|View single post by Esprit2|
|Posted: 11-27-2015 09:41 pm||
The current head gasket is the Goetze composite gasket (or JAE sells their own aftermarket clone). It requires the use of either Lotus' later upgraded head studs (Lotus Part Number B912E7029Z), or the ARP studs that are available for the 9XX engines, along with a significantly higher torque.
The Lotus spec calls for the use of a Torque Angle Meter instead of a torque wrench. Use the following tightening procedure and notes:
1) Check that the cylinder liner nip is within spec:
... +.001 to +.005 inch (+ .025 to +.130 mm).
2) Use Lotus upgraded cylinder head studs (B907E0224Z) identified by a dimple machined into the top end. Tighten into the block (with oiled threads) to 37 - 41 Nm (27 - 30 lbf-ft).
3) Make certain all mating metal surfaces are absolutely clean and dry (wipe with brake, carb or contact cleaner).
4) Fit the composite head gasket DRY.
5) Put the cylinder head in place before oiling the washers & head stud threads and fitting the nuts. Tighten the nuts using a torque/angle gauge, in a sequence from the center outwards, in the following steps:
i) 20 Nm (15 lbf-ft) initial pre-load via a torque wrench.
ii) +75 Degrees
iii) +40 Degrees
iv) Wait 5+ minutes (longer is better)
v) +20 Degrees
The net result of Lotus’ torque angle spec is a higher final torque/ clamping force than was produced by Lotus’ original 70-75 lb-ft torque wrench spec. Do NOT consider the old spec and new spec as different but interchangeable... they're very different.
I've had mixed results installing the composite gasket dry as instructed. I now prefer to apply a little Wellseal, or Permatex Aviation Form-a-Gasket around the oil passage between the block and head (apply to both sides of the gasket). In my more paranoid moments, I'll also apply a little around the full perimeter of the head & block, both sides of the gasket. That only addresses coolant and oil leaks. At the cylinder liner seal area, the gasket must be installed DRY.
If you use the ARP studs, then ARP specifies the use of a torque wrench, as follows:
6) Apply "ARP Ultra-Torque Fastener Assembly Lubricant" to the washers, bottom of the nuts, and the stud threads (the lube is included in JAE’s ARP kit).
7) Torque the nuts in several smaller steps to a final setting of 110 Lb-Ft. (arbitrary, but something like 50, 75, 100, 110, with the last step being small).
With either procedure, torque the nuts from the center of the head outward, in a criss-cross pattern.
As mentioned in post #19, "IF" you don't replace the original low-spec head studs, then stay with the original 'Lotus' torque spec out of consideration for the lo-spec studs. You won't be getting the full advantage of the composite gasket, but you won't be over-stretching the weaker studs either.
Note that the J-H head torque spec was too high, crushed the old gasket, and caused problems with blown gaskets. Lotus reduced the torque spec to a level that didn't crush the gasket, or over-stretch the studs. If you're going to stay old-school, it would be better to follow the Lotus torque spec instead of the one in the J-H Workshop Manual.
Lotus Cylinder Head Torque Spec:
(Tighten Cold, Oiled Threads & Washers)
70 Lbs-ft - Front & Rear Pairs
75 Lbs-ft - Three Middle Pairs
And again, work up to the final torque in several stages.
For your autocross engine, I strongly recommend that you replace the original head studs with either Lotus' later upgraded head studs (B912E7029Z), or the ARP studs.
Last edited on 11-27-2015 11:51 pm by Esprit2