HELP!!!!...sbc engine noise

[SR71]

a friend has a 406 sbc that we put together many years ago. it has been hanging on a stand sealed up for the past 10 yrs. the valves were not adjusted so there was no pressure on the valvetrain and he rotated it every few months to keep it from sticking.



well, he finally got a car to put it in and we installed it. we prelubed her, adjusted the valves and fired it up. we then broke the camshaft in (hyd flat tappet) per the mfr instructions. things went great. good oil pressure and temp. I idled the engine down to about 950 rpms and she sat there loping and sounding badass. and then........

Rich pulled her in gear. when the converter drug the idle down a little bit, she went to tapping pretty darn loud. the noise seems to be coming from the right hand bank. it sounded like a lifter waaay out of adjustment, so I ran the valves to zero lash with the engine running. sounded great again until we pulled it in gear. the noise goes away when you idle the engine up, but comes back when it chugs down.

the tap seems to occur at about half of engine speed so we think it is valvetrain related. we checked the valvetrain for any mechanical interference and found none. then we installed a new set of lifters and broke them in again. we still have the same problem. we even swapped the roller rockers out for pivot ball long slots and the tap is still there. the distributor was the next thing that I checked. no dice.

we also checked the convertor bolts, flywheel bolts and then the headers and oil pan for any contact. nada.

the engine is hanging on the stand again with the pans and heads off. we cannot find anything wrong. no witness marks on any of the parts either. the cam and lifters look new.

this thing ran like that raped ape of lore. but the tapping noise was obscene at idle in gear. and this was while holding 35psi of hot oil pressure. the heads are 210 afr's w/2.08 valves and there is no p to v contact.

I am all out of ideas. any help is appreciated.

[regal454]

Have you ruled out a header gasket leak?

[SR71]

yes sir. when you drive the car it is perfect untill you come to a stop. and even then it takes a few seconds at a constant chug for it to start tapping.

[regal454]

Are the valve springs matched to the cam? 210 AFR's will most likely come with a soild roller type valve spring which is way too much pressure for a flat tappet hydralic.

[SR71]

yes sir. we changed the afr springs out for the ones that cam with the cam kit. the cam is a comp nitrous hp with matched springs and retainers. rockers are comp pro magnum.

the engine acts like a lifter is bleeding down. but oil pressure is good and we installed a second new set of lifters in case one of the first set was bad.

[sam 74]

maybe a sticky valve, did you run a compression check to see if there was a problem there?

[BuzzKillian]

I'm just going to throw this out there.... I saw in another thread where the torque converter cover was hitting and making a noise like that. Just somthing to check. I know it sounds absurd.

[SR71]

compression was 225 psi across the board.

checked the converter in the car and looked for witness marks after pulling the engine....nothing.

thanks for the help guys. keep the ideas coming.

[NDubs68]

Similar thing happened to me. Out of the blue got this horrible metallic noise when id put in gear. Turned out that flexplate was moving just enough to make contact with the gear on the starter. All was better once i retightened the starter bolts. But it sounded like it something was letting loose on the passenger side. So i hope this helps

[Josh]

Oil supply to a lifter blocked? Can you back off each lifter one at a time while the engine is idling to cause it to tic. if you get to one that does not change with backing it off you may assume that one is not getting pumped up.

[sam 74]

can you tell what side of the engine its coming from? maybe get a vid with the motor running?

[SR71]

Similar thing happened to me. Out of the blue got this horrible metallic noise when id put in gear. Turned out that flexplate was moving just enough to make contact with the gear on the starter. All was better once i retightened the starter bolts. But it sounded like it something was letting loose on the passenger side. So i hope this helps

I'll check the starter and flywheel for marks. we have had 2 different starters on the engine (one was a powermaster mini starter) and it didn't change anything.

Oil supply to a lifter blocked? Can you back off each lifter one at a time while the engine is idling to cause it to tic. if you get to one that does not change with backing it off you may assume that one is not getting pumped up.

seems logical to me. but we can't find anything blocked. I set the valve lash to zero with the engine running. all lifters ticked then quieted down.

can you tell what side of the engine its coming from? maybe get a vid with the motor running?

pass side. the engine is apart on the stand right now.

[SR71]

an oiling problems seems to be the most logical thing. usually when you set the valves to zero lash with the engine running, oil soaks the headers and inner fenders. well, the rockers were oiling. but not one drop hit the headers or inner fenders. and this engine has a hv oil pump and shows 35 psi in gear warm.

and the strangest thing is that the rear oil galley plugs were dry when we pulled them. the galley isn't obstructed, but the plugs were bone dry.

[NDubs68]

Cam bearings not lined up correctly?

[jtm311]

How about the clearance on the piston bolts to the inner walls? only be cause it will happen at higher RPMs

[Chevelle598bb]

How about the clearance on the piston bolts to the inner walls? only be cause it will happen at higher RPMs

Piston bolts?

[jtm311]

Sorry the connecting rods. I started to write about the piston rings.

[Chevelle598bb]

Gotcha. I was thinking possible rod bolt/rod to cam clearance. I have had built many 400 sbc and have had to run small base circle cams depending on the rod used. The op stated there are no marks on the cam or rotating assembly. Usually a rod to cam connection is catastrophic anyways.

Now I am intrigued by the dry oil galley plugs. While the motor was sitting for 10 years was it covered? All plugs and galleys sealed up? Maybe a pesky dirt douber or scale/corrosion is blocking a galley.

[SR71]

the engine was fully assembled, oil pan, vc's, intake, spark plugs, ect. the carb flange and exhaust ports were sealed off.

the rods are scat forged stock style 5.7". we had to slightly clearance a couple of them for the first cam. the current cam has ample clearance.

[SR71]

How about the clearance on the piston bolts to the inner walls? only be cause it will happen at higher RPMs

the tap only occurs at low rpm....below no load idle.