This is for my second car (300M). I need to bore my TB from 67mm to 70mm. Do you guys know of anyplace in VA, MD or DC that do this kind of job.

I have called several places but no one does TB boring. I am desperate. LOL
The TB and the 70mm plate has been sitting in basement for over a year now. Thanks

 

Amy machine shop with a decent mill should be able to indicate center from the existing bore, bore larger, and do it all in less than an hour. Check with some of the small machine shops in your area and see if any are hungry.

 

In the DC metro area? Yea, good luck. I don’t know a machine shop in the area that doesn’t have more work lined up then they want and that would take random small machining projects, I’ve tried… and this is coming from someone that thought that I would be able to call in a couple of favors owed to the shop that I worked at… no dice.

The owner of Burtonsville performance machine service suggested that for small projects the best bet locally is to make friends at one of the local research institute shops, but my wife works at APL and a friend used to work at NIH in the same department with contacts and still had no luck, I never did find anyone locally.

FWIW, I’ve rigged a fixture to do this on my drill press for my crossfire throttle bodies (managed to very carefully cut them out to 54mm) which worked surprisingly well. This is what the rough cut looked like:


Assembled with a spacer that was cut on the same fixture:


Shot from the top assembled (at this point I’d smoothed/polished the bore, the casting was actually that crappy, it was sort of layered and very porous):

 

Depending on feedrate and tool speed, and the right insert, that "crappy, porous" material can be machined to an almost mirror finish. That's why I suggested a machine shop or someone with machining experience. (I didn't presume to think that included the Capitol.) Baltimore may be your best bet in that region. Typical automotive machine shops really don't have a lot of skill or experience in fine tolerance machining, holding a critical surface finishes, production type tooling, specialized coolants for material/chip flow control, etcetera. Most of what's done there is one-off, repair type work. The processes and techniques are completely different, and usually just don't need to be highly precise in order to get the job done right. You'll never see tolerances in microns in most automotive machine shops.

 

While a proper cutter on a mill or a lathe would have done a much better (mostly faster) job, it would not have resulted in a better final finish. The picture from the top is a bit deceptive, most of the bore looks nice and smooth and shiny like the finished picture from the bottom and the finished bore in the wood spacer, but the dots in the picture from the top are actually holes in the casting from casting porocity. I’ve used the same setup on an LT1 throttle body and the thing came out perfect, GM’s castings just got much better in 15 years.

Going northish towards Baltimore doesn’t really buy you anything till you get past Aberdeen proving grounds, most of the shops till then are either production shops, government shops or shops doing a lot of government work and aren’t interested in small BS work… I figured that I might find something near BWI airport (for miles everything is an industrial area) but I found that they were either tied up with government or research projects (NASA Goddard, Grumman, a whole mess of small aerospace contractors.

I’d bet that you’d have better luck in some of the corners of NoVA (but I know that PanAm or whoever owns that stuff now has been snatching up tons of similar facilities in the area), or maybe heading south towards Richmond or southern MD (Indianhead…), I know of some industrial and welding shops down that way and I never bothered checking for machining stuff.

OTOH, at that point you’ve pretty much covered about 4 hours worth of distance, more then that in weekday traffic… have you tried online? I know that that there is at least one guy doing it and selling them on ebay…

 

If you run into a porous casting again, try an insert with a larger radius, and less relief. They tend to roll over the grains as they cut them off rather than shear them sharply. Your coolant makes a difference, too. I know it's far easier to experiment with tooling, feeds, and speeds in a production run, since the scrapped pieces used for the R&D of tooling and setup are usually expected as yield variance. You generally don't want to do that with the ONE piece you have to make right in this kind of situation. That's another difference between repair machining and production machining.

 

Is that spacer made out of wood ??

I know they exist, do they last at all ?

 

Yep, made out of hardwood soaked in SIG aircraft dope to make it fuel proof… worked fine for years on the car without any issues.

FWIW, I just disassembled and cut up a vortec truck TB… If you’ve ever seen one you’ll know how different this is then stock, I removed the constricted area behind the throttle plates, the steps in the machining in the bore, blended the whole thing…