The 4300(4270 and the like) was a bigger tractor, the cab is different and the hood larger and longer. It was the bigger truck for hauling which shared a cab to a paystar which was a heavy duty on/off base chassis
the S and F series were based more on vocational - delivery trucks, single axle dump trucks,school buses etc.
Having smaller hoods and cabs, granted there are always options for dual axle, wider cab i believe, set back axles etc
Im sure there is more to it and I think I have most of it somewhat correct, Dave can correct me!
Using rtv silicone, you will really only need the mold release for 2 part molds, and Easy at home recipe is simply petroleum jelly, just graze the jelly surface to pick up most of the oils and spread away, you can mix it with mineral spirits to create a thinner substance but it works both ways.
Resin speed fluctuates with not only its mixing time of a specific brand/model resin you are using but also the temperature and mass of the object you are casting. thin walled items will set up slower than a thicker object but the speeds arent very noticeable with a fast kicking resin. The biggest problem I see with folks casting items as a hobby is they use a fast set resin..and it really ticks people off when they get bad parts which is understandable, Most resin casters have been there.
While mold design and air key ways play a big part in how easily the air travels in and out on a mold, the big culprit is the fast set resin, how fast is yours? I recommend a medium speed resin without pressure pots, heck smoothon makes a very slow resin also that will give you 20 minutes of MIXING time..which if I was a patient person who wanted to get the most out of my resin with more than enough time to knock out most of the air bubbles. id use it. It has a demold time of 2-4 hours but that can be a bit longer depending on size of item and air temp.
Checkout smooth-on smoothcast 305 and 310 if you wanted to try a new resin.
Now the molds themselves, have any pictures? how are they vented? ive found when casting tires using 1 vent hole that is both a fill port and vent. tap of the mold a few times on a hard surface when almost filled, will knockout the air pocket..however that's using smoothcast 305 medium set resin so i got enough work time, you may not have that.
You can try putting your resins in the fridge before you mix to buy you a minute or two, some folks do that..i never tried it though.
If you need a quick release using household items, good ol vaseline/petroleum jelly works well, just lightly graze a brush/your finger on the surface of the jelly to get its oils and rub the half of the mold.
Michaels use to carry plastikote till the valspar name swap happened, however the remaining lacquer went to clearance. I bought abut 10 cans for 2 dollars at the few michaels I have in the area. last year
I would avoid all starter kits, why? The resin you get has a really fast setup time, this can discourage many folks starting out. You will need to work quickly, and to be honest it is just a hassle. Most often you will also get a 1:1 silicone, which doesnt last very long making parts.
I would start this way..
Smooth-on makes many silicones and resins with many set up times in "trial kit" packaging, the same size items found in the starter sets, its just you are picking what would be a better experience.
Smooth-on smoothcast 305 for white parts, or 321 for tan parts these resins are the same just a different color, it has a 7 minute mixing time and a 30-1hour demold time, it is much easier to use than the faster stuff as it allows you knock out air bubbles or pick them away.
Silicones, this is where I would use a 10:1 mix silicone, you will need to weigh it with a gram scale, but its really easy..it sounds more complicated than it really is.
Smooth-on mold max 20 would be a great way to go, you get about 45 minutes of actual mixing time with it, allowing you to pour thin streams to get the least amount of bubbles in your mold.
Now you can try the smooth-on mold start silicone which is 1:1 mix and very durable, but platinum based silicones dont play nice with some masters, so i would hold off on it till you get your feet wet.
Some folks may suggest the Oomoo 1:1 silicone but that stuff is not durable at all, you can tear it with your hand, its only good for a handful of castings ..a bit more if you baby it.
It is pricey...but the way I see it, I spend the money and buy the 16lb kit (im on my 3rd one) a typical tire weighs about .20 ounces, so I can get 5 tires to 1 ounce. Also if you dont want to order from them directly (they are in Pennsylvania) get it from "brickintheyard mold supply they are in texas.
I used there dye..but I used smooth-ons and saw no difference, but thats only my experience.
To be honest I dont have a ratio, lol...I just squeeze it into the 1 gallon jug, get a real good mix and test its clarity, if it still looks clear green i will add more dye till its not as translucent.
Greg, Try polytek PT Flex 50, I use it for all my tires. its a casting rubber rather than a molding rubber so the viscosity is about 600! which for a rubber that is thin. I can pour tires and demold them in 45 minutes.