How to ID the heavy duty 300 six
 

Hello,
How do you identify the 300 six heavy duty engine from the standard engine? I have a 78 F150 4x4 that has a GVW of over 6000 pounds. it should have the heavy duty engine but, I don't know what engine I have.
Thanks, Joel

As far as I know, the HD 300 was the same as the regular 300. The only differences are a different exhaust manifold (the outlet goes straight down instead of curving towards the rear), some had a forged steel crank shaft (but not all), and there's some debate as to the possibility they had a different cam. Other than that, there isn't a whole lot of difference between the two.

I doubt a F-150 ever had the HD engine unless it was swapped in. The HD 300 would be found in a F-600 class truck.

Hello Harte3
Actually, the 1978 Ford truck shop manual says trucks with 6000 gvw has the heavy duty 300 six.
Regards, Joel

I should know the difference as I took care of a bunch of these in a fleet. The p 500 had a different head than the 600. It seems to me the 600 had sodium cooled exhaust valves the exhaust manifold as someone else said the forged crank as far as I know the cam was the same except it drove thru steel timing gears{and they were not noisey}. All those engines were reliable and had good long lives if maintained. We had some abusive drivers and they held up. Newspaper fleet GVW ment nothing, when I'd see them loaded up I often got into some difference with the delivery supevisors. kotzy

Most of the HD engines I've seen also had lower compression then the standard 300's. They had different pistons ( they were either a shorter compression height or larger dish ) .

Really there isn't anything too special about the HD's unless you had one of the early ones with the forged cranks.

Bumping a very old post here, but the 1978 service manual says:

The special 4.9L (300 CID) I-6 HD engine .. is the same as the light duty engine except for heavy duty pistons, intake and exhaust valves, valve springs, water pump, radiator and radiator hoses. The special engines also have a magnetic oil drain in place of the standard plug.

Are these really that special / rare / tough? I think I've come across one in my travels and am tempted to pick it up, if the price is right.

There's no mention of the forged steel crank shaft?

All of those things you listed are things you can do when you rebuild the standard engine. But the forged steel crank is the rare, and sought after, piece.

They mention the crank a little earlier... shown below...

https://cimg3.ibsrv.net/gimg/www.for...b4384d1de1.png

The main parts to the HD that most people are interested in are the steel cranks and the HD exhaust manifolds. Either of those parts can bring more money then a complete standard 300 engine. The 300 HD engine itself is not really that special. It's a low compression engine designed to be worked hard in a big truck ( like a F600 ) .

I wouldn't pass up a deal on one, just for the resale value of the above parts. But like AB was saying you can accomplish more by just building a standard 300.

Reproduction manifolds are available for $250 (last time I checked) and EFI manifolds are almost as good. That kind of puts a cap on what someone is willing to pay for a used manifold. Also, people interested 300s aren't typically high spenders (they would be Jaguar or BMW i6 enthusiasts if they were).

Buying old domestic truck stuff based on an expectation that you can resell it for more is generally a losing proposition unless you only buy things that are selling for pennies or do dishonest things to dress stuff up so people pay more.

I've made money on every 240/300 I've ever bought. There is always someone looking for stock carbs, manifolds, pulleys, brackets, distributors, etc. And I've never had anyone complain about the parts I sold. I buy most of mine for around $50 each but won't pay more then $100 for a engine. At those prices I can make a profit on them and still get the crank, rods, blocks and heads that I want for free.

And on the HD manifolds there are also plenty of people that buy those repop manifolds. And had fitment issues and were unhappy with them. So there are people out there that prefer original ones. I personally don't like the HD manifold anyways. They are still a log manifold no matter what size the outlet is. I will always prefer a ported pair of EFI ex. manifolds over a HD one. Or even better yet a pair of full length headers .

There is always someone out there looking for a steel crank. So selling one is pretty easy. As long as you don't get greedy and try to sell them for $700-$800 like I've seen some on Ebay recently. $200-$300 is more realistic.

If you don't over pay for a HD engine it's hard to go wrong buying one. The problem is unless you can visually confirm it's a steel crank, before you buy the engine. You have to assume it's a cast crank and pay a price that is fitting for a cast crank. I won't pay over $100 for any 240/300 no matter if it's a industrial, HD, LD whatever. Because unless I build it myself a used engine is just a core. And you have to pay the appropriate core price. Unless it has an aftermarket intake or finned aluminum valve cover, $100 is the max price for me to buy one.

I have definitely appreciated using the stock equipment on mine. There's something awesome about the fact that it still works and something nostalgic about the fact that it's stock. I'll keep you posted on the purchase.

Just make sure to block of the heat riser on the HD exhaust manifold of you plan to run one. They don't have the butterfly/shut off valve that the standard manifolds do. If you don't block it off, you will have fuel issues( vapor lock, etc. ).

I have wondered why Ford did that [open heat riser] on the HD engine? The only thing that makes sense to me is that these engines were made to run @ 3,000+ RPMs and maybe [?] the temperature was kept at a minimum with the extra exhaust gas flow.