The Ultimate GTO

[kitbash]

So I moved on to the wheels. The Rally 2's used on the real car have never really been kitted too well. The ones in the Monogram GTO kit are WAY too big, the ones in the Monogram '70 Trans Am have slots that are comically incorrect, the Revell '68 Firebird's are too small and mis-shapen...

But Scale Equipment LTD. has a slick little set that includes separate, plated trim rings. The wheel portion is damn near perfect, too.

As far as tires are concerned, I've never yet seen a muscle car tire I've liked that works with the Monogram kit. So I'm punting....

I'll try to adapt a set of the old JoHan break-in-half NASCAR tires.


I started off by separating a wheel from SEL's sprue, and back-sanding it to a workable thickness. Then I carefully opened up the slots.


Then I did the same thing to one of the chrome trim-rings. The plating has to be treated with respectful TLC...it flakes off really easy.


The first thing I noticed is that the trim ring is too big for the tire. Not by much, but too much to force the fit.

So I mounted a conical industrial grinding stone in my tooling vice and "twisted" the tire half back and forth to increase the diameter. I could have used an x-acto blade, but this is more uniform (and faster, too).



If you look carefully, you can see the difference. I didn't remove much, but the modification was essential to ensure a non-stress fit against the brittle resin.


After that, the trim ring popped in easily. BTW, I'm not doing a Michael Jackson tribute; I always wear a cotton glove when I'm man-handling chrome.



I'm really anxious to paint up one of those resin wheels and see how it all looks when it's done. The chrome trim ring is a little too shiny for my taste; next time I'll show how I knock down that bling look a little to resemble the stainless steel the factory actually used.


More to follow...

[dlphnfn]

Ah... SEL wheels!! Those things are trick!! Here are mine that I mounted on a 70 Goat a few years ago.

Keep up the good work!!
Erick --

[kitbash]

Now THAT'S what I'm talkin' 'bout! Those look excellent! You can see what I mean about the tires though...I've never seen a set that works well with Monogram's 'oversized' 1/24 scale. The JoHan tires will need a lot of tweaking.

thanks for posting that shot; you got the paint just right and clearly SEL's wheels are the only way to go.

I wish Performance Plastic Products would come out with a good set of Goodyear Polyglas for 1/24 cars...

[kitbash]

The cylinder head work grinds on. I have the exhaust flanges shaped (I'll show them in a later post) so now it's time to make the head ready to accept them. The exhaust port length needs to be increased and the angle changed.

I tacked on some bits of sheet stock, looks like .060 thick.


then I just started whittlin'. I block-sanded the ends of them to get the proper angle....


...then started blending them into the ports. You can see the one on the end has been done there.


Once they're all blended in, I can add the exhaust flanges. I'll resin-cast those flanges tonight; I want them to look identical. there's also some other stuff that needs resin-casting for the head and valence.

While I'm at it, I'll start working on the gasket surface of the head that contacts the block.

You can see it there; it sticks out a little and you can see the shapes of the cylinders and bolt holes. I want that gasket surface to be on the head.



I'll rough it out and make it fit later; most of it won't be seen anyway. I' punched out the basic cylinder shapes from .015 platic using a paper punch.


then I started adjusting the contour so I could glue them together end-to-end.




More to follow.

[kitbash]

Okay so I have enough stuff prototyped up to justify the hateful act of resin casting. I hate resin casting, but strangely I end up molding up roughly 80% of everthing I touch. I guess I'm paranoid about wanting to do something twice and having to make two scratch-builts. I dunno.

Anyway, here's a quickie on how its done.

I lay out the parts on a flat surface and build a box around them. Usually I jam-pack a mold box with stuff, but in this case I wanted to use a box I already had and I didn't have that many things to cast.

BTW, the twelve little intake trumpets there are for a Porsche 917/20 "Pink Pig" project I'm doing for my daughter.


I use GI-1000 RTV silicone. It's a two-part deal. It's not the best, but it's not too expensive and it's easy to use.


It's important to stir/mix both constituents. Lots of people don't do this and end up with 'soft' molds.


Another important issue is to get the ratio more or less exactly right. It's 10:1 by weight and any big-time deviations will come back to haunt you. I use a good quality postal scale for measuring.

Also, good ventilation is a must. The vapors from this crap are known to be neurotoxins. I mix in front of the window and run my fan at full blast.


then, after a thorough shaking, I weigh in the catalyst.

[kitbash]

Then I stir like an SOB; you do not want any unmixed components in the cup.


Thing is, the stirring introduces a galaxie of air bubbles to the mix. These bubbles will potentially ruin the mold because a bubble can settle on a part and create a hollow space. When the rubber sets and you remove the master, you'll have a sphere of air touching the surface of the mold cavity. When you fill the mold with resin, the hollow sphere of air also fills and when the part cures you have a "wart" on the part.

So you have to de-aireate the cup full of mixed rubber.

I built up this vacuum chamber setup years ago for just this purpose. The rubber won't de-aireate below 29 inches of mercury so you need an industrial pump.


Here's the cupfull of rubber in the chamber; you can see the rubber actually rising in the cup as the bubbles expand and fight their way out of the cup.

Moments later, the cup overflowed as I'd screwed up and mixed too much material for the size of cup I had.


Look carefully and you'll see rubber on the handle, sides of the cup, etc. What a friggin' mess.

[kitbash]

All that's left is to trickle the rubber into the mold box. This has to be done fairly slowly and carefully so that rubber will find it's way into every little nook and cranny. I know some people just dump the rubber into the box and I suppose that works...but I don't like to take chances so I trickle it in off the end of a popsicle stick. Here's the parts mostly covered up.


I also had a box full of 1/43 Pink Pig parts to do...


In 24 hours I'll de-mold everything and cook the rubber molds in the oven for an hour or so at 150 degrees. I find cooking the molds gives them that last little 'cure' that makes them hold up a bit longer. Most molds don't survive past 50 pulls or so.

[kitbash]

While I'm waiting on the "cake batter" to finish cooking I'll take a look at the intake maifold. It's going to be a challenge.

Here's what the real RA-V manifold looks like:


I'll explore the possibility of using the Monogram GTO manifold as a starting point. I'm skeptical, but....

I grabbed one out of the parts box and started hacking it up.


Turns out there was a lot to do to get it close enough to the right shape to decide weather or not I could actually use it.

I cut out that stupid distributor and opened up the appropriate air spaces, then split it lengthwise and widened it.



I have a bad feeling that by the time I get it into shape I could have carved one out from scratch...but I'm gonna try it anyway.

More to follow.

[tuned.by.twenty]

I'm amazed at how this is coming along!

[kitbash]

Here's how the finished molds turned out; I cast some parts off them.


There's no air bubbles and the molds are nice and sturdy.


I start by placing the molds on a small nylon cutting board that I use only for casting.


There's about a jillion different compunds you can use, I've been having pretty good luck with this Polytek Easyflow series.


It's a simple 1:1 mix. It has about a five minute pot life, which is plenty of time to coax it into a mold and do all the other stuff you need to do.

You pour equal amounts into two separate cups...

[kitbash]

...Then do your mixing in a separate, third cup.



Then you stir "enthusiastically". You have to be VERY careful here....you need to ensure thorough mixing with no excess of either component sticking separately to the side of the cup. But at the same time, if you stir too roughly, you'll induce a sea of air bubbles that will end up being cast into the part.


For filling the molds, I like to use a curved-tip syringe. It lets me get resin into every nook and cranny, while just dumping it in tends to trap air bubbles at the bottom of the cavity.


Then I shoot the molds up..



Any air bubbles I see, I flush out with the syringe.


The next part's a little tricky.

With open cavity, or "slush" molds, the idea is you just dump resin in and have a part with a 'bad' side to it. I don't like my bad sides to be too bad, so I take a 4" X 5" rectangle of thick plexiglass, and lay it carefully on the mold surface.

This squeezes all the excess resin off the top surface of the mold and gives me a nice, flat uniform back surface to all the parts. Otherwise you'd have a big, unwanted blob of resin on the backside that you'd have to sand off.



Here's my sure-fire cure for those pesky, tiny little air bubbles that you can't ever "tune" out of the mold...I use a pressure pot.

These are nothing but pressure painting cans, and can withstand pressures up to 50 p.s.i.

The idea is, the air bubbles are trapped in the resin at atmospheric pressure. If you pressurize the bubbles, they'll naturally shrink down. AS long as the bubbles are small enough, they effectively disappear.

[kitbash]

So you slide the wet molds into the pressure chamber and clap the lid on as fast as you can and secure the four wing nuts and stick a compressed air line on the valve and pump that sucker up to 50 p.s.i. and that's the whole show.

If you can get all these gyrations taken care of inside the five minute window, you're golden. The resin will gel, then set, then cure.




After 40 minutes or so, you take the mold out of the chamber and peel it away from the plexiglass. If everything worked right, here's the result.



Peeling the sheet of parts away from the plexiglass, you have a super-thin skin of resin that holds them all together and is really easy to back-sand when you're ready to remove them.


Remember my brass turn-signal bezel half? Here it is next to a resin duplicate. A couple more and I can trim them up and assemble them.


More to follow.

[tuned.by.twenty]

Wow.

[Dean23]

WOw this is an insanely good build. I find your casting very interesting....I dont think I have the patience to do that.

[Raceman]

The casting HOW TO ist great.