4 bearing cam in 3 bearing cam tower?

[rwest]

Hello,

I was going to send my 77 CIS cams in to have them ground to an SC profile, but the price was just slightly less than just getting new, so I decided for new, but the lady said all the new billets have the fourth bearing on them, but that it works just fine in the 3 bearing tower. She did have me measure the bore so the bearings would be correct.

Besides being a bit odd because the 4 bearing towers have a larger bore, maybe they start everything with the same billet and mill down the bearing area to size for earlier cars? do you know if having the fourth one just spinning in space is a problem?

Thanks,
Rutager

[Catorce]

Not ideal, but doesn't seem to be a problem. I personally would change out the cam towers, but thats just me.

[rwest]

It is one of those things that just doesn’t seem right, but apparently works, although not sure why they couldn’t just mill the 4th bearing down when grinding the rest?

[rwest]

And, oh Catforce, been following your case project- very cool, not something I see in my immediate future, but always good to have choices.

I have a friend with a CNC mill and just making simple things takes a great deal of work, your case work is almost unbelievable.

[Flat6pac]

Once I cut an SCcam four bearing cam bearings smaller to fit the 3 bearing carrier.
Bottom line was the cam wouldn’t fit because the lobes wouldn’t clear the smaller holes of the carrier.
Bruce

[tom1394racing]

I have a set of 3 bearing 964 profile cams that would be a nice upgrade for your 2.7.

PM me if you would like to follow up.

[Henry Schmidt]

Interesting question.
The billet cam blanks are all the same. They just grind the journals down from 49mm to 47mm.
What makes this interesting is that most if not all 77 cam tower are 4 journal.
The casting are the same as the casting used for 78 SC. The difference is the cam bore is smaller (47mm vs 49mm) and the unused journal is not drilled for oiling.
To be clear, the 77, 2.7 engine uses a 3 journal cam but the housing has 4 journals.
The journal that would be free (unused) with a 3 journal cam is not drilled for oiling. If it was drilled there would be a loss of oil pressure do to the missing cam journal.
These cam towers (77 2.7) are cool because you can drill the housing to make it a 4 journal housing (good for high RPM/racing motors). In fact, if you use a 4 journal cam in a 77 cam tower you have to drill it for oiling or the cam will seize in the housing do to lack of oiling.
We cam convert them for you or you can drill and plug them yourself.
The way you can tell if you have a 47mm 4 journal cam tower is to count them or look to see if the cam tower has one un-drilled casting and one drilled.

[Henry Schmidt]

Originally Posted by Flat6pac

Once I cut an SCcam four bearing cam bearings smaller to fit the 3 bearing carrier.
Bottom line was the cam wouldn’t fit because the lobes wouldn’t clear the smaller holes of the carrier.
Bruce

Cutting down a 49mm cam to fit the 47mm housing gives you a great cam to regrind.
Lots of base circle so you have lots of cam options without welding.

[Henry Schmidt]

Originally Posted by tom1394racing

I have a set of 3 bearing 964 profile cams that would be a nice upgrade for your 2.7.

PM me if you would like to follow up.

Just a heads up:
With 964 cams and stock2.7 CIS pistons you may have a clearance problem. Valve pockets may be required.

[Catorce]

Originally Posted by rwest

And, oh Catforce, been following your case project- very cool, not something I see in my immediate future, but always good to have choices.

I have a friend with a CNC mill and just making simple things takes a great deal of work, your case work is almost unbelievable.

Thank you!

[rwest]

Originally Posted by tom1394racing

I have a set of 3 bearing 964 profile cams that would be a nice upgrade for your 2.7.

PM me if you would like to follow up.

Hi Tom,

Thanks for the offer, in doing the “research” for what cam I was going to use, I talked with Steve Weiner and he told me that on the 2.7, the 964 comes on at higher rpms and the SC would be better suited to my style of driving.

[rwest]

Originally Posted by Flat6pac

Once I cut an SCcam four bearing cam bearings smaller to fit the 3 bearing carrier.
Bottom line was the cam wouldn’t fit because the lobes wouldn’t clear the smaller holes of the carrier.
Bruce

Thanks for the heads up, I’ll double check with the cam grinder.

[rwest]

Originally Posted by Henry Schmidt

Interesting question.
The billet cam blanks are all the same. They just grind the journals down from 49mm to 47mm.
What makes this interesting is that most if not all 77 cam tower are 4 journal.
The casting are the same as the casting used for 78 SC. The difference is the cam bore is smaller (47mm vs 49mm) and the unused journal is not drilled for oiling.
To be clear, the 77, 2.7 engine uses a 3 journal cam but the housing has 4 journals.
The journal that would be free (unused) with a 3 journal cam is not drilled for oiling. If it was drilled there would be a loss of oil pressure do to the missing cam journal.
These cam towers (77 2.7) are cool because you can drill the housing to make it a 4 journal housing (good for high RPM/racing motors). In fact, if you use a 4 journal cam in a 77 cam tower you have to drill it for oiling or the cam will seize in the housing do to lack of oiling.
We cam convert them for you or you can drill and plug them yourself.
The way you can tell if you have a 47mm 4 journal cam tower is to count them or look to see if the cam tower has one un-drilled casting and one drilled.

Henry,

Such great information, thank you. I just checked my towers and it sure appears that I have the fourth bearing surface and it will need to be drilled out if the cams come with the fourth bearing. Can you give me a rough cost and turn around time? As you can see, they will need a good cleaning too!

[rwest]

In case anyone is interested, my engine is a 77 2.7 and I will be putting in SC cams and Mahle 2.7RS pistons and cylinders. I’m using a Bitz EFI with the CIS throttle body, MSD ignition with the stock distributor and points.

Reason for rebuild is a foreign object in #5 and 3 bad exhaust valves- very poor leakdowns on those 3 cylinders and almost perfect numbers on the other 3! I’m just doing the top end.

Best,
Rutager

[racerjay]

Dude, there are bigger fish to fry, a 4 journal housing would be ideal, not necessary.
I would not grind the extra journal down its a waste of time and money. Have run into it a hand ful of times, just make sure the mating surface is less than .002'' warpage and run it

[rwest]

Hi Racerjay,

It turns out, thanks to Henry for pointing it out, is that the 77 has a 4th journal already, so I’ll either need to add an oil passage to the bearing or have the 4th bearing removed from the cam.

Rutager

[Henry Schmidt]

Originally Posted by racerjay

Dude, there are bigger fish to fry, a 4 journal housing would be ideal, not necessary.
I would not grind the extra journal down its a waste of time and money. Have run into it a hand ful of times, just make sure the mating surface is less than .002'' warpage and run it

The extra/forth journal is not necessary but it is an upgrade.
Prepping the house to supply oil to the forth journal is easy (inexpensive) and makes the cam more stable.
Simply drill through the housing at the boss provided and plug the access hole.
You can use a simple aluminum plug or we tap it and install a threaded plug.
Small upgrades over 60 years are how the 911 engine earned it's mystique.

[rwest]

Originally Posted by Henry Schmidt

The extra/forth journal is not necessary but it is an upgrade.
Prepping the house to supply oil to the forth journal is easy (inexpensive) and makes the cam more stable.
Simply drill through the housing at the boss provided and plug the access hole.
You can use a simple aluminum plug or we tap it and install a threaded plug.
Small upgrades over 60 years are how the 911 engine earned it's mystique.

Thanks Henry,

What size bit would you use, particular angle, finishing of hole in journal and source for threaded plugs?

Rutager

[356RS]

Originally Posted by rwest

In case anyone is interested, my engine is a 77 2.7 and I will be putting in SC cams and Mahle 2.7RS pistons and cylinders.
Rutager

Mahle 2.7RS P&L's in a CIS engine?

[rwest]

Originally Posted by 356RS

Mahle 2.7RS P&L's in a CIS engine?

I have an EFI kit installed, the airbox, throttle body and intake runners remain, but no WUR, fuel distributor or any of the other bits except the AAR which just gives extra air until warmed up.