Bought a 78 F250 300six a few weeks ago, spent all the time between then and today getting it rolling and took it out for its first real trip this morning. The thing smokes like a freight train, runs like a mortally wounded dog, and has no power. Now I've never driven a properly maintained 300six before but I know people that have and I've read the forums on here. Mine won't accelerate uphill, in fact it slows down. And we're not talking about steep hills here either. So I have a smoky six with no power. I've thought about it and I've decided I'm going to rebuild the motor. It needs it. Its got some kind of mortal problem. Hole in a piston, rings stuck, burnt valves, broken head gasket, cam lobes worn away, something serious. I have no idea what it actually is mind you.

Now heres my questions.

Do they make a master rebuild kit for this motor to take it back to stock? Just a regular, pistons, rings, bearings, and gaskets, maybe a timing set or oil pump, a rebuild kit.

If they do make one, who sells it? I've looked on summit and jegs and rock auto. Rock auto sells one but its outrageous for as popular as this motor is and what it is they're offering for it.

If nobody makes a master rebuild kit for it I'm just gonna tear it down, new cam and lifters, new valve springs, P&P the head, new pistons and rings, and new main bearings with all new gaskets and then whatever else looks worn while I'm in there. Anyone want to add to that?


What I'd like to do is get the Offy DP manifold and put a quadrajet on it, run a header going into duals with cherry bombs, comp 260 cam, chevy 292 rockers, the usual stuff without having to take the motor out of the truck.

 

I wouldn't run duals off an inline 6 300, your low end torque will suffer as a result, i'd run a single 2.5" exhaust.

 

Your going to rebuild this motor without taking it of the truck? If your going thru the trouble of rebuilding the motor it might be wise to take it in and have it hot tanked and checked out.

 

Its not that I don't believe you Montana_highboy but why exactly would my low end suffer? I've always wondered about the whole thing. Isn't less resistance always better?

Next I don't think rebuilding a motor is that much trouble at all. My plan as it stands is to drop the pan and pull the head and just take a good hard look at everything and then decide my next plan of attack. Could be I rebuild it in the truck, could be I pull the motor, could be I buy a short block from someone off here or maybe my head is cracked and I dont need to touch the bottom end at all. But if the cylinder walls look good and I don't have any roasted bearings then I can replace the main bearings without removing the crank and the connecting rod bearings will be a cinch when I replace the rings and/or pistons, and the head would be rebuilt on a bench either way. I'm not trying to do anything real fancy here, I just need a reliable truck to get me through this winter. Come the spring I might pull it and do it all up right but for now I just need a running truck.

 

Read this thread here... https://www.ford-trucks.com/forums/8...00-engine.html... in the the end every guy is going to make up his own mind but there is legitimate science behind exhaust theory.

 

I agree that the motor can be refreshed as it sits in the truck. Ive done it on an old dodge Ram minivan. Replaced a piston with a hole in it and went. Get this the van had a Mitsubishi motor. If your gonna keep the truck for a while, I would personally pull it and get new freeze plugs and cam bearings installed.

 

An "in-frame major" for a 300. You're wasting your time and energy. Pull it, hot tank it, get the oil pan back on it right, the mains torqued correctly, and put it together clean, not with some swirl of dust or dirt of cat poop in it.

jmo, ymmv.

Check these pics out if you want to risk putting it together with some dirt:

https://www.ford-trucks.com/forums/8...-1k-miles.html

 

Thanks for the info Montana_highboy, now I know.

And I can believe that minivan had a mitsubishi motor, the ford SHO taurus had a yamaha motor in it. I'm pretty sure I can replace the cam bearings in the truck but Id have to look into the freeze plugs. And like I said I may do this right in the spring, it just has to make it to spring.

 

Why don't you diagnose the engine to see how bad it is?

Those 300s could smoke all day, but still will run at night.

 

85e150six4mtod you make it sound like I'll be rebuilding it in the middle of a sand storm, I've rebuilt I don't know how many motors between the rails and never had any problems, its not that hard to keep things clean if you put forth even a small degree of effort, this ain't my first rodeo. The oil pan only goes on one way, and torque wrenches shockingly enough work upside down just as well as they do the other way. I work 6 days a week and I dont have time to fool with pulling the motor just to make it look shiny when theres no other reason in the world (yet) to pull it. Its like I said in another reply, if I get the head off and the motor needs pulled I'll pull it but if theres no reason for it then I won't waste my time.

Jermafenser I did diagnose it, its wore out haha. The carburetor is rebuilt and tuned, the timing is correct, the ignition system has been gone over and repaired. When I got the truck it didnt have any oil in it. I filled it up with oil before I fired it up the first time weeks ago. After my trip out today, it was a quart low, and it didn't leak out. Its got blow-by like you wouldn't believe. I have no doubt in my mind that it'll keep on keepin on but I don't want to have to throw a quart of oil in it every day, you know? I'd have to say its got some valve seals that don't seal anymore, sure I could throw in some valve seals and see what happens, I'd rather pop the head off and make sure thats the only thing thats going on.

 

I'd also recommend a compression check before you pull the head. haha i almost put head(s). Since it's the same cylinder displacement as a 400 (dunno exact stats for the 300 a manual may have that info), I would guesstimate it would be around 160 psi. If the rings check ok, as I suspect should, then I would check the valve guide clearances and valve seal condition. Hope this points out where the oil is going.

 

compression checked, compression failed, the motors comin out.

 

you might still want to pop the head off first. beings that it is a 70's motor, it is designed to run on leaded fuel. running on unleaded for so long might just have fried you valve seats. and you might just have wore out guides lettin oil run like crazy. im not sayin that you dont have bad blow by, but you might just see how much of it might be the head.

 

Uh, no.

Valve seats can crack from the engine overheating frequently, constant/great differences in temperatures...or from detonation, excessive valve lash, etc. Gas wouldn't even begin to harm the valve seats unless the gas is the direct result of detonation. All 1973/79 trucks already were designed to run either unleaded or leaded.

Oh, really? Worn guides = blowby, period.

 

now see what happens when i start posting in the middle of the night? lol. HOWEVER. i do know of a case on a 74 f250, think it had a 360, where the heads were not made for unleaded, and it wrecked his valve seats. but for the most part, im just an idiot!