Sorry for the comment out of ignorance- didn't mean to ruffle any feathers (sorry for being such a hoser)! The only molds I've dealt with were either metal or rubber (and this was over 20 years ago). Anyway, soundes like things are working well- looking forward to your updates.
Got the mold to work and the core. Still a bit crude but we are making progress. Used a baked sand core. The clam shell set up of the mold works well now. I need practice now. Here are my two babies sitting inthe window. Preheated the mold just before pour. Not too hot just enough so we could see it smoke here and there. Put a bit of mold sand in the bottom of the mold to help with realease and to stop leaks. Seemed to work and that will be machined anyway. The seam for the clam shell joint is minor and positive so the lathe can get rid of it . Gotta quit for a couple of days. Worn out. Don
What kind of a sand mix are you using for your cores? I've heard of using linseed oil to make baked cores, I've never done any molds with a core.
I chucked it up in the lathe as cast and machined the lower skirt area. Monday i will turn it around and cut the top and ring grooves. Am I satisfied yet. Not quite . But I am a whole lot closer than I was a week ago and I have had a ball! Baked mold core. I mixed my green sand (the stuff I found here BTW) 1 part wheat flour and 20 parts sand. I mixed it well. I tempered (moistened) it with molasses water which is 10 parts water to 1 part molasses. I spread the sand flour mix out on a flat area and sprinkled the sand with the molasses water till it it just got a little darker. I made a paper liner of the exact diameter and placed it in the first piston i made then packed in the above mixed combo. Not crazy tight but snug. Being in the paper which was taped together it slipped nicely out of the piston. I placed it in the bottom plate of my mold which has two holes in the bottom and shoved a bit till some of the sand protruded through the holes just a bit. I had asked MRS D about baking in her stove. She replied by showing me a toaster oven on sale in the weekend flyer. I found a cheaper one at CTC . $18. I put in the bottom plate with the core paper and all. in the oven and baked it at 300 degrees 2 X 15 minutes. Surprisingly the paper didnt burn. I carefully removed the paper and the core was now stuck on the plate to which is a bonus. The core is quite stable and after the pour and cooling I had to smash it.This is the first sand core I ever made . It was good but I know now I can do better. I am however going to finish this piston first as it is good. Don
Wow! Simply amazing-great job! I'm curious how the crank mods turn out, andhow these pistons work for you. I'll stay tuned...
No. because of the increase in stroke I will not need a big dome. The head cc is only 44 . ------ I didnt know paper burns are 451 Thanks. So would it be safe to think wood is similar? If so I can make a wooden mold for the core and bake it . Then all my cores would be the same.
Might be ok. I think in production foundries, sand cores are removed from the core box, allowed to air dry then baked. If you were to bake a core inside the core box, it will take more time for the heat to soak through the piece. Solid wood is also prone to cracking when force dried. If you had some Baltic Birch plywood, it could be laminated into a block, then machined to make the core box. Plywood is more stable, less likely to crack.
I was involved with pistons and piston manufacturing for over forty years. A steel mold (or mould in Canada?) is not a good idea, but it might be o.k. if you turned enough stock off the casting. Sand casting would be better for what you are doing and not hard to do if you want to do your own casting. It would be easy to make a pattern and go to a small foundry. Check your local Yellow Pages. Research shell molding pistons just for more info. <OMelt down some old pistons if you want to get a good alloy. It doesnt take a lot of heat. Ive melted pistons with an acetylene torch to cast in a steel mold (making slalom ski fins, backroom at GM). <OSteel plates are usually cast in around the pin holes, and are called chill plates as someone mentioned here. This gives density and strength around the pin holes. <OPistons used to be cam ground but have been complex turned for several years now. Both cam grinding and complex turning are very precise machining and the grooves are too, and the pin holes too. Pin holes are offset to control piston slap when cold on start up. Offset was usually about 0.060. Racing pistons in my experiences were on center and not offset.
Strange, I didn't see anyone saying it couldn't be done. I did see some expressing concern and advising caution. Amazing how often people chime in with something they thought they read. Reading comprehension is your friend.
I have melted down old pistons for these. 454 chevy to be exact. I understand exactly what you are saying about the steel mold. I still am not satisfied with mine. I have some grindng to do. I understand about pin offset and have given it some consideration. I will do a sandcast later on. I have to make some mold boxes but have actually started on it already today. I have never tried a two piece mold . cope and drag so i was a bit nervous about that. Of course I never tried this before either. I am learning as I go though and really enjoying the trip! We have several foundries nearby and I have had manifolds etc made but this project is all about doing it myself. That is my whole motivation for trying this. Thanks Don
Sounds like fun. One of the guys I worked with made some hugely oversize pistons for his antique John Deere several years ago. Tractor pulling, 'stock' class. We all got involved. He had them cast at one of our foundry suppliers, then machined in our machine shop. Not exactly like doing it at home, but these were the largest pistons we ever worked on. Just turned them round. Worked just fine but no high rpm there.
A lot of guys like me with Ford 400's may be interested to see how this turns out. It's easy to destroy. Any chimpanzee can do it. But it takes a lot of thought and perseverance to create. I think it's built into us to want to. Keep up the good work! It's very satisfying to watch your ingenuity, struggle and eventual success. I'm rooting for you!
Thanks. Little my little I make mistakes and figure out how to correct them. Lots of the tips have been helpful.This is to me very interesting. I need to pour through a sprue I think so will make a lid for this mold with a sprue and riser. That way I wont get the cooling depression.Also less waste and machining. I couldnt wait for that though so these were poured with the top open. I have to reward myself regularily with a pour to keep up my interest. Don
I think one or two people expressed concern about mixing water with sand and having an explosion. It is possible. Due to the nature of the sand mixture the water doesn't get trapped (providing it is sparse enough) and is released between the grains as steam. I have also heard that it is good to perforate the sand mold so that the steam leaves more quickly; molten aluminum readily absorbs hydrogen and this is where porosity comes from; and water is 1/3 hydrogen. Degassing the melt with nitrogen (bonds with hydrogen) bubbled up through the melt or degassing tablets, and generously venting the mold while not poking through into the chamber is supposed to help keep the porosity down. Iron can change the physical charactaristics of the alloy to make it weaker, but I think it is the crucible that the aluminum is melted in that is the problem here and not the mold. Petrobond is supposed to help avoid the problems with green sand molds but some people don't like it because it is messy. I've read that a well vented, properly mixed green sand mold works very well.
Here is a link to a guy's website who makes very nice castings for medical equipment for hospitals in what is a very simple homemade green sand foundry with what is essentially a modified Gingery-type "bucket" furnace, propane powered instead of charcoal, just shows what can be done with simple equipment: http://www.stinsonvoyager.com/HomeFoundry.htm
I checked it out. Very interesting . My burner is a lot simpler but it works well complete melt in 15 to 20 minutes. I will probably make my mold boxes tomorrow. I have all the stuff by the saw. I am still comitted though to making this metal mold do the job but see no harm in trying a sand one either. Don
I think one or two people expressed concern about mixing water with sand and having an explosion. It is possible. Due to the nature of the sand mixture the water doesn't get trapped (providing it is sparse enough) and is released between the grains as steam. I have also heard that it is good to perforate the sand mold so that the steam leaves more quickly; molten aluminum readily absorbs hydrogen and this is where porosity comes from; and water is 1/3 hydrogen. Degassing the melt with nitrogen (bonds with hydrogen) bubbled up through the melt or degassing tablets, and generously venting the mold while not poking through into the chamber is supposed to help keep the porosity down. Iron can change the physical charactaristics of the alloy to make it weaker, but I think it is the crucible that the aluminum is melted in that is the problem here and not the mold. Petrobond is supposed to help avoid the problems with green sand molds but some people don't like it because it is messy. I've read that a well vented, properly mixed green sand mold works very well. <!-- / message --><!-- sig -->__________________ When I was casting the wire wheel adapters I discovered that if I let the mold air dry after the mold was formed, even a couple of hours these type of problems disappeared. It was the success of that project that got me back at this one. Don
I'm making the patterns for a small lathe and will be trying to cast them soon, and I've been studying up on the process and threads like this help a lot. I want to learn as much as I can about this. Every bit of info is helpful. Casting engine parts in aluminum is about the coolest thing I can think of! P.S., Those violins are beautiful.
if your thinking about casting some small scale to start pm me because i would be interested for some over sized ones for a weed wacker bike im building. thanks
Here is the piston with more machining. I have also located the ring grooves . Top ring MUST be .150" down to survive comfortably. I am making this a two ring. Why because I am only going 1/4 mile tops. This piston looks no different than out of the box ones to me. Would I use it? Yes I can honestly say i would. However I have a few mods I would like to do. First I have to grind a few bumps out of my steel mold and make some minor adjustments. I need to positively locate the core the same exactly for every piston so I will make a wood fixture for that. The mods needed are minor . The basic idea works. I will completley finish this piston over the next few days (I hope) and will post as it goes. BTW when making wooden patterns dont forget to make them too big and make any holes too small. The shrink rate is about 3/16 if an inch per foot of diameter. One book showed how to make a foundry ruler for aluminum by using a normal ruler as a guide and placing the new stick to be marked on an angle then transferring the numbers accross with a square. I did that when I made my flow bench only horizontaly so the idea will work I know. Don Oh yeah I also made a pair of molding boxes this morning. The glue on them is drying as we speak.
Just did the calculations on using a 170 block and a 198 crank if I can stuff it in the block. Compression distance I calculated at 1.4825. (Difference in stroke is .515". 1/2 that since it comes up 1/2 that higher and 1/2 that lower to make the whole .515" is .2575" increase in hight up the Bore at TDC. The 170 is a zero deck engine stock so if i move the pin in the piston by that much the new piston will also be zero deck at tdc with the new stroke. I measured the newly minted piston and the pin hole will be well centered in the cutaway part of the skirt. I am cranked now! These are just my initial calcs . I will sit down and triple check everything before I bore the pin hole. Also have to drill oil ring drain holes. That wont be fun but that's life. Compression ratio will be just above 11.9 from initial calcs.
Hey Don, you think you could make a set .030 over for a 400 Mopar that would bring the compression up to a REAL 9.5:1 and not weigh 10 lbs each like the stock ones do? Just asking . . .
Why do it? Because he F'in can! I would kill to go hang with this guy for a week. (plus it looks from his svelte figure and sounds like his wife can cook too LOL) Go read up a little on him and then ask why he does stuff like this. http://www.google.com/search?hl=en&source=hp&q="Don+Dulmage"&btnG=Google+Search Sorry Don for maybe exposing some of your talents but you deserve a little more respect I feel. This ain't just some crazy old Canadian guy in his garag... well ok got me there, but he knows his shit! All my best and respect from Texas to y'all.
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