Short or Long stroke

[Matt Blast]

This is a longstroke 2.5 case (911/70) and a crankshaft that I broke a few years back. The engine still ran well enough to get around the track and then shut it down. I found that I could wobble the pully by hand without much effort. Fortunately the case was not destroyed as this is the original case to the car. This case is now a shelf decoration and the crank will make a nice lamp someday.

Matt

[Flunder]

Matt:

Please tell us:

Was the 70.4 crank cross drilled?
Was the original 911/70 case shuffle pinned?
What flywheel was on the engine when the crank broke?

Are you building a the replacement engine to shortstroke of longstroke specs?

Thanks, Tom

[Matt Blast]

Hi Tom,

The crank was not cross drilled.
The original case is a 3R/3R and was not pinned.
The flywheel was stock (nothing lightened).

The next engine is a long stroke built on a 7R and shuffle pinned with crossdrilled crank and standard flywheel.

Matt

[a911s]

Sounds good. Make sure your chain covers are shuffle pinned and you have a big oil pump.

[Jeff Higgins]

Randy - I've never heard of shuffle pinning chain covers until you it mentioned earlier on this thread. What does that do for the motor? Did you do that on your 2.8/2.7, and is it something I should consider on my 3.0?

[gled49]

me too? Gordon

[a911s]

Mike Reischel recommended it with early aluminum cases used in high horsepower application, since they do not have as many locating pins in this area as later cases/chain cover housings. Apparently there have been some leaks in this area in some of the vintage race 911s using early aluminum cases, and the additional locating pins prevent this from occurring. I did not add more pins in this area on the first build of my motor (and did not experience any leaks), but we did add them during the second build since we had the time. A later aluminum case has these extra pins already, Jeff.

[Jeff Higgins]

Thanks for the explanation, Randy. So, essentially, it's just a matter of applying a later improvement that Porsche had come up with to their first effort at 911 cases. There are a couple of dowel pins at the chain box to case seam on my motor, so I guess I assumed they all had that. I could see where they would be needed as power and rpm's increase.

[gled49]

Me too, OK. The update is a good thing. The two per side solid dowels are removed and in there place goes studs and hollow dowel. Gordon