Top ring groove is a milimeter or metric . I took the dimensions from a 5.7 piston. Same for the second ring. (from a 5.7) I dont think I would use the narrow oil ring again. Drilling the tiny drain holes is too tricky. I broke a drill off in there and fooled around for two hours with a needle getting it out. Besides with only a compression ring I think the 3/16 style oil ring would do better on smoke control. I learned a lot machining this piston. I need the core slightly higher so the holes for the oil ring come out into the core. A couple did but most I had to drill for. I lost a bit of lower dimension not clamping the mold to the base as it has a small leak. It is still good but not perfect. I MUST get in the mold with my die grinder and make it perfect. The imperfections while they would not affect performance are not acceptable to me. You can see in the shot of the oil drain holes where the weld was not trimmed well in the mold. That is easily fixed. You have to machine pistons a certain way so you can chuck them true and must leave the final work for the end like the inside skirt taper. Luckily I have remachined enough pistons to remember this but it was not always so. Final weight was 410 grams. I was surprised. Piston does not seem weak in any area to me I am confident it would perform. Re 400 pistons. The ones I had made for Christophe Schwartz;s Lemans practce car engine were made to my specs by Ross. I forget what they weighed (690?)but it was less than stockers for sure . They were forged and 9.6 to 1 comp. Last i heard that motor is still running with only a intake pan or tray needing to be replaced this year. That is 5 years of hard road racing. I am pleased with it. Anyway. I pushed this through. It was fun. I have learned a lot. Before the snow falls We will melt a bunch of old pistons and cast probably 8 cores to work on when we are bored during winter. First though I must find a 198 crank and see of I can stuff it in a 170 block somhow. Thanks everyone for the tips and encouragement. So is it possible to homecast cast pistons and come up with a useable product? I would say absolutley ,yes. Is it easy? nope! But it is fun D
Cant Unk. I have to make a lub channel instead. I rough finished the pin hole in the mill. I aways hone for the final. Don
Couple of shots from last weeks pour at Don's. Heading over this am, another session coming up. Don is trying another mold. Will get some pics. It's just 2 Old Farts having way too much fun!!!
When I get my mold boxes done, I'm casting you a Hamb award of some sort. this the the best thread i've read in a long time.
Some knowledge, wisdom, patience, time, food, tools, throw in a nap once in a while spells danger. And now they run in pairs...soon there will be many...this could be trouble in the making!
I just got the image of a couple of guys communicating with a series of grunts and eyebrow motions The piston comes out of the mold and one guy points to the milling machine and says "Uh! Uh Uh!" the other raises an eyebrow and says "Uuuuuuhhhh!"
Actually we worked together 68-69 (AMC BMC Jag Triumph). Not a whole lot of converstation goes on, tis true. Anyway the sand mold was a disaster. Gotta use a baked core for the inner otherwise the steam just bubbles away. In fact we made some aluminum bubbles. Spent the whole morning after the illfated pour melting down 12 pistons that a friend donated. Vern was dosing off so he finally went home. It was too exciting for the old guy! I baked a couple of batches of muffins after he left. Used up a whole tank of propane but I want a good supply of ingots for winter. It is pretty messy melting old pistons. When I recast them as muffins I get rid of the crap and get a nice clean ingnot that fits in my melt pot nicely.
I have come to some conclusions. Some may not be right but so far this is what I think. Sand casting . It is good for "one off" parts but the finish or surface is not that great. Even some professional casting I have had made required a lot of finish work like this manifold lid I had cast at a local foundry. I no longer have pics of it in its rough state but i was not impressed. It took a whole day to make it pretty. Still if I need a roughly shaped part for a project that i will be machining or cleaning up I would use it in a heartbeat. I had some injector bodies cast this year at a local foundry. They were not a whole lot different in finish. Sands . Oil bound sand works better than water bound. Steam (from water bound sand) is a real issue when casting hollow stuff. Drying out the sand mold with a heat lamp overnite might work. I may try that. Baked cores work well. I had no trouble with my baked core and it was easy to make. I shall make a wooden forming tool first before I do any more piston casting so all my cores will be indentical. I am really tempted to try a baked sand mold as well. The big trouble with a sand mold is it isnt reusable. You have to make a new one everytime. When I did the motorcycle adapter cast i was able to repair my oil bound sand mold and cast in it three times. I was lucky I think. Permanent Steel mold . is my favourite. Casting is dimensionally good everytime. I can chuck them in the lathe right out of the mold and the runout is minor. The very first cut you make is most important because it establishes the "Register " for all other machining operations. When modifying or machining these home cast pistons I cut the bottom of the skirt square first. After that I go to work on the diameter. Once I have those two operations at right angle to each other I can go ahead and machine to my hearts content knowing all will be well. I next cut the crown of the piston square (even if I will change that later ) because I can now mount it in my milling vise and not worry is it square or not. Someone mentioned spincasting. I was in Holland a few years ago (Visited with our NL Mopar Hamber) and went to a pewter factory. They were casting pewter in a spinning deal like a big wheel. The hot metal was forced hard into the molds by the centrifugal force. That would probably produce a very strong piston (using aluminum of course) compared to gravity casting which is what I used. However it is getting to comlicated for this old fart. Someone younger might want to try that. Clay Mold. I would like to try sometime baked clay molds. I believe they could be reusable and might give a better surface finish. I reserve the right to be wrong but this is what i think so far. Don
Maybe try Investment Plaster. Used for doing Lost Wax casting. Should give a very nice finish, but will be slower. Probably have to heat the investment, after it has dried., to get the best results. The right molding sand, will improve the finish.
i wish i could see all the parts of Burt Munro's piston mold, what are you doing to prevent core shift?
Core shift. As for the sand core I bake it already mounted on the bottom plate of the mold. it has 2 7/16 holes and before baking i push on it slighty to register the sand to those holes however after baking it is actually stuck to the plate anyway. Other wise as for general shift,you make the raw casting biggger and the core smaller and machine out the errors. Actually other than fixing the weld areas of my mold I am very happy with it and how it works. I figure it will only improve "HOWEVER!" I went to the craft store to day and bought some natural clay. I wraped my first poured piston in Clingwrap and then molded very thick a clay jacket around it with a sprure built in. I then with a very thin blade cut through to each side of the piston. (the flat side) In 3 to 4 days it is supposed to dry enough to handle . Then it is out to the toaster oven for the bake off. I put XXX on both halves. My wife asked why since I dont partake of alky. I told her, "Because Sweety, this is "real" homebrew!" Might work, might not. This is the only way i know to fnd out. BTW I found Steve CH Casting pistons book today. Now I remember why I gave up several years ago. Glad I couldnt find it while I was doing it. Don
I have the plaster too. I tried it years ago and had a big blow up while trying to cast some emblems for my MW car. I guess you are right . If I baked it it might be ok. Don
Real Clay will shrink as it dries. Not sure how much. Maybe do a test. You could build the piston up with masking tape first, then apply the clay. When firing clay,or investment plaster, it is usually heated slowly to 250 F , to drive off the bound water. Then it can be heated faster.
Thanks. Hopefully the cling wrap will absord the shrink. I didnt realize that it shrunk when it dried. The mold is a bit loose anyway . Maybe it will be ok because of those two deals. Oh well I will know in a couple of days. Thanks for the tip. Keep it under 250 for the first till the water or moisture is gone then turn up the heat. Ok. Thats the stuff i need to know. I missed crafting 101. Don
It needs to be dry to the touch, before it goes in the kiln. How long that takes, depends on how thick it is. Water expands by some huge % when it turns into steam. Very dangerous. If you are planning on pouring Aluminum into the ceramic mold, be prepared in case it cracks from the thermal shock. Preheating may help. If i wanted to try clay, first choice would be a clay with a lot of Grog in it, like a Raku clay. Air setting sand might be a better idea.
I have no idea what Raku clay is. Apparently this is a natural clay that will air dry but can be treated like any other clay. I guess if it splits it splits. What i should be doing is finshing up my steel mold , fixing all the little spots in it and making a baked sand core molder. I guess i am kind a worn out for awhile and this is a nice distraction. Don BTW failure doesnt bother me. It is success that scares me!
Don, A couple of things, if you can come up with some powered graphite, cut it (thin) with alcohol, brush it on your sand mold to increase smoothness of mold and part, burn off the alcohol off that reduces water/steam problems some. Have you brought one of your turned pistons up to operating temps and check it for expansion rate of your metal? I'm enjoying the ride! wish you were closer I could play along.... Be safe! tt
There really isn't really a Raku clay, Raku is really a family in japan that makes a certain style of pottery, its sometimes used to refer to a style of firing pottery. All clay is air dried to a "bone" dry state before firing for pottery. the slower you allow it dry the less likely it is to crack. I made pottery for a while there are many different types of clay with different characteristics, usually the maximum firing temperature, but the process of working with it is relatively the same up to the firing point. Hope that helps -Kris
Ok, I am learning . Thanks. I am exhausted. I spent the morning playing my homemade fiddle at the 1802 Station Jam and came home about 11. I have been baking alumnum muffins ever since. Baked all the aluminum melt I had from the donated pistons. Now have a bucket full of muffin shaped clean ingots. Even made my wife Linda special one with her intial cast in it. Gotta score a few points now and then! I took a picture of it and it is below. I was worried about the ceramic thing so i asked her if she had any old pottery cups she didnt like. Three seconds later i had one in my hand. I hid it behind my heavy wood pouring stand and poured it. I got almost half poured, no trouble then ker-bang. You were right! Now what . Maybe i will take your suggestion and make a small mold, fire it and then pour it to see how this clay reacts. I dont understand yet why that happens. The ceramic has seen for more heat than aluminum ever will . Anyway I will search further before risking a pour. Worst case senerio I can make styrofoam pistons and bury them in my sand and pour that way. Thanks for the graphite tip. Don
Are you putting steel stiffening ribs in the skirts? If this is about making race pistons for the leaning tower of power,then maybe you can look thru parts catalogs for a stock application from another engine with a useable bore size that can be used on your application. There are companies that make steel rods in whatever length and journal sie and width you need if you need to make a custom length rod to use a piston from another application. It is cool what you are doing,but cast pistons with factory stiffening ribs are a risky deal in a race application. I would be very nervous running pistons like yours. This is pretty much how we build race motors with oddball strokes and deck heights,we just go by the bore size and compression height we need and see how close we can get in an off the shelf piston.
The problem is in the temperature gradient. When you poured, the ceramic was HOT on the inside, relatively cool on the outside. The inside wants to expand faster than the outside. Eventually the stress exceeds the strength of the material. That is also why Investment Plaster is typically preheated to 1200 F. Then there is no shock when you pour your metal. Molding Sand doesn't have this problem.
I think those are to reduce expansion, so you can run tighter clearances to reduce piston slap at start up.
Personaly i would think the way to go would be a steel mold with a baked sand core. That way you could keep the steel mold and just bake up a bunch of cores and crank 'em out. Just my $.02
In one of the Egge piston videos, they show preheating the steel mold. I'm guessing, after the first one is poured, it will hold enough heat that there is no need to preheat before every piston.
Nervous? I am not really as I have been building race engines for 41 years. I have made many pistons from oversize cores. Here is how I think. If this was a customers engine I would not even consider this. Why? Because I think it is risky? No .Because a customers engine is not an experimental engine. It has to work without trouble from the git go for a good long reasonable amount of time. However me, I am now 60, retired and curious. At best if I am lucky I may get to go racing 30 or 40 more times in my entire life. I built every inch of the Sr dragster myself, including the steering wheel the shifter the front axle the chassis etc etc. And of course the engine. I even tried successfully the six snowmobile carbs on a home brew IR manifold. Now I want to make and pour my own pistons. I know just from 41 yeares of experience in both racing and genral mech/mach that this piston is strong enough. I know in some areas it is stronger than the pistons I melted to make it. So that I am not worried about. Making 6 exactly the same is the big challenge to me so i will make 8 in case i have a mishap. It is just something I want to do. Since it is my car my gold and my problem if it isnt successful what can it hurt? No one but me. I am keeping my current engine too so at best I would lose a weekend. Humour me. This is for fun. I have learned so much in just the last 2 1/2 weeks I can hardly sleep. To me this is what makes life worth living. To others I understand it is not , maybe even stupid. But what if it works? I remember when I built my first fiddle. A guy asked me where I bought my "tone woods." "Tone woods?" I said. "I got the wood at home depot." He almost passed out. Now I have made 8 and had them played by some very good (and famous) fiddlers too. But like this project, I make them for me. I dont sell them so I figure it is no bodys problem but mine. But I have had so many of the "you cant do that" things turn out great I have learned to step out and give it a shot. The pres of Weisco Canada has been watching and said I am current with how pistons are made in China today. He actually had nothing bad to say , just wanted to see the finished product. Would it compare to theirs? Of course not . Will it fail? I doubt it. Am I learning? yes. Am I having fun? yes. Does this project challenge me? yes. Am I excited.? Man i am so cranked my wife says I am talking about it in my sleep. These are for me the golden years and I intend to make them as exciting as I can. My health is failing as i age and I get stiffer everyday. Some you will understand why I want to do this. Others will think I am crazy but you should know I have been for a long long time. Vern will tell you in case you are in doubt. So far its working for me. Don Oh yeah, about using pistons from another engine in the block. I guess I should tell you the current slant six engine and only engine the car has had has 194 Chev 6 cyl pistons in it. Yes It is bored that much oversize. I was told that wouldnt work too.
Always something interesting going on at your shop Don.... Your a real insperation for me. Did you see dad at the station today?? He would get a real kick out of this project your into!!!! Hope to catch up to you in the near future, maybe get a first hand look at the process??? Good luck with it either way.
The Jalopy Journal
