scratches on piston head and tapping noise

[rogus]

I recently bought a rebuilt sbc 355 after being able to hear it run. After installing it I get a loud tapping noise from the number 8 cylinder. I used a camera to see inside the piston chamber thinking something might have gotten into it through the intake manifold but there was nothing there. There was however a number of scratches on the top of the piston head between the valve reliefs (4 opposing valve reliefs separated by the middle top of the piston). It's the middle between the valve reliefs that is scratched up. I ran the camera into the number 4 piston chamber to see if it had scratches on the piston head there as well but it didn't. Not sure what is causing this? Any help would be appreciated.

 

[CopperNick]

So my question to you at this point is, Do you suspect the presence of matching scratches or other damage on the faces of the valves in the cylinder? If so, a normal camera can't swivel to look up and see the valves but a bore camera can. Basically it is the same kind of inspection tool as what the plumbers use to scope sewer and water lines to look for damage or blockage, only a lot smaller to get into tighter places.

Also, have you gone ahead and removed the valve cover and physically attempted to move the rocker or the pushrod to see if they are loose?

After that, have you given any consideration to removing the oil filter and filleting it to retrieve the filter media from inside the canister so you can spread it and check it for debris or micro-shrapnel?

Finally, is your peace of mind worth the $$ for the gaskets and the labor necessary to remove the intake and see what's to be seen down in the valley, and then, finding nothing in there, go the next step and pull the head completely???

You say you are seeing scratches and that, to me, is a symptom. Up to you as to how deep the dive will be before you get an answer to what caused those scratches and what will have to be done to fix the issue.



Nick

 

[rogus]

So my question to you at this point is, Do you suspect the presence of matching scratches or other damage on the faces of the valves in the cylinder? If so, a normal camera can't swivel to look up and see the valves but a bore camera can. Basically it is the same kind of inspection tool as what the plumbers use to scope sewer and water lines to look for damage or blockage, only a lot smaller to get into tighter places.

Also, have you gone ahead and removed the valve cover and physically attempted to move the rocker or the pushrod to see if they are loose?

After that, have you given any consideration to removing the oil filter and filleting it to retrieve the filter media from inside the canister so you can spread it and check it for debris or micro-shrapnel?

Finally, is your peace of mind worth the $$ for the gaskets and the labor necessary to remove the intake and see what's to be seen down in the valley, and then, finding nothing in there, go the next step and pull the head completely???

You say you are seeing scratches and that, to me, is a symptom. Up to you as to how deep the dive will be before you get an answer to what caused those scratches and what will have to be done to fix the issue.



Nick

Also, have you gone ahead and removed the valve cover and physically attempted to move the rocker or the pushrod to see if they are loose?

I have the valve cover pulled. Planning on checking the rockers/pushrods next.

After that, have you given any consideration to removing the oil filter and filleting it to retrieve the filter media from inside the canister so you can spread it and check it for debris or micro-shrapnel?

Got to admit I hadn't thought of that.

Finally, is your peace of mind worth the $$ for the gaskets and the labor necessary to remove the intake and see what's to be seen down in the valley, and then, finding nothing in there, go the next step and pull the head completely???

With as loud as that tapping noise is I don't think I have a choice. I must admit however that this is new territory for me in that I am not sure what I'm looking for...unless I find a nut or washer or anything else that might be blaringly obvious it doesn't belong there. If I pull the head and see marks on the valves I'll need to be back here looking for diagnostic help and just hope it doesn't come to that.

 

[CopperNick]

Okay, given your responses I think that Step One here might be for you to score a filter cutting tool, looks mostly like an old style can opener except that it lays flat on the screw end of the filter and as you turn it, it cuts the end off so that you get into the can and extract the filter paper. The more you say "Knock" the more I wonder if your noise is a transmitted one that is actually coming from deeper in the engine. Filleting the filter should give you a fairly accurate idea of what is or has happened and the nature of the event.

Just as an FYI here, I am not going to be any more specific about what might be causing your Knock simply because there are several potential sources, any one of which might be the culprit and I do not want to aim you in the wrong direction. What you are about to engage in is sort of the mechanical equivalent of a medical biopsy. By filleting the filter you are exploring for signs and indications, just the same as the doctor is doing when he/she grabs a piece of skin or tissue for the lab to evaluate.


Nick

 

[rogus]

Okay, given your responses I think that Step One here might be for you to score a filter cutting tool, looks mostly like an old style can opener except that it lays flat on the screw end of the filter and as you turn it, it cuts the end off so that you get into the can and extract the filter paper. The more you say "Knock" the more I wonder if your noise is a transmitted one that is actually coming from deeper in the engine. Filleting the filter should give you a fairly accurate idea of what is or has happened and the nature of the event.

Just as an FYI here, I am not going to be any more specific about what might be causing your Knock simply because there are several potential sources, any one of which might be the culprit and I do not want to aim you in the wrong direction. What you are about to engage in is sort of the mechanical equivalent of a medical biopsy. By filleting the filter you are exploring for signs and indications, just the same as the doctor is doing when he/she grabs a piece of skin or tissue for the lab to evaluate.


Nick

I had wondered if it was possible for the sound to actually be from somewhere else. I imagine that could only happen if the noise was somewhere next to the the crankshaft area?

 

[383_StealthRam]

Reading through this, if the piston is kissing the valves just slightly that could certainly be caused by spun/worn/missing connecting rod bearing on that cylinder letting the piston travel higher up that it normally could. CopperNick spot on imho to get that oil filter cut open and look for the glitter evidence which would likely be there if you have a bearing issue, or other mechanical breakdown happening.

Keeping with the borescope possibilities, if you have the intake off, and distributor out you may be able to get that borescope down past the cam, or else up through the oil pan drain plug hole and try to view the back two cylinders rod ends while you turn the crankshaft (back and forth) and see if you can see play from spun/worn bearing.

Sounds like you got some work cut out for you...hope you find what it is.

 

[rogus]

Reading through this, if the piston is kissing the valves just slightly that could certainly be caused by spun/worn/missing connecting rod bearing on that cylinder letting the piston travel higher up that it normally could. CopperNick spot on imho to get that oil filter cut open and look for the glitter evidence which would likely be there if you have a bearing issue, or other mechanical breakdown happening.

Keeping with the borescope possibilities, if you have the intake off, and distributor out you may be able to get that borescope down past the cam, or else up through the oil pan drain plug hole and try to view the back two cylinders rod ends while you turn the crankshaft (back and forth) and see if you can see play from spun/worn bearing.

Sounds like you got some work cut out for you...hope you find what it is.

I appreciate the help.

 

[bracketchev1221]

What do these scratches look like? Between the valve reliefs does not sound like a valve contact issue as it normally hits the tops of the valve reliefs first. Pull the valve cover off and start it and see if you can pinpoint the noise better.

 

[rogus]

What do these scratches look like? Between the valve reliefs does not sound like a valve contact issue as it normally hits the tops of the valve reliefs first. Pull the valve cover off and start it and see if you can pinpoint the noise better.

Thank you for the info. If I start it without the valve covers on how do I contain the oil?

 

[Sweet_Johnny]

They sell little clip-on splash guards, you can cut the tops off of some old valve covers, or just deal with the mess. I've had the best luck just dealing with it and cleaning up afterwards.