Hot Rods 21 stud flathead tap/knock noise under load

hey all , looking for some ideas to start my search. I recently had an issue when driving my roadster home . Pulled into the garage and had a steady line of oil dripping underneath it, reeealll solid line not like a drop here or there. It was unknown to me, and oil pressure was fine . It was about 20 minutes plus of highway driving , and ended up being about 2 quarts low when said and done. I have now developed a tapping noise, not a hard knock. It is only under a load that i hear it, and can't pinpoint the noise or where its coming from. With a screwdriver to the ear i feel like i can hear it lower on the pass side, but higher up on the drivers side. I pulled each plug wire one by one and did NOT lose the noise. Any ideas of where to start or what to do to begin diagnosing it? I attached a pic so you can see the severity of the leak. But since then ( and a full oil change ) I am not losing any oil while driving it.. darn things a mystery engine. Where do i start!?!? Thanks everyone!

 

I should mention too, the car overheated prior to my 20 minute drive home. Pulled over, let it cool down and topped it off.. since then had to replace radiator .

 

It’s a 34 Babbitt flathead also

 

So you never found the oil leak and now it stopped leaking?

 

Drain your oil and check theres no metal flakes....these engines have fully floating rod bearings ..pain in the arse..

 

Don’t seem to show any metal flakes in the oil , all Looked good

 

After getting it home , I hadn’t started it in about a week . Checked and was 2 quarts low. Did fresh oil , since have driven it about 3 times around town to check and don’t have any leaks and oil is still at full level..

 

Bttt


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Man I'm baffled, and I generally know it all.

Perhaps you built up some crankcase pressure as a result of the overheating, thereby forcing some oil out. Is your cooling system pressurized? I would next to a compression check to see if any pistons suffered from the overheat.

 

I would believe that the rear oil seal is a slinger. Oil is more easily lost out those then the rope seal. As the rear main bearing wears, it will have a tendency to "pump" oil out the back. The rear main will have shims in it if they have not already been pulled out. They could be removed if the main is loose. Can also loose oil if going up a long hill.

I have the slinger oil seal in a Model A banger and in a 24 bolt V-8. They work fine.

Neal

 

Any updates to this? Have you found the source of the knock or the oil leak?

 

Blowby yes it is a pressurized system , and I’m thinking you might be right about the crankcase . I will do a compression check and see where I’m at ... man this is driving me crazy


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fresh motor? old wore out motor? how many miles have you put on ?

 

The oil leak hasn’t returned , the knock hasn’t gotten better or worse .. been raining a lot so haven’t driven it too much . Still researching and trying to figure it out


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Came out of a running 34 , has a rebuild tag on it but probably from years and years ago . Unsure of mileage but I’m sure it’s seen quite a few since the rebuild . I soaked it when Intake was off and cleaned it as well as I could without disassembly , new heads and gaskets but that’s about the extent . Prior too this it ran great , rarely passed 160 on the temp


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The oil leak trail that you showed going into you garage is familiar to me. I had a good running Model B banger. I could drive around locally and it would not lose much oil. When I took it out on the highway, it pumped oil out the rear main and would lay in the bell housing, dripping out the hole for that purpose. On my engine, the main bearings are wore out and too much end play. Crankshaft moving front to back and who knows where else pumping the oil out. I switched it out for another Model A motor when I got tired of adding oil and having the dripping mess in the shop.

The knock could be lifters or bearings. You say the knock is worse under load. To me that would be bearings which would make sense with the oil leak.

It probably won't heal itself. Use it until, you like me, get tired of the mess.

 

'Knock' on acceleration (under load) dictates TOP of reciprocating member, not bottom (bearings) unless 'heavy knock', which would be main bearings.

Possible cracked a piston skirt when it overheated. That or it's 'pinging'. (a hot spot from carbon broken loose when hot?)
You did mention mileage unknown...
1. Compression check. If nothing obvious, try:
2. Remove spark plugs one at a time, start engine each time one is removed and listen with a towel over that open plug bore to muffle noise from compression air. When noise ceases, it's that cylinder.

 

What Blowby had said.....and by the way did you see where it was coming from ?

 

I’m kind of thinking the piston skirt myself , I did pull plug by plug and listen to narrow it down and it never changed .

 

I couldn’t narrow it down at the time it was all over since driving home on freeway . And now the leak has left ( and it does have oil in it haha )

 

Compression check is done. Although seemingly low maybe ??? , it was rather consistent
1-50
2-55
3-55
4-50
5-55
6-50
7-50
8-55

I’m leaning towards a bent valve / spring issue . Intake will come off tomorrow and we’ll see what we got

 

Here is a video of the noise to give y'all a better idea, sorry for quality, but did what i could

 

pretty low numbers, did you have the throttle wide open and spin the motor 3 times around ?

 

This is just coil wire off and turn over

 

pull all the plugs out, wire the throttle wide open (pull the coil wire or otherwise disable the ignition) and spin the motor over 3 revolutions and that will be your correct compression numbers. as you do each one, first try it dry, and then squirt some oil in and do it again. a slight rise would be normal, and a big change in the number would indicate worn out rings

 

The noise stopped a couple times in your video, at about the 6 and 11 second marks. Does it consistently do this? Fuel pump?

 

The reason for the stop was me lifting off the accelerator it’s only under a load that it makes the noise

 

As this is my first flathead I’m learning as I go , once the intake was off all looked good . Valves went up and down , springs compressed and nothing stuck or appeared bent. I did find that the fuel pump push rod hole was wide open. Plugged it and got another 20 lbs oil pressure at idle .. opened the inspection cover from transmission and the noise projected out of there much louder .. maybe time to dig into clutch / flywheel area


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so, you have an electric fuel pump, or gravity? getting 20 psi from just plugging the push rod hole is strange. these older motors do not make a lot of pressure, low at idle is quite normal. henry said 10 pounds for every 10 mph. crude theory, but its not far from reality on a 34 motor. while you have the intake off, on the front left side of the valve chamber is the pressure relief spring and valve, perhaps just clean and inspect while in there. sorry no other ideas about the noise at this time. another thought, while you have the clutch cover off, try to pry the crankshaft back and forth to see how much end play the crank has. a dial indicator would of course be the correct way, but just a visual check would tell if the thrust broke off the main bearing. spec i think is about 6-8 thou which you wont see with just a pry bar, but if it moves a noticeable 1/6" inch or so you should get an indicator on it to know for sure.