How can I tell if my motor (2.7) has been rebuilt?

Fidalgo911S · 10-31-2006, 11:43 AM

Only reason I ask is my 2.7L in the '74 is still going strong. I hit 110,000 miles earlier this summer before I pulled it for a tranny rebuild and new clutch.

There are two signs that stand out besides the miles. One, it has a newer exhaust system that includes the crossover tube, but has a cat bypass and a one-in-one-out muffler. The head studs are fine. I checked the torque and only a couple needed to be tightened. It burns a bit of oil but not bad. And drives great.

So that got me thinking, was it rebuilt before I bought it? I have receipts going back to 66,000 miles but not before. Are there any tell-tale signs that I'd be able to see? Or is it a time bomb?

Dan in Pasadena · Dan in Pasadena's Garage

Fidalgo,

My '76S has just over 126,000 miles and it has not been rebuilt. The tell tale sign of a rebuild would be to get under it and see if there is evidence of Case Savers or Time Certs at the head studs. Mine shows no such evidence.

Now, this doesn't ABSOLUTELY guarantee it hasn't been rebuilt. I suppose someone COULD have rebuilt it in the old days without doing them...but why? Generally these engines failed early because of pulled studs due to high heat generated by the thermal reactors & 5 blade fan Porsche installed at the factory to raise temperatures up high enough to burn excess NOX. The heat in combination with the dimensionally smaller case margins around the larger spigots a 2.7 displacement required and the use of a magnesium case for these larger spigots/barrels.

Whew, run-on sentence, sorry. Just before I bought my car from a relative he had it thoroughly inspected and they found a number of loose studs - one of the obvious signs of studs beginning to pull. He opted to torque them and they have held, so far for over 5,000 miles. They did a lot of other work too - new dizzy, rebuilt fuel dizzy, all tuneup items, valve adjust, a host of other stuff. My car runs awesome. But it does leak some oil and I have done the oil t-stat O ring, breather gasket, etc. Not leaking from return tubes. I have been told it is likely some warpage on the cam towers, but I don't drive it near enough to worry too much about it yet.
I don'think your car is a timebomb IF the TR's ANd the 5 blade fan are loooong gone. If it is kept in good tune and not allowed to over heat (got an external oil cooler? Incredibly, I don't!) I tink you may see some more mileage. Having said that? Start saving money!

Walter_Middie · Walter_Middie's Garage

Fidalgo,

I had over 160K on my 2.7 L before I decided to rebuild it - and I also don't have an external oil cooler. I was convinced that the engine must have been rebuilt at some time, but I was wrong. When I took it apart, it was the first time it had been touched. I was able to re-use lots of still good parts, because I didn't wait until it started to destroy itself. Keep those head nuts torqued, drive it, and enjoy it.

randywebb · 10-31-2006, 03:17 PM

PNW cars have a much happier life than ones in the hot deserts/high traffic areas.

Elombard · 10-31-2006, 03:21 PM

How loose were the head studs you torqued...as said above isnt that the beginning of the end?

Jgordon · 10-31-2006, 04:03 PM

take it apart and examine all the pieces. If they all look relatively new, it was probably rebuilt.

74-911 · 10-31-2006, 05:21 PM

Quote:

Originally posted by Dan in Pasadena
Generally these engines failed early because of pulled studs due to high heat generated by the thermal reactors & 5 blade fan Porsche installed at the factory to raise temperatures up high enough to burn excess NOX. The heat in combination with the dimensionally smaller case margins around the larger spigots a 2.7 displacement required and the use of a magnesium case for these larger spigots/barrels.

The '74 2.7 engines did not have thermal reactors and I think they all had the 11 blade fans so the overheating was perhaps less of an issue with them. I had my '74 2.7 (no external oil cooler) rebuilt at 90K miles. The head studs were all OK, however the exhaust valve guides were long gone. I think the valve guides may be more of an issue with the 74's if driven in a very hot environment (such as South Texas).

Fidalgo911S · 10-31-2006, 05:49 PM

Quote:

Originally posted by Elombard
How loose were the head studs you torqued...as said above isnt that the beginning of the end?

Maybe 5ft-lbs off. Not much. The nice thing since the car is an S it has the front oil cooler, and, being a PNW car I've yet to get it above 175 degrees in the summer. It's almost always cold here.

Sounds like it's never been rebuilt

Rouxzy · 10-31-2006, 06:04 PM

My '77, 2.7 had over 135k miles without a rebuild.
Tom

Dan in Pasadena · Dan in Pasadena's Garage

Quote:

Originally posted by Fidalgo911S
Maybe 5ft-lbs off. Not much. The nice thing since the car is an S it has the front oil cooler, and, being a PNW car I've yet to get it above 175 degrees in the summer. It's almost always cold here.

Sounds like it's never been rebuilt

S's didn't come with external oil coolers - at least not in '76. Not sure about '74. And of course it make zero sense that Porsche wouldn't have made the TR and 5 blade fan-equipped cars equipped with a good cooler stock. Sounds to me liked planned obsolesence.

304065 · 11-01-2006, 10:09 AM

Hi Nate.

A good telltale is to pull off the chain covers and look at the number of brown chain ramps vs. the number of black ones. The current thinking is five black and one brown, but the original would have something different, probably all brown.

While you are inspecting, look at the amount of wear on the ramps. Compare the height of the pressure surface to the height of a new ramp, this will be a good guide. Also, look to see whether the chain tensioners are original. Remember that there have been five types of tensioner over the years: open cup (SWB only) reservoir type (68-69) 930 type (thin boss -80.5) and second 930 type (thick boss) and Carrera. You can rule out the first two and the last one, so depending on the thickness of the boss it will tell you whether somebody updated to the later tensioners along the way. Which again, is no guarantee that somebody didn't rebuild the engine.

Engine tin mod? Revised cooling baffles should be visible below the engine. Check the service bulletin to see how they were cut to improve airflow. As this was a well-known, free modification, most conscientious rebuilders would have done it.

Finally, the factory often sealed bolts with yellow and red witness marks. It's a long shot but see if these are in place!

Good luck!