Technical Flathead runs rough after acceleration and has therewith oil pressure drop

Hi all, I did a search, yes I did.
But cannot find what I got...
I drove my Flatty in the 36 coupe today a little rougher on the German Autobahn. Car was running strong for hours this day with no doubt.
After using the acceleration lane while entering another Autobahn, the engine sounds rougher and felt weak. I decreased speed and rpms. I learned than that in 5th gear at low rpm (about 1500- 1700) when pressing the acceleration pedal, the oil pressure drops one point down. (4 to 3) - normally up to 6!
Without gear, still standing car and acceleration the engine without load the oil pressure seems normal and decreases with the rpm...as usual.
Car does not make unknown noises in idle. (Clicking, rattling, knocking)
Thank you for every opinion and recommendation.




The H.A.M.B.

 

Oil may have just thinned out after the long run?

 

Thank you for this hint.
I will change oil tomorrow immediately!
Hopefully it will be better than.
That would be the easiest job.
I had really bad ideas - but lets see.




The H.A.M.B.

 

Are you saying you are at 4lb oil pressure at 1700rpm.? Oil pressure should increase with an increase in rpm .

 

What oil pan does it have and how much oil was in it? It is possible the oil was overfull and the crank was whipping or aerating oil it which would cause the loss of oil pressure

 

Check for gasoline in the oil. I.E. a leaking fuel pump.

 

You are right, oil pressure should increase with rpm.
This is what it does when it stands still.
- not in gear.
5th gear pushing the pedal, without increasing much rpm, but force in the engine, the oil pressure DE-creases....


The H.A.M.B.

 

But could this let the engine sound rougher....? Like it is a little unbelanced?


The H.A.M.B.

 

That worries me,,,,,,is it rough like bad spark plugs or rough as in a lower end problem .
4 pounds of pressure really worries me .

Tommy

 

You might be thinning the oil on a long run. My 51 merc with a flatty does drop a little after a couple hr run.hot about 15 lbs at idle at 60 to 65 mph it stays at about 50 lbs.

 

Hi Tommy, I never had bad spark plugs.
That was an idea of my friend here, too.
Will check this, also.
Thank you



The H.A.M.B.

 

I think there is a little confusion re the oil pressure .. when the poster says 3 or 4 Im pretty sure he means Kgs /cm 2 4 kgs works out at 42psi approx so oil pressure would be fine for a running flathead . Rev drop in 5th would also drop pressure as would the increased engine temperature from running prolonged speeds . 5th gear lower revs if your running a mechanical fan would also decrease cooling a little .

The rough running is unlikely to be anything to do with oil pressure if it rattled or grumbled you would have a problem but rough running/ drop in performance is more likey to be in either the ignition system or the carburation , either leaned out or if its an old holley / Ford / 94, to rich due to faulty power valves . I found a problem with mine rough running .. Thought it was a coil issue ( ballast or unballast resisted coil) after many coil swaps between both types it turned out to be the condensor .. swapped in a new condensor, rough running solved ..

 

Hi, I will try this, too
I am just changing the oil and opened the smaller cap of the oil pan - Filter of oil pump looks good.
Will close and refill with good oil right now. Than change Spar plugs and condenser...
Thank you every single one for answering.
You are all great!



The H.A.M.B.

 

Forgive me on the pressure issue,,,,,,I just assumed PSI,,,,yes,,,”,,4 to 3,,,,, but usually runs at 6 ,,“,,,,now I understand .
Pressure is probably just fine .

Probably just a condenser like was suggested .

I will.bet it is cool running that old hot rod on the Autobahn,,,,Lots of attention I’m sure .
Do you have any pics of it,,,,,I would love to see them .

Tommy

 

Took a while for me to work it out Tommy and to be honest , if I hadnt just fitted a cheap set of gauges to a car that happened to have the Oil pressure reading in KGs I would have thought PSI too.. I had to look up the conversion when I run the motor up .. 4kgs was 42lbs I wasnt that clever that I actually knew that , lol it was just a coincidence that I had came across it just recently ..

 

Good catch!

Sent from my SM-T560NU using The H.A.M.B. mobile app

 

Hi all and thank you for all your opinions and recommendations.
I am always happy to have so much guys here with that big experience.
I opened the screwed cap at the bottom of the oil pan.
No meaningful metal flakes or other bad stuff.
Checked the metal Cache of the oil pump - also ok.
Reassembled everything put new oil in - 20w50 as before with zinc
Instead 50 it reads 60 on my stewart warner, now - sorry for the wrong unit.
Engine makes no wrong noise when idling.
Rising Engine rpm increases oil pressure as it should be..but not as high as before.
Hmm - ok, will have an eye on this when driving.
Ordered new spark plugs.
Will change condenser tomorrow.
Dizzy is from Bubba.
Please find some pictures in the attachment.
Will let you know what is going on.
I was thinking, I killed a main bearing or something, to be honest.






ATTACH=full]4809388[/ATTACH]


The H.A.M.B.

 

nice rides...

 

I have a Bubbas dizzy in my 8ba .. No critisism of Bubbas , shit happens sometimes but the issue with my intermittent poor running was that the wire of the condenser had rubbed through the insulation and was intermittently shorting on the base plate . It took a while to find as the wire was semi secured with a dob of blue anti tamper ( same stuff was on a few screws and bits) so it wasnt really suspected . bit the bullet, removed the condensor and the under side of the wire had rubbed through .. kinda baffled me how it could have happened but it did .. Installed the condensor from the original loadamatic and fired it up..and been driving it ever since .. Just one of them things ..

I take it that your initial readings were KGs as I thought and you have since swapped to a more conventional measurement gauge .. ?

If you dont have any glitter in the oil there shouldnt be anything going on untoward . Is it a french flathead ?

A budy of mine runs a french block and he has a hell of a time keeping oil in the motor given that he has tried everything to reduce the oil pressure which is like yours in the 60lbs mark .. His problem is he blows the crank seals and destroys his clutch . I am definately not a flathead expert but 60lbs is pretty high , mine runs away fine at a steady 42psi at 160 F at 60mph ( I dont hve a rev counter sorry) at hot idle around 450 rpm the oil presure will drop to around 10 psi . Its by no means a fresh engine , it was cut out of a 53 Ford 2 door, sat around the garage for a few years before being dropped in my coupe .. I changed the oil and filter, added bubbas ignition and a new 97 and pretty much drive it every day

Hope fully your problem wont be mechanical, sounds unlikely but were not riding along with you to be able to see and hear wahts happening so were kinda guessing..

 

The Motors Manual calls for 57 Psi at 40 MPH,,,,,,so 60 psi doesn’t sound all that high .
That spec is for mid 40s Ford V8 up to 1953 .

I don’t think our friend from Germany has any mechanical issues .
Probably just an ignition issue ?

Tommy

 

Hi all, I changed, oil, changes spark plugs and condenser of Dizzy.
Oil pressure is good again up to 60
I found three cracked plugs - see attachment.
Do you think this can change the noise of the engine - to sound rough?

Thanks for your opinions

...I found out that the clicking noise is the pcv valve which sometimes clicks when it opens and closes in idle after reving the engine up to 4,5k - this was new for me - if I shut of the engine and restart it is gone..any idea?
Change the spring from the pcv..?



The H.A.M.B.

 

Drove the car now - low oil pressure when acceleration under load.
Think I killed a rod bearing....
Look here:



Car sounds very rough, too
Think I have to reassemble the engine




The H.A.M.B.

 

Oh, that's a good one.

For troubleshooting keep in mind the basics. Pressure is a result of resistance to flow. When the gauge shows there is pressure in the system that is because the amount of oil flowing from the pump into the engine is greater than the engine can accept, so there is resistance to flow, and pressure.

So, if pressure drops either there is a reduction in the amount of oil flowing, or a reduction in the resistance to the oil flowing.

In the case of amount of oil flow, well, if the engine accelerates that will increase the amount of flow, not decrease it. There could be a case where the oil level was low, and acceleration causes the oil to flow to the back of the oil pan, uncovering the oil pump pickup and starving the pump of oil, causing a reduction in flow of oil to the engine, and a loss of pressure. But I don't think there is enough acceleration going on here to cause that.

So, if there isn't a loss of flow that means there is a reduction in resistance, right?

The loss of pressure occurs under a load, and as soon as the load is reduced the pressure soars back up. What would cause a reduction in resistance when the engine is under a load? Bearing clearances opening up?

 

Hi and thanks for the details - think you are right - rod or main bearing issue - this is why the oil pressure decreases...cause it can flow with low resistance....
So - disassembling the engine and make it better...
Think I have to take it out the car....
Or would you try it from underneath the car..?



The H.A.M.B.

 

I'm not a flathead guy, but I'd much rather work on the bottom end of an engine standing up than lying on my back. Can you get to all the bearings with it mounted in the car? (are they inserts, not babbit?)

I've rolled new bearings in old engines with the engine in place, especially on heavy equipment where you have quite a bit more room underneath to access things (how many have torqued main bearings on a Cummins engine lying on your back?), I've even done it on an old Chevy 6 in a Suburban, but not in a 30's Ford. Hopefully someone with experience on that can/will chime in.

 

if the cracks in the porcelain are tracking then yes they can cause rough running as you will be potentially misfiring on 3 cylinders .. the miss fire wouldnt cause the oil pressure drop though . Your video demonstrated the problem really well , so weel infact im going back to watch and listen again..

If there is a low rummble or clattering ( death knock) then I would say a bearing might be shot but can it be the oil pressure relief opening , I could be talking bollocks , but this is only anecdotal, at 60psi my buddies blown flathead throws a hissy fit and spews oil . the load would /could cause the cracked plugs to misfire . but that doesnt explain the drop in pressure other than the increase revs /load increasig the oil pressure sufficiently to open the oil pressure relief causing the pressure to drop before you pop a seal .. It there is a horrible death rattle , then default to bearing issue .. but I would think it would be getting worse and noticeable when simply revving the engine while stationary , there would be a knock if you lost pressure ..

My old worn flathead idles when hot with around 10lbs oil presure and a steady 45lbs when running .. regardless of load .. If I were a gambler I might put money on pressure reliefe valve ..

 

I just re watched the video several times . I noticed through the steering wheel that the revs barley increased ,likewise the speedometer barely registered an increase in speed ? I tried to listen for the death rattle but it really just sounded like it was running real rough.. ( still doesnt explain the pressure drop) Are the gauges using electric senders or capiliary tubes ? was the video taken before or after you discovered the cracked plugs . what carb/s are you running ( not relating this to the pressure drop but the rough running) A drop in oil pressure wont make the car run rough , It might make it really noisy in a real obvious horrible death rattling unmistakable knock but you can still hammer it untill it throws a rod or siezes solid , the performance wouldn't necessarily decrease because you drop oil pressure ..You havent siezed it , so nothing slowing you down.. I woud also suggest that if you have developed a large bearing clearance that as soon as you fire up and reach running temp , regardless of the load you put on the motor , the increased bearing clearance already offers less resistance so the pressure will be low before you kick its ass .. Kicking its ass wont decrease the pressure any further it will just cause the crank to knock due to the reduced cushion of oil , At 30 psi the flathead would probaby still be good for a few thousand miles of carefull driving .. ..

Im just thinking out loud hear , If I could stand next t the car and see and hear exactly whats happening it might be more obvious .. but diagnosing the problem remotely isnt as simple , so just giving you some hope

 

Isn’t the pressure relief valve under the intake on these earlier Flatheads ?
In the main oil galley at the front .
It might be worth a check .
The video showed an erratic pressure reading with not a very much noticeable rpm load .
It’s worth looking into I think .

Tommy

 

Have you taken a reading on the engine with a vacuum gauge ? what reading did you get?
just curious as to a possible leak or distributor issue.

 

I never knew a vacuum gauge could tell you so much .. very usefull

Ref the pressure drop vid, I watched it a few times now and dont understand how you "loaded" it to drop the oil presure when the speed and revs barely registered any change .. It looked like you were doing around 60 at 2500 rpm pretty much constant.. the only gauge that registered anything different was the oil pressure gauge ..