Can 47mm cam tower be bored to 49mm?

[TargaCoupe]

I'm building a 3.3L SS engine based on a 1978 SC 3.0. It came with 3 bearing cam towers and 906 cams with MFI which I sold to get a newer cam to go with a modern EFI system.

I picked up a pair of 4 bearing cam towers but unfortunately one of them is the 1 year only 4 bearing tower with the smaller 47mm bore for the old style cams. The other is the correct 49mm bore. I'm having trouble tracking down another cam tower and was wondering if I can just take the undersized cam tower to a machine shop and have it bored out to 49mm. Anyone see any issue with that?

[SBell]

If I remember correctly, the 47mm 4 bearing cam towers do not have the oil passage for the 4th bearing drilled out so you will need to do that unless it's already been done. Other than that I believe the casting should be the same. Henry at Supertec has a thread somewhere about drilling for the extra bearing.

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[Jim Dorociak]

I have (1) 47mm cam tower available if that helps. Jim

[TargaCoupe]

Thanks for the offer Jim but I've already purchased a set of 49mm Dougherty cams for the project.

[gled49]

4 bearing 49mm started in 76 forward with casting numbers changing from 911 to 930 to 964, all the same, just check dimensions and cross drillings.

[stownsen914]

I've heard of the transitional 4 bearing, 47 mm cam towers. Let's see if anyone chimes in here. I've not heard of boring them out, but it seems plausible that it can be done. Only thing is it might be a bit pricey due to setup time if you're the first/only customer needing this done.

It's a little surprising you can't find a 49 mm cam tower. You've tried a WTB (yeah, I know ...) ? Maybe call Henry at Supertec.

If all else fails, you could call some of the usual suspects in Porsche machining like Ollies to see if they are set up to bore your 47 mm cam towers.

[Rosco_NZ]

There’s plenty of 49mm 4 bearing out there .. put a WTB in the parts section.

[targa72e]

There were castings with the same part number that came with either 47mm or 49mm journal sizing, late 2.7 47mm early 3.0SC 49mm. You could machine 47mm larger or sleeve 49mm smaller but I think by the time you have the machine work done you would pay more than purchasing a good used set the correct size used.

john

[Henry Schmidt]

Supertec is now offering this service. We can bore 3 or 4 bearing 47mm cam towers to 49mm.
We offer a complete restoration service. [remove studs, flatten all sealing surfaces, pull plugs and clean spray bars. In the case of boring 47mm, 4 journal cams to 49mm, we also open the oiling passage to make the 4th journal functional.