FT REBUILD
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FT REBUILD
I'm about to pull the motor from my 69F750 and give it a rebirth. I believe I have out found from replacing a couple of things already recently that I have a 391FT. such as a larger housing on the end of the distributor, different oil pump drive size ect. I'm wondering if when I go to give the engine an overhaul, can I replace the steel 391 crank with a 428 crank designed for an FE (everything will be aftermarket), with rods and pistons to match? From what I have read the 428 crank will have a shorter and also smaller diameter crank snout, is there some way to overcome this?
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Welcome to FTE!
I moved you to Large truck as more people speak "FT" here.
I see what you are trying to do here. More beans. What kind of use does your F750 get?
There are bushings to make the FT cover work with the smaller crank. Those, iirc, are found on 330 MD engines. But I can't find one via a search, so that may be an issue.
However, it all goes back to use. Car components are not going to stand up to heavy truck usage. Compression is too high, and you can end up with burnt or sinking valves real easy.
I moved you to Large truck as more people speak "FT" here.
I see what you are trying to do here. More beans. What kind of use does your F750 get?
There are bushings to make the FT cover work with the smaller crank. Those, iirc, are found on 330 MD engines. But I can't find one via a search, so that may be an issue.
However, it all goes back to use. Car components are not going to stand up to heavy truck usage. Compression is too high, and you can end up with burnt or sinking valves real easy.
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So if I was to find this bush, or failing that have one turned up, to make the FT timing cover work, would the harmonic balancer then not work with the shorter snout? Or could a car type balancer work here providing I have the rotating assembly internally balanced? I do want to be able to use the truck as a truck if ever the need arrives but its being restored to be more of a show off promotional vehicle, not to be used for any heavy haulage on a regular basis. I originally bought it to put graft in a 6V53tt that I have in the shed, but decided to continue with the current engine. If the engine is set up to run on premium unleaded, why is the extra compression an issue? Id have thought so long as its not pinging, or running lean and detonating, this shouldn't be a problem? Here to learn though!
Cargo Master
Joined: Dec 2015
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From: Harned, Ky
The 391 crank is steel and has a much larger snout thus using a larger spacer and balancer, the rear flange is also bigger so the 391 flywheel would be loose on a FE crank with only the bolts holding it centered.
I don't know how much noticeable torque increase the 428 crank will make in that app, but the mismatch of parts needed along with the weaker 428 cast crank wouldn't be worth the hassle to me.
One of the reasons for the big snout and steel crank is some FT apps had 5-7 groove pulleys with belts operating several different devices, this puts a lot of stress on the end of the crank, FT flywheels are drilled for a 12 or 13" clutch verses a FE's 11".
I don't know how much noticeable torque increase the 428 crank will make in that app, but the mismatch of parts needed along with the weaker 428 cast crank wouldn't be worth the hassle to me.
One of the reasons for the big snout and steel crank is some FT apps had 5-7 groove pulleys with belts operating several different devices, this puts a lot of stress on the end of the crank, FT flywheels are drilled for a 12 or 13" clutch verses a FE's 11".
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yeah I get that the crank is bigger, seeing if anyone has successfully used the smaller crank in that block is all. There's nothing driving off the front of my engine so using a smaller balancer is no issue. The smaller flywheel is potentially more of an issue though, if I was to use the smaller crank and also fly wheel its potentially not going to be able to hold up to long distance towing? the truck is rated to 24-1/2tonne or 54000pounds GCM. Has anyone successfully off ground a 391 crank for some more stroke? or know of a company producing bigger stroked FT cranks?
Fleet Owner
Joined: Jan 2004
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From: Brentwood,CA
If you want a 428 just build a 428 and go completely away from the FT. It's not a good working engine in a heavy truck. Also your numbers are way to high on the towing weight. These trucks were 31,500lbs or 33,000lbs max combined gross.
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Logistics Pro
Joined: Oct 2006
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From: East Central Ia
You would be hard pressed to tell the difference of 20 cubic inches in that large of a truck. Small valve and small port. I drove a couple for couple of years. Sometimes loaded foot on the floor for miles at a time pulling hills. If Ford could have got away with cast crank it would have, I bet they tried it first during testing.
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All things considered, and that would include brakes and steering and tires, IMO if a 292 will make an empty F600 run along just fine all the way up the the limits of the steering a brakes, a properly running 391 with a 5 & 2 would be a hot rod even in the slightly heavier F750.
You're not going to fly out of control with more power, but again, all things considered, which includes liability, a 391 should carry the day.
Call me silly.
You're not going to fly out of control with more power, but again, all things considered, which includes liability, a 391 should carry the day.
Call me silly.
Fleet Mechanic
Joined: Feb 2007
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From: Mooresville, NC
"Retrofitting" FTs with FE stuff (hard to identify visually on their own in a junk yard) can be messy -- I think longer term (parts wise) the FE route (390 w/CJ heads, 428, etc) is the way to go. I have several FT engines on stands (e.g. 330, 391, etc) and they're STOUT and in some ways [webbing, cranks] far stronger than FEs, but parts interchange / availability is a nuisance / irritation --- not worth it. The problem (generally) with used FT parts is many came from fleets (330 for example in U-Haul trucks, others) and have very high mileage / usage.
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