351C 4V running rough

[digithead]

So I bought this 73 convertible with a 351C. Built as 2V but someone made it 4V with a new Edelbrock 650CFM 4bbl carb and a new Weiand 7516 Intake. I had a mechanic friend came over and listen to it and he agreed its not purring. Starts fine. Runs rough. So we dont know what all was done to motor, as it was torn down and redone before I got it. So I took off carb to get closer look as to what was done and what make/model parts were put on. My buddies fear was some guys just toss parts at motors all bolt on without getting stuff properly matched.

In these pictures you can see the ends of intake manifold gaskets. Neither one looks right to me, but I am not a 351C expert. Can someone here tell me if maybe he put in wrong gaskets? I cannot believe they should be sticking out this much?

 

[MeZapU]

Anyones guess until you tear into it. Printo-seal gaskets kinda suck anyways and there appears to be no valley pan gasket.

 

[rocket366]

There is a 2 or 4 raised marking on the heads to indicate 2v or 4v heads.

The intake manifold needs to match the heads.

Pull the intake and see whats going on.

Let the fun begin.

Paul

 

[digithead]

There is a 2 or 4 raised marking on the heads to indicate 2v or 4v heads.

The intake manifold needs to match the heads.

Pull the intake and see whats going on.

Let the fun begin.

Paul

THanks Paul. I have intake and carb off now. Wheres the 2 or 4 marked? Dont know where to look.

 

[Paul of MO]

The manifold end seals have pushed out - it is better not to use them anyway. Instead use a bead of black RTV to seal the front and rear "lips".

I would pull the manifold, clean everything real good, and replace the intake gasket as it is very possible that you have a intake leak.

I always use the metal pan type gaskets and do not close up the cross overs on street engines. It makes winter cold starts much more pleasant to leave them open.

While the manifold is off you can look for bent push rods and other clues to your problem. You have a pretty good chance that a new intake gasket will solve your issue. If not you have only wasted 30 bucks and a few hours.

Be sure that you get the right gasket - 2V and 4V heads are different. Get the gasket for the heads not the intake. The 2 or the 4 is on the front corner of the head next to the intake.

- Paul of MO

 

[digithead]

The manifold end seals have pushed out - it is better not to use them anyway. Instead use a bead of black RTV to seal the front and rear "lips".

I would pull the manifold, clean everything real good, and replace the intake gasket as it is very possible that you have a intake leak.

I always use the metal pan type gaskets and do not close up the cross overs on street engines. It makes winter cold starts much more pleasant to leave them open.

While the manifold is off you can look for bent push rods and other clues to your problem. You have a pretty good chance that a new intake gasket will solve your issue. If not you have only wasted 30 bucks and a few hours.

Be sure that you get the right gasket - 2V and 4V heads are different. Get the gasket for the heads not the intake. The 2 or the 4 is on the front corner of the head next to the intake.

- Paul of MO

Thanks. It did not have end seals, just a long bead of some grey goop. Why dont end seals work well? They always fail so most folks just use RTV? I will look for my 2 or 4 markings. Not knowing what the PO did is tough. I was assuming maybe stock 2V heads it came with, and he got new intake and carb and bolted on.

 

[rcadd1ct]

http://www.summitracing.com/parts/WND-7516/?ibanner=MobileSwitchNo

Shows to be a 2v manifold

If the ports are the same size you have 2v heads.

If they are bigger you have 4v heads.

 

[digithead]

http://www.summitracing.com/parts/WND-7516/?ibanner=MobileSwitchNo

Shows to be a 2v manifold

If the ports are the same save you have 2v heads.

If they are bigger you have 4v heads.

Thanks. So if i get it right, if he bought correct intake it would be a 2V model, to mate properly with 2V heads. even though its getting a 4BBL on top? If for some reason the PO upgraded out on 4V heads then he bought wrong intake, correct? If they are 2V heads, would he have been better off when rebuilding it to go full 100 yards and switch it to 4V heads?

 

[rocket366]

The 4 is raised on the bottom right corner of these heads.

Paul

 

[rcadd1ct]

http://www.summitracing.com/parts/WND-7516/?ibanner=MobileSwitchNo

Shows to be a 2v manifold

If the ports are the same save you have 2v heads.

If they are bigger you have 4v heads.

Thanks. So if i get it right, if he bought correct intake it would be a 2V model, to mate properly with 2V heads. even though its getting a 4BBL on top? If for some reason the PO upgraded out on 4V heads then he bought wrong intake, correct? If they are 2V heads, would he have been better off when rebuilding it to go full 100 yards and switch it to 4V heads?

The 2V 4V designation is fords. Aftermarket does sell 4 barrel intakes for 2v heads.

And the need for 2V or 4V heads a widely debated......to save you the search it all depends on your goal on performance and other parts you plan on adding.

 

[digithead]

The manifold end seals have pushed out - it is better not to use them anyway. Instead use a bead of black RTV to seal the front and rear "lips".

I would pull the manifold, clean everything real good, and replace the intake gasket as it is very possible that you have a intake leak.

I always use the metal pan type gaskets and do not close up the cross overs on street engines. It makes winter cold starts much more pleasant to leave them open.

While the manifold is off you can look for bent push rods and other clues to your problem. You have a pretty good chance that a new intake gasket will solve your issue. If not you have only wasted 30 bucks and a few hours.

Be sure that you get the right gasket - 2V and 4V heads are different. Get the gasket for the heads not the intake. The 2 or the 4 is on the front corner of the head next to the intake.

- Paul of MO

Paul, why not use end seals? Do they always fail so its better just to go with RTV right from the start (I assume)?

 

[mjlan]

I'll offer my $0.02 and Paul can add his- blocks and heads are 40 years old at this point, and it's very difficult to tell how many times or whether they've been cut at all. Since RTV is compressible before it sets up, there's less chance of the intake being held up by the China walls of the block and not sealing to the heads. A nice bead of RTV will seal up and squeeze out if needed to allow the intake to sit down on the heads. You can verify any alignment issues by sitting the intake on the block dry and checking with a feeler gauge at the top of the head vs. the bottom to make sure the intake face is square to the head.

 

[Paul of MO]

I'll offer my $0.02 and Paul can add his- blocks and heads are 40 years old at this point, and it's very difficult to tell how many times or whether they've been cut at all. Since RTV is compressible before it sets up, there's less chance of the intake being held up by the China walls of the block and not sealing to the heads. A nice bead of RTV will seal up and squeeze out if needed to allow the intake to sit down on the heads. You can verify any alignment issues by sitting the intake on the block dry and checking with a feeler gauge at the top of the head vs. the bottom to make sure the intake face is square to the head.

Yep. (That's my 02 cents worth)

Cork end seals split and rubber end seals push out each and every time.

- Paul of Mo

 

[barnett468]

Do they always fail so its better just to go with RTV right from the start (I assume)?

Nope, I have never had one come out in all the engines I have done in the last 40 years using my technique, however, as mjlan mentioned, it is possible for the clearances to no longer be correct . . This is especially true of aftermarket intakes, especially Chinese ones . . I have had Chinese ones where they sat so high on a box stock uncut engine that there was literally clearance between the intake and the end seals when I set the intake on to check the clearances . . After seeing this, I used black Permatex gasket maker.

Not all silicone sealers are created equal, and the ones that say gasket maker on them are the best for this app . . One of the reasons they are best is because they are typically thicker than non gasket maker sealers which helps prevent them from flattening out before you can install the intake.

As long as the intake provides enough crush on the end seals and they are properly installed on an oil free surface with good sealers that are allowed to dry sufficiently before the engine is run, it is IMPOSSIBLE for them to pop out . . It will simply never, ever, happen . . If they all always popped out, there would have been zillions of recalls for warranty repairs when they were newer cars.

Mechanics are like surgeons, they are not all equally skilled, but you unfortunately you often don't know if you have a lesser skilled one until after the operation, and if you had a mechanic that said they will pop out if he installs them before he even checks the clearance, you better find yourself another mechanic that may know what they are doing.

..

 

[4Vforever]

Do they always fail so its better just to go with RTV right from the start (I assume)?

Nope, I have never had one come out in all the engines I have done in the last 40 years using my technique, however, as mjlan mentioned, it is possible for the clearances to no longer be correct . . This is especially true of aftermarket intakes, especially Chinese ones . . I have had Chinese ones where they sat so high on a box stock uncut engine that there was literally clearance between the intake and the end seals when I set the intake on to check the clearances . . After seeing this, I used black Permatex gasket maker.

Not all silicone sealers are created equal, and the ones that say gasket maker on them are the best for this app . . One of the reasons they are best is because they are typically thicker than non gasket maker sealers which helps prevent them from flattening out before you can install the intake.

As long as the intake provides enough crush on the end seals and they are properly installed on an oil free surface with good sealers that are allowed to dry sufficiently before the engine is run, it is IMPOSSIBLE for them to pop out . . It will simply never, ever, happen . . If they all always popped out, there would have been zillions of recalls for warranty repairs when they were newer cars.

Mechanics are like surgeons, they are not all equally skilled, but you unfortunately you often don't know if you have a lesser skilled one until after the operation, and if you had a mechanic that said they will pop out if he installs them before he even checks the clearance, you better find yourself another mechanic that may know what they are doing.

..

Agree 100% and do basically the same thing as Barnett and have never had any dramas, ever and have done many, many engines over the years all without this so called failure. Also I've had engines where the clearance was much smaller than the gasket thickness and used just goo on these engines, again without problems. Did come across a real head scratcher though many years ago, the customer installed a new intake and it problems with idling and running. After finding where the problem lay, pulled intake to find what looked an air bubble had pushed some silicon out of the valley. Reassembled with new gasket set and problem fixed and another happy customer.

BTW Barnett loved the last part of your post, gave me a good giggle, lol

 

[Paul of MO]

Not all engines - just 351c's with aftermarket intakes. Just not enough space between the intake and the front and rear of the block.

Hard to force a 3/16 of an inch seal into a 1/8th of an inch gap.

This is what Edelbrock says

- Paul of MO

 

[Don C]

I would check the compression on all cylinders, the roughness may be a valve problem.

I am assuming your mechanic friend check the common things like rotor, cap, points, wires and spark plugs.

 

[digithead]

Thank you so much. Going away to warmer place for 1 week (Cancun). When I return I will tear into it and see what I can find out. Learning about 351C engines.Over the years ,I had to learn some Wankel rotary for RX7, then I had XJ6 jag with straight 6 with tons of issues, then a BMW 750iL V-12 with a crazy ass engine. I think I have learned a lesson here. Learn 1 engine, learn it well, stick with it in all your hot rods LOL. By the time I understand them I see the damn car and get something else!

 

[MT91106]

The bigger thing on the 4V heads is the exhaust size the ports on the exhaust are monsters vs the little 2V heads. When i rebuilt my 351-4V it had headers on it took them off due to them leaking (plus rebuilding the motor) and found out they were 2V headers on 4v heads so were choking off the exhaust flow. So found a set of factory cast iron exhaust manifolds put them on and people think it has headers on it since it flows so well and sounds so good and throaty. I always use silicone instead of the end seals as well because they sometimes push out while trying to get the manifold in place so just a better fix instead of using them, you still get a really good seal (mine has never leaked).