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Aluminum Air Compressor Connecting Rod Repair

Posted: Wed Oct 13, 2010 2:42 pm
by jakeru
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.)

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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.

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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. ;)

Re: Aluminum Air Compressor Connecting Rod Repair

Posted: Thu Dec 09, 2010 9:01 pm
by Ji Gantor
Great repair Jackeru.
Is there a bearing that lines the rod?

Ji

Re: Aluminum Air Compressor Connecting Rod Repair

Posted: Fri Dec 10, 2010 1:17 pm
by jakeru
Thanks Ji. No removable bearing shell; its just precision machined metal (aluminum rod) on precision machined metal (polished cast iron or steel crank journal), with oil splash for lubrication.

Re: Aluminum Air Compressor Connecting Rod Repair

Posted: Fri Dec 10, 2010 7:46 pm
by Ji Gantor
Hi Jakeru,
That is some seriously good work.
From my experience welding cast ali you always seem to end up with some small air pockets.
I guess you could weld cut weld cut until there are none left but why would you. The heat may distort it past usability.
After all as you said they will act like oil galleries anyway.

Ji

Re: Aluminum Air Compressor Connecting Rod Repair

Posted: Thu Dec 30, 2010 10:31 am
by Zoomie
You could possibly ream it out oversize and press in a journal/bearing. Might be a tad stronger and would likely be more durable. great weld repair Jakeru!