Is there anything special about a 7R case

[pjv911]

I noticed this guy selling a 7R 2.7 case boasting its a better case to build on. I emailed him in question but he never replied. I ask because I have a 74` 2.7 7R case in my car and was just wondering. Thanks guys

http://cgi.ebay.com/ebaymotors/aw-cgi/ebayISAPI.dll?ViewItem&item=598033078&r=0&t=0

[pjv911]

anybody?

[Bobboloo]

The main difference over the previous mag cases is that it has more internal reinforcement. Particularly around the main crank bearings. The idea was to keep the case from distorting under high stress loads.

Bobby

[Bill Verburg]

The 7r was the last and strongest of the magnesium cases. It was introduced in 73 as part of the updates for the 2.7RS package. There were 2 versions one for the 84mm 2.4 liter pistons with 92mm spigots and another for the 90mm 2.7 pistons with 97mm spigots, The 92s can be machined to 97mm to accept the 90mm pistons for 2.7 conversions.

The 2.4's are a 911/50, 51, 52, 53, 61, 62, 63, 91. These use the smaller (92mm) spigots but are more desireable since these cases do NOT show the same heat stresses that the 2.7's do, even though machine work is needed for the 90mm RS & 92mm RSR cylinders.

The 2.7's are a 911/41, 42, 43, 44, 46, 47, 48, 49, 82, 84, 85, 89, 90, 92, 93, 96, 97, These have the 97mm spigots that will accept any 90mm cylinder and even the 92mm RSR ones without machine work. I would avoid the 76-77 ones if possible, as these cases almost always are warped and need LOTS of machine work to fix everything.

[gohan]

How can I identify which one of 2.4's 7r or 2.7s 7r case (from outside)?

[Randy W]

Gohan, it will say 7R at the end of the numbers on top of the fan housing. As far as the comment from the seller that the magnesium 7R case is the best to build on - IMO it depends on what you want to end up with. If it's a 2.7 RS engine then a 2.4 5R case will be fine, if it's a 2.8 RSR engine, then yes, the extra ribbing on a very late '73 or '74 case will best. However if you want a high horsepower 3.5L, you probably want to start with an aluminum case from a 3.0/3.2.

Randy Wells

[jluetjen]

It may sound like a stupid question , but does Bill's answer mean that a 2.7 crankcase could never be used for a 2.4 or 2.2 because the spigots are too big?

[Bill Verburg]

does Bill's answer mean that a 2.7 crankcase could never be used for a 2.4 or 2.2 because the spigots are too big?

correct!

[Loual]

Based on this thread, I took a look, and my fan housing number ends in 5R... I expected 7R since it's a 1975... although it has an October 1974 build date... USA model. Is 5R correct?

[J P Stein]

Er.....the crankcase casting # is on the case. The fan case casting# is.........

As for the usability of any of these 7R cases, they're kinda like a box of chocolates, you never know what you're going to get till you hang it on a boreing mill. IMO, straight and true is unlikely on any of them.

My own late 76 case was drag honed (on the crank bores), decked, squared and timecerted (case saver, actually) for around $300. It also had the advantage of the bypass mod being done from the factory.
I priced over size main brgs (OD) JIC......"600 bucks, if we can find em" was the quote.

[Loual]

Let me rephrase my question. Was a 7R case standard on all 1974-77 USA 911 2.7s?

[JSDSKI]

On my 72 911T the numbers are visible above the pushrod tubes. The left case part number ends with 4R and the right case with 3R. I hope it means left and right. Or does it mean bastard rebuild sometime in the past? In other words, should both end with 4R?

The car has MFI and the VIN ends in 1362 so it was probably built about middle of the model year, before the CIS model.

Expert opinion???

[Kahuna]

Thy're not push rod tubes, they are oil returns. They transfer oil from the heads back to the sump.

As stated above the 7R was introduced for the 73RS some 2.4s, got it as did most if not all 2.7s

Porsce has a history of introducing new parts and castings as they become available. There is often an overlap of new and old pieces used in conjunction with each other.

[gohan]

Oh, that's why 2.4s and 2.7s has the same 7R numbers even though the size of the spigots are different!