ear thing. The sound definitely is loudest when I put the screwdriver to the head right above the intake manifold around cylinder 1 and 2.

I'll try the looking through the spark plug hole.

This may be a little late to ask, but is there another way of telling TDC without using the crank pulley? Mine seems to have worn off the marking. On the cam pulley, there was a hole that seemed to line up with a marking on the cylinder head when I was at what I thought was TDC. All the valves that were closed and open were also in the right formation at what I thought to be TDC.

[Petros]

If you did not specifically look for a broken valve spring you may not notice it during a valve adjustment.

You can find top dead center (actually you just need to examine the piston, so any position with the piston up is good enogh) by removing the spark plugs and just turn the engine slowly until you can see the piston through the spark plug hole.

Also, when you see the piton through the spark plug hole, move the front pulley back and fourth a little to watch the piston moment. One time I had half a piston skirt break off, which still ran okay, but caused the piston to slap back and fourth in the cylinder making a clacking noise. When I pulled the head off I could see the movement of the piston when I rotated the crank.

it is also possible you have a damaged or bent exhaust valve, but you would not have good compression if this was the case.

Good luck

[Neu]

The only way to really tell if it's the wrist pin is to take it all apart...

it's very loud, but otherwise you can't tell too well....

It'll come from the lower end of the engine.


This is what happened to the first engine in my tercel. Wrist pin was causing a vicious knock, and i decided to have a lil fun in the woods with it.
Suddenly the knocking went away..and so did the sides of cylinder 3 for me..along with all of my oil. engine seized up pretty quick

Also try getting it down to one cylinder by unplugging the plug wires cylinder by cylinder, if you can narrow it down to one cylinder that'd be nice.


Also, I found out how to diagnose this. Hook up a timing light to whatever cylinder is giving you the trouble, (it may not even matter though) the wrist pin/piston pin will blink half as much as a valve knock apparantely. This makes sense I guess. So if it's a very quick knock, it's most likely the valves, if it's slower its probably the pin. The valves/lifters will make noise twice per flash, the pin once per flash of the timing light.

[Petros]

Neu reminded me of something, a very quick and simple test. If you try pulling the spark plug wires one at a time while it is running, and the noise goes away, it is almost certainly in the lower end (rod, bearings, piston, wrist pin) on that cylinder. If it does not go away it is likely in the head/valve train, and it could be anywhere.

If in the low end, there is no way around it, the engine has to come out and be taken apart or replaced. If it is in the head/valve train, it can likely be fixed without major work. At worst, you may have to pull the head, a big job but no special tools required and in can be done on a weekend.

Good luck

[CT9A]

Neu reminded me of something, a very quick and simple test. If you try pulling the spark plug wires one at a time while it is running, and the noise goes away, it is almost certainly in the lower end (rod, bearings, piston, wrist pin) on that cylinder. If it does not go away it is likely in the head/valve train, and it could be anywhere.

If in the low end, there is no way around it, the engine has to come out and be taken apart or replaced. If it is in the head/valve train, it can likely be fixed without major work. At worst, you may have to pull the head, a big job but no special tools required and in can be done on a weekend.

Good luck

Crap, that's exactly what happened with cyl. 1.

Here's my plan of attack, tell me if this is do-able. This is the same way I rebuilt many Honda motors.

Drop the oil pan, pull the piston, re-ring and/or replace the piston/connecting rod/wrist pin/etc. Normally I would pull the head and hone from the top, do a new head gasket, etc. etc., but with this being a very low budget fix, I think I'll take my chances and try to get it back on the road with just a new piston (or whatever part ends up needing to be replaced) and some new bearings on the piston.

I know it's not the right way, but does anyone see any major flaws that just make this a really bad idea? Again, goal is to get the heap on the road again for as little money as possible (hell, its not even my car!).

[Neu]

your cam will be out of spec and this will happen again

[CT9A]

your cam will be out of spec and this will happen again

Could you please elaborate for me? I'm not sure I understand why the cam would be out of spec and how it would cause this to happen again. Not challenging you, just curious as to why.

Also, how long do you think it'll hold together until it happens again if I went this route? Unknown, or XX,000 miles?

[Neu]

I actually dont know, but i have two friends that have done this on their R engines, and both times within a year they engines pretty much grenade themselves. One friend it was 4 months, the other was about 10 i think.

I think it has to do with it's hard to get everything perfect, like you can if you flip the engine over on an engine stand.

I just wouldn't do it, but if it's a budget fix, you could possibly be good. Just be careful.

[CT9A]

Ouch, an R engine.

What exactly happened when the engines grenaded, if you don't mind my asking? I've built numerous GS-R and B16 motors like this without pulling the block out, but I've never just done one cylinder and not the whole thing.

As long as I don't trash the block or the crank, if I get another 10 months out of it, I'll be happy. The person driving the car will be moving to GA by then, so I can take all the time in the world to rebuild everything after that.