[boodlefoof]

I recently purchased a used '67 400 engine to drop into my Tempest as a temporary engine to keep the project moving. The story on the engine was the old "it ran four years ago when my buddy pulled it." So, I decided to tear it down to check it out and paint the thing blue again (instead of its current red) before trying to fire it up.

Unfortunately, I have trouble leaving well enough alone... While looking over the heads, I noticed a lot of casting flash in there and decided I would clean them up just a bit. One thing led to another and I decided to remove the air injection bosses from the exhaust ports. That is a pain in the neck. Now that I've ground them down, I'm still left with football shaped holes in the roof of the exhaust port for the plugged air injection system.

Should I fill these holes with something, or just leave them as is? I've attached a picture of the rough cut boss.

[steve25]

If they go into the main injection passage you need to remove those two square head plugs and get the grindings out of there,and if they are open to that main passage you can press a steel tube into that to seal off all 4 holes in one shot ,or tap each one of those holes for Allen socket studs and seal them off.

Leaving them open is no where near as bad as leaving the center two cylinders exh crossover passage open if you run headers!

It's even more of a pain in the Butt to grind them out of the latter 4,5 and 6 series head with there smaller valve bowl!

[boodlefoof]

Originally Posted by steve25

...

Leaving them open is no where near as bad as leaving the center two cylinders exh crossover passage open if you run headers!

...

Actually... I was thinking about closing off the exhaust crossover in each head and have been reading up on doing so using Cotronics Resbond.

I like the idea of putting an allen head screw in each air injection hole to plug them. That would allow for a smooth exhaust port roof. Pressing the tube in through the side will keep each port from talking to one another, so to speak, but still leaves those holes in the exhaust port roofs. It has been a long time since my college course on aerodynamics! But, I think that hole will cause a disruption in the air flowing over it.

If I use an epoxy to block off the exhaust crossover in the middle ports, perhaps I might be able to use the caulk gun to pump the Resbond into the air injection passage to seal them all up. Thoughts?

[steve25]

Don't fret over having a non perfect area at that point on the port roof, as even if it still had a hump length wise down the port it does not effect the peak flow more than 3 to 4 cfm! What is of a concern is ridges going left to right across the port roof and down and out.
What you should do is sand down the casting nub on the crown of the short turn and widen the short turn around to the crown of the floor for big air flow gains and leave the flange area at its stock size, no gasket match!
On the center ports that head bolt boss can be cut back .040" in each runner to make for greater width over the short turn.
Use the Allen set screws and the Ciramic epoxy to block the cross over area.

[boodlefoof]

Thanks Steve. That course of action sounds right about what I had planned for the exhaust port! I haven't measured yet, but my plan also included opening the throat a little, but leaving the machined wall surface alone.

On the epoxy of the air injection system, couldn't I just use epoxy to full the holes in the roof of each port and not have to worry about drilling and tapping for the set screws? I'm thinking that if I remove the plug at one end of the head and push the epoxy in through there, it would have nowhere to go except out through the holes in the ports. Thoughts?

[steve25]

Just use the epoxy to fill those holes in the port roof andthe Exh cross over, do not waste in on the main passage, but if you do not have the epoxy yet instead use hydraulic cement to fill that main passage.
In fact I have been using this stuff to fill exh crossovers for a few years now and it's easy to control and far far cheaper than the high temp epoxy and holds up great!

What I would do is just fill that main passage with the stuff with the head tilted on a angle and it will flow into holes on the port roof and plug those off in the process!

Make sure the port roof is clean enough to let tape adhere and as the cement just starts to bleed out of those holes in the port roof place a strip of duct tape over them to end the out flow.

Just to a test mix or two before you do the real pour as the stuff sets up pretty fast, so get a feel for that time frame first!
After the fill let the head sit for two to three days so the stuff cures fully before you fire up the motor!

[boodlefoof]

Thanks again Steve. FYI for all, I spoke with Cotronics and they have a product (Durabond 952) that is capable to 2,000 degrees, has expansion/contraction characteristics very similar to cast iron, is made to adhere very well to cast iron and which comes in a putty form. I'm going to give it a shot.

[boodlefoof]

Following-up on my own thread. I just got around to mixing and filling the exhaust crossover with the Durabond 952FS. While the tech folks at Cotronics described it as a "putty" it turned out more like a paste. Perhaps I could have mixed it a little lighter to produce a putty, but I think this turned out OK. We will see how it sets up.

The instructions say you can mix from a low of 100:120 (powder to liquid binder) up to 100:140 high by weight. I went about 100:135. At this mix, it poured pretty well through a funnel... a bit thicker than chocolate syrup. More like honey or molasses.

I'll let the exhaust crossover set overnight and pour the air crossover in the morning.

[GRX]

On my 670's I just drilled & tapped for screw in allen plugs and seemed to me leaving that boss helped eliminate chance of eddy currents behind the valve stem.

Let us know how the Durabond works. Considering whether to go that route or the aluminum fill method.

[boodlefoof]

Well, here is another update. The 952FS says it takes 24 hours at room temperature to completely set before you stick it in an over to cure it more. It also says it is workable in the mixing bowl for 2 hours, so you have some time to play with it before pouring. I probably should have gone a little slower with my exhaust crossover pour.

I don't think it will end up being fatal, but by this morning the exhaust crossover fill had slumped just a little in one corner as the mix settled, leaving about a 1/8'' deep pocket on that side. I had used a funnel to pour it last night and filled to right where I thought I wanted it to minimize grinding. I probably should have poured slower to minimize bubbles and over-filled just a little in anticipation of air coming up to the surface. This morning (12 hours later) the mix still had a little give to it when pressing firmly with my finger, hence the slight surface cracks you can see. I'll probably end up grinding it down just a bit, roughing it up and topping it off again with more filler to bring the level back up.

On the air bosses, I decided to pump the paste in with a syringe and some clear rubber tubing. I slipped the tubing over the end of the syringe and started pumping in through the last air boss until the mix started coming up out of the next closest hole. Over the next hour I let it sit for the mix to settle and air to clear and then topped it off. Here is a pic of one of the filled air holes (the grey spot) behind the valve stem hole.

Edited to add that a one pint kit would do the job. I used a little less than 180 grams by weight to do the air bosses for two heads and as best I can figure I used about 750-800 grams to do the exhaust crossovers. I mixed up too much (a whole batch) when doing the exhaust crossovers and had quite a bit left over that I could have used for the air bosses, but I had to let the exhaust crossover firm up before I could move the heads to do the air bosses.

[boodlefoof]

Update:

I let the stuff cure for about 40 hours at room temp and then threw it in the over to bake at 200 degrees F for 2 hours. All looked good. I let them cool completely back to room temp and then set the oven to 400 degrees for the "post cure" per the instructions.

After a few minutes, I noticed a bit of steam coming from the oven. I popped it open to find that the Durabond had swelled slightly (about 1/16'' out from the intake manifold surface) and a liquid that looked like the binding agent was weeping from a pinhole that formed on that surface. I shut it down and let it cool. An inspection of the cooled part showed similar swelling and weeping from the valve side. The exhaust air boss fills looked fine. Thankfully, there don't appear to be any cracks in the heads around the exhaust crossover.

I called Cotronics and spoke with them about the situation. Their tech indicated that due to the size of the crossover pour it would take much longer to cure. Since it hadn't completely cured before I fired it to 400 degrees, the water in the mix started boiling off. I asked whether this could impair the product such that I would have to remove it and start over. He indicated that it would not be a serious problem and suggested I cook it for several more hours at 200, then pump more Durabond into any pinholes and cure again and the newly applied Durabond will bond to the old.

We will see how it goes. For others trying this, be forewarned. Let it cure for a long time under 212 degrees F before doing the post-cure!