[Z Code 400]

I got a call this weekend to come and look at a recently built 455 that mysteriously locked up Saturday afternoon. The engine is based on a commercially-purchased reciprocating assembly, ported 6X-4 heads with filled crossovers and was assembled by the owner.

When we popped the valley pan off, I found a bent/broken pushrod and the camshaft broke in three distinct pieces. Further examination revealed a 'slug' of aluminum had fallen out of the crossover (in the valve pocket) and held the valve open. The piston slapped the valve, drove it backwards and apparently, snapped the camshaft.

My question is twofold;

What is the best method for removing aluminum from the crossover without overheating/distorting the head???? Secondly, what I the best method/material for filling the crossovers so this doesn't happen again????

Thanks!!!!

[Schurkey]

Did only a portion of the aluminum fall out? If so, I'd say that it sounds like the aluminum was done in multiple "pours". The bond between pours is not so good.

Gotta install the aluminum in ONE POUR per head. That way you have a one-piece aluminum slug that shouldn't break apart. I'm told that "take-out" forged pistons work nice for this once melted.

I know of at least one company selling a zinc/aluminum mixture; supposedly has a lower melting point than piston aluminum.

[steve25]

If you drill it from the manifold flange side with multiple 1/4" holes at a 15 degree angle or so to pass the drilled hole into the exh bowl you will be able to shatter it and get it with a chisel.
And yes, filling the crossover must be done in one OVER FILLED pour, which means grinding back the over fill into the nedded valve bowl form, some 40 minutes of work per bowl if its over filled enough to get the right shape.

[Z Code 400]

Yep...

Aluminum has a grain in it, like it was poured in stages. Wouldn't you want to heat the head prior to filling?????

[wheelspin]

Search, and you will find a much better & safer compound than molten aluminum for this task.

Les

[Mr. P-Body]

Robert,

Many people insist that "pre-heating" is mandetory. In very cold weather, we DO "warm" the head. But aluminum disappates heat so quickly, there is little or no "trauma" to an iron head when hot aluminum is poured into it. We always "bump" the seats afterward, just to be certain (unless the valve job is done AFTER the pour...). And it MUST be done in a single "pour" so what you experienced doesn't happen.

Over-pouring isn't necessary, either. We did some flow tests a couple years back. If the "bowl side" of the exhaust port has been filled "up", and recontoured, it will not flow any more gas than if the "fill" didn't come all the way to the "top". The cavity becomes a "high pressure" area and the escaping exhaust gasses just "bounce" off the trapped ones. We did not gain 1 CF when the port was over-filled and recontoured.

Wheelspin,

We've tried numerous methods. Furnace cement seems to be the "other" candidate. It's not "permanent" like the aluminum, though, as it can "burn out" eventually. To date, we've found nothing better than aluminum.

FWIW

Jim

[shaker455]

I've used zinc and also Cotronics ceramic type epoxy.

Had no issues

[Z Code 400]

Thanks to all....Robert

[Steve Barcak]

Sorry to read of this failure.
I did that procedure in the 90's while building my 455HO. It was done in my kitchen with an iron skillet and setting the head up on some plywood and also using a torch with a rosebud tip and some used forged pistons.
Since then, with 173,000 miles, I have not had any problems encountered.

Not sure why some of it would have fallen out.

Steve
Hosting-
12th annual Pontiac Heaven April 8-11, 2010 Phoenix
www.pontiacheaven.org
8th annual Nostalgic Show & Go! April 11, 2010 Phoenix
www.nostalgicshowandgo.org

[lust4speed]

Last one I did, the head shifted and we got a half height pour. It's really no fun drilling the aluminum out for a re-do. The side of the port sneaks right up on you if you're not super careful and continuously check what the drill bit is doing. I cleared a 3/4" tunnel that expanded out on the manifold side for the re-pour. Even stopping the pour for a split second can allow separation.

Wheelspin finally showed me the light and I stopped using the aluminum pour. The ceramic material he recommended has a higher melting point than aluminum, and it can be molded for 10 minutes after the pour to the desired port shape. It grinds just a little easier than aluminum, but is a much harder material than JB weld: http://www.cotronics.com/vo/cotr/cm_castable.htm

While we always pre-heated the heads, I did have one pour that we must have had the aluminum way hotter than it needed to be. About 10 seconds after the pour there was a loud SNAP that really sounded like the head cracking. We couldn't see any damage, but took the head in for a pressure test to be sure that the water jacket wasn't breached where we couldn't see. by the time I paid for the test, the ceramic price looked very reasonable.

[Half-Inch Stud]

Gotta install the aluminum alloy in ONE POUR per head.
Here's how I like it done:

Pack 0000 steel wool into both valve bowls, with effort to effect a nice bowl curve at crossover. Hold each steel wool in place with a valve stem.

I do this, but could be argued as not needed: Place head(s) on BBQ Grill set on low. So the heads are super-warm when handled. Makes for nice work height...

Heat Aluminum Alloy (from piston is nice) (I used 6061 for 1 fella) until melt, and scrape dross as you go. You need to develop the propane-fired, shielded-steel heat cup & sturdy handle. I use a porcelin "Chemistry Lab" stirrer to remove dross.

Pour from Intake flange side in one quick pour with enough aluminum to reach within 1/4" of the flange. Apply JB-Weld to Flange-fill hole for exhaust-tight seal & smooth pond-like finish.

Much Happiness when Steel wool is removed. HIS

No maintenance has been needed on such filled heads.

[Cliff R]

I do ours much like HIS recomends, but use an old Coleman two burner gas stove to heat the heads. Pack in the steel wool, make one solid pour, no worries.

More than likely the heads were too cold as was the molten aluminum being poured into them, so it "layered" and one of the chunks fell out........Cliff

[Z Code 400]

Mick,

I like the idea of using a ceramic material. I also like the fact that you could lay a piece of small steel tubing in the port (that can be pulled out later) when pouring to vent a small amount of exhaust heat up to the intake to improve cold driveability.

Which one of the ceramic mediums do you use?????

[Pontirag]

yea, one continuous pour, some say you dont have to pre heat the head but its a good idea. and clean the surface of the cross over befor you pour. pour in exess of what you need and grind away the exess. personally I think pouring aluminium and any foriegn material in the engine is a scarry prospect. just block it off with a thin sheet of stainless or get gaskets with the block off added(?). The real issue is Is it nessessarry? Not blocking off the crossover but going to the extream of pouring AL or introducing any thing into the engine when its kinda risky, a little extream and with safer simpler solutions and reallyfor how much additional benifit? Some say it makes a set of dual exhuastes sound more agressive. hope that aint why yer doin it?

[steve25]

Since I have used the ceramic stuff their is no going back!, its SOO much less of a process over going thru all the steps to do a aluminum pour that the price that some mention does not even enter into the discussion!

[Mr. P-Body]

Pontirag,

The purpose of filling over "blocking" is to provide true isolation, one cylinder to the next. This known to gain power across the RPM range, but at the point of resonance moreso than any other. I suppose some do it for "sound", but most for performance. Simply blocking the crossover only stops the heat from crossing. The slight gain from a "cooler" air/fuel charge is not the primary purpose. If you have good 4-tube headers, there are real gains to be "had". If you have stock exhaust or 3-tube headers, it's a waste of time in all but a "max" effort.

FWIW

Jim

[Pontirag]

I agree but befor I went that route I would try a few other things like a good tune up. It just seems to risky. To gain Isolation only affects the cylinders that have those cross over runners. The idea of Isolating I understand but reading all the post's and a few articles encouraging the practice claim that the cross over runners affect flow. Isolation and flow are two separate issues. Presumabley, filling the runner and then grinding the runner contour will obtain measurable incrase in power. I never seen a comparison between block off the runner vs filling the runner and grinding the runner that shows a increase. Not to say it aint so but I aint seen a comparison. Most who recomend it are promoting a service ....at a cost. For ultimate power it requires alot of effort . I supose if ya got nothing to do this winter...

Somebody posted earlier that the flow difference between filling the runner and not shows a minimal flow difference.

Again, ,it comes down to an objective comparison of just those variables...presuming all others are constant but that is never just the case. anybody who goes to that extream wil probably fine tune the engine to take advntage of that change.

again I dont know but I have not seen a objective comparison from a dyno results. or a summary of other tunning suggestions to take fuller advantage of the benifits of that change alone. It is hard to isolate that one factor alone and show its advantage

[TinjunTribe]

Originally Posted by steve25

Since I have used the ceramic stuff their is no going back!, its SOO much less of a process over going thru all the steps to do a aluminum pour that the price that some mention does not even enter into the discussion!

I have read many posts on this subject. There are at least 3 different Cotronics product #s referred to on this board. One stated it was based on a recommendation from a tech at Cotronics (the product that you mix to a consistency of toothpaste if I remember correctly).

Others used the Cotronics product that is available in caulk gun tubes (brown in color).......

I like the sound of this, less dangerous, etc..... Which Cotronics is the right danged one?

And who has the most miles on a Cotronics filled set of heads?????? Something to be done right the first time, and done for good for sure.

If pouring Aluminum (or Mondello stuff) from the manifold surface,,,,do you pour biased to one side, let it fill up then overflow into the opposing opening, or just dump into until its slightly below the surface level without worry?

Thanks, I am about to get into a set of heads and need to decide, molten metal or ceramic............


edit:

Cylinder Head Abrasives (ruffstuff.com) recommends 16 oz. Resbond 2300° 907GF specifically for this purpose http://www.cotronics.com/vo/cotr/ca_putties.htm as have other posts here

Poster Above recommends 4000°F Rescor™ Castables

I am pretty sure I've seen another one of their products in another post............

[Pontirag]

Back in the day I visited a local speed/machine shop and saw two guys using a peiece of aluminum rod barstock and a cutting tourch to melt the aluminium and allowed it to drip into the crossover passage on the heads. thought it was a clever idea...back then.

now I'm not so sure.

[lust4speed]

I'm using RESBOND 940. It's rated at 2,000° and "fast cure". The fast part isn't really descriptive since you still need to wait 24 hours before any cleanup grinding.

I believe the problem with people checking "flow" of the center exhaust ports are not taking into account the reversion or back flow from the other cylinder. Yea, on a flow bench the more holes you have in a port the higher the flow number. In the real world the exhaust from the adjacent cylinder is coming over and doing all sorts of nasty things to the other exhaust exit. Remember also that the unfilled crossover affects cylinders 4/6 & 3/5 or 50% of the engine.