300 6cyl swap

bubba22349

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Yes if the 86 short block has those Pistons in it I think it will be right, but there are some strange aftermarket Pistons I have seen used by rebuilders sometimes, they look like a flat top with round hole that is offset to the one side of the piston top. Yes am fairly certain everything from the EFI engine should transfer over to the 1986 short block once the EFI head is swapped on. The EFI front crankshaft Dampner and timing tab bracket on the left front side of the 1991 engine is also part of the front dress parts that you would also need to change too.
 

Mr. Bob

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You never know what the rebuilder did, but if they stuck with stock type pistons, it should look like the pic below. I'm not sure if Ford used the same EXACT pistons over the years, but the same parts are listed for every motor from 1975-1995. It's going to be a lot more work than it sounds like just swapping the block over, because as Bubba pointed out, you will need to swap over all the front bits, but they should all bolt on the same... I think. I'm no expert, and this may be uncharted territory, but I'm fairly certain that the only change in the actual block was to cast in a plate to cover the fuel pump hole. You'll need to cover that if you use the 86 motor, but they make plates specifically for that purpose (or you could easily make your ow

Good afternoon Mr. Bob, and welcome. I have a 1990 F-150 that I converted FROM factory EFI to carburetor. The project was much more arduous than I anticipated. If you want to convert the 91 to carburetor, you will have to reconfigure the entire fuel pump system. The EFI pressure is 10x more than a carburetor can withstand. Also, if you have an automatic transmission in the 91, it will not shift correctly without the signal the EFI ignition system generates. There are other issues, like throttle linkage, etc. This is NOT a plug and play deal. I have many years of experience, but that project kicked my butt, and I regret I did it. As one who has gone that route, I strongly recommend you keep the 91 as EFI. As others suggested, put the EFI head on the 86 block, and put it back in as it was originally. Yes you can swap your accessories from the 91 to the 86 block. Two things not to overlook: You will have to get a block-off plate for the 86 mechanical fuel pump. Also, you will need to put a 91 water pump on the 86. The serpentine belt drives the water pump in the opposite direction as the V belt pu And yes I'm trying to keep the 91 EFI

Yes everthing should transfer from one block to the next. The front crankshaft Dampner is also part of the front dress parts you would need to change too.

Dampener? Is that the same thing as a harmonic balancer
 

Mr. Bob

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Good afternoon Mr. Bob, and welcome. I have a 1990 F-150 that I converted FROM factory EFI to carburetor. The project was much more arduous than I anticipated. If you want to convert the 91 to carburetor, you will have to reconfigure the entire fuel pump system. The EFI pressure is 10x more than a carburetor can withstand. Also, if you have an automatic transmission in the 91, it will not shift correctly without the signal the EFI ignition system generates. There are other issues, like throttle linkage, etc. This is NOT a plug and play deal. I have many years of experience, but that project kicked my butt, and I regret I did it. As one who has gone that route, I strongly recommend you keep the 91 as EFI. As others suggested, put the EFI head on the 86 block, and put it back in as it was originally. Yes you can swap your accessories from the 91 to the 86 block. Two things not to overlook: You will have to get a block-off plate for the 86 mechanical fuel pump. Also, you will need to put a 91 water pump on the 86. The serpentine belt drives the water pump in the opposite direction as the V belt pumps.
So I'm good to go if I order a new or remanufactured head for a 91 bolt it down on the block of the engine out of the 86? Couldn't I use the water pump on the 86 and just put the Serpentine pullies on it?
 

bubba22349

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Yes they they can called both those names by different people. But again since the EFI has that Surpentine belt drive it will need that matching bottom pulley on the Dampner to drive that belt. No on using the 1986 water pump the water pumps on the EFI turn backwards plus they have a different front hub. Edited
 

Mr. Bob

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Yes they they can called both those names by different people. But again since the EFI has that Surpentine belt drive it will need that matching bottom pulley on the Dampner to drive that belt.
So can I use the same harmonic balancer that's on the 86 engine and just change the pulley?
 

Pontus

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Ok I see what you were talking about I'll have to order a new one just so I won't have to go back and replace it later
That'd be best since the rubber tends to rot out between the pieces and cause issues. Speaking of which, not to hijack, but it's probably relevant... Looking at the parts available, some seem thicker and come with an "exciter ring". What's the difference? The ones with the extra width seem to be whole castings not an extra part, so why would one want one without the cast on ring? Isn't that a necessary part?
1626393324878.png1626393337943.png

And for my carbed EFI motor that I'm building, do I even need the extra ring? Would the extra weight save wear on the #1 piston and bearing or cause more?
 

Mr. Bob

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That'd be best since the rubber tends to rot out between the pieces and cause issues. Speaking of which, not to hijack, but it's probably relevant... Looking at the parts available, some seem thicker and come with an "exciter ring". What's the difference? The ones with the extra width seem to be whole castings not an extra part, so why would one want one without the cast on ring? Isn't that a necessary part?
View attachment 7648View attachment 7649

And for my carbed EFI motor that I'm building, do I even need the extra ring? Would the extra weight save wear on the #1 piston and bearing or cause more?
I've never even heard of an Exciter ring so I don't know what one is I don't mind you asking you a question hijacking as you call it we can all use the information
 

bubba22349

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The late 1995 1/2 4.9's to the last 4.9's in 1997 used a different EFI systems that is MAS, they also used yet again another different crankshaft Dampner design,

Pontus, you wouldn't need that later (1995 1/2 to 1997) Dampner to use on a carb system. Are you going to use the surpenetine drive? If not and your using the older V belts then you would need to use the 1986 down Dampner.

Mr. Bob, The exciter ring is used for a crank trigger ignistion system the 1991 EFI engine dosnt have that type ignistion.
 

Pontus

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Well, the thing is that my 95 motor came with the thicker dampener. And why make the exciter out of 10lbs of extra iron? I am planning on keeping the serpentine belt, so I need to figure out which one to get. I was going to use the old one until I read reports of it failing and considered the fact that it's 26yrs old exposed to Wisco road salt.
 

bubba22349

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Yours must be the late 1995 MAS EFI then! But you said you going to go with a carb now right I assum that your going with a different distributor also like a DuraSpark II or another. So if your not using the 1995 ignistion that needs an ECM to control it there would be no need to use a Dampner with an exciter ring so you could probally use that 1987 to 1995 EFI Dampener in your above pictures to be able to keep the Surpentine drive system. As far as using the heavier Dampner though in wouldn't matter much if it was an extra 10 Lbs. Since it's still balanced to a zero imbalance / neutral just like all the other 240, 300, or 4.9's. Dampeners, they all are is spinning in the circle around the crankshafts centerline so there is no side loads to crankshaft or the #1 Rod and piston so it also can't improve or cause extra wear to those parts either. The one thing it being heavier dose is take a little longer to spin up and spin back down again.
 

THE FRENCHTOWN FLYER

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One thing I learned from working on serpentine systems is that they tend to wear out the top if the #1 main bearing. That is because all of the belt tension is in one direction, whereas with multiple V-belt accessory drive the belt loads tend to counteract each other and cancel out. Belt tension with a poly-V tends to be higher in order to drive all the accessories through one belt.
 

Pontus

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Yeah, I think I'll just get the smaller version. Are there any better options than the off brands cheapos available at Rock? Like something that doesn't have crappy rubber in it?
 

Frank

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Yes if the 86 short block has those Pistons in it I think it will be right, but there are some strange aftermarket Pistons I have seen used by rebuilders sometimes, they look like a flat top with round hole that is offset to the one side of the piston top. Yes am fairly certain everything from the EFI engine should transfer over to the 1986 short block once the EFI head is swapped on. The EFI front crankshaft Dampner and timing tab bracket on the left front side of the 1991 engine is also part of the front dress parts that you would also need to change too.
Yes that piston with the offset small hole only has a volume of 19cc. Probably too much compression with EFI head/ stock cam.
 

Mr. Bob

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Yeah, I think I'll just get the smaller version. Are there any better options than the off brands cheapos available at Rock? Like something that doesn't have crappy rubber in it?
If you're talking about the harmonic balancer or the dampener they all have rubber in them because it absorbs the vibration
 

Mr. Bob

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If you're talking about the harmonic balancer or the dampener they all have rubber in them because it absorbs the vibration
I've been pretty good fortune with Rock Auto Parts I haven't had a problem with them and shipping has gotten a lot faster something to take into consideration for example are you paying for the same quality with a big name on it I used to work on washers and dryers Kenmore and whirlpool parts all made by General Electric I'm met a guy one time was a field supervisor for a big major Industrial company he told me this information concerning batteries one if you put a disconnect switch like he had on his bumper on your negative side of your battery your battery will last longer and all batteries are the same just different company labels and prices
 

Mr. Bob

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Yes that piston with the offset small hole only has a volume of 19cc. Probably too much compression with EFI head/ stock cam.
This is all good information to know I put the truck up for sale as a whole hopefully I'll get enough money I can just buy another engine and pay somebody to remove the old one and install it the remanufactured one I'm as I can find much it cost to rebuild one right now I've got to get a timing chain in my Toyota but if I don't sell the truck in order to conserve money then I'll know this information if I decide to go ahead and use that engine out of the 86 model or find another truck to put it in and just have a remanufactured installed in the 91 I hope that y'all keep discussing this stuff because I'm getting a lot of information maybe for future reference at least help me make my decision on what to do which way to go
 

wallen7

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So I'm good to go if I order a new or remanufactured head for a 91 bolt it down on the block of the engine out of the 86? Couldn't I use the water pump on the 86 and just put the Serpentine pullies on it?
no serpentine water pumps have reverse rotation
 
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