Because it is a raw casting it is not perfect. To use the maximium meat of the casting for the skirts I need to centre it as perfect as possible. Notice I said it is to ball park it. It is not for final centreing but to get it close so when you come to the final .001" s you havent spent ten minutes fooling around to get it to it best possible spot. . I found I was spending a lot of time getting it in the ball park zone. Once there it is not too hard to get it nearlly perfect with the dial indicator but because it is a rough casting you are chucking a slightly different shape each time. The rough cast skirt just protrudes through the bored hole in the jig. That gives you a decent centre of the skirt to work from and chuck it then begin working it to perfect before the first cut. Normally when i rework pistons I am using a machined core and I have done a lot of that but this is the first time I had to machine a rough cast core and this little device helps cut my set up time. Slide the rough casting in the hole. Set the jaws so it rotates without rubbing and then remove the jig and do the final with the dial indicator. The jig registers postively off the ways and was made using lightly trued piston already chucked and cut in the lathe so it was true . I like it anyway. Saves me time and prevents costly mistakes. If it isnt right it is obvious. With a slipper skirt you dont have 360 degrees of dial indicator to work with. Maybe only 80 to 90 degrees. Don I was chucking the dome.
I went to the shop just before suppper, i took a unmachined raw piston casting and using my wooden jig set it up. I was able to take my first cut in about 3.5 minutes and it was a good one with contact on both skirts. It was a very light cut too. To set up the one I used to make this jig i spent over 1/ hour and it wasnt as well set up as this one. Maybe i just got lucky. I will try another tomorrow. The graphic i made shows (to me anyway) why it works. Rough casting , no real good surface to indicate from . Jig gets it in the right place right away and you can fine tune it from there. It was awful close though when i finished using the jig. I was surprised. Don
Here is the first one off. Still have to drill the oil holes , bore the pin once i am sure where I want it. (when I have a 198 crank in my block, so far i dont have one)This is higher compression than the first one I machined a couple of weeks ago. Don
dam that almost looks like a real piston, so your holding this on the outside with your 4 jaw? will the pin be free floating? so what does the top ring look like, i have never seen just one compression ring
Don. really nice. Thanks for all the hard work in posting this stuff. My thought on having a metal insert for the core. If you put enough draft in it, as in a self releasing taper, would not the slug want to walk itself off the insert as it cools rather than grabing/sticking to it? What I remember about off setting the pin was tha Smokey did this on the early Chevy which had an offset pin for noise control. He put the pistons in backward and found a gain. I did flathead pistons and also found a gain on the track, not dyno proven. And I used .060 over pistons and offset turned he skirts to standard and thus had a .030 pin offset. And the tech guys could not figure it out. Up to you, maybe on the Generation II Piston project? Frank
Single comp ring pistons have been around as long as I have I fear. Lunati offers them just for one as do several others. You sacrifice a little of this and a bit of that but you hope that the loss of friction you gain will pay you back. Also you can make the piston probably 80 to 100 grams lighter. These will be press fit. In my many years building BB mopars for racing and hot street I got very familiar and very fond of pressed pins. I know how to make them bulletproof and to me the clips spiral-locs or ****ons depending on your choice are just extra unecessary parts waiting to fall out or give you trouble. The biggest drawback with pressed pins is you can't lean over the table and say "I am using full floaters with spiral locs." (which are also very reliable. BTW) Pressed pins done right DO NOT EVER give trouble. Top ring is a normal compression ring but is the new metric thinner width (mm). Oil ring is old style 3/16" but I guarantee it will be made by Hastings Ring with their "flexivent" design. Don
ALuminum shrinks about 0.15" per foot, depending on the alloy and pouring temperature. Even with a 5 to 7° draft it might shrink onto the core without squeezing it out and this will cause it to crack or set up internal stresses that can cause a crack later, maybe even during machining. On second thought, though, a taper like that might make it easy to pull the core out while the piston is still hot. A ring on the end then stick a rod through it and tap it out with a hammer. The finish from the core where it contacted the core box (sides) is pretty good. The only rough looking part is the end (under the top face) where the core was patted down. This will probably not affect the function; the ridges don't look real sharp to cause stress risers.
Indeed. Pretty much any fast revving high RPM engine will default to two ring pistons now a days. They've had the technology figured out for a lot of years now. It's not super high dollar tech either, as we've run uber-lightweight two ring pistons in our alcohol race motors for years. That's oval racing, not drag, so they live a rough life, but they hold up just fine. Those motors had compression ratios of almost 20:1 too, so it's not like that single compression ring has a hard time sealing.
I tried a real slope on the orignal core .I even had two 7/16 bolts rigged to pull the core. It was in so tight I cranked till i broke the bolts off from the weld. Eventually I had to mill it out on the milling machine. I am relatively happy with my baked sand cores. It really is fairly easy to do and they dont give any trouble. If I run a gapless I should run the older wide compression ring because a gapless is really two rings overlaped simply put. The metric ring is already pretty thin. The there is the big question Do you really get more power with a gapless. Hasting Rings would call that into question and even our practice of file fitting. In their own testing they found no Hp loss till If memeory serves me .052". Then there are the hypereutectic guys running .026 to .030"gap They claim the gap is almost nil at operating temp. You have to think through all this and know that somewhere in there the truth lies but it may not be as obvious as we would like to think. GenII? I think it will happen. I built these to see if it could be done. It can, no question about it. Would I change some things? Sure I would. I would start with a bigger mold for one thing. I am pretty happy with these though. When you go back and read the whole thread and how i got into this sort of incidently after doing the other castings even myself I find it hard to realize what went on during the last 2 1/2 weeks. I am quite satisified with the pistons though. If you had one in your hand I think I can safely say you would never guess it was made here. I think those who have seen them would tell you that too or at least I like to think so. I will probably run a end mill in the top of the core depression for a quick clean up but it isnt real bad. It would just be prettier. Don If you read my mopar book you will know I am big into the reverse hanging of production type pistons. These however will be centered. I may get fancy later on. Who knows?
You're happy with the sand core. Then I'm Happy, too. This is a great project. I ran Total Seals on a few engines and was the most impressed on the reduced blow by. Really no blow by. This resulted in cooler oil temps and overall a cooler engine which led to no skirt scuffing. But these were not drag race engines, so maybe that wouldnot be a concern for you. Carry on I was thinking that the reason for casting just enough for this job this time was because if you needed to change the design, then you'd make a fresh batch with the changes. I approach this the same way. Frank
"Hypereutectic" pistons use a different Aluminum alloy, with a lot of Silicone(?). This reduces the expansion, but also reduces the heat transfer. So you can run tighter clearance on the skirts, BUT they hold more heat in the crown and require larger ring gaps. Learned about that in Harry Ricardo's book.
I am already thinking there but I must exercise some self disipline. I have my current engine needing a light freshening, a cam move (retard from current setting. Some fresh valve springs and a wheelie bar with a spring or shock so I dont injure my back again. (I am still sore from my last p***. )It needs also a better set of headers built for it. I have a slant six tunnel ram 3/4 built. A stroker I sold needing an external oil line made up and then delivered to the buyer. (482 cube 440 based with Indy heads) My 63 Dodge has been sitting on jack stands for a month waiting for its new lower A frame bushings and I have to decide if i am going to sell it or not. I have a big Block Chev oval port Engine to build for a ol friend who actually said to me "Donnie, will you build me a Bb Chev motor before you die?" It getting cold and i have wood to bring in as well. Then there is the other rail which needs at the least the rear end narrowing finished so i can at least move it around. Or yeah there is the violin with its back that you can see in some of the pics I took inside. It needs to be finished too. Good thing I am retired. I've got no time for work! Don
I am back at what I should be doing. Getting ready for winter. Gotta get the rail put away and the other rolling around and the 63's lower bushing finished. I am really having to squeeze size wise. I may have to reowrk the mold and repour but that would just be more fun. As far as making servicable pistons I am there. But i really want to bore the little engine to the max. Some of these wont quite clean at that size I am afraid. I could use them but I wont because It isnt pretty with unmachined spots. I was looking at the mold a few minutes ago thinking how I might be able to put a shim at the seam, file a couple of spots and get more than enough. However as you all remember I just started out to see if I could do it. I can. Now I want it fancier. I have other priorities right now though but am ok with that since I now know I can do it. Don This is how this all started a couple of weeks back in case anyone forgot or missed how I got into this adventure. "Because of the success in casting the wire wheel adapters i am going to try something I always wanted to do. Cast my own slant six racing pistons. "
Just found this thread, and Im speechless! Thanks, Im happy when I see guys (and girls) not being afraid to do things by their own. I think you are doing a great job and researching Don, I really hope you get your own pistons in the engine. Looking forward for read the rest of the story! Lars
Ok Budd , ya shamed me back to it. I went to the shop and made a .125"shim for the seam. That made enough difference to give me what i want. I also took the big rat tail to the two spots in the mold I dont like. (lower left from the seam was the worst.) Must have warped during welding. I also see the mold shell does not sit perfectly straight on the plate. I will fix that. I will spend a lot of time getting it right I think. I will also make a new bottom plate as the one I have I just scabed together as the first batch was melting. I will make it so it also positively locates the baked sand core. You know to be honest when I started I was probably as doubtful as some of you guys even though I defended the idea. Now having cast 17 pistons and machined a lot of them finding no voids I am realizing this is a very very doable thing. EVen though I dont need them right now because I have a 10.90 goal for my current engine I will poke away at this and hopefully will get it exacxtly the way I want them to be. The last one I showed you all is perfect quality wise (to my eye anyway) but like I said i am not getting a finished piston at 3.5 bore and that is what I want. I promise i will keep it updated as I progress but i have to get some other stuff done too. This is an aside and always was but it did get my attention too when things started to go right. So like the song says. "please be patient. its a work in progress." Don
I feel the same way when I try to think of all the little and large projects in my garage aswell, only I still got about 20 years of work to do next to that...
I am still hoping someday to get there again and have a tour of your shop. Still in the same building? AH but you are an inspiration to this ol boy as well. Right from the start you always had lots going on! Don
Same building, only it's interior space is somehow getting less and less every so often, haven't yet figured out why exactly. I think the number of parts I have in my garage is somehow related to the universe... it's always expanding! You're always welcome here Don. I wouldn't mind to drive the both of you around the region aswell in one of my cars if you like.
As we age you know we go back a long way dont we. I was thinking just yesterday of the first pic you sent me of your Chrysler sitting at the gas station. I think i still have it here somewhere. We were both a lot younger ! And the night we had a snack at the hotel was great too. Next time i will time my visit for a car event. Linda says HI Don
Worked on the mold shell today . Some of the mods can be seen here like the shim which is now welded to the one side. File grind polish fill and repeat is what I am up to. Don
OK! I haven't checked in here for a while, looks like you are making some good progress! I need to come back here tonight when i hav time to read more. Good job Don!
looking good, so is the Dia. the same for the ring area and the skirt? i seem the recall seeing pistons with a center mark on the top, you know like for a live center in the tail stock, that along with running two jaws on the inside and two on the outside maybe you could cut the whole piston without turning it around, i'm just think.
Normaly when pistons are machined the first step is to machine a register on the bottom.This is the basis for all machine work measurements. From this point the pin bore is roughed in and you use a draw bar thru the lathe spindal to hold the piston onto tooling in the lathe chuck(draw bar grabs a pin in the pin bore).Doing it this way eliminates having to dial in each piston,a live center can be used to stableize during finish cuts on the skirts and ring grooves, and will not leave jaw marks.
Yes I agree . When I was machining pistons from other cores the very first operation was to cut the bottom then everything goes from there however I discovered when working i with a rough casting using my little wooden invention I could sneek a bit more diameter out of the blank doing this first then rechucking to true the bottom. It will be a moot point soon though as the reworked mold will give me a better blank and I can return to normal proceedures. I am learning as I go. Today we whipped up a new burner. Air blast supplied by the shop vac. We tried it on woodpellets. Not too good. Only ,melted for a short time then was not hot enough. Tomorrow we try charcoal. Vern hopefully has a few pics from the more dramatic moments that he might show us. I also built a refractry sort of cement balnket on it tonight. I will cure it in the morning probably with the wood pellets as it will be a gentle fire compared to what i expect tomorrow with charcoal. Don Often pistons are cast or forged with a bump for a live or dead centre and it is not uncommon if you need a place to do that to epoxy one on an existing piston or blank. Normally once I get a rough blank to the semi state like in the video I then set it up like it was a normal piston and machine away. The area around the rings must be at least .020"smaller than the skirt diameter. Even a bit more is better.
Don, I hear you loud and clear on the inefficiency of air die grinders. Before I could afford a good compressor I bought a Dremel flex shaft motor which holds 1/8 and 1/4" tools. I got it with the variable speed foot pedal. Dremel doesn't make them any more, but Foredom makes nicer ones anyhow. They aren't cheap, but I've seen them reasonable on EBay. http://www.foredom.net/ If 3.5" bore doesn't work out there are plenty of metric rings at 88.5mm/3.484", but I'm sure you knew that. The 198 crank will fit the 170 block, but according to Dutra you'll have to put the crank in your lathe or otherwise trim a couple counterweights. I was going to do this same stroker 170 build-up, but I'm going land speed racing rather than drag racing. I found an empty line in the SCTA record book that needs a 2.01-3 liter engine so I'm doing a stock stroke 170. Best of luck on the next round of castings!
I/ve heard of him! Many times in a mopar when counterweights have to be machined one finds in fact it is that the block casting is simply not relieved the same.This is especially true in the 440 crank 400 swap. It actualy takes only about 1/2hour to fix the 400 block so that is not a problem and all you do is relieve the factory machining back about 1/4 inch so it is the same as it was in the 440. For some reason no one seems to understand or do it. Maybe it is too obvious or too straight forward. But if I have to machine the counterweights I will. I have my current 225 out to 3.5625 bore and have now 4 years of running and some very hard racing on it. I checked a 198 block and it wont stand that. I intend to check this 170 block as I have it all stripped out. Wonderful idea of going for LSR. I wish you all the best. Maybe I will come and watch .Thanks for the info. Don
Here is the new charcoal (we hope ) furnace curing its cement refractory blanket and lid. I call it Abdul. Here is Abduals fitting which fits the shop vac perfectly. This was built from s**** lying around in the shop and altogether took less than an hour to make. The centre core is a s**** pece of well tile or pipe. The outer shell is an old helium party ballon tank from Walmart I used in a tig welding experiment. I had ventilated it with my trusty Winchester .22 magnum so it could be disposed of. The snorkel for the blower is an old roll bar stub. The cement was in the garage for about 17 years and the sand i already had dug up. I also raided the wife/s new bucket of kitty litter to make the mix a little more resilient. Might be no good but we shall see in a couple of days Don
The Jalopy Journal
