View single post by Esprit2
 Posted: 09-24-2021 07:55 am
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Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 550
Does your engine have a gasket between the head and cam carriers, or are you just following the old Workshop Manual? A Tech Service Bulletin eliminated the gasket in 1976, so I'd be surprised to stumble across a JH that hasn't been upgraded by deleting the gasket.

When the gasket was eliminated, a small rubber O-ring was added around the oil transfer hole at the front of each cam carrier. The O-ring required that a small counterbore be cut around the hole. Check each cam carrier for the presence of the counterbore.

Older 907's can be converted to the newer configuration. All that's required is that a small counterbore be milled into the bottom side of the cam carrier, centered about the oil passages, to accept the O-rings for the cam oil passages.

O-Ring Counterbore Details:
. . . . . . SPEC METRIC / . Calc'd Inch Decimal / ~ inch fraction
Dia. 12.30 -12.44 mm / 0.48425" - 0.48976" / ~31/64"
Depth 1.20 - 1.30 mm / 0.04724" - 0.51181" / ~3/64" (.046875")

The factory service tool (no longer available) was a 31/64" cutter with a 11/32" pilot drill.

The O-ring is Lotus part number: A907E6202Z. Two are required, one per cam carrier. Your favorite JH or Lotus parts specialist has them.

The cam carrier joint sealant originally specified in the Jensen Service Bulletin, Loctite Product 23, was replaced in Lotus’ own original spec by Loctite 504. While 504 is still available, it’s old-tech, expensive, and was replaced by Lotus’ still-current spec, PermaBond A136. PermaBond is not marketed in North America and is difficult to find on this side of the pond.

The direct cross-reference is Loctite 515, an anaerobic flange sealant. It’s sister product 518 is less viscous and easier to apply, will fill larger gaps, and is generally easier to find at retail. Loctite 515 & 518 are most commonly sold through industrial supply houses, like Graingers. 518 is also private labeled as Permatex Anaerobic Gasket Maker, and sold through retail auto parts stores and hardware stores.

Don’t simply apply a generous bead to one side of the joint and squish it together. Instead, use a flux brush to 'paint' on a thin film around the perimeter on both sides of the joint (cam carrier and cylinder head). Lay a paper shop towel over the buttered joint, very lightly pat it down (don't 'rub'), and peal off the towel. 518 is a bright red gel, and the light film that remains will be so thin it’s barely pink. That's all that is required, and more just oozes into places where it's not supposed to be. Repeat on both sides of the joint (head & cam carrier) and assemble.

If you get 518 into one of the bolt holes, or onto a bolt, it makes a killer thread locker. Don't go there!! Stay respectfully clear of all the bolt holes.

When shimming valve clearances, dry shim short by .0005” to allow for the film thickness of typical anaerobic sealants… 518, 515, Anaerobic Gasket Maker, A136, etc. Then when the sealant is added during final assembly, it will 'float' the cam carrier up that last half a thousandth of an inch to the target clearance.

0.005-0.007" Intake. - shim to 0.0065"
0.010-0.012" Exhaust - shim to 0.0115"

Shim to the top of both clearance ranges. The clearances will close up with miles of use/wear, and must be re-shimmed when the clearances reach the bottom of each range. The clearance ranges are NOT there to allow for sloppy workmanship, they are the WEAR LIMITS. Shim to the TOP of each range.

The JH manual's torque spec for the cam carrier fasteners is too high, and risks stripping the threads in the aluminum head. Use the later Lotus torque of 14-16 Lbs-ft.

The JH Workshop Manual was never updated, and is out of date in many ways, including many of the torque specs. Every JH/ 907 owner should have a copy of both "Section EA, Engine" and "Technical Data A (TDA)", from the "1983-87 Lotus Turbo Esprit and Esprit S3 Service Notes". There's 910 Turbo engine details in there you just ignore, but there's also lots of good info that never appeared in the JH Workshop Manual.

As Brett mentioned, you can download copies from the "Files" section of the Jensen-Healey Facebook page. I'm not fond of Facebook in general, but that "Files" section is a handy library.

Tim Engel

Last edited on 09-28-2021 06:02 pm by Esprit2