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  • gm tpi parts

    i took on a job to polish the airbox on a gm tpi setup and it is going to bite me in the butt. this is the worst casting i have ever seen. the more i sand and wheel the more the pits show up. i have sanded this from 120 to 600 and polished starting with vented/ black when sanded it is smooth as glass. when hit with the wheel it goes to heck, pits show up and the surface is rough visually (dull shine). i have resanded and wheeled 3 times since, always the same result. wheels are clean and raked, and lightly charged. the last time around i started with loose white and the same thing. i am at my wits end(not a far journey) . the customer is antsy and i am totally unhappy with the results hence i cant charge for not being able to finish the job. any suggestions guys? thanks in advance.
    cliff
    when in doubt polish it out/ why replace it when you can refinish it
    G2 Polishing and Powdercoating

  • #2
    I ran into this with cast valve covers. They were Offenhausers so you think high quality, right? The pits were horrendous. They not only look bad but as you are finding out they don't allow the wheels to do their work properly.

    I was doing the covers quite cheap so I just told the guy that was the best I could do, and explained why. He was very happy with the job and understood completely. You might consider cutting your price and taking a loss if necessary to retain your reputation.

    After that I made sure I put a disclaimer with my quote regarding the fact that if pits show up, there's nothing I can do with them.

    The best solution in my opinion would be to plate with copper to fill the pits, sand and polish, then give it a good 3-part plating job. I'm thinking of partnering with a plater for just such items (don't wanna mess with all those chemicals myself yet...).

    BTW, when you polish try over-loading the wheel with compound often - it seems once the pits are full of compound the wheel works a little better...

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    • #3
      Hi, I don't know if this is a gm tpi intake or not that I just did for this one local guy but yeah they are messed up and this one was real old and abused too. Looked like someone beat on top of it with a wrench or something. But I bought these 3" sanding drums where you cut sandpaper of whatever grit you want and put it on the rubber backed wheel. You wrap the paper around the wheel and there is a slot where you put the ends into. Then you lock the ends in with this little tool set up that comes with them. They work great. I do those wheels up to about 600 then I wet sanded till 1500-2000. Then black and the two white bars I bought from here. The intake pipes are a pain in @#%. I really couldn't get in between but I made it look the best I could. Plus his pipes had dents and stuff all in them. Strangly you can't polish deep dents out. LOL. Like I said I don't know if this is a tpi set up because I'm a Ford guy and I usually polish SVT Lightning and Thunderbird SC parts such as blowers, plenums and such. Anyhoot here is a few pics I hope I can post them. Guy was real happy with it too. The pipe pics he gave me 2 sets so I kinda did a before and after shot. I also have alot of pics of Lightning polished parts that I have done too. I hope I'm allowed to post pics here, if not sorry to admin and I won't do it again. I enjoy your forums and don't wanna get the boot. Thanks Kevin





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      • #4
        yes that is the same as i am working on. i am very impressed with how good yours came out. i have sanded this thing again back to 120 grit and got most of the pits out worked op to 600 wet with a palm sander. by the way that is the best way i have found to sand lately. i use a squirt bottle of water and dampen it with a spritz. then sand till i get a pastey texture. flush and repeat. i got the part smoooooooth. hit the wheel and it went to ****. i give up. i will let the work go for a big discount. mpierich thanks for the advise on that, the customer may not be happy but he wont be mad and negative for my rep.
        whitelightning welcome to the forum, as for posting pics, rock on bro they are great shots of even better work.
        when in doubt polish it out/ why replace it when you can refinish it
        G2 Polishing and Powdercoating

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        • #5
          Originally posted by pickleboy
          i will let the work go for a big discount. mpierich thanks for the advise on that, the customer may not be happy but he wont be mad and negative for my rep.
          Start telling them upfront that the metal itself can prevent a prefect polishing job, then charge what you wanna charge. It takes as long or longer to do the work, no matter what the results, and it ain't your fault.

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          • #6
            not all the castings are the same. i have found that the import metal is better than the gm casting.

            the pits are out gassing little pores that are in the metal while it is casted 50% of all casting is done with a sand and the rest is in a mold .

            but out of all the part's i did the supra turbo valve covers come out perfect . i did a set for a guy and his car was in one of them sport concept mag's. that made my day..

            turbo:


            non turbo:

            (hint a 10 year old helped on these)

            here are a few more



            before and after :

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