Rod not falling freely

[911231]

My son and I are just starting a 2.7 Rs spec motor. Last night we assembled the crank as per Wayne's book, checking all clearances with plastigauge. All were the same and dead on. But one of the rods does not fall freely of its own weight every time.It falls sometimes but not as quickly as all the others. It is just a little tighter. We assembled with locktight. it rotates smoothly without binding. Questions:
1) should we take it apart clean and reinstall. 2) if yes, do we need to get new rod bolts.

[vmisquez]

I would dissemble and find out why the rod is sticking. You should be able to reuse your existing rod bolts.

[Steve@Rennsport]

Take it apart and measure concentricity of the bearing shells, and the rod's big end.

Do NOT reuse a factory rod bolt,...these are one-use stretch bolts. ARP bolts may be reused as long as they stay in spec.

[911231]

Thanks for the input. We will take apart and order new rod bolts (we are using oem). we torqued down using digital torque wrench but guestimated the 90 degree +- 2 at the end. Is there a simple conventional torque measurement that can be used rather than the degree method? THanks for the help. Al and Chris

[Steve@Rennsport]

You MUST torque-angle factory bolts for accuracy and integrity. Snap-On makes a decent angle guage that can be used with any torque wrench and its inexpensive enough not to guess at such critical operations.

[911231]

Thank you very much Steve, I have ordered a new set of bolts and we will redo them all. I will get an angle gauge from Snap on. Thanks again, Al and Chris

[davehg]

I found this thread while searching the origin of the RS2.7 MFI build I purchased from DC Automotive. Al (911231) had been building this engine with his son Chris for over a decade.

911231 passed away a few years ago, and his family sold the engine back to DC Auto. I purchased it near complete about 18 months ago to transplant into my 1974 911 S, and had Bernie Buschen at European Auto do a complete tear down and rebuild. It was helpful to read the threads here including this one, which led me to suspect issues in the build. The problem identified in this thread had persisted, so Bernie ended up replacing the head studs and crank bearings and a few other issues. While the case was great (it had received extensive Ollie's service), we opted to use a 74 case, boat tailed and shuffle pinned, to match the year of the car, but everything else was reused (except bearings and head studs, of course).

Happy to say with the rebuild, the engine is fantastic and pulls amazing. It stayed with stock RS 8.5:1 pistons, but the DC30 cam Al used really makes this thing pull strong in lower RPMs, and the power is linear all the way past 5k (still in break in).

Fun to see the p/o's older threads. Here's the completed engine in the car, in case his son Chris visits the forum and wants to know what became of his dad's engine project. Thanks in advance for all the attention to detail as the engine was super nice, and even with a complete tear-down rebuild, no regrets on the acquisition. The engine is spectacular and transforms the 74.

[cgarr]

When you rebuild rods they are torqued to spec then honed to size, taken apart to assemble on the crank and torqued again, that's the second time they are used?

[PeteKz]

Machine shops I've dealt with will use the OLD rod bolts to torque up the rods for honing. The new OE bolts should only be used once, according to Porsche. If you use ARP, they are reusable.

However, I have been asking and searching and have still not got a good answer why the Porsche conrod bolts should not be reused. They are not torque-to-yield on the 3.0 and earlier engines, therefore, from an engineering perspective, should be reusable. The smaller bolts (9mm) on the 3.2 engines with a 74.4m stroke handle higher forces than the 10mm bolts on your 70.4mm stroke engine. The 10mm bolts have more margin of safety.

If I were rebiuilding a 2.7 engine, I would retorque them.