Welding Pistons

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Looking for some advice from anyone who's welded pistons before.  I'm looking to put a small dome on a 42mm Stihl Chainsaw piston for a compression increase.  I'm a little concerned about the heat softening the alloy and causing catastrophic failure.  The engine turns at 14,000 RPM.  I was figuring 4043 as it's a high heat application (although IIRC Shovelon has welded pistons with 5356).  Will balance the weight by removing part of the skirt.  I'm gonna do this on crappy cylinder first in case it grenades.  Any advice?TA Arcmaster 300CM3XMT 304S22P12 suitcase feederX-Treme 12VSOptima pulserTA161SMaxstar 150STLHypertherm PM45OP setupStihl 020AVP, 039, 066 Magnum
Reply:To increase compression, you'd be better off having .010 " milled off the cylinder head. I would not weld on a piston to increase engine compression. Raising engine compression can also introduce other issues with your motor. Too high of compression can lead to detonation issues (fuel ignites before the spark plug fires) from the heat of the higher compression. This will lead to a very short engine life. You must use high octane or even race fuel to make the engine last with this issue. I would not want to dis temper the piston by welding on it. Why do you need more compression in your chain saw? A cylinder honing and fresh set of piston rings may be what your looking for to freshen this small 2 cycle motor up.JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:What he said..^^^^^^^^No need to tear down a whole engine..Mill the head.Or I could do it for ya if you send it to me....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:heres a saw all ready for you...lolOf all the things I lost I miss my mind the most...I know just enough about everything to be dangerous......You cant cure stupid..only kill it...
Reply:How much piston to cylinder head clearance do you have?Could you use a thinner head gasket to up the compression?How about a splash fuel additive?Balancing will be difficult. Do you have a scale that weighs in grams?Make her smoke, Bobby! Make her smoke!
Reply:I'm thinking part of the problem is that alot of chainsaws have the cylinder and head cast in one piece. Lowering the entire cylinder would increase compression somewhat (and possibly more important, reduce the distance between the piston and the squish area in the head at TDC, as long as it doesn't get too tight). Unfortunately it also lowers the ports in the cylinder, making them require some careful regrinding to return them to original height - quite sensitive especially for the transfer ports, as shape & angle there controls how the air & fuel loops through the cylinder and flushes the exhausts out. More info about the engine and the goal of the operation would help. Even if it doesn't turn out to be a welding job at all.
Reply:Turbo charge it! Back in the 70's when we first started running skidoos one of my friends fixed some burned pistons with 2 part epoxy. It was very hit and miss... some lasted for years, some grenaded fairly quickly. If you are determined to try this, epoxy might be a good guinea pig to see if you like the results. You would need to get the piston surface extremely clean and roughed up enough to hold the glue.  I rather strongly suspect you won't be impressed.250 amp Miller DialArc AC/DC StickF-225 amp Forney AC Stick230 amp Sears AC StickLincoln 180C MIGVictor Medalist 350 O/ACut 50 PlasmaLes
Reply:I've built many 2 cycle snowmobile race motors. I spent several years ice oval racing snowmobiles myself, now my kids are ice oval racing and I'm building their sleds. I'd never weld on a piston. Turbo charging a small chainsaw motor seems a bit impractical to me. What is the use for this chainsaw going to be?JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:It's a stihl 025.  Rebuilding a few, just for fun. Clamshell design homeowner saws.   The top of the crankcase and the cylinder/head are one casting.  Part of the problem with this "clamshell" design.  The combustion chamber is about 4" from the lip of the crankcase surface.  I'm tempted to put a gas lens on my torch, fill the entire cylinder with argon, and try to put some aluminum in there with a 3" stick out on the tungsten.  Cannot lower the cylinder onto the piston by design.The saw model has the perfect weight to power ratio.   I figured if I was playing anyway, why not try to increase the output a little.  The pro saw in the series, the 261, has a detachable cylinder and regularly sees 180-190 psi of compression.  The 250's pull around 160 at best.  Interestingly enough, the 261 only makes .2 BHP more than the 250 despite 5cc more displacement and the higher compression.Just playing, that's all.  I think a muffler mod and carb retune will get me where I need to be on it's own.Last edited by Drf255; 11-09-2014 at 06:36 AM.TA Arcmaster 300CM3XMT 304S22P12 suitcase feederX-Treme 12VSOptima pulserTA161SMaxstar 150STLHypertherm PM45OP setupStihl 020AVP, 039, 066 Magnum
Reply:Originally Posted by Drf255I think a muffler mod and carb retune will get me where I need to be on it's own.
Reply:Just throw in some bigger jets, and then retune it, or find domed pistons from a similar engine, i wouldn't go adding filler metal the piston to gain a few measly pounds of compressionMiller Spoolmate 200 w/t S-52 WirefeederMM 211'09 Miller Trailblazer 302
Reply:I have a little experience here, you will gain a lot more out of that saw with a little careful work on the ports. Get a dremel and a selection of carbide cutters and sanding drums/craytex rubber points and do some learning. Squaring off the ports (still must have a radius so the piston rings can't drop into the port) a little and raising the exhaust port slightly will shift the power up in the rpm's. Angling the transfer ports toward the intake side of the cylinder and upward will help with cylinder clearing and let the saw breathe better.Go to arboristsite.com and read for days, theres a few users there that build some wicked work saws.
Reply:Originally Posted by ironmangqI have a little experience here, you will gain a lot more out of that saw with a little careful work on the ports. Get a dremel and a selection of carbide cutters and sanding drums/craytex rubber points and do some learning. Squaring off the ports (still must have a radius so the piston rings can't drop into the port) a little and raising the exhaust port slightly will shift the power up in the rpm's. Angling the transfer ports toward the intake side of the cylinder and upward will help with cylinder clearing and let the saw breathe better.Go to arboristsite.com and read for days, theres a few users there that build some wicked work saws.
Reply:I'm back again.The cylinder is now ported.  Again, the issue is I'd like a compression jump. I only have 1/16 filler in 5356 which is supposed to be a no go for high heat applications.  I know Terry said he's welded pistons with it before.  I have 4043 in 3/32 and up.  Too big for piston work.  The combustion chamber is 4" deep.  I ordered 4XXL cups for my 20 series torch.  I may play around with just filling the entire cylinder with argon and trying a 4" stick out with a lens.  So it sounds like combustion chamber filling looks like my best option.TA Arcmaster 300CM3XMT 304S22P12 suitcase feederX-Treme 12VSOptima pulserTA161SMaxstar 150STLHypertherm PM45OP setupStihl 020AVP, 039, 066 Magnum
Reply:@ Drf255 -  sure you've seen this bro, http://weldingweb.com/vbb/showthread.php...minium-Pistons.  The thread references 4047 Al filler for pistons containing 9-12% Si (common).  Probably tough to determine the exact composition of the Al alloy Stihl is using for 42mm pistons.  5356 filler should not be used in applications of service temperatures above 150deg F because of the potential for stress corrosion cracking.God luck!"Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:I used to race pro-am 2 stroke dirt bikes in my younger days. Welding the head up and then turning down was a common practice to change the squish.
Reply:Thank bro.  Ordered some 4047.  Wasn't that cheap.  $14 a lb.  If you need, let me know.TA Arcmaster 300CM3XMT 304S22P12 suitcase feederX-Treme 12VSOptima pulserTA161SMaxstar 150STLHypertherm PM45OP setupStihl 020AVP, 039, 066 Magnum
Reply:@ Drf255 - good call.  Let us know how she runs.  That link you PMd me was cool.  PreHeat and go.  Aloha."Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:In the seventies they would shave the bottom of the cylinder to move the ports down while raising compression, while shaving the head for more compression. I can't think now how it would benefit, snowmobile racers would pack the crankcase full of Bondo, then crank it over to create some benefit. My 1972 340 EXT was good for 95 on lake ice!
Reply:Have you measured squish to see how much room you have?I've owned two MS250s, and they're not bad saws.  Power to weight is good, but I was never impressed with the saws and ultimately sold both.  That being said, I've read on arborist site that they do OK with a muffler mod, but not sure how much tuning can be done.  I know the 250 didn't have a fully adjustable carb, not sure about the 025.  Does your carb have adjustable L & H jets?
Reply:@ 7A749 - the 4943 has 5-6% Si, no real advantage over 4043 for this app.  4047 has 11-13% Si, better for wetting in."Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:Originally Posted by ManoKai@ 7A749 - the 4943 has 5-6% Si, no real advantage over 4043 for this app.  4047 has 11-13% Si, better for wetting in.
Reply:Originally Posted by ManoKai 5356 filler should not be used in applications of service temperatures above 150deg F because of the potential for stress corrosion cracking.God luck!
Reply:Don't weld to much material on the piston, port the cylinder and it should be ok. Should be a nice little project and let us know the outcome. I once milled the head down on a honda cr250 for a kid who wanted more compression, I told him I could mill it .10 but he insisted he wanted more. Went to put the head back and it ran great but hard to kick over, well he decided to rev the heck out of it turning the spark plug into a glow plug and the engine shot up to max rpm. kid ran away scared because the kill switch was useless and shutting off the fuel did nothing, at this point the engine was about to blow so I took off my shirt and plugged the exhaust which saved the bike. I am wondering if you put to much compression on a chainsaw would it do the same ?
Reply:Originally Posted by NinjaRayDon't weld to much material on the piston, port the cylinder and it should be ok. Should be a nice little project and let us know the outcome. I once milled the head down on a honda cr250 for a kid who wanted more compression, I told him I could mill it .10 but he insisted he wanted more. Went to put the head back and it ran great but hard to kick over, well he decided to rev the heck out of it turning the spark plug into a glow plug and the engine shot up to max rpm. kid ran away scared because the kill switch was useless and shutting off the fuel did nothing, at this point the engine was about to blow so I took off my shirt and plugged the exhaust which saved the bike. I am wondering if you put to much compression on a chainsaw would it do the same ?got a hell of a memory Terry ! I don't think the OP can't mill the head as typically the smaller chainsaws are a one piece design like trimmer engines. I guess he could always add more filler to the center and make it kind of a pop up piston with out screwing with the ports. Another way of going at it would be pop up followed by milling down the base and piston outer edge the same amount . Not to much ! Attachment 937781
Reply:If anyone cares, I did it.  The 4047 flowed nice.  AC Squarewave150Hz70%EN2% lanthanated 3/32Lens w 8 cupPreheated w propane torchNo lathe, so had to hand sand.  Had to grind off an area to clearance the plug.  A perfect dome hit.  It's a very small chamber.  Last edited by Drf255; 12-21-2014 at 06:07 AM.TA Arcmaster 300CM3XMT 304S22P12 suitcase feederX-Treme 12VSOptima pulserTA161SMaxstar 150STLHypertherm PM45OP setupStihl 020AVP, 039, 066 Magnum
Reply:That's probably going to create scavenging issues with your porting. Good luck and please do tell how it runs!
Reply:This is an interesting post for sure!! Can't wait for the details on the running!  Thanks for posting
Reply:Nice work Al!  Glad the 4047 worked out for you.  Keep us posted bro "Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:Originally Posted by doylexThat's probably going to create scavenging issues with your porting. Good luck and please do tell how it runs!
Reply:Originally Posted by ManoKaiNice work Al!  Glad the 4047 worked out for you.  Keep us posted bro
Reply:good job, Will have to pick some 4047 and try it out. Would like to see a video when its running if possible?
Reply:Sure.  Went a bit overboard with the dome.  Thank god I had to clearance for the plug.  Stock compression is 150 psi.  I'm at 210 now without ring breakin.  May go as high as 230 after breakin.TA Arcmaster 300CM3XMT 304S22P12 suitcase feederX-Treme 12VSOptima pulserTA161SMaxstar 150STLHypertherm PM45OP setupStihl 020AVP, 039, 066 Magnum
Reply:What's your squish at? Put a piece of solder in the spark plug hole with it all together and crack it over. Then measure the thickness. You can run .035 clearance maybe a touch less. Turn ur timing up a few degrees. Run it rich and slowly keep adding e95 until it runs good. Keep checking your plug.
Reply:That thing will detonate like a sob unless you run higher octane. Getting ur squish right help prevent detonation
Reply:Two friends in the seventies wasted some time on this issue. I believe the owner was cheap, wanting to avoid the cost of a new piston. The other, a GE employee, and welder was always looking for side money. It repeatedly blew a new hole.
Reply:Originally Posted by Drf255Most old 2 stroke boat motors have a sharp rise on the intake side of their pistons.  Deflects the mix upwards as the exhaust vents.
Reply:Old outboard:12v battery, jumper cables, and a 6013.I only have a facebook page. https://www.facebook.com/pages/VPT/244788508917829
Reply:Well, it runs great.  Here's the thread on the build if anyone's interested.  http://www.arboristsite.com/communit...ession.269144/Had to shave down the dome considerably.  I was hitting 270 psi with an oiled cylinder before hand.  Now at 195 psi dry.  Ran a tank through it.  Lean it out into tune and hit 20,500 rpm, richened up for safety to 13,500 rpm.No destruction.TA Arcmaster 300CM3XMT 304S22P12 suitcase feederX-Treme 12VSOptima pulserTA161SMaxstar 150STLHypertherm PM45OP setupStihl 020AVP, 039, 066 Magnum
Reply:I think you got things a little back wards. You wanna have the rings dry and a very light coat of trans oil on the cylinder wall. Then break in rich with a good load on the motor to break in the rings. Lets see the plug?
Reply:In what parallel universe do we build hot rods from homeowner saws. I think my Jonsered Super 930, or my son's Husquvarna 385 will out cut it. Unless you race in class of displacement, there is no substitute for CCs. The line from Crocodile Dundee stays with me: " I don't need a gun, I've got a Donk". My sons have an entourage. Members of the crew include Danny, 'Ox' and Sean, 'Skeeter' They are 6'7" and Skeeter is 6'5". The little brother is 310 lbs . It's not all muscle, there must be 150 lbs of bone. A bar & chain fitted to a Chevy 350 isn't too big for them. They think my saw is for sissies!An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.
Reply:I would rather the 024 over the 044 stihl.12v battery, jumper cables, and a 6013.I only have a facebook page. https://www.facebook.com/pages/VPT/244788508917829
Reply:Originally Posted by Willie BIn what parallel universe do we build hot rods from homeowner saws.
Reply:Originally Posted by Drf255It's called having fun and learning Willie.  Also called practice and doing what others said can't be done.  Next on the block is an 028S, 026PRO, and an 066Maggie.
Reply:If I had the time to play with small motors I would definitely try making my own piston in the lathe. For fun of course.12v battery, jumper cables, and a 6013.I only have a facebook page. https://www.facebook.com/pages/VPT/244788508917829
Reply:@ Drf255 - build and do what enamors you bro.  Always.  For me, the action is the juice.  Before long you'll be fab'n hypereutectic pistons for the woodcutter market.  WatchOut Keith Black... "Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:The concept is neither unfamiliar or offensive. I have a distorted view of life on Long Island. I think of you as the sort of people who live on a 5 acre estate, spend the first waking hour each day choosing the perfect necktie, then move on to delegating chores. You ask your secretary to choose a birthday gift for your wife cause you're too busy. Then spend 15 minutes on the phone ripping the gardener an extra one cause you stained new Feragamos sp? from clippings he missed on the 10' walk to your Bentley. What's a guy like that want with a chainsaw. Please forgive my ignorance. Clearly not everyone on LI fits my stereotype.An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.
Reply:Originally Posted by Willie BThe concept is neither unfamiliar or offensive. I have a distorted view of life on Long Island. I think of you as the sort of people who live on a 5 acre estate, spend the first waking hour each day choosing the perfect necktie, then move on to delegating chores. You ask your secretary to choose a birthday gift for your wife cause you're too busy. Then spend 15 minutes on the phone ripping the gardener an extra one cause you stained new Feragamos sp? from clippings he missed on the 10' walk to your Bentley. What's a guy like that want with a chainsaw. Please forgive my ignorance. Clearly not everyone on LI fits my stereotype.
Reply:In the seventies I had an EXT snowmobile. My brother in law, then his friend, both skilled mechanics, had already owned it. Small displacement racing was very big in the day. People seemed to focus on 340 class. These free air engines had a lot in common with chain saw engines. People moved ports, enlarged ports, shaved bottoms of cylinders and heads, domed pistons, and filled voids in crankcases. Some carburetor set ups were remarkable! These machines were hot! My 340 would hit 95 on lake ice! Of course everybody did all those things, everybody's clutch came in at about 8,000 rpm. I weighed in at 135 then, that was my edge. If you wanted to win you needed to level the playing field. All the winners cheated. After a race, they started taking the head off one side of your engine to confirm your displacement. These Kawasaki's had interchangeable cylinders, A 440 would fit in place of a 340. As one side was easier to remove than the other, people routinely used a 440on right, and a 340 on left. Only after you won repeatedly, would they do both. The plastic trophies cost $5.00 to make, it was all for bragging rights.To someone such as a student at Paul Smith's College where my son is, your pursuit would be no surprise. I have somewhere got the notion you are a dentist. There is the surprise.An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.