Støttebolte og toppakning til Lotus 907 motor.
The original JH / Lotus head studs were just barely adequately strong for the correct torque spec used with the original steel-asbestos-steel gasket. And then, just to screw things up, the Torque Spec called out in the Jensen-Healey Workshop Manual was too much (too high) for both the studs and the gasket.
1) It could crush the gasket, leading to a blown head gasket.
2) It could yield the head studs, which means the anticipated clamp force didn’t get to the head gasket (the studs ‘stretched’ instead), leading to a blown head gasket.
In Lotus’ Workshop Manuals that followed (Elite/ Eclat/ Esprit), the torque spec was reduced… and then reduced again. If you’re working on a J-H 907 that has the original head studs still in place, then DO NOT USE THE TORQUE SPEC GIVEN IN THE “J-H” MANUAL!! To the best of my knowledge, the J-H manuals were never updated in that regard. Was there a TSB??
Use Lotus’ second revision, reduced torque given in the Lotus Workshop Manuals.
Jensen-Healey Torque Spec
83 – 87 lbf-ft (11.38 – 12.03 kgf-m)
Too much torque, the studs stretched, and the gasket crushed. Bad & Bad.
Lotus’ 2nd Revision Torque Spec: < < < < < < < < < < < < < < < <
70 lbf-ft ( 9.7 kgf-m) Front & Rear Pairs, Oiled threads & washers.
75 lbf-ft (10.4 kgf-m) Three Middle Pairs, Oiled threads & washers.
Lotus’ final spec for original steel-asbestos-steel gasket and original head studs.
In Jan 1993, Lotus introduced the Goetze Composite Head Gasket. Production of the original steel-asbestos-steel gasket ceased at that time.
The new composite gasket required a significantly higher torque in order to achieve the required higher clamp load. More than the original studs could tolerate. So the same TSB also introduced new, high strength head studs that were capable of supporting the new higher torque spec. Same basic part number, but with a B-Prefix (B907E0224Z). The new studs were visually identifiable by a ‘hollow depression’ machined into the top end.
The new torque spec called for a totally different tool… a Torque Angle Meter (TAM) replaced the torque wrench. It measures degrees of rotation, not torque.
Cylinder head (tighten cold, oiled threads):
i) 20 Nm via torque wrench to set a uniform starting point.
ii) + 75 Degrees
iii) + 40 Degrees
iv) Wait 5 minutes
v) + 20 Degrees
The resulting “torque” was something in the mid-90’s Lbf-ft. Way more than original J-H or Lotus flat-top studs could handle.
“IF” you installed a new composite head gasket, but used any of the original, lower torque specs, the composite head gasket would hot have been adequately “clamped”, and the result would have been a blown head gasket.
Later, independent Lotus parts specialists (JAE was one of them) started providing ARP head studs as an option. They are stronger than the new Lotus, B-Prefix studs (hollow dimple on top), and required yet another, higher torque spec. PLUS, the ARP studs used a fine-pitch thread, which means the geometry produced more clamp force for the same amount of torque… plus the torque spec was higher. So “higher-higher”
PLUS, ARP insisted that the studs, washers & nuts be lubed with their own, “ARP Ultra Torque™” low friction lube be applied to the threads & washer/ hex nut interface. The low friction means that more of the applied torque goes toward producing more clamp load, and less is wasted on over-coming friction. So, the net result clamp load is “higher-higher-higher”
110 lbf-ft (15.2 kgf-m), with ARP Ultra Torque™ lube applied to all Stud & Nut threads, and Washers.
To complicate things even further ARP revised it’s special lube, and further revised the coefficient of friction, AND the resulting new torque spec. If you have any of the old, original ARP lube, you can use it “IF” you kept/ know the original torque spec that went with it IF YOU DON’T KNOW THE CORRECT TORQUE SPEC FOR THE ORIGINAL ARP THREAD LUBE — THEN DON’T USE IT!!!
The new/old ARP studs are the same, only the ARP LUBES changed. Confused. Then just buy some new, current ARP Lube, and use it with the current ARP Torque Spec…. as given above: 110 lbf-ft.
The resulting clamp load(s) were dramatically higher than with the original J-H / Lotus torque specs. But, the Goetze composite gasket could stand the higher clamp pressure, so all was good.
HOWEVER, if a Composite head gasket is installed in an old J-H / Lotus 907, which still has the old-spec, A-prefix, flat-top studs, AND if you knew the old studs would not survive either the updated Lotus Torque, or the even higher ARP torque… so you used the “safer” original J-H / Lotus torque specs, then you did NOT produce enough clamp load on the composite gasket, and that would lead to a blown head gasket.
That about covers all the ways you can screw-up installing the head gasket.
IF YOU CANNOT FIND AN ORIGINAL SPEC STEEL-ASBESTOS-STEEL head gasket (Lotus has not made them since Jan 1993), then a composite gasket is your only choice. That might be an original Goetze gasket from Lotus, or one of the clones sold by independent J-H & Lotus parts vendors… like Delta Motorsports and JAE.
If you go composite, then remove all the original J-H / Lotus head studs (flat top ends), and replace them with either…
1) The 1993-onward Lotus studs with a hollow depression on the top end (B907E0224Z), and use the Lotus Torque Angle spec, or…
2) The ARP studs, and use the torque spec that is correct for the version of ARP LUBE that you have (old or new). Don’t guess. If you don’t KNOW what you have, then buy some new/ current ARP Lube, and use the current ARP torque spec….
110 lbf-ft. Don’t guess!!
Earlier, ARP specified a 90 lbf-ft torque for use with the “SUPER LOW” coefficient of friction “ARP Supra-Torque™”… which they have not sold in many years.
Later, ARP changed to 110 lbf-ft torque for use with the current “HIGHER” (but still low) coefficient of friction “ARP Ultra Torque™”…
That’s as of the last time I checked, which has been a while. When you buy, ASK for the specific name of the ARP lube you’re getting, AND ASK for the correct Torque Spec that goes with it. Don’t get caught in the wrong by a moving target LUBE and TORQUE Spec.
STUD VISUAL ID…
Lotus original head studs have a flat top end, coarse threads, and a ‘metallic’ finish.
Lotus 1993-on head studs have a hollow dimple top end, coarse threads, and a ‘metallic’ finish. Original ‘metallic’ might be ‘DIRTY-DARK’ now, but it will still look like it started out ‘metallic’.
ARP head studs have a flat top end, “FINE” threads, and a BLACK finish… like Black Oxide. No ‘metallic’ showing.
Later/ current ARP lube, “HIGHER” (but still low) coef. of friction = ARP “Ultra” Torque™.
Required a 110 lbf-ft torque.
Early, no longer sold ARP lube, “SUPER LOW” coef. of friction = ARP “Supra”-Torque™.
Required a 90 lbf-ft torque.