67King

Doing the rod bearings. I am not sure what toque setting to use. In section 10 of the manual, it says 75 + 5 N-m (55 + 4 lb-ft), in section 13, it says 75 N-m (55 lb-ft). I have never seen that kind of spec before. I've seen one number, a number plus an angle (TTY), and stretch (requires strain gauge), and used all three methods.

What does the "+5" mean? I would expect breakaway torque to be close to 20% higher than the first setting (i.e. 90 N-m, or 66 lb-ft of torque). So I would expect that if I were to add 5 N-m or 4 lb-ft to the baseline, the fastener would not move.

The last engine I built I built with Crower rods which used 3/8" bolts. I used a strain gauge to 0.005", but the alternative torque spec was 50 lb-ft, which is pretty close to an M10 at about 70 N-m. It was spec'd with lube, rather than oil.

I am assuming that, due to the age of the engine, that it would have been spec'd with oil (20W-50?). Can anyone confirm?

67King

Bump. Bueller?

FWIW, I did 59 lb-ft, and am getting between 0.038-0.051mm (scale on the plastigauge), which is on the tight end of spec (0.034-0.092mm). Unless I hear otherwise, I'll button it all up with that clearance, but I would still appreciate any insight folks have into what the heck that spec the Porsche manual calls out means.

Rogue_Ant

I just did rod-bearings (new motor I'm building). I did 59lb-ft, and got pretty much exactly the same clearance (plastigauge) as you...

fortysixandtwo

I don't have a standard to reference, but I would read that as 75 -0 +5Nm where 75Nm would be the target torque, vs shooting for the nominal value of 77.5Nm.

All of the other typical torque call outs are present in the FWSM
Multi stage torque sequences are listed by stage1, 2, 3, etc...
Example:
1st stage: 30Nm
2nd stage: 50Nm

Torque then angle in degrees is labeled as such
Example:
1st stage: 18 lb-ft
2nd stage: + 90°

Torque range is listed as typical
Example:
25-30Nm

To possibly confuse things further, the 968 manual list the connecting rod nut as a 2 stage sequence with threads and surfaces lightly oiled:
1st stage: 18 lb-ft
2nd stage: + 90°

67King

I was doing them in 2 stages because of the clearance issue (doing this in car). To elaborate, breakaway torque is significantly higher than rotating toque (analogy - start pushing a heavy box along the floor, it takes more effort to get it in motion than to keep it there, exact same phenomenon). If I run out of space and manage to get, say 52 lb-ft, when I ratchet it, and start again, it takes more than 59 lb-ft to get it started. Then you'd need to loosen it and start again. That's all well and fine, but with the serrated teeth on the washer side of the nut, if there is any truth to the theory that those teeth yield and can't be retorqued, I can't loosen it and retorque without ruining the nut. Anyway, I was setting it to 47 lb-ft, then 59 lb-ft (accounting for a 20% increase in torque required for breakaway). That is neither here nor there, but maybe if someone reads this at any point in time, it might save them from making a mistake.

The torque plus angle is TYPICALLY associated with torque to yield fasteners. As Chris White pointed out to me in a thread about head bolts, that isn't necessarily the case with Porsche. TTY fasteners, however, are pretty much industry standard now, but they didn't make it on the scene until the early 90's (to my knowledge).

I've never seen a range like that specified with a critical fastener (mains, rods, and head bolts). Your interpretation certainly makes sense, so maybe this is another exception.

Thanks for teh insight. I'm comfortable with the clearance, and I know that in a "perfect" world, the fasteners would be clamped at the exact same pre-load at which they were clamped when the rod was machined. But I'll never get that just doing the bearings, so a good clearance along with factory recommendation is a pretty decent surrogate.