Hi - My brother and I rebuilt the sbc in his '56' chevy about a year ago with mild comp cam, flat-top pistons, comp roller rockers, edelbrock aluminum heads, and air-gap intake. All bearings are new and block was bored and honed. Trans is a 4-speed Muncie. I have rebuilt my own engines for over 40 years without any serious problems, but I am certainly not a professional mechanic. Now - here's the problem: After about a 1000 miles on the engine a tapping starting. The engine needs to be warm and it cannot be heard until about 1900 rpm. We have used a stethoscope, taken fan belt off to make sure it is not the alternator or water pump, clutch in or out or driving or standing still doesn't matter, readjusted valves and checked push rods for straightness - with no luck in finding problem. We hate to just start tearing top end of engine off looking for "something". Engine runs very strong. I am hoping you guys have some suggestions on the next step. My brother is getting incredibly frustrated. Thanks for any help you can offer. Brian (dirtcop)
I had a problem like yours it turned out to be my spark plug! http://www.jalopyjournal.com/forum/showthread.php?t=167503&highlight=noise
When I get to that point I had cut a hole in some old valve covers so I could get to the rockers and bought the clips to cover the oil holes so the olil does not go everywhere, then I would go to each rocker arm and put a wedge a peice of wood inbetween the rockers and twist it to dee if the noise disapeared or was reduced. It maybe one or more. I know it is very crude method but it has serve me well.
Sounds like you've covered most of the bases, put your stethoscope on the fuel pump if you've still got the mechanical one. Could be the pump drive rod.
What type of cam-hydraulic? Flat tappet or hyd. roller? Solid? You mentioned re-adjusting the valves. Did you find any that were loose? When you broke it in, did you add any ZDDP additives? Wondering if you don't have a lobe going flat.
did you check your harmonic dampener?? if the rubber is bad when they warm up they sometimes will make a inconsistent knocking. Look to make sure that the rubber is not cracked or coming out of the side or missing all together. I wouldn't recommend running it without one, but if you have another one switch it and see what happens.
My thoughts exactly. Does it "pop" through the exhaust or carb when you reach the 1,900 rpm mark. A worn lobe can seem to run ok at lower rpms, then pop or backfire at higher rpms. How do I know that, because I am changing a cam as we speak due to, I ***ume, no, make that hope, incorrect break-in procedure, and lube (zddp).
Thanks for the responses / ideas. It's a hydraulic cam & lifters. Kind of doubt if it's a flat lobe - already went through that deal (but that has not been ruled out, just really hope that is not it). Break-in additive was added and engine broken in per cam instructions. Car runs great, no backfire, pulls nicely. Great ideas so far - the search continues. Thanks
i just chased some mysterious valvetrain noises...here is what I found My dipstick was in backwards and was hitting the crank, don't ask me how, it must be curved to stay close to the pan wall, and after checking the oil it went in backwards, only found it cause I had my hand on it and felt the vibration when the motor was running. Also had a compressed vavle cover gasket cause the tips of the rockers to hit the valve covers...repalced the gasket and it went away Also found a manifold flange bolt was loose... good luck.
Is the noise heavy enough to be wrist pin? Pull the plug wires one at a time and listen for a change,,,,,
Bad news - finally checked everything out and by pulling plug wires knew that the #3 cylinder had some kind of problem. We pulled the top end off and I dropped the pan yesterday and popped #3 piston out. Rod bearing is totally wasted. This is my brother's worst nightmare, we have to rebuild the engine again. I don't know what went wrong - engine only had 1,000 miles on it, pretty gentle driving (certainly no great rpm action), all clearances were checked and double checked during ***embly, all new parts, and correct break-in lube and additive. Sometimes life just ****er punches you for no reason. We'll get her done again. Thanks for your input. dirtcop
Sorry for your troubles, but thank you very much for following up this thread with what you figured out. Too many times someone asks for help, then you never hear what the solution ended up being.
Im new here and have wondered about help post,i never found out what the problem was,so thanks for the follow up.........................YG
One of the main causes of early engine failure will always be contamination, I have seen plenty of decent machine work get destroyed from dirt/shavings/gl*** bead/sludge left in oil galleys etc. ***uming it is a small block Chevy, the front and rear 3 oil galley plugs must be removed as well as the plug on the deck surface that closes a tooling hole. You will also find a 1/2" cup plug below the main cap. Using long nylon brushes to rifle the oil galleys and running a brush from the main holes up to the cam bearing holes is always a good move. Personally I always wash the block with hot soapy water,that is pretty fool proof. There are other areas that can introduce contamination. If the crank is reground the oil holes must be brushed with nylon brushes and clean solvent (Mineral spirits will do) from the main holes to the rods. The stock type SB Chevy oil pan has a flat baffle in the front which is closed off on the oil pump side, boy does that collect sludge from years of not fully draining during oil changes. Look closely at the rod bearings, if they show a lot of fine scratching while the mains are a lot cleaner then contamination was probably the problem, the rods get fed oil from the mains. Think clean!!!
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