Aluminum Air Compressor Connecting Rod Repair

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A customer brought in a damaged connecting rod from a Hitachi "wheelbarrow" style air compressor.  It had a badly gauled up big end ID, and there was a crack all the way though the wall of the big end.  Looked like it was run with the dipper starved of oil (I'm betting from either being run with a low oil level, or an excessive "tilt" angle.)A new connecting rod on one of these apparently costs a *lot* more than you'd probably guess, and since there was a "AL recycle" symbol cast into it, I decided  might as well take a go at a repair.I vee'ed out the outside of the crack with a carbide burr, and found it welded decently.  I then reamed out the galled material from the ID of the big end, and built the material back up using 4043 filler; TIG welded using an Everlast Super200P.  I did the build up first around the edges with my usual "focused arc" settings.  Then I filled in the middle areas, trying a "balanced arc" / 50% balance / DCEN setting (which was kind of fun, because of the mellower noise it made and also how it "wetted" the surfaces out nicely beyond the actual molten puddle.)After the welding operations were performed, I used a hand reamer to open up the big end to about .008" under final diameter, and honed it the rest of the way using a 240 & 400 grit flapper stick.  This left a nice, smooth finish, cleaning up the visible honing chatter marks.  Ended up with about .002" clearance.I did get a little bit of porosity in the welding operations, probably from contaminants inside the material (maybe from not reaming the galled material completely out), however I think those little voids might actually prove to be helpful little oil reservoirs.
Reply:awesome job there, hope it holds up well for your customer, looks good miller 330a bp TIGmiller dynasty 200DX TIGmillermatic 185 MIGthermal dynamics cutmaster 101 plasma cuttersnap-on YA5550 plasma cutterhypertherm powermax 30 plasma cutterbaileigh CS225 cold sawetc....
Reply:I am in awe.
Reply:Nice job, but a rod?  I never did an al rod, but have done similar to steel rods. Do everyone a favor and give a report whether it works well or fails. My concern is heat treatment is gone.PeterEquipment:2  old paws2  eyes (that don't look so good)1  bad back
Reply:DCEN??????????You sure about that?If so explain how that did not melt into a puddle on the floor..I may NOT know inverter machines but aluminum done that way all "Shiney" and stuff is AC.DCEN with straight helium would just blow that away.And like Peter stated..(In not so many words)I believe it will fail also.....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:C'mon guys give it a chance, what is the worst that could happen?I know that is a repair that I could never do.
Reply:Originally Posted by zapsterDCEN??????????You sure about that?If so explain how that did not melt into a puddle on the floor..I may NOT know inverter machines but aluminum done that way all "Shiney" and stuff is AC.DCEN with straight helium would just blow that away.And like Peter stated..(In not so many words)I believe it will fail also.....zap!
Reply:Thanks for the compliments, guys.castweld - I did express concerns to the customer prior to attempting this repair (although primarily, it was not being able to recreate the inside geometry accurately enough.)  He originally brought it still attached to the crank, still installed in the crankcase, and asked if I could just weld it like that.  I told the customer I could not make it as good as new, but he was still interested in a repair attempt, due to the high replacement part cost.  He also intended to only use the compressor just as a second, backup.  So I figured, why not let him pay me to learn? Anyhow, since the material is subject to highly cyclical, push-pull forces (pull sucking air in, push compressing it), fatigue related failure is likely the main concern at design stage.  To combat this, it is likely the part is probably actually designed with relatively low material tensile loading.  If I hear any feedback on how it works though, I'll post it here as a reply.
Reply:Originally Posted by zapsterDCEN??????????You sure about that?
Reply:Also to clarify what my usual "focused arc" settings for welding aluminum are:80% DCEN300 Hz pulsingsharp tungsten, with a flat on the tiptight arcoh and also can't forget (for Zap  ):AC
Reply:Originally Posted by castweldNice job, but a rod?  I never did an al rod, but have done similar to steel rods. Do everyone a favor and give a report whether it works well or fails. My concern is heat treatment is gone.Peter
Reply:How did you get the rod off the crank?  All the Hitachi compressors I found online had honda engines and I thought they had bolt on caps.I see a holy block in your future....  This must have been the rod from the pump.  Either way, it's a questionable repair at best. If repairing the rod cost less than replacing the rod, then you work too cheap.  I would have replaced the rod even if the repair was free.Last edited by Boostinjdm; 10-14-2010 at 01:17 AM.My name's not Jim....
Reply:Originally Posted by jmanHeat Treatment?
Reply:Hey jakeru, got any more pics of those "fingers" that you used to prop up the rod?
Reply:boostinjdm - Yes, it was a rod from the air pump of the air compressor, not from the internal combustion engine.  The crankshaft didn't have counterweights, so the rod could be slid (carefully maneuvered...) across the crank onto the machined rod journals.  Anyhow, I just let the customer decide what to do and informed him of the risks, he had already researched replacement parts cost, so no reason to second guess or re-research his info there.  Like I said before, I made the customer aware I had some concerns but they were willing to pay me to do it anyway.  It wasn't real quick project, but didn't take me longer than a day either.  It was kind of a fun project for me anyway.  I like pushing the limits and doing new things.  In this case, seeing what kind of tolerances I could muster with hand tools.  But then the build up operation ended up being kind of fun too.forhire - thanks.  I'm not sure what alloy it was, but can add that it looked die cast (maybe some kind of pressure cast?); like it was cast in a hard metal mold, not sand anyway, based on a very smooth finish and fine casting detail.  I can also add that it had no problems with hot cracking / crack sensitivity when welding, which I've noticed some heat treatable Al-Mg-Si alloys (or at least, 6061, maybe 6063) can.Found this source on common die cast aluminum alloys, indeed there are a couple with Si+Mg > .1% = heat treatable alloys I think (A360, and A390.)  And wow are those some high Silicon contents!http://www.kenwalt.com/DiecastingAlloys.pdfShadil - here is a thread I made about the welder's fingers on welding tips and tricks forum (more pics inside):http://forum.weldingtipsandtricks.co....php?f=9&t=728
Reply:removed duplicate postLast edited by jakeru; 10-14-2010 at 03:49 AM.
Reply:???? how did you make the big end was round and straight, and then measure it?
Reply:I used some adjustable hand reamers.  I bought a set from harbor freight (came in a wood box, made in India) just for this job.  I ended up using the two largest sizes (the largest is spec'ed for up to 1.5" diameter):Rotating the nuts at either ends causes the multiple cutting blades to slide up / down ramped grooves machined into the tool, which causes them to expand or contract uniformly.  The chattering I got would have probably been reduced if I had a proper handle for the tool, which I did not.  (I did most of the reaming by holding the workpiece by hand, spinning it around the reamer clamped in a vice.  Supporting something lightweight by hand is not a very rigid way of doing it.)  The tool was OK, left round holes, but could also probably use a little TLC / "blueprinting" I didn't feel like doing to possibly reduce the chattering also.  Not sure if I'm going to do invest that effort now and keep them or not, it felt I was fighting it a bit.I measured diameters using 6" digital calipers, which I find are useful for all kinds of things.  Quick, precise to .0005" / .01mm, and accurate / repeatable.  Button toggles between mm/in:
Reply:Originally Posted by jmanHeat Treatment?How does the 'Heat Treatment' come into play when speaking about a 'CAST' Aluminum Part?  Do you believe that it is a risk due to the part being fixed, thus weakening the 'original aluminum'?  Wouldn't this repair be quite strong due to the 'new AL' covering the 'entire' uppermost part of the rod, including the crack that was filled in?Cheers,
Reply:Well put peter, if the rod was solution/aged hardened then that will be lost near the weld.I also agree with your first post, the issue has been decided, and the part repaired well (at least I think so considering what jakeru started with) so now the results are important.If it fails do you forever fear, or do you learn more about the animal your playing with. I have to admit I'd be pretty timid about trying this... Leaving it to a younger person seens like a good idea!Matt
Reply:Originally Posted by Matt_MaguireWell put peter, if the rod was solution/aged hardened then that will be lost near the weld.I also agree with your first post, the issue has been decided, and the part repaired well (at least I think so considering what jakeru started with) so now the results are important.If it fails do you forever fear, or do you learn more about the animal your playing with. I have to admit I'd be pretty timid about trying this... Leaving it to a younger person seens like a good idea!Matt
Reply:If you don't mind divulging...  What did you charge for this repair?
Reply:Thanks for your interest, airwolf, but not interested in publicly sharing that info.
Reply:please update on if it holds together or not!I am curious what RPM the pump spins at.. I am sure it is WAY less than an IC engine rod, so the stresses are probably more compression than tensile, and it might be just fine long term!
Reply:Originally Posted by jdchmielplease update on if it holds together or not!I am curious what RPM the pump spins at.. I am sure it is WAY less than an IC engine rod, so the stresses are probably more compression than tensile, and it might be just fine long term!I don't necessarily expect to hear any feedback from the customer on how it worked, but "in the name of science", I will try to follow up with him about it to find out.Just give it a week or two first, OK?This is just his 2nd / backup compressor, and he may not be getting it back up and tested out immediately.  I'm not going to pester this guy: "have you tried it yet?"  "Have you tried it yet now?"  "How about NOW?"
Reply:yeah, & some times with a job like this, as long as you got paid you may not even necessarily want to know... no news is good newsmiller 330a bp TIGmiller dynasty 200DX TIGmillermatic 185 MIGthermal dynamics cutmaster 101 plasma cuttersnap-on YA5550 plasma cutterhypertherm powermax 30 plasma cutterbaileigh CS225 cold sawetc....
Reply:Sometimes the mark of a GOOD welder is knowing when to say NO.Forged connecting rods (air compressor or IC engine) are where I say no thanks.Customer was fortunate the first failure didn't take out the entire compressor head.  Second failure probably won't be so lucky.Let's see.  A day of labor to repair?  Unless you're working for peanuts, that can't be a "cost effective" repair.  I guarantee you can buy an entire air compressor pump (Northern Tool, 4 HP pump, 13.2 CFM, $299) for less than my daily shop rate.Not trying to "rub it in" but the comment about the "voids" serving as "oil sumps" told me everything I needed to hear.  Several other posters have already done a good job of explaining why this "repair" is questionable at best.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:Doesn't surprise me that aftermarket replacement compressor pumps are available in that price range.However, whether one might be a "no hassle, direct bolt on fit" replacement to the hitachi pump, and of comparable quality / performance, could be a whole 'nuther story...  I could see potentially long list of problems for the customer going this route: incompatible physical dimensions, bolt mounting pattern, flywheel diameter, v-belt "offset" and/or v-belt groove "depth" or incompatible crank nose (preventing easily swapping over the original flywheel), air outlet pipe connection, etc.  Addressing any one of those risks could have easily taken a good bit of his time and/or money.Not to mention, he may not like dealing with remote, mail order / internet only type of outfits.  Or waiting for slow ground/freight shipping of a heavy pump.  (As I was able to turn around his rod repair pretty quickly.)I'm guessing that one or more of the above reasons explain why the aftermarket pump repair option wasn't apparently even on his radar.
Reply:I tend to agree with SundownIII.  $350 to $400 in repair time for a part that may or may not work is pretty tough to justify.In my shop, I would probably have suggested a replacement pump, helped to source a used part, or maybe even refered him to a CNC guy to make a new part.  Either way, it looks like you did a good job of what you had to work with and I know that often times, the customer wants things done regardless if they make sense of not.
Reply:Originally Posted by jakeru...... and honed it the rest of the way using a 240 & 400 grit flapper stick.  This left a nice, smooth finish, cleaning up the visible honing chatter marks.  Ended up with about .002" clearance.
Reply:Originally Posted by SundownIIISometimes the mark of a GOOD welder is knowing when to say NO.Forged connecting rods (air compressor or IC engine) are where I say no thanks.Customer was fortunate the first failure didn't take out the entire compressor head.  Second failure probably won't be so lucky.Let's see.  A day of labor to repair?  Unless you're working for peanuts, that can't be a "cost effective" repair.  I guarantee you can buy an entire air compressor pump (Northern Tool, 4 HP pump, 13.2 CFM, $299) for less than my daily shop rate.Not trying to "rub it in" but the comment about the "voids" serving as "oil sumps" told me everything I needed to hear.  Several other posters have already done a good job of explaining why this "repair" is questionable at best.