Engine swap help
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Tuned
Joined: Apr 2023
Posts: 468
Likes: 67
From: Near SLC Utah
Engine swap help
Hey y'all, its a bit of a story so buckle up. Purchased a 1991 f-250 35w last year and has been problems ever since, testing sensors daily, trying to get it to idle, pass emissions, the list goes on. The head gasket blew and I took the heads off and replaced them, lapped the valves, and put valve shims in where needed. But recently the engine has been ingesting oil, a quart every 100 miles. Figured out that it was being ingested through the intake via the PCV I believe, it is a lot of oil to be ingested but I found a lot of oil in the upper intake manifold. Made a list and went from top to bottom. I decided to run a compression test, they are sitting around 60 PSI, I don't wanna tear it back down I am out of patience for this engine. I want to swap it with the 460, I know I will need a new transmissions, drive shafts, engine harness, and a engine computer. What do yall think? What all do you guys think i would need for a swap. Thanks!
Super Moderator
Joined: Apr 2004
Posts: 34,503
Likes: 2,820
If you are sucking that much oil via the PCV, you must have:
--an oil drain back problem.
--a bad pcv
--improper air flow for the pcv
Is your setup like so? You should have a "closed system" as illustrated. Air from the aircleaner housing goes in one valve cover, fumes etc are drawn out of the other one via the pcv to a port on the intake.
The Basics of Positive Crankcase Ventilation (PCV)
--an oil drain back problem.
--a bad pcv
--improper air flow for the pcv
Is your setup like so? You should have a "closed system" as illustrated. Air from the aircleaner housing goes in one valve cover, fumes etc are drawn out of the other one via the pcv to a port on the intake.
The Basics of Positive Crankcase Ventilation (PCV)
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
Why make life so much tougher? Just get a replacement 351W and be done with it.
I you want to do the swap: If you get the same model transmission you will not have to change the driveshafts. Do not use any of the donor engine's harness. Keep the harness that you already have. Extend any sensor wires as needed. Yes, you will need a computer for a 7.5L engine. You may need to remote mount the oil filter or use a 90 degree adapter. That may not apply for a F250/350.
I you want to do the swap: If you get the same model transmission you will not have to change the driveshafts. Do not use any of the donor engine's harness. Keep the harness that you already have. Extend any sensor wires as needed. Yes, you will need a computer for a 7.5L engine. You may need to remote mount the oil filter or use a 90 degree adapter. That may not apply for a F250/350.
Cargo Master
Joined: Oct 2011
Posts: 2,251
Likes: 304
From: Kenner,La.
Oil consumption
As far as PCV valves are concerned be sure it is a genuine Ford part. Years ago I had a used 86 CV that would blow out a cloud of smoke every so often. I even changed the valve guide seals with with no improvement. I mentioned it to a Ford dealer shop foreman and he said to get one from the parts counter. Problem solved.
Thread Starter
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Tuned
Joined: Apr 2023
Posts: 468
Likes: 67
From: Near SLC Utah
If you are sucking that much oil via the PCV, you must have:
--an oil drain back problem.
--a bad pcv
--improper air flow for the pcv
Is your setup like so? You should have a "closed system" as illustrated. Air from the aircleaner housing goes in one valve cover, fumes etc are drawn out of the other one via the pcv to a port on the intake.
The Basics of Positive Crankcase Ventilation (PCV)
--an oil drain back problem.
--a bad pcv
--improper air flow for the pcv
Is your setup like so? You should have a "closed system" as illustrated. Air from the aircleaner housing goes in one valve cover, fumes etc are drawn out of the other one via the pcv to a port on the intake.
The Basics of Positive Crankcase Ventilation (PCV)
Thread Starter
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Tuned
Joined: Apr 2023
Posts: 468
Likes: 67
From: Near SLC Utah
The PCV on it right now is a MircoGard from O'Riellys . So I found the donor engine and transmission its the M5OD I have the same one but for small blocks on the 351w right now, I was wondering about the transfer case I have on it right now, I will get the tag for it when I get a chance. I imagine the fuel system wont need to be changed its got the dual tanks. Do you guys think I would need new motor mounts? I appreciate all the help, none of my friends have done an engine swap this big.
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Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
M5OD was never installed behind a 460. It would be a ZF5. Very different animal. L
Motot mounts and frame perches are different.
Motot mounts and frame perches are different.
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Fleet Mechanic
Joined: Jul 2019
Posts: 1,317
Likes: 313
Why make life so much tougher? Just get a replacement 351W and be done with it.
I you want to do the swap: If you get the same model transmission you will not have to change the driveshafts. Do not use any of the donor engine's harness. Keep the harness that you already have. Extend any sensor wires as needed. Yes, you will need a computer for a 7.5L engine. You may need to remote mount the oil filter or use a 90 degree adapter. That may not apply for a F250/350.
I you want to do the swap: If you get the same model transmission you will not have to change the driveshafts. Do not use any of the donor engine's harness. Keep the harness that you already have. Extend any sensor wires as needed. Yes, you will need a computer for a 7.5L engine. You may need to remote mount the oil filter or use a 90 degree adapter. That may not apply for a F250/350.
Thread Starter
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Tuned
Joined: Apr 2023
Posts: 468
Likes: 67
From: Near SLC Utah
So my truck is a 91 the donor is a 92, worse comes to worse and the wires don't match up I will just get another harness, I imagine I can frankenstien it together. The only thing I am worried about is if there is something on the 351 that the 460 doesn't have or vise versa. I will look into the smog system when I get a chance.
Fleet Mechanic
Joined: Mar 2014
Posts: 1,926
Likes: 116
From: Saskatchewan Canada
Nothing is going to match up between 91 and 92 harnesses. You would best start looking for a 91 7.5L wiring harness. You may be able to use an engine harness between 87 and 91, but 92 was a year of big changes.
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