4 bearing cam in 3 bearing 911 cam tower

[jkh2cpu]

Will a four bearing camshaft fit / work in a 3 bearing cam
tower? Are there potential problems with the cam shaft
drive? This is going in a 1974 engine with 1974 chain
drive gear.

John.

[tharbert]

According to my search foo, the 3 bearing cam tower carriers would need to be bored and later 4 bearing races used to match the later cam bearing size. See post #9.

BTW, I miss Grady!

[jkh2cpu]

Well I'm in a quandary. I recently ordered an SC grind for
my three bearing cam towers, and the manufacturer of
these cams says that they are 47 mm (my cam towers
measure 47 mm) and they will work in my cam towers.

I guess I'll have to wait until the westcoast shop opens up
and I can speak with them. I'll be highly irritated if I'm
getting wrong information from the cam grinders.

[BURN-BROS]

Hi John,

Yes, the 47mm 4 journal cam will work with no issues in a Early 3 journal cam tower. If you have later 47mm cam towers and need to drill an oil passage to use the cam.

[jkh2cpu]

For me, early is 1974.

So I can rest easy and put the tums away?

John.

[BURN-BROS]

Provided that the cam towers are original to the engine then yes, you are good to go.

[jkh2cpu]

Thanks for that info.

The other part of the question was about the hardware
that holds the chain wheel onto the camshaft. I have the
old system with the 46 mm nut.

John.

[BURN-BROS]

You will need the following parts

900 082 072 01 cam bolt qty 2

930 105 163 00 cam washer qty 2

You will also need the later cam timing tool

torque bolts to 88 ft/lbs

[jkh2cpu]

Thanks! I guess this will not break the bank.

John.

[Flat6pac]

I'm not in garage to measure but what I do know is
The 4 bearing cam doesn't fit in a 3 bearing carrier. The 4 bearings are larger
I did, years ago have a 4 brgs cam turned down to fit the 3 bearings holes.
The lobes wouldn't pass through the 3 bearings
The 3 bearing cam with SC grind will be reduced on the back side to accommodate lift and duration.
Bruce

[jkh2cpu]

Thanks for the input, Bruce. I'm purchasing 47 mm cams,
and the cams that came out of my towers are 47 mm, so
I should be good to go. I also just got off the phone with
the manufacturer, and I am assured that these new cams
will fit in my old (early 1974) towers.

John.

[DSPTurtle]

Yes, web cam billets are now "only available" in 4 bearing. They fit just fine as long as you specify its for a three bearing tower.