About 4 months ago I bought a 1976 F-100 with the FE390 on it. The truck had one owner, it was used until 1987, that was the year on the license plate, so I will say it was sitting under the sun for about 20 years. When I bought the truck I replace some parts and start the engine. The engine starts without a problem, but it seems that the passenger side has less power than the driver side. I did a compression test by following a mechanical manual ( I am not a mechanic), on the driver side the compression was about 120-130 psi, on the passenger side it was between 30-40 psi, so I did a wet test as specified on the manual, but the compression stay the same, based on the book this could be because of the valves, but the book also mentions that if two adjacent cylinders have the same low compression it could be due to a head gasket.

I do not want it to do an overhaul on the engine right now, the truck needs also work on the suspension, so I was going to start with the underbody of the truck and work my way up. My question is, that if the problem with the compression could be because of the gasket, and if it is, could I replace the gasket. Also, would I need to replace the valves so the truck can run with unleaded gas.

Any advise is greatly appreciated.

Thanks

 

Congrats on the '76!

For the 390FE to run unleaded...it is recommended that you do a valve job. Based on your description, I am leaning towards a valve job anyway. Think of it this way. You need to replace the head gasket to do the valve job...so might as well take the head in...and get it checked. They can let you know within minutes if you have bad valves.

IMO...it is better to do the engine, tranny, axles, etc. mechanicals first...before spending money on the rest. Even if it is just changing out all the fluids...and checking those items out...at the same time.

Good luck...and enjoy!


biz

 

I don't think in 40 years as a mechanic I ever saw a head gasket blown on all 4 cylinders on one bank. The chances of it happening are astronomical. It sounds like the valves are not sealing on the passenger side. When you do the valve job, do both heads.

 

Biz4two and Bear 45/70 can I just do the valve job on both heads for now, and not do a complete overhaul, at least this way I can move the truck around.

Thanks for your help.

 

Sure you can but with an engine that has sat that long you take a chance of having rings stuck too and then you will be tearing it down again to fix that if at least you don't pull the pistons an make sure they are free. But I've seen valve jobs only done lots of times with good results.

 

Yes...a valve job can be done...without doing major engine work to the block and lower end. From there...you can eval what you need done...and take it a step at a time.

Good luck with it...and keep us posted on your progress.

biz

 

I removed the heads and the intake manifold, some of the valves were cracked, and some of them had a football shape instead of a round shape. I decided to do a complete overhaul, I have seen this combination of engine components before on another thread.

KB150 pistons
Crane 343901 camshaft

I would like to install a Edelbrock intake and carburator, also port and polish the stock heads.

How will the fuel efficiency be on this truck with these componenets.

Thanks for all your help.

 

Me thinks the truck was running real poorly and that's why they parked it all those years ago.

 

Hi all , you mite like this one , when i found my old truck in this paddock on a farm in australia , it started up and ran , i floated it home , i check the timming , carb , leads , and it still ran like a dog , i took the sump off i found four conrods on one side turn the wrong way , short one side long one side
now i no y it ran like a dog on three legs , that was 7 years ago and it was a 292 in a 1963 f700 now a 361 is going in fully rebuild i only use three old parts
block,crank,rods after that the lot new

 

What about the new engine componets, will it be fuel efficient, or will it be using a lot of fuel.

Thanks

 

Ive got similar Pistons, my cam is way different thou. I get 11-12 mpg on the hwy. fuel economy and these trucks dont mix...v8's are really hard to get fuel MPG Out of - these trucks dont have overdrive - AND they are like driving bricks.. heavy and square..

 

Will I be better off swaping the FE390 engine for a 302. Will the 302 be more fuel efficient than the 390.

Thanks

 

Actually...you would be better off going with a 360FE over the 390FE in regards to a better fuel efficient engine. IMO...I would go with a RV cam (Erson comes to mind), Edelbrock intake and 600cfm carb. Believe it or not...going with long tube headers will make a huge gain. If you are going to run dual exhaust...then a 2.5" works best. Or a single 3"...

The 302 is a fine engine, but it is a different family of engines. So...expect to change motor mounts, tranny issues, etc. IMO...any savings in cost of fuel will be spent making the mods work.

Back in the day when I had a 360FE in my '76 4x4 with the mods listed above...I would get 18mpg doing 55mph. Now with my 390FE with a slightly different build...gets me 14mpg at 70mph.

Good luck...

biz

 

As far as swapping in a 302 it depends on what you want to do with the truck. The 302 was designed as a car motor and in that application it's awesome. If this is a 2wd truck you just want to cruise around in then it will work fine, and yes it could get a lot better mpg than an fe. You'll need new perches for your motor mounts, easy enough to pull out of jy and either a new tranny or a new bellhousing and maybe need a new driveshaft but other than that pretty simple. Or you can keep the fe and build it like a big block, it all depends on what you want to do.

 

Rebuild the 390. For what you'll spend swapping to a 302, you can buy a LOT of gas. Rebuild the 390, add an RV style cam, Edelbrock Performer intake, top it with a 600 cfm vacuum secondary carb, or keep the stock 2 bbl intake and top it with a Holley 350 cfm 2 bbl. Add headers. Keep your foot out of it and with the C6 and something like 2.50 to 3.00 gears in the rear, it'll get mid teens or better in mileage.