knocking at start up again
 

About a week ago I was reading a thread about knocking noise for about 30 seconds at start up. Suggestions were to short #s 2& 3 spark plugs to confirm it's slop in in the middle main Babbitt. Questions....is that a sure fire way to determine that? I did that and no change. That test and after talking to Tom Jordan at Snyder's who told me bearing knock doesn't go away on it's own. engine runs fine....good compression...no blow by, just the knocking at start up. If or when I drop the pan, what do I need to know about about seals and gaskets when I reinstall the oil pan. Just doing my homework before I jump into things. Thanks for any thoughts.

Re: knocking at start up again
 

Perhaps the rear main has been modified with xtra drain holes in attempts to stop leak, and has a little extra clearance--- all the oil drains out and knocks till the oil gets back--- guess it could be any of the bearings if the oil grooves and wells were done wrong--- even small hole in dipper tray

Re: knocking at start up again
 

One other thought before dropping the pan. I had what sounded like a bearing knock, but turned out to be the cam walking forward and backward due to a worn spring and plunger inside the timing cover. When I put the timing pin in with engine running and pushed, the knock went away.

Re: knocking at start up again
 

does the knock have a rhythm to it? Like is it a constant tapping or does it tap 2 times then stop for a bit then starts tapping again? walking cam or loose oil pan baffle will be intermittent, engine crank or rods should follow a rhythm..

Re: knocking at start up again
 

Could it be a valve needing adjustment? Thinking oil may not be in valves yet.
Is this something just stating or has it been there for awhile?

I am not an expert so I am asking to give some ideas for future with my rigs.

Thanks for the help.

Re: knocking at start up again
 

Definitely not intermittent. More of a rythem. Wouldn't the timing pin catch in the dimple in the timing gear if the engine was running? This might be a coincidence but I never had the knocking until I went to detergent modern oil. Previous owner use 30 weight straight oil.

Re: knocking at start up again
 

I use straight 30 in all my cars. I read somewhere that multi-viscosity oils are too thin at start-up for babbitt clearances. I know others will disagree with me on this, but straight 30 weight has served me well for 40 years. John

Re: knocking at start up again
 

Bingo! You changed to detergent oil and may have moved sludge around the engine. First check for good oil flow, remove the slotted plug on the side of the block above the oil pan, or loosen the drain back tube and see if you have oil flow. This is to see if the oil pump is not clogged, if it slow to start flowing then you need to clean out the pan. The valve chamber will need to be cleaned out also.
Please check for oil flow before driving so you may save an engine rebuild ! Hopefully you haven't hurt the engine

Re: knocking at start up again
 

It doesn't "catch", but the pin just falls in to the dimple every time it goes by. It will still help to eliminate the cam walking back and forth.

Re: knocking at start up again
 

Yup, detergent oil is working overtime removing years of sludge, i would drop the pan and clean it out along with the oil pump screen, valve chamber, and carefully check the dipper tray for pinholes now that the sludge has been unclocgged from them....

Re: knocking at start up again
 

Thanks again guys......hope all I find is sludge and I'll check for cam movement to. Car won't be used till it's fixed right and I will post my findings.

Re: knocking at start up again
 

If the noise doesn't go away then I'd look for bad babbit.

If it's a light ticking that goes away I'd look for collapsed piston skirt.

Re: knocking at start up again
 

You can bet the modern detergent oil is the culprit .My mother in law had a prewar car which used straight 30 grade it was dispensed at the local filling station with a hand crank pump and jug . This was the mid sixties and the filling station also had sealed cans of "Shell X100" detergent oil new on the market . I told her never to use this oil and as the car did burn a bit of oil I knew she would need oil when I was away at sea . Sure enough the trying to be helpful garage lad sold her the new oil (he told me it was much better). One can killed the motor ,knocked out the big ends etc etc and the car was junked as beyond economic repair . I have used cheap detergent oil for 35 years in CLEAN engines and never a problem .

John in lovely day Suffolk County England .