2.7 Rebuild: two final questions
 

Dear friends,

It has been a long time coming, but I finally found the time to complete my rebuild of my 1975 2.7 engine. Many people here have helped me enormously, so first a few words of thanks: I have practically worn out my signed copy of Mr. Dempsey's book; my transmission was rebuilt by Gary Fairbanks and he did a marvelous job; the UPS driver got a kick out of the huge numbers of shipments from our host; the engine case was machined by Ollies in Arizona and I have never seen better work; Elgin machined cams for me, likewise beautiful work; the heads were prepared by Anchor Atlantic and they went so far as to stamp my name on them!

The shakedown is going much better than I anticipated. Since I am a first time rebuilder, I had imagined all kinds of disasters, but the nearest thing to a real problem was when the rear view mirror fell off! My wife said that this is because I am very careful, but that is not true. I am just very lucky, and I have had very good help.

There are two things I am hoping the collective wisdom of this forum can help with. First, I am simply ignorant of what the normal operating temperature of this engine should be. I am breaking in the engine quite aggressively, as Dempsey's book suggests, so maybe the engine is getting hotter than it will when I revert to my normal college-professor ways, but it seems to be settling in at about 220 degrees by the temperature gauge on the dashboard. Is this correct? The owners' manual is very vague on this point, and I haven't been able to find the correct range in the shop manual, either. Would the car benefit from an external cooler? I am thinking about having one installed.

The second question concerns warm starting. When the engine is cold, it starts like a champ. After the engine is fully warmed up, if I stop the engine, and restart it within a minute or two, it starts on the first compression stroke. However, if I wait for 10 minutes or so, the engine won't start at all; it cranks very well, but there is no hint of combustion. The only convenient option is to wait for about an hour, and then the engine is cold and starts easily. I am assuming that the fuel system is losing pressure somewhere. I am getting a replacement pressure accumulator tomorrow morning, but if that doesn't cure the problem, is there something else I should check? A check valve somewhere, perhaps? If I need to buy pressure gauges, do you have any recommendations? By the way, this problem precedes the engine rebuild.

The engine particulars: 1975 stock 2.7 engine, with Elgin SC cams, and oil bypass modification, stock Bosch CIS injection.

Thank you very much in advance for any advice on these two points. I'll write up a fuller narrative of the whole adventure if there is interest. I have about 2 million pictures I can share.

Best regards,
Dan

Dan,


JMHO,.........You do NOT want to operate a mag-cased engine at high oil temps. I want to see 185-195 deg operating temps under normal conditions. At 210 deg, you are losing power and the propensity for oil leaks increases.

Install a Carrera oil cooler & fan on your 2.7 and it will live a VERY long time. :)

The 1975 911S did not come with a front oil cooler (for the USA cars), and adding one is your best insurance for a long lived engine. 220 is hot, 250 is too damned hot!

Hi Steve, since it's relevant to the OP and your suggestion:

What case modifications are necessary to add the Carrera oil pump?

Can the regular intermediate shaft be used?

Any other mods to be aware of?

The Carrera oil is a drop-in (case must be split) and requires the Carrera sump plate. The oil bypass mod must be done to the case for any engine prior to 1976.

IS's are interchangeable.

Dan:

As others have said, 220°F is too hot. It's certainly worth installing an external cooler and thermostat and be sure to run an 11-blade fan. I have a rebuilt-to-stock 2.7 and am running an external Mocal cooler with some ducting. Running down the highway in warm temps (85°F+) the engine only reaches ~195°F.

Regarding your warm start dilemma: You might get lucky replacing the accumulator, but most likely you have some other issues as well (probably with the WUR and warm control pressure). A test gauge may seem expensive, but you'll use it:

Pelican Parts.com - CIS K-Jet F.I Tester w/ Case

There are numerous threads on CIS troubleshooting here; I recommend searching and finding those. Here's a link to my favorite search utility:

http://forums.pelicanparts.com/porsche-911-technical-forum/884815-custom-forum-search.html

My car is also a '75 and maybe you've got the same components as mine. Here's a link to a thread where I have the control pressures and WUR chart:

http://forums.pelicanparts.com/porsche-911-technical-forum/780952-sorry-yet-another-cis-troubleshooting-thread.html

Good luck.

Dan,

Did you have new CIS injectors installed at time of rebuild?

Also, what fan blade are you running?

Thanks for the help everyone.

In answer to the questions: I did not replace the injectors --- they are what were in the engine when I purchased the car 4 years ago. Also, the fan is an 11 bladed magnesium fan.