Mercury crank

[34PKUP]

Originally Posted by GOSFAST

Hi Tom, without a doubt, have all 4 tapped. The nice part about the Merc's starting with the 5/8" plugs is they don't need drilling, they're already the correct size to just tap for the 3/8" NPT thread!

Thanks, Gary in N.Y.

P.S. In all my time doing these builds we've literally done hundreds of those crank holes, more than 90% were Merc's, we did some Ford's way back in time.

Just curious, why is it necessary to take the time and effort to tap holes and insert threaded plugs? When the original Ford type plugs were used on literally millions of cranks (not hundreds) without any problems (known to me).

[Desoto291Hemi]

I would venture to guess that it is just a safety precaution.
One less thing that could go wrong,,,you know.

We tend to run more pressure in our engines now,,,,so a plug could possibly blow out.
Also,,,,you need to remove them to clean the passages . So might be a good time to upgrade. Of course,,,like you said,,a plug worked for millions of engines before.

However,,,I will probably use a fair amount more oil pressure,,,so,,,I know what direction I am leaning towards.
Thanks for the reply Gary.

Tommy

[40 Deluxe]

Originally Posted by Desoto291Hemi

I would venture to guess that it is just a safety precaution.
One less thing that could go wrong,,,you know.

We tend to run more pressure in our engines now,,,,so a plug could possibly blow out.
Also,,,,you need to remove them to clean the passages . So might be a good time to upgrade. Of course,,,like you said,,a plug worked for millions of engines before.

However,,,I will probably use a fair amount more oil pressure,,,so,,,I know what direction I am leaning towards.
Thanks for the reply Gary.

Tommy

Why "use a fair amount more oil pressure"? Is it really needed? It will heat the oil more by churning it through the bypass valve as well as require more horsepower to drive the oil pump. Bearings are lubricated by the hydrodynamic wedge action of a rotating shaft. The oil pump merely supplies the needed oil to the bearing.

[Desoto291Hemi]

Well my reasoning is I have heard many stories of only 10 pounds of pressure before.
I am sure that some engines will live with that,,,,,but,,,the stresses placed on a high performance engine are greater.
Yes,,,the hydrodynamic wedge is there,,,,but,,the added load is detrimental to the oil film provided on the journal.
The load against the journal doesn’t just increase,,,but it could increase by the square,,or even the cube.

Also,,,some oil passages are not as friendly to good flow as others are.
Some cranks are machined where the oil passages actually act as a pump themselves.
The angle of the passage,,,the angle the oil hole comes out on the rod at top stroke.
This can act as a pumping action,,by centrifugal force,,,,it literally helps sling the oil through the crank.

Also,,,,during some high rpm,,,high load forces,,,the oil can stop in its tracks,,,,,for just a millisecond,,,.
There are a lot of forces involved,,,,that is why they went from just dippers and oil slingers.
The power levels got to the point that it couldn’t lubricate anymore and the pressurized oil systems were created
Then later,,,,the full filtration filter systems evolved as well.

I don’t plan on too much pressure,,,I like to have al least about 30 or so at hot idle,,,then around 60 at RPM.
Just my observations.

Tommy

[flatjack9]

I've got over 60,000 miles on my engine and the oil pressure never drops below 30 lbs. 60 at startup. This is with a stock 8BA pump. The 10 lb stories are old history.

[Desoto291Hemi]

Sponsored Links (Register now to hide all advertisements)

Hey Flatjack,

Good to hear that.
Like I said,,,I don’t intend to use too much pressure,,,just a fair amount.
By the way,,,what pump do you use,,,stock type Ford,,,Melling?

Tommy

[tubman]

I don't think you can beat a stock ford pump if it's in good condition. Certainly don't use a Speedway Motors pump. I put one in a brand new engine and it only made 15 lbs at hot idle. I replaced it with a known good Ford (tested by none other than "flatjack9"), and my hot idle is now 35 lbs.

[Desoto291Hemi]

Awesome Denny.
That is information that I can use.

Since this is a crank thread.
What about the Merc cranks,,,,do they hold up well in stock form,,,or should they be modified for oil flow?
This flathead stuff fascinates me,,,I’m like a kid in a candy store.

Tommy

[Bored&Stroked]

Originally Posted by Tim Ayers

Ron,

Have you found that the extra weight impacts fuel economy in any way?

There is a severe impact --- due to the heavier Merc crank, I have found that I have had to counterbalance that with a heavier foot on the gas pedal . . . the net result is that my mileage tends to suffer . . .

[Ol' Ron]

Flatjack9, 10/30 oil??

[flatjack9]

Yes