Welding Aluminium Pistons

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I'm into building 2 stroke race engines, they don't need to run long, but they need to run fast.In some cases it would be an advantage to be able to build up a couple mm on the center of the piston crown to reduce head volume and increase compression. I figure this is fairly doable just by adding a pad of 5356 filler on the center of the piston crown and then turning it down on a lathe. Is 5356 the best option for filler though? Pistons have a lot of silicon to control thermal expansion and make them harder. They need to stand up to temperatures about 280 C or 550 F, but are not subject to extreme loads.The second more difficult moddification I had in mind was building up the sides of a piston skirt, I have herd of this being done before, Some work to remachiene the pistons after, but I think I can manage that part ok. In this case the loading is a lot higher, but temperatures less than 100c or 210F.Any thoughts on filler or heat treatment. How is welding going to effect grain structure in the high silicon aluminium alloy?Thanks First pic shows a slight pop up on the piston, I would like to build this up higher, second pic shows piston skirts, the piston on the right has a wider extended skirt, this is what I would like to add to the piston on the left.I know the machiening is very close tolerence <0.001, I'm ok with that part. This is not production stuff, just one off experimental projects. Attached ImagesLast edited by Timberwolf; 09-11-2008 at 08:49 PM.Lincoln PT185 TIGLincoln 175 MIGLincoln 240 amp AC StickLind Needle Arc plasma welderPlasma cutter, soon???
Reply:I did try to build up a scrap piston crown a while back, but at that time was still having a hard time with aluminium welding in general. Quite a few hours practice and a couple hundred bucks of argon later and I think I am ready to give it another try. I used 4043 filler here in the fist atempt a couple months back and got too much heat. it did hold up to distructive testing of the cross section pretty well but fractured along an inclusion.Will do a better job controling heat next time. Attached ImagesLast edited by Timberwolf; 09-11-2008 at 09:10 PM.Lincoln PT185 TIGLincoln 175 MIGLincoln 240 amp AC StickLind Needle Arc plasma welderPlasma cutter, soon???
Reply:Can't you just mill the head?DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:The heads are attached, one piece castings. I have made heads and converted the jugs to two piec heads, but depending on race rules that's not always permitted. Another option would be to weld up in the top of the head, but would not be easy to work (weld and machiene) down in a  4 inch deep hole only 2 inches across.Here are a couple pics, First is a standard jug. The second is a jug with custonm 2 piece head. If I make a two piece head than no need to weld on the piston crown as the combustion chamber can be resized as requred. However in some cases it would still be an advantage to make the piston skirt a couple mm wider. Attached ImagesLincoln PT185 TIGLincoln 175 MIGLincoln 240 amp AC StickLind Needle Arc plasma welderPlasma cutter, soon???
Reply:Couple more, custom with two piece head and a standard stock jug with attached head. Attached ImagesLincoln PT185 TIGLincoln 175 MIGLincoln 240 amp AC StickLind Needle Arc plasma welderPlasma cutter, soon???
Reply:If you're looking for silicon, go for 4047 instead of 4043.  12% silicon.  Most LWD's should have some in stock, or can get in for you in a day or two.  550 F isn't a problem since the eutectic in the weld wont even go plastic until around 1000 F.Regards, KbnitI r 2 a perfessional
Reply:I understand welding the piston dome for compression.What is the purpose of welding the piston skirt?9-11-2001......We Will Never ForgetRetired desk jockey. Hobby weldor with a little training. Craftsman O/A---Flat, Vert, Ovhd, Horz. Miller Syncrowave 250
Reply:Craig,I think it stops the compression from bleeding down the sides of the piston.  Wider skirt prevents the piston rings from flexing as much.I r 2 a perfessional
Reply:Will look into some 4047 filler, thanks. That is likely closer levels of silicon to what is used in pistons and jugs.With going to extremes in getting these things to go fast it helps to have very wide ports, in some cases wider than what a stock piston will cover and seal.A custom CNC billet piston is worth several hundred bucks plus the design work, custom forgings more yet. So if there is a way to build up a little here and there it could be worth while.Also do some welding on the jugs themselves to allow extra ports and larger intake and exhaust flanges, so that 4047 might be the ticket for that too. Jugs also use quite a bit of silicon to keep thermal expansion in check and make them a little stiffer and heat reistant.Lincoln PT185 TIGLincoln 175 MIGLincoln 240 amp AC StickLind Needle Arc plasma welderPlasma cutter, soon???
Reply:???  The skirt doesn't seal things, the rings seal things.The top of the piston does the compression and reacts to the combustion pressure.The rings seal the piston in the cylinder.The skirt helps hold the piston together and makes an area to connect the connecting rod to.5356 is NOT the right material.  It is not recommended/rated for service temps over 150F.4047 as stated is about the highest silicon level you can get in a filler, at 11-13% Si .  4043 is 4.5-6.0% Si.  5356 is 0.25% max Si, but has about the most Mg in a filler alloy.Lincoln lists 4043 and 5356 as cut length fillers, but has 4043, 5356, and 4047 listed as spooled filler (aka MIG wire).As to what is the 'right' filler to attempt what you want to do, 5356 is NOT a good choice, but the correct choice really depends on -what- alloy the piston is made of.  It could be a wrought heat-treated alloy, it could be a wrought non-heat-treated alloy, it could be a cast alloy again in heat-treated or non-heat-treated alloys.In the pics of the pistons, the right piston is beefier and the arrow points to a bump-out in the skirt area that looks like it is there as 'beef' for the con-rod connection to make it stronger.Crazy Canucks and their chainsaws.    The best laid schemes ... Gang oft agley ...
Reply:Timberwolf, Side question. What are your home made heads made from (you have my wheels turning)? Mondo job. Is anybody trying to put a water jacket on head or barrel or both with a small thermo siphon (heat circulation of the water - no pump) radiator somewhere on the rig? Too big?How long to these engines have to run after start up and warm up?Stew
Reply:??? The skirt doesn't seal things, the rings seal things.
Reply:Ding, the light goes on. They're two stroke motors, with holes cut in the cylinder walls for intake, tranfer and exhaust ports. The piston skirt controls the opening and closing of these ports.That's a heck of a wide port if you need to weld up that corner of the skirt.Looks like you're going to get a lot of BANG fer yer buck. 9-11-2001......We Will Never ForgetRetired desk jockey. Hobby weldor with a little training. Craftsman O/A---Flat, Vert, Ovhd, Horz. Miller Syncrowave 250
Reply:Bear in mind that pistons are not round/cylinderical to take thermal expansion into account. The piston crown has to deal with far more heat than the skirt AND the gudgeon pin bosses mean that the wall thickness of the skirt varies lots so they tend to taper from top to bottom and be a few thou out of round.I don't know the fine details of 2 stroke tuning but i do a fair amount of barrel/crankcase welding for one of my gearbox reconditioning clients- his hobby is building Lambrettas that can out drag most things! Port welding (to change timing), adding an extra transfer port, he's even had me weld around transfer ports (build it up to the OD of the fins!) in his continual search for more power He takes perverse pleasure from getting me to weld in the most awkward places (torch hand stuffed IN the barrel, filler bent and added through one of the ports, welding half blind trying to peer through a different port, sometimes via a mirror!). Steers clear of welding pistons though. Nothing to with cost as he's always having barrels re-nikasiled and these bikes are pretty much no expense spared.Might be a different story with such short running times though, he expects at least one evenings worth of 'baiting' before a rebuild!You should be able to find 4047 pretty easily in straight lengths, most of the big players produce it
Reply:Welding piston domes? No problems there, esepcially for that little toy engine, 4047 should fit the bill as stated above. Might be wise to stress relieve the casting however, or else it will relieve itself the first time you run the engine and may warp to a shape that invites mr. stick. Now as far as welding skirts and machining them, forget it. I dont know you, but I know you dont have the capability to measure, develop or machine a skirt profile. Think its round, or a simple oval? Think again, and it only gets worse with power density.
Reply:Originally Posted by hotrodderhis hobby is building Lambrettas that can out drag most things!
Reply:Ahh, the skirt seals off the intake and exhaust ports in a 2-stroke.The rings still do seal off the combustion chamber and enable the piston to compress the air-fuel mix and to hold the pressure in the cylinder so that the piston can be forced downward by said combustion pressure.  Poor ring seal means poor compression and/or ring blow-by.Bloody wide port if the entire skirt 'width' is the port width.To me, it still looks like the smooth (casting) material increase in the beefy aftermarket piston leads to more strength.  Your ports in the other heads look more round or even in the rectangular ones, the height/width ratio is no-where near excessive enough for those (relatively) small piston skirt extensions to matter.  Besides, even if the port -was- of a dimension that the shown skirt 'bump' matched the port dimension, what would happen during the rest of the piston travel when the 'straight' part of the skirt wasn't blocking the port anymore?See attached pic with a really wide port (in pink) and the straight part of the skirt that no longer seals off the port (in orange) once the piston moves. Attached Images  The best laid schemes ... Gang oft agley ...
Reply:In some cases you dont not need to make the whole skirt top to bottom full width, as the ports are trapazoids or else there are small boost ports added beside the main ports. But take the piston on the right, it would be nice to add 2mm a side right above the bump to keep the port sealed and permit a wider port or auxilary ports.The picture of the piston is just an example, some pistons are nearly full circle and have plenty of room for ports, however there are other motors with narrow skirts maybe only 65% of the bore diamiter, and these are the one that need a little widening.As far a piston shape, yes many automotive and larger pistons are oval, however not one of these small two stroke pistons is oval. They are all round and just have a slight taper cut in the top 1/2 and inch or so. I can mangage that machiening. And I don't mind doing a little hand lapping to bring things down to the 4th decimal place if need be. I know this chainsaw racing is a bit hard for most to wrap their head around, guess i'm a bit of a hightech redneck. But it's not just a passing whim, this is something I am fairly serious about and have invested some time and coin into. Here are a couple wider ports from the inside, they are getting out close to the limit structually, but that where they need to be.I will have to look into stress relieving and heat treatments some more. Attached ImagesLincoln PT185 TIGLincoln 175 MIGLincoln 240 amp AC StickLind Needle Arc plasma welderPlasma cutter, soon???
Reply:Originally Posted by MoonRiseBesides, even if the port -was- of a dimension that the shown skirt 'bump' matched the port dimension, what would happen during the rest of the piston travel when the 'straight' part of the skirt wasn't blocking the port anymore?See attached pic with a really wide port (in pink) and the straight part of the skirt that no longer seals off the port (in orange) once the piston moves.
Reply:Put some weld on the outside of that cylinder to build up the thin places and open up the ports even further
Reply:Been thinking on doing just that also. So far I mostly cut the existing flanges off and bolt on a block, but welding would be quicker. There is concern for warping the bore, but quite often the jugs get bored out and replated anyway so that takes care of things getting a smidge out of round.With the intake and transfer ports though there is a right size, going bigger is not better. Sure they can flow more, but if velocity goes down too much in the port then low speed opperation suffers. Most races require starting the saw on the ground and then making 3 cuts so the saw needs to go from 0 to say 18,000 RPM in less than half a second and have no flat spots in acceleration. Couple videos for anyone who is interested, first is a 59cc muffler saw, second is 80cc class piped saw.[ame="http://www.youtube.com/watch?v=sIbwQK_jr-I"]http://www.youtube.com/watch?v=sIbwQK_jr-I[/ame][ame="http://www.youtube.com/watch?v=F-iKroEAU14"]http://www.youtube.com/watch?v=F-iKroEAU14[/ame]Last edited by Timberwolf; 09-12-2008 at 08:01 PM.Lincoln PT185 TIGLincoln 175 MIGLincoln 240 amp AC StickLind Needle Arc plasma welderPlasma cutter, soon???
Reply:Damn I need you to build me a motor for an RC airboat project I got... I want a small motor to stay lite "I got a 21cc" , I know the TQ wont be high but I'd like it to spin the prop a little faster....I've taking a Weed Eater FeatherLite 21cc and trimmed off all the wacker stuff to end up with a big RC motor....Just didnt know about the extremes some people went to on these types of motors.Dude you rock......
Reply:Can you triple port the exhaust? You can get some more area and that way your not getting past that 80% threshold where the rings start bowing out of the bore into the port. Transfers are really tricky, right size, right height, right cross section angle so they point at each other, right up and down angles, etc. etc. You know all this already though more then likely.I didn't pay close enough attention to the cylinder pics, I see now they look to be nikasiled and not the iron bore setups I'm use to dealing with. I'd guess if you were concerned about the bore surface warping and then the plating flaking off you could make up a fixture in your mill to bolt it down to snuggly while you weld it to do the build up work. From the bottom where it goes on the cases and the head area too would probably be the best bet. Make it extra heavy. It would have to help the situation. What kind of fuels are you guys limited to?
Reply:Depends on the race, some places or classes limit you to pump gas, other times nitromethane and methanol is ok but no pressurized fuel. Sometimes it's anything goes. Attached ImagesLincoln PT185 TIGLincoln 175 MIGLincoln 240 amp AC StickLind Needle Arc plasma welderPlasma cutter, soon???
Reply:HAHAHAHAHAHAHAHAHAA chainsaw with nitrous on it. Holy **** that is hilarious.That's some bad chain saws.  I've done some crazy mods to 2 stroke bikes but never the small chain saw  or weed eater engines
Reply:Timberwolf, Too freakin' much! You are an inspiration to we 2 popper fans. Man, you are Livin' the dream - I am in awe!When I was building air cooled motorcycle motors in the 60's, I used to assemble, set up a big furnace fan/blower towards the cylinder, set the bike up on a big work stand and start the thing up. I'd run it gently for a few and then bring the r's up some towards the end of about a 5 minute run. Shut down, pull the head and cyl, piston off the rod (after it was cool). I took 600 grit sandpaper and went around the skirt over any area that showed a flat color - meaning where that piston had a high spot, raised from the heat of running. Since we also had steel cylinders, I did the same on those high spots.Reassermble and repeat, running a little harder, and higher. To work the engine a little harder, get it up to temp more I would drag the rear brake a little. I can't remember how many times I did this on-off routine on average but it seems like about 4 -6 would hand lap all the expandable areas off. Those rocket motors would really hang in there in desert races for the guys and in my case, Flat Track or Short Track.Are you still doing that kind of hand lapping today on these little motors?Also, I remember Puch in Austria were the first to add a transfer port window that blew some intake mix under the piston crown. It's only purpose was to cool the top a bit. I think those were what were called 7 port motors. Anyway, they noted that adding the cooling got them a few more horsepower.The attached pic (this from early 60's Go Kart motor) on the right shows a view of openings on the cyl side for extra transfer ports. I wonder if you couldn't machine out a small area and weld in a small block of aluminum right up against the cyl with the inside hogged out for an additional transfer port path, or are you alreadybeyond that?You go guy.Stew Attached Images
Reply:Timberwolf, small add on. You may already know this. I talked to Al Pizzano at WISECO for some info on a rig I am working on. They are pretty approachable. Additionally, in my case I inquired about some STEEL replacement cyl liners, just FYI. He directed me to LA Sleeve.I don't know if any of these contact names/numbers would be of value but I figured I'd pass the info. These price quotes are as of Sept 2007.StewRE: Wiseco Help‏ Pizzino, Al ([email protected]) LA Sleeve in California can be reached at 800-822-6005. We can build pistons as a custom but the minimum is four pistons and they would cost about $225.00 apiece. Regards, Al
Reply:I assumed that the piston skirts would follow a similar design to their larger cousins. If they're definately that simple... Originally Posted by Shox DrBl00dy hairdriers
Reply:Originally Posted by JonE30HAHAHAHAHAHAHAHAHAA chainsaw with nitrous on it. Holy **** that is hilarious.
Reply:Yup, what one will flow better?LA Sleeve in California can be reached at 800-822-6005. We can build pistons as a custom but the minimum is four pistons and they would cost about $225.00 apiece. Regards, Al
Reply:Well I tried a piston today, whole plan was just to get the process, not mess with machiening much and do some distructive testing.Here is the junk piston I started out with.Cleaned the top off on lathe, then added a pad of filler, no dimes, just a smooth dome. 85 amps with 1/16 Lanth 1.5% electrode. 4043 for filler 1/16 for big areas, .035 for small spots. I tied .040 electrode, but could not carry enough curent for the crown, but might be good for the skirts.Then just turned a quick crown onto the piston. Attached ImagesLincoln PT185 TIGLincoln 175 MIGLincoln 240 amp AC StickLind Needle Arc plasma welderPlasma cutter, soon???
Reply:Next tried to weld some build up on the skirts, really in over my head, but went not too bad, had a little trouble tieing the bead in at the top where the skirt joins the crown. That would take some practice. Then 2 min of grinding just to get the excess off, really would take some machiening to get the built up skirts looking decent.Next whent at distroying the piston, crushed it in a vice first and it took quite a squeezing before the skirts broke followed by the skirt webs. All well away from any welds, and where I would have expected due to the thin cross section.Then squeezed the remaining skirt across the piston pin to see how the weld on the skirts would hold up. Attached ImagesLincoln PT185 TIGLincoln 175 MIGLincoln 240 amp AC StickLind Needle Arc plasma welderPlasma cutter, soon???
Reply:Next milled down the under side of the crown and cut some sections to get a closer look at the crown buildup.Broke a few sections of the crown in different directions, both hot and cold. Cold the seld was stronger than the piston material, hot though It might have been slightly weaker. But in any case looked fine. And by the look of it I only cut into the base metal 0.010 to 0.020 at the most. Did not find any inclusions to speak of, fusion seamed good all over, looked at the metal under magnification, grain is a little finer in the weld than the piston, but no sign of enlarged grain structure or crysalization where the two meet. Feel pretty good about building up the crown, the skirts would be pretty sketchy though. May try to build up a crown on a good piston and give it a test run. Attached ImagesLast edited by Timberwolf; 09-14-2008 at 10:04 PM.Lincoln PT185 TIGLincoln 175 MIGLincoln 240 amp AC StickLind Needle Arc plasma welderPlasma cutter, soon???
Reply:I'm for making the piston lighter, not heavier.  It's true the rings seal the combustion chamber...But the skirt seals the piston while it's compressing the crankcase.Try something like teflon coating. It takes up clearance but won't harm anything if it comes off. If you really want to get technical...Try searching for ( Gordon Blair; Prof. Queen's University of Belfast )He has two stroke engine modeling software that is available from the SAE.It's probably hard to find an "employed engine designer" that hasn't studied his work.The best things in life all come on a stick!
Reply:Tx, coatings on the pistons do work, have experimented with a few. In these engines, ceramic on the crown is a big helper. It works in three ways heeping more heat in the combustion chamber makes for more heat in the combustion cloud and a higher internal pressure that builds more torque. Also it keeps heat out of the crown some so the crown swells less and less heat is but into the base of the engine wich help improve charge density.Quite familliar with G. Blairs work and writings, if they make sence the second or third time you read them then you are doing good. I have some engine design software, it saves a lot of trial and error, but like any such progam, garbage in garbage out, you need to know what to imput in and what your looking for.Anyway, all that is outside the welding aspect. Any thoughts on the welding and testing on this piston??? Thanks, The engine stuff I figure I have a pretty good handle on, but the welding, I'm here to learn.Lincoln PT185 TIGLincoln 175 MIGLincoln 240 amp AC StickLind Needle Arc plasma welderPlasma cutter, soon???
Reply:The welding looks to have gone fine. Without the correct reagents to do proper etches you've gone about as far you can. Too late now but did you mic the slug before and after? Given the clearances involved it'd be nice to know if/how much things moved
Reply:Originally Posted by RabidfishIt's probably hard to find an "employed engine designer" that hasn't studied his work.
Reply:Skirt stayed within .0015, ring went on no problem after the welding, and piston pin inserted fine, so that should be close enough I think. Found a local source for 4047 filler I think, just going to have to buy a little more than I need right now.Lincoln PT185 TIGLincoln 175 MIGLincoln 240 amp AC StickLind Needle Arc plasma welderPlasma cutter, soon???
Reply:Are these reed valve motors and is the crankcase properly stuffed to boost your primary compression ratio?
Reply:These are piston ported motors. A few guys have tried to put reed valves on them with hit and miss success. The reeds have only worked on the larger motors run with tuned pipes. For the most part cases on these little motors are quite tight and given they are super short strokes with with bore to stroke in the 1.4:1 plus range even before overboring it's not hard to achieve lots of base compression. The cranks in these motors are lobed, so that brings up another welding topic welding these lobed cranks into full circle cranks.Problem with reeds though on the small motors is the plenum volume after the reeds that becomes part of the base volume. Also given the desire is just for maximum power at high RPM there is little advantage using reeds in the conventional sense, however some designs using a hybrid of reeds and piston porting have shown to work.Lincoln PT185 TIGLincoln 175 MIGLincoln 240 amp AC StickLind Needle Arc plasma welderPlasma cutter, soon???
Reply:Here is a CHAINSAW.http://media.damagedreality.com/V8ChainSaw.avi...zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Originally Posted by zapsterHere is a CHAINSAW.http://media.damagedreality.com/V8ChainSaw.avi...zap!
Reply:Originally Posted by deadman1474Zap are you back for good?
Reply:Timberwolf, been a few months npow. Just wonderted where you are in your "season" and how your mods turned out. Understand that none of this is a static situation, always finding out more and continually modding.I sent you the Wiesco link.Stew
Reply:I have not really tested out the welding yet need to put some hours on it and see, looks promising though in the little bit of testing I did. Did do some welding on a cast cylinder though and it worked pretty well. Right now been playing more with ceramics and coating on the pistons. One thing I want to try is to fill in the lower ring groove. Not sure if it would be best to try to fill the square groove as it sits or notch it out on Lathe and then weld into a more "V"  or "U" shaped groove. Attached ImagesLincoln PT185 TIGLincoln 175 MIGLincoln 240 amp AC StickLind Needle Arc plasma welderPlasma cutter, soon???
Reply:Originally Posted by Craig in DenverI understand welding the piston dome for compression.What is the purpose of welding the piston skirt?
Reply:Rojo:Thanks for the reply. Unless it's at a factory level, I'm still thinking that welding on a piston is a bad idea. Instead of welding the second ring grove shut, why not just leave the ring out? There would be less reciprocating weight and less piston distortion??TIA, Craig 9-11-2001......We Will Never ForgetRetired desk jockey. Hobby weldor with a little training. Craftsman O/A---Flat, Vert, Ovhd, Horz. Miller Syncrowave 250
Reply:I personally would not be eliminating rings. You need 2 of them for sealing/ wiping the cylinder wall. Plus, thew 2 rings tend to help with centering the piston in the cylinder so there is not galling on the sides of the piston.I have to admit, this thread is a lot of fun to watch; we all love R&D, and destructive testing!!!And then, after so much work...... you have it in your hand, and you look over to your side...... and the runner has run off. Leaving you holding the prize, wondering when the runner will return.
Reply:What kind of chains to those things run?DewayneDixieland WeldingMM350PLincoln 100Some torchesOther misc. tools