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Any Ford 300 six guys on board ??

General engine tech -- Drag Racing to Circle Track

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GLHS60
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Any Ford 300 six guys on board ??

Post by GLHS60 » Sun Nov 03, 2019 7:44 pm

I'm replacing a cracked exhaust manifold on my 1981 FI50 with a 300 inline 6

I noticed the original exhaust manifold had no gasket between the manifold and head.

However, all the replacement intake gaskets I've found have a joint intake/exhaust gasket.

I've searched many sites have found varying opinions on using the gasket as is.

Some separate the exhaust portion from the intake gasket and some don't.

It seems common for the exhaust gasket to leak after installation so I'm trying to decide.

Anyone have any experience with this issue??

Thanks
Randy
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woody b
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Re: Any Ford 300 six guys on board ??

Post by woody b » Sun Nov 03, 2019 7:54 pm

Separate the gaskets and only use the intake part. The exhaust gasket will shrink, the blow out, causing a leak. It's been years, but I've done a bunch of them.
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Re: Any Ford 300 six guys on board ??

Post by enigma57 » Mon Nov 04, 2019 5:41 am

Your 1981 300 inline 6 uses a typical cast-iron 1-piece log type exhaust manifold and 1-piece log type intake manifold that are bolted together under the carb plenum. Check all gasket sealing surfaces including those for the riser gasket beneath the plenum. If any are rusted/pitted but not so bad that they cannot be milled a small amount to make a smooth sealing surface, take care of that before joining them together.

After you have replaced the under plenum riser gasket between them and joined your intake and exhaust manifolds together (loosely at first)...... Trial fit the manifolds without intake and exhaust gaskets to your head. Snug up bolts (or studs) holding manifolds to head evenly to 10 ft./lb. Then, tighten the bolts (or studs) holding intake and exhaust manifolds together. This is necessary to align them properly with one another.

Remove manifolds as a unit and look closely at the gasket sealing surfaces of both manifolds where they bolt to cylinder head. Again...... Check both with a metal straight edge or framing square and if they are uneven, warped, rusted or slightly pitted...... Have a machine shop do a skim cut to true them. And do this with them bolted together as a unit just as you now have them.

Same thing (if needed) to corresponding gasket sealing surface on cylinder head. Check for rust, pitting and make sure no warpage. If those surfaces are straight and true and not pitted, any good aftermarket or OEM style gasket should seal them if you torque them properly and then come back the following day and retorque before starting engine.

Also recheck torque following first heating/cooling cycle after running engine and you should be good to go. Begin at center of intake/exhaust and work concentrically from center outwards in 2 or 3 incremental steps same as you would when bolting the head to the block. 20 ft./lb. should be sufficient torque for fasteners holding manifolds to head on these engines.

I have disassembled a few OEM installations (both inline and V-type engines) where no gasket was used at the factory exhaust manifold. And I have read Sanderson's installation instructions stating that a thin coat of high temp silicone RTV can be substituted for gaskets on their exhaust headers.

However, I am uncomfortable doing a gasketless reinstallation personally, so I have always used a good quality aftermarket or OEM exhaust manifold gasket going back on. And if its the multi-layer steel core laminate type exhaust manifold gasket found in most Chevy gasket sets...... Or even a high end aftermarket dead soft aluminum or copper gasket...... I coat both sides of the gasket(s) with Copper Coat when reinstalling the intake and exhaust manifold on an inline 6. Whether it uses a 1-piece gasket for both or separate intake and exhaust gaskets. Same for donut gasket where exhaust pipe connects to exhaust manifold.

Exhaust studs and nuts where exhaust pipe bolts to manifold...... Cheap insurance...... Use new if you are going to keep the truck for some years more. Me...... On a keeper, I like heat treated carbon steel studs (grade 5 minimum, grade 8 if you can find them) and thick brass nuts as used on older cars and trucks and having an additional thread or 2 for increased thread engagement. But that's just a personal preference. If you are considering stainless steel fasteners, read this beforehand with respect to galling and consider brass nuts rather than stainless nuts on stainless studs for exhaust......

https://www.boltdepot.com/fastener-info ... lling.aspx

Hope this gives you some ideas,

Harry

P.S. >>> Here are gaskets for your installation from a couple sources. You can probably find (or order) the same gaskets at your local auto parts store, as well......

If you opt for separate intake and exhaust gaskets......

1. Fel-Pro Intake Manifold Gaskets MS901571......

https://www.summitracing.com/parts/fel- ... /make/ford

2. Mahle Intake Manifold Gaskets MS16040X......

https://www.summitracing.com/parts/mah- ... /overview/

3. Fel-Pro #1447 exhaust manifold gasket set......

https://www.summitracing.com/parts/fel- ... /make/ford

4. If you opt for 1-piece intake and exhaust gasket plus separate riser gasket......

5. Remflex #3005 1-piece intake/exhaust gasket set + riser gasket (not the cheapest, but a very good gasket and worth every penny) I am using the equivalent Remflex 1-piece gasket for my 292 Chevy inline 6......

https://www.summitracing.com/parts/rfl-3005

http://catalog.remflex.com/FORD_Header_ ... p/3005.htm

6. AP Exhaust #8717 or EXD #HG017 Donut gasket for exhaust pipe......

https://www.summitracing.com/parts/aph- ... /make/ford

http://exhaustdirect.com/HG017.html

Note: Not sure if you can get them anymore, but 390 Ford engines in the early 1960s used a donut gasket that was identical dimensionally to the one used by GM for 2" exhaust except that Ford made their gasket from a soft metal (looked like aluminum) and these would last forever on mid-'50s and early '60s Chevys. If this is the type and size donut gasket your '81 300 Ford inline 6 uses, see if you can find a couple of the 390 Ford soft metal donut gaskets and hang on to the 2nd one as a spare. They really were one of Ford's 'better ideas'.

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Re: Any Ford 300 six guys on board ??

Post by woody b » Mon Nov 04, 2019 6:59 am

Harry is describing the manifolds perfectly but these didn't have exhaust gaskets from the factory. Just the exhaust manifold bolted to the head. On older vehicles with cast iron manifolds any time I used the gaskets that came in the kit they ended up burning up and leaking.
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Re: Any Ford 300 six guys on board ??

Post by enigma57 » Mon Nov 04, 2019 7:49 am

:D I know, Woody. Not disagreeing at all. They may work just fine without gaskets if all the seating surfaces are straight and true.

I just never was comfortable running them without gaskets, so I always used gaskets when putting them back together. Had good luck with regular cast-iron exhaust manifolds using steel core laminate gaskets and Copper Coat.

Headers were a different matter altogether, though. Never had a set of tube type headers that didn't leak no matter how careful I was. Back then, we had header gaskets cut from sheets of asbestos. I'd soak them in water overnight before installing them and retorque them after running the engine the following day. All that stuff. But nothing seemed to work.

Best regards,

Harry

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Re: Any Ford 300 six guys on board ??

Post by Steve.k » Mon Nov 04, 2019 10:22 am

Those manifolds constantly warp out of shape. These guys have a good selection of parts for 300 6. https://cliffordperformance.net/store?o ... ord-240300

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Re: Any Ford 300 six guys on board ??

Post by PackardV8 » Mon Nov 04, 2019 11:24 am

My machinist removes exhaust gaskets from the remainder of the gasket sets he sends with the short block or long block. Sometimes a buyer will come back complaining about missing exhaust gaskets and my guy has to spend time explaining how he did him a favor. His favorite story is the guy who came back some months later complaining about valve tick. My machinist listened and immediately heard exhaust leak. Questioned, the customer refused to believe him it shouldn't go together without exhaust gaskets, so the customer bought them and installed them. They'd burned out in less than six months.
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Re: Any Ford 300 six guys on board ??

Post by Kevin Johnson » Mon Nov 04, 2019 11:37 am

https://www.slantsix.org/articles/manifold-install/types-mounting.htm wrote: The important thing to remember is that this big, long exhaust manifold is designed to "slide" across the gasket surface and move around as it heats & cools. A stamped steel gasket is the best for allowing movement but is also the hardest to seal. The thick material gaskets are the opposite, easier to seal but they don't allow much manifold movement, which can lead to a cracked manifold.

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Re: Any Ford 300 six guys on board ??

Post by Steve.k » Mon Nov 04, 2019 12:47 pm

The last 300 i did i had it planed straight again. With the steel gasket last 3-4 years before it started to leak. However i never tightened back up or retourqed after some run time which likely would have helped.

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Re: Any Ford 300 six guys on board ??

Post by enigma57 » Mon Nov 04, 2019 4:32 pm

Wow! Learning a lot here. Especially liked the slant 6 article. There were a few things there that I had not considered. Will keep them in mind when I install my 292 manifolds.

I had a slant 6 many moons ago ('62 Dodge Lancer) and it had a cracked exhaust manifold which I replaced with one from a '76 Dodge Dart that had the larger 2-1/4" outlet size. Really woke up the little 170 when the exhaust was uncorked and entire system was replaced with larger pipe and a turbo muffler.

Best regards to all,

Harry

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Re: Any Ford 300 six guys on board ??

Post by GLHS60 » Wed Nov 06, 2019 3:49 pm

I sure appreciate the comments and links!!

Respectfully, I'll be following the recommendations of woody b and Jack Vines.

Thanks
Randy
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Alberta,Canada

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Re: Any Ford 300 six guys on board ??

Post by enigma57 » Wed Nov 06, 2019 5:40 pm

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GLHS60
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Re: Any Ford 300 six guys on board ??

Post by GLHS60 » Wed Nov 06, 2019 7:56 pm

I appreciate the good wishes Harry!!

Although I wont be using an exhaust gasket I'll follow your advice aligning the manifolds.

Thanks
Randy
enigma57 wrote:
Wed Nov 06, 2019 5:40 pm
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Re: Any Ford 300 six guys on board ??

Post by enigma57 » Wed Nov 06, 2019 10:55 pm

Wish you all the best. One thing I might suggest...... You will need the riser gasket that installs beneath the carb plenum where the intake and exhaust manifolds join together.

When you are ready to install your intake and exhaust manifolds as a unit...... Leave the bolts that hold the intake and exhaust together at the plenum just a bit tighter than hand tight.

Then tighten the bolts (or studs) that hold your intake and exhaust to your head to say 10 ft./lb. Start in the middle and work concentrically outward as if you were bolting a head to an engine block.

(This tightening sequence will allow your intake and exhaust to align with your head surface before you tighten your plenum bolts.)

Now tighten your bolts joining the intake and exhaust at the plenum to 15 ft./lb.

And lastly...... Finish tightening the bolts (or studs) that hold your intake and exhaust to your head to 20 ft./lb. As before, start in the middle and work concentrically outward as if you were bolting a head to an engine block.

Happy Motoring,

Harry

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Re: Any Ford 300 six guys on board ??

Post by cardo0 » Fri Nov 08, 2019 12:55 am

Yea I had a Ford 300 six in a late 80's pickup. It had the unbend-able I-beam front end and just a great running motor. Late 80's truck but almost no smog gear on it. I could just step into the engine compartment when I needed to work on it. Drove to long to my first tune up found the rotor tip was just a small toothpick when I got around to replace it. :o Anyways I recall that Ford forgot to use gaskets on the exhaust manifolds. And I think the procedure was just to tighten the shared bolted clamps with the intake if leaks started. Been so long ago I can't recall if I had a shop install gaskets or not but I do remember I was surprised when I saw the exhaust manifold was naked. Sorry if that's not much help but I think that was the only flaw in that truck that I can remember.

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