Webber mounting rubbers

[davidc]

I've bought a set if those rubber thackery alternatives to re mount the webbers.

Do I tighten them up fully the back off a bit or do they need careful gaping?

If so what gap am I aiming for? I say aiming as I've no idea how I'd do the lower nuts!

David

[oldchieft]

I just tighten them up using new nyloc nuts evenly till there is a small gap between the steel cups.

Jon the Chief

[Fred Talmadge]

That's why I like the metal thackery washers, you can measure the gap and not rely on "feel"

[Esprit2]

The gap you must care about is the one on either side of the soft mount's sandwich plate. There are many brands of plastic soft mounts on the market, and each use different thickness O-rings and gaps, so read the instructions.

If the vintage Lotus OEM metal soft mount is used (period correct for an Elan's Twin Cam), the gaps should be .040" (1 mm), all around on both sides of the spacer plate. More specifically, 0.35 - 0.50 inch (0.89 ? 1.27 mm).

Even the later Lotus OEM metal soft mount, as used in the carbureted Turbo 910 engine, used much thicker O-rings that required a 0.080" (2 mm) gap. If you've recently ordered the "Lotus" soft mount, which one did you receive... thin or thick? Use the correct gap for it.

There's also an aftermarket soft mount that consists of a thin stamped steel plate with an integral, over-molded O-ring.

With all the many aftermarket soft mounts that are available, READ the instructions to learn the correct gap. There isn't just one size O-ring used for all, and then one appropriate gap size.

Use good judgment. If it appears you are crushing the crap out of the O-rings? then don't. You'll just ruin them, or they will squirt out of the joint, causing air leaks and poor running.

*~*~*
The bolt hole spacing in some aftermarket soft mounts is not correct, especially the plastic ones (they shrink over time). If the spacer plate binds on the studs and won't move freely, then spend a little time with a round file to trim both holes equally 'oval' until the plate moves freely. Tightening the joint is just an exercise in frustration if the spacer plate is bound up.

*~*~*
Clearances at the Thackeray washers (steel springs) or rubber grommets are secondary to those at the soft mount spacer plate, above. If tightening the nut until the springs (steel or rubber) have "their" correct gap results in the soft mount being either too loose or crushed, then adjust the nut untils the SOFT MOUNT is correct. It's #1. If you can get both spring and spacer gaps correct at the same time, then great.

For the Thackeray washer, the target range for the coil gap is 0.35" - 0.50" (0.89 ? 1.27 mm), with a minimum of 0.030" (0.76mm).

The rubber grommets depend upon where you got them. One provided by Redline Weber uses a rubber grommet, ONE cup washer and a Nyloc nut. The instructions say to tighten the nut until all the clearance is out of the stack up, then turn the nut another 1.5 turns. Since the M8 nuts have a 1.25 pitch thread, 1 1/2 turns is equivalent to 1.88mm (0.074") of crush/ pre-load. Or, rounding up a bit, roughly 2mm (0.08?).

Other rubber grommets I've received from Lotus specialists include the grommet, TWO cup washers and a Nyloc nut. For them, the instruction was to tighten until the soft mount's gap was correct. However, I've found that sometimes the two opposing cup washers make contact with one another before the gap is right at the soft mount. In that case, I remove one cup washer and then tighten until the soft mount is correct.

Do not allow two opposing steel cup washers to make contact. The point of the spring (steel or rubber) is to allow flex movement. When steel parts stack-up goes solid between the nut and flange, there is no movement. Do what you need to do to fix that (ie, remove one cup washer).

*~*~*
On the original Thackeray washers, there's a gap between the opposed ends of the top and bottom coil ends. Then a center coil is formed into a zig-zag as it snakes between those ends. Finally, the ends are 'squared', or formed to be parallel so they sit well between flat surfaces (nut & flange).

Cheap aftermarket knock-offs eliminate the formed zig-zag, resulting the straight diagonal center coil passing closer to the ends, and leaving less room for compression before contact is made. Also, they don't square the ends of the coils so they're parallel. Avoid those cheap springs if possible, and use proper Thackeray washers.

*~*~*
Steel Thackeray washers are prone to fatigue fractures due to vibration. Those on the top studs are more subject to failure, and those on the bottom rarely if ever fail.

The rubber grommets are subject to failure after prolonged exposure to fuel or it's fumes. Since fluids run down hill, the grommets on the bottom are more subject to failure, and those on top last a long time.

One recommended compromise is to use rubber grommets on top, and steel Thackeray washers on the bottom. The best of both worlds.

Regards,
Tim Engel

[davidc]

thanks for all replies, gives me something to think about.

[Fredtech]

David & Guys.
I've been using the "Dave Bean" method. Rubbers on-top, Thackery's on the bottom. Seems to work
fine for me.