Hello all. Just have a question in regards to the "full flow" mod on a flathead. I picked up a fresh built 51 mercury that looks to have the mod. I am trying to figure the plumbing to the remote oil filter and my question is why are the in/out holes in the block 3/8 if the oil line is going to be 1/4 with a restrictor. Or do I need to run a bigger line then 1/4?? Any help will be appreciated.
They were both "out" holes. One was for the pressure gauge sender if you wanted to mount it there. The other went to the filter via a 1/4" line. With the mod I would guess that one of the holes has been modified to go to the oil gallery and the other to a filter. My guess would be that in order to ***ure enough flow to the bearings you would need a 3/8" line, in & out, minimum. Since the holes are 1/4 pipe thread it should be a simple plumbing job using off the shelf fittings. Now --------------------------------------------------------------------------------------------------------------------------------------------- Are you sure it's had the full flow mod ??? It's not likely. You need to make sure. The stock setup: The holes are stock and don't look to be altered. Any hole can go to the filter inlet through a special flare fitting with a .040" - .060" restriction and the filter return line went to a fitting on the oil pan, all using 1/4" tubing. The twin holes can can go to the oil pressure sender and the other hole used a 1/4" pipe plug (for future use). All you need is 1 reducing bushing - 1/4" - 1/8", 1 br*** flare fitting (1/8" pipe to 1/4" tubing), and 1/4" pipe plug (s) to suit.. The rest should be on your filter.
Looks very similar to the oil mods on my block . When using that modification,,,,,,,the lines are not 1/4 inch anymore . You must use a larger line and a normal oil filter,,,,,,,otherwise the engine will fail . The hole in your pic,,,up near the blue tape is not stock,,,,it has been added by someone. You need to see if the transfer galley tube has been blocked off . Try and put an Allen wrench or anything in the horizontal hole and see if it is blocked by a plug . Tommy
I installed a ‘full flow’ filter kit on a ‘53 Merc flathead about 12 years ago. It consisted of a modified oil pump that delivered the oil through a fitting in the side of the oil pan, lines to a remote filter mount, through the filter and back to the engine block to the main gallery for distribution. My recollection is the lines were 1/2” id, but possibly 3/8” id…..it’s been awhile. I feel certain anything using 1/4” lines is unsuitable for a true full flow system. Ray
Hnstray , That is the full system that is routed like that,,,,,,and in my opinion,,,is complete overkill for one of these engines,,,,unless an all out race mill . No disrespect intended . The oil pump mods are expensive and the entire kit to do the change gets in your bill fold . This other mod is almost no cash outlay ,,,,,and is described in detail in several places on the internet,,,,,very simple to do . Tommy
Thanks for the info guys. Someone spent alot of money on this motor and that is why I suspect the mods been done. But the guy that built it has p***ed away so I can't verify. I added the block off screw up to to split the holes, and working on setting up the modern style remote filter. So if not 1/4 then 3/8? And will I still need a restrictor or not? Thanks again The attached pic is what I had seen that lead me to believe the mod was done.
If you have the mods and blocked the tube,,,,,,you will definitely need a regular remote filter and do not use a restriction in the filter system . The lines should be for the 3/8 pipe thread fittings,,,,,,I think the I.d. Of the lines is near 1/2 inch inside,,,,,,,they mic close to around.450-.475,,,,,very close to 1/2 inch . Imagine the filter line routing just like the diagram in post #6,,,,,,one line out,,,the other back in,,,,,,,,the line in goes straight to the oil galley transfer tube . Tommy
Stock system If you do it this way you will be fine. Big lines are good. Some say you don't even need a filter. They say just change the oil ever 2 or 3 thousand miles. I change my oil once a year that works out to every three thousand miles. I chose to do the more extensive/expensive/time consuming oil pump and remote filter change. Shown below. It has been working fine. I always have a lot of oil pressure.
I don't know, but it looks to me like the oil p***ages visible through the holes have not even been cleaned. If that's true I would suspect stock oil system and possibly shoddy workmanship.
The Jalopy Journal
