What causes cracked 2F intake manifolds?

[HawkGunner]

The obvious answer is heat. Got it. Particularly in the place where they commonly crack, at the heat riser.

I just got my motor pulled, and got my exhaust and intake manifold off. Lo and behold, a cracked intake. Bummer. I'm hoping I can get it welded.

After cruising the forum, it would seem that a stuck exhaust heat riser valve would be the cause, but mine is free moving. I "tested" it by heating the bimetal coil with a small torch, and watched the valve activate seemingly as it should. Whether that happens or not when the engine is running, I can't say.

So assuming my exhaust heat valve is working (is this a poor assumption?), and the heat riser area isn't being blasted with hot exhaust the whole time, what else might cause the crack? Is this just a designed-in Achilles heal?

The PO did a hack job on an attempted fix. I intend to fix it properly, whether by welding it or replacing it altogether. Should I go with headers and a fluid heat riser, or what?

 

[Poser]

If it were me, I would source a known good intake manifold and install one of those stainless steel shields along with a new gasket, get the whole intake and exhaust sealing surface at the cylinder head milled flat, install the assembly and not worry about it again.

 

[brian]

40 years of heat cycles, alum can't take that much movement.

 

[HawkGunner]

Got it, I'll replace the piece.

And look for an extra. Since it apparently really is the Achilles Heel in the whole thing.

 

[Tools R Us]

Could replace the manifold, and it could crack again, how many heat cycles has the used one had? If you are going to use the block off plate and correctly seal it, doesn't really matter that the intake is cracked, the plate will seal it.

Heat Riser Block Off Plates for your F/2F

Cruiser Outfitters

 

[ryanwk628]

Do you need it? How much cold weather driving where you need to warm your carb do you plan to do in Austin? Block off plate is probably the way to go

 

[HawkGunner]

@Tools R Us, but if I use a block off plate, the engine doesn't function as intended.

@ryanwk628, my road trips and adventures extend all the way to Alaska for hunting trips. More frequently I drive home to Virginia for Christmas and Thanksgiving. It gets cold in the Appalachians.

My truck needs to operate as intended in all environments.

I think I'm gonna go with headers and a fluid riser.

 

[ryanwk628]

@ryanwk628, my road trips and adventures extend all the way to Alaska for hunting trips. More frequently I drive home to Virginia for Christmas and Thanksgiving. It gets cold in the Appalachians.

My truck needs to operate as intended in all environments.

I think I'm gonna go with headers and a fluid riser.

So with all that highway mileage and cold starts, have you looked into EFI?

 

[Tools R Us]

@Tools R Us, but if I use a block off plate, the engine doesn't function as intended.
...
My truck needs to operate as intended in all environments.

Then put it fully back to stock.

I think I'm gonna go with headers and a fluid riser.

Then it wont operate as intended/stock. When cold started, the exhaust is fire hot, right now, coolant takes much longer to warmup. By the time the coolant is warm enough to do any good, the manifold is also warmed by head contact, etc. Then when the intake cracks, coolant is sucked into the intake.

When running the block-off plate, the manifolds are still bolted together, so heating happens. With a header the intake runs significantly cooler, not necessarily a bad thing. Have run many with headers, other than being slightly more cold blooded at startup, no issue. The one that I have been around/worked on with the coolant warmer, didn't perform any different than the other header motors. It's the one that slightly cracked the intake, we fought it for a while, thought cracked head, head gasket, etc, before figuring it out. Disconnected the coolant lines, plugged the holes, no more problem.

 

[brian]

Headers yes
Heat riser no, nothing but a pain in the ass, leaking mess.

 

[CHCP]

Could replace the manifold, and it could crack again, how many heat cycles has the used one had? If you are going to use the block off plate and correctly seal it, doesn't really matter that the intake is cracked, the plate will seal it.

Heat Riser Block Off Plates for your F/2F

Cruiser Outfitters

last fall I was dismantling a F155 that had headers and found a block off plate that had two 90 degree pipe fittings welded to it, I would assume that they were connected to the different sides of the cooling system and provided cooling to the intake manifold, never saw anything like it before and it looked manufactured.

 

[HawkGunner]

Then put it fully back to stock.



Then it wont operate as intended/stock. When cold started, the exhaust is fire hot, right now, coolant takes much longer to warmup. By the time the coolant is warm enough to do any good, the manifold is also warmed by head contact, etc. Then when the intake cracks, coolant is sucked into the intake.

When running the block-off plate, the manifolds are still bolted together, so heating happens. With a header the intake runs significantly cooler, not necessarily a bad thing. Have run many with headers, other than being slightly more cold blooded at startup, no issue. The one that I have been around/worked on with the coolant warmer, didn't perform any different than the other header motors. It's the one that slightly cracked the intake, we fought it for a while, thought cracked head, head gasket, etc, before figuring it out. Disconnected the coolant lines, plugged the holes, no more problem.

Full stock seems to be a less good option here, since the intake will inevitably crack again. Which is what im trying to avoid...
At least until I get around to doing a V8 or Cummins motor swap.

@ryanwk628 suggested doing an EFI upgrade. And after considering this for a while, I think this, in conjunction with a solid intake block off plate(as opposed to a fluid riser) is the best option.

Correct me if I'm wrong please, but the intake needs to be warmed to allow for proper atomization of the cold fuel. With EFI, the injectors atomize the fuel correctly from the start. So, a Blockoff plate wouldn't cause the typically associated cold start issues we see when running a carb. And, even running a stock exhaust manifold, there wouldn't be any overheating issues with the intake manifold.

In addition to the other benefits of fuel injection.

The only downside I can see is that an EFI kit is expensive...around $1200 to $1400. But thats not much more than everything required to install a good set of headers.

Does anyone know if there are hot start issues with an EFI'd 2F motor?

 

[Tools R Us]

... Correct me if I'm wrong please, but the intake needs to be warmed to allow for proper atomization of the cold fuel. ...

It kinda helps with that, the primary intention is to help with intake icing in cold/humid weather. Don't know that it is needed, lots of them have run with a header, no preheat, how many have had icing problems?

Once the motor is running at temp, the cooler the intake is, the more HP the motor can make. It's only briefly helpful on cold starts, if even then? If it were a problem it's easy to fix, draw heated intake air from around the exhaust, again, this is only briefly helpful on cold starts, if that.

Intake icing/poor cold atomization can happen, carb or EFI, if you have this problem, it needs to be addressed regardless of fuel introduction choice. I have never seen or heard of it being a problem on a F motor, but I don't live in an arctic climate.

 

[brian]

how many have had icing problems?

I froze a Weber that was giving me fits once.
Was on a warm humid day.
Cruiser sputtered to a stop, the carb was frosty when I opened the hood. Was one of those "how is this even possible" moments.

 

[Tools R Us]

I froze a Weber that was giving me fits once.
...

I have froze a bunch of them,,, on air cooled WVs.

 

[HawkGunner]

It kinda helps with that, the primary intention is to help with intake icing in cold/humid weather. Don't know that it is needed, lots of them have run with a header, no preheat, how many have had icing problems?

Once the motor is running at temp, the cooler the intake is, the more HP the motor can make. It's only briefly helpful on cold starts, if even then? If it were a problem it's easy to fix, draw heated intake air from around the exhaust, again, this is only briefly helpful on cold starts, if that.

Intake icing/poor cold atomization can happen, carb or EFI, if you have this problem, it needs to be addressed regardless of fuel introduction choice. I have never seen or heard of it being a problem on a F motor, but I don't live in an arctic climate.

That's very interesting. So really, a blocked off intake with a carb and a well tuned choke is just as good as anything else.

And with headers, you don't run the risk of a cracked intake manifold near as much as with it connected to stock exhaust. I mean, I've never had an intake manifold crack on anything else.

I would also guess that intake icing would only occur in arctic climates, and with a poorly sealed motor. I mean, even today people in Alaska run battery and block heaters, so im not sure that even the heat riser thingamajig would make a difference in those climates.

 

[HawkGunner]

I froze a Weber that was giving me fits once.
Was on a warm humid day.
Cruiser sputtered to a stop, the carb was frosty when I opened the hood. Was one of those "how is this even possible" moments.

Under what conditions did this happen?

 

[brian]

Don't recall details....was almost 20 years ago.
Irrc there was a base gasket leak and some pissed off wide open throttle runs.

 

[HawkGunner]

Don't recall details....was almost 20 years ago.
Irrc there was a base gasket leak and some pissed off wide open throttle runs.

I've never frozen a carb. But thats pretty much what I suspected.

What was designed to run as a mostly sealed system, wasn't running that way.

In any case, that's still an impressive feat hahahaha