Fixing loose aluminum in crossover
 

I pulled my intake manifold last night to diagnose a strange noise coming from the valley pan area and found that the aluminum in my exhaust crossover has come loose and wore its way through my intake gasket. The noise I was hearing was exhaust dumping out onto my valley pan through the area of the intake crossover that I had to grind away for clearance when I installed my Tomahawk valley pan. The aluminum fill in the head is recessed about .03" from the intake gasket surface, so I was wondering if I applied a thin layer of JB Weld over the filled area, would it hold the aluminum slug in position and keep it from getting looser at it bounces around in the port? I am not sure what the temperature is at the intake gasket surface, but both regular and high temp JB Weld are only good for 550 degrees. Has anyone here ever had the aluminum fill in their crossover come loose, and how did you fix it? I am really hoping that I don't have to pull my head.

So the aluminum you used to fill the port in the head is loose, if so how long did it last before it because loose and started to leak? I don't trust JB weld for ****.

Mine did that. Could hear the noise too. I ran 2 small screws on 2 sides between the slug and the port. Little self tapping screws. They sit between the slug and the port wall. They cut into the slug and half the dia. of the screw pushes against the port wall. They push the slug inwards and hold it tight. Take a chisel and break the screw heads off flush. Been like that for years now.

I used JB weld to block off the upper port of a set of later heads without any problems.
Of course this was just the upper port so I could put a tripower manifold on the later heads. I've run it like that for years.

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There is less than 2000 miles on the engine.

After reading about this same issue happening to many people, the metalsmith in me thinks it comes from melting down piston stock. As we know pistons contain a certain amount of silicon. At the factory even distribution is maintained through agitation, temperature control, and oxygen levels in the melt area.

Being that many who perform the cross-over fill at home, or in a non-foundry type shop, those standards are not easily maintained. So uneven distribution of silicon results. Therefore you get uneven expansion and heat transfer rates within the poured slug. A while back someone here mentioned they got better results from melting down aluminum window frames than piston stock. Likely because of the alloys involved. Just my 2 cents ...

:ranger:

I like the screw fix more than the JB Weld. My worry would be that the JB Weld seems to have a period where it gets really runny after being put in place and before it sets, and I'd be afraid that it could migrate down to the valve seat.

After closer examination, I found that the aluminum pour had several cold joints and the piece in the passage to the #5 cylinder exhaust port was not connected to the rest of the slug and very loose. I was concerned that the piece could come loose and make its way into the exhaust valve, so the engine came out and the heads are off.

Because the heads are still pretty fresh with only about 2000 miles on them, I really didn't want to completely strip them and go through the preheat and hot pour aluminum for fear of something distorting. For that reason, I have decided to remove the aluminum and fill with Resbond 940HT.

I called Cotronics this morning and spoke with an engineer who recommended Resbond 940. Being that the smallest container available was a quart for $98.00 and I only need a pint or so, we decided to go with Resbond 940HT, which was available in a pint container. He stated that the 940HT had the same properties as 940, but was resistant to temps of 2800 degrees rather than the 2000 that 940 was rated for. The pint of 940HT was $64.65, however they add a $20 fee because it falls under their minimum order, so it cost me $84.65. I should receive the Resbond in a little over a week, so I have time to get everything prepped and ready for the pour.

Here is a thread for you. Notice post #12 where the Resbond needs to be heat treated in an oven. Best of luck!

>> Filling exhaust crossovers with Resbond 940HT

http://classicoldsmobile.com/forums/...ond-940ht.html

Is there a better Aluminum to use other then pistons? Would Cast be better then forged? I was planning on busting up some pistons. I'm getting things ready to do my first fill on a set would prefer not to have this issue.

Does it help to pre-heat the head when filling?

I did Resbond in my heat crossover several years ago, I put some kind of putty (like silly putty) in the valve ports and poured the Resbond through the exhaust ports. I did not heat treat the Resbond, but let it sit for a few days. It has held up fine so far.

I found the post I was looking for that had the tips and suggestions from way back.

http://forums.maxperformanceinc.com/...ight=crossover

I think the issue is the silicon also, but I think it stems more from the fast cool down of the pour when the head is not heated !
I use Hydrualic Cement now for these fill jobs and if you line the exh port at the crossover opening with duct tape and then pack foil into the bowl to hold that shape you will have a pretty good shape to that back of the bowl area flow wise!
The stuff sets up pretty fast so you want to mix enough to get the fill done in one shot, then after a 2 day dry out time, or a 4 hour cure time in a 150 degree over your good to go!

Do you have an old aluminum intake you could use.

The preheating is necessary for multiple reasons. First, the aluminum will cool rapidly when it hits the cool cast iron and solidify before it completely fills the crossover. If that happens, you will have multiple "loose pieces" in the port rather than one solid slug. The other reason for preheating is to keep the cast iron from experiencing thermal shock when the molten aluminum is poured into the cast iron at ambient temperature. That rapid heating can cause lots of bad things, including cracking your head.

Some will ague that you can use an oxy-acetalyne torch to heat the crossover passage before pouring the aluminum, but I would not recommend it. That is too much heat introduced too rapidly to an isolated area and, in my opinion, is just as dangerous as pouring the molten aluminum into a cold cavity. The only correct way to do it is to gradually heat the entire casting before making the pour and allow it to cool slowly.

Heating cast
 

The other thing to think about when heating the cast iron heads is the thermal shock that can happen after you pour the aluminum if you have any doors or windows open to create a draft over the heads. This can cause a cracked head in the blink of an eye. I would wrap the heads in some insulation or bury them in some dry sand on the garage floor and leave them for 24 hrs. Ed

Sounds like I should stick the head in the oven at 450 for 20 minutes. Wife will love that.

Heating cast
 

The welders I know suggest that you only heat the cast at a rate of 100*F/hr. Same as cooling at that rate. If I were to use an old stove in the garage to preheat I would set the oven to 200*F and stick the heads in. Then in an hour or two adjust the oven temperature to 450*F and leave alone for another hour or two. Ed

Reading the post that Rhort linked refreshed my memory. I filled the valve bowls with molding clay from a craft store so I wouldn't have to do any machining on them and poured the Resbond through the valve ports. There was a little shrinkage of the Resbond, but not much. On the exhaust side, I covered the ports with a piece of plastic garbage bag held in place with a piece of sheet metal.

isolating center exhaust ports
 

Since my engine was assembled long ago and I didn't want to tear it down, I fabbed some aluminum plugs for the ports at the intake manifold. Someone had posted that if you at least isolate the two exhaust ports, even though you don't fill and clean-up the port, that you would reap the benefits for exhaust tuning. I can't wait to hear if the exhaust note changes too.