Dissimilar metals question...
04-09-2016, 10:16 AM
#16
Three Wheelin'
After sifting thru threads which display whole boatloads of stupidity and childish insolence regarding these cars, not only do we have THIS going on as a refreshing antidote, but actual folks who know something about that which they speak.
I am invigorated !
Thanks for a great discussion ^^^^^^^^^^^ this kind of thing gives me hope these cars will be around for awhile; maybe even that some of them are in the right hands and not just getting their interiors plastidipped and glow stix placed under rocker panels, fastidiously being videotaped to ooooh and aahhhhhhhhhhhh over while contemplating the next 'sbc refinement' or suspension modification involving dual wheels or 4 wheel drive and a 23 inch tire combination.
I am invigorated !
Thanks for a great discussion ^^^^^^^^^^^ this kind of thing gives me hope these cars will be around for awhile; maybe even that some of them are in the right hands and not just getting their interiors plastidipped and glow stix placed under rocker panels, fastidiously being videotaped to ooooh and aahhhhhhhhhhhh over while contemplating the next 'sbc refinement' or suspension modification involving dual wheels or 4 wheel drive and a 23 inch tire combination.
04-09-2016, 12:45 PM
#17
Rennlist Member
Thread Starter
Hi tom,
Copper and stainless aren't actually to far off from each other galvanically. Also since the helicoil is relatively small compared to the copper it makes it even better.
That said it is a wet area and usually helicoils would be installed with a corrosion inhibiting compound or primer, which you can't do because you need conductivity.
You can use the stainless helicoils, but you need to seal off the stack-up with sealant or some grease afterwards to prevent water from getting in there, then you should be good.
I'm a materials engineer in aerospace. I do this all day long. We have this issue a lot with stainless helicoils installed in aluminum, which is worse then copper. As a rule of thumb, if you can keep water from getting in then galvanics isn't a concern. All water should be considered as an electrolyte, not just salt water. There are so many contaminants in the engine area and on the road that it's never going to be pure water anyway.
Copper and stainless aren't actually to far off from each other galvanically. Also since the helicoil is relatively small compared to the copper it makes it even better.
That said it is a wet area and usually helicoils would be installed with a corrosion inhibiting compound or primer, which you can't do because you need conductivity.
You can use the stainless helicoils, but you need to seal off the stack-up with sealant or some grease afterwards to prevent water from getting in there, then you should be good.
I'm a materials engineer in aerospace. I do this all day long. We have this issue a lot with stainless helicoils installed in aluminum, which is worse then copper. As a rule of thumb, if you can keep water from getting in then galvanics isn't a concern. All water should be considered as an electrolyte, not just salt water. There are so many contaminants in the engine area and on the road that it's never going to be pure water anyway.
On the other hand, Porsche saw fit to put a zinc-plated steel into those threads, so adding a SS insert can't be any worse, right?
Last edited by Tom M'Guinn; 04-09-2016 at 02:52 PM.
04-09-2016, 05:27 PM
#18
Rennlist Member
After sifting thru threads which display whole boatloads of stupidity and childish insolence regarding these cars, not only do we have THIS going on as a refreshing antidote, but actual folks who know something about that which they speak.
I am invigorated !
Thanks for a great discussion ^^^^^^^^^^^ this kind of thing gives me hope these cars will be around for awhile; maybe even that some of them are in the right hands and not just getting their interiors plastidipped and glow stix placed under rocker panels, fastidiously being videotaped to ooooh and aahhhhhhhhhhhh over while contemplating the next 'sbc refinement' or suspension modification involving dual wheels or 4 wheel drive and a 23 inch tire combination.
I am invigorated !
Thanks for a great discussion ^^^^^^^^^^^ this kind of thing gives me hope these cars will be around for awhile; maybe even that some of them are in the right hands and not just getting their interiors plastidipped and glow stix placed under rocker panels, fastidiously being videotaped to ooooh and aahhhhhhhhhhhh over while contemplating the next 'sbc refinement' or suspension modification involving dual wheels or 4 wheel drive and a 23 inch tire combination.
Hold on, gotta dig something up from another forum...
THERE!
Sorry, I just had to go
a moment. I agree, this is good stuff, and stuff I'm considering cause I'm getting ready to replace a bunch of my hardware when I put it all back together. I kinda want to go SS, but just unsure how well that will work out in the long run with the aluminum. The interwebs has conflicting info on the matter... But based on the condition of many of my stock bolts threads, I really want to do something, and the heads are getting stripped. It's been taken apart a few too many times before I got in the picture it seems.
I didn't get a whole lot of response on my thread I started about it...
04-11-2016, 04:10 PM
#19
Rennlist Member
Thread Starter
I was able to find an M8 helicoil made of phosphor bronze, which should be significantly better than a SS helicoil from both a galvanic corrosion and electrical conductivity perspective. They're make by Chrislynn Inserts and distributed by treadtoolsupply.com online. They are rare, so couldn't order online, but they hunted some down for me when I called. 
Part No. is 84060BU in case anyone else is looking...
Part No. is 84060BU in case anyone else is looking...
04-11-2016, 04:44 PM
#20
Rennlist Member
Just for posterity, could you also modify a copper plug? Drill out the center and tap it to size, then tap your stripped hole for the plug's NPT thread, and run it in? Assuming the plug still had a drive on it to run it in, like a recessed square drive larger than the OD of the drilled hole.
04-11-2016, 05:27 PM
#21
Rennlist Member
Thread Starter
Just for posterity, could you also modify a copper plug? Drill out the center and tap it to size, then tap your stripped hole for the plug's NPT thread, and run it in? Assuming the plug still had a drive on it to run it in, like a recessed square drive larger than the OD of the drilled hole.
04-16-2016, 12:09 AM
#22
Rennlist Member
Thread Starter
To close the loop, here is the bronze insert in place. With a copper washer and bronze bolt, I'm thinking it's better than new... Either way, it's good to go....