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| Joined: | 05-01-2005 |
| Location: | Minneapolis, Minnesota USA |
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LOTUS Chilled Cast Iron: (A or X)026E0024Z
0.218" thick crown / 22mm skirt
Pre-1988, Twin Cam, 907, 911, 912 and early 910.
LOTUS Steel: B920E0017Z
0.224" thick crown / 21mm skirt
1988 on, 912 HC Exhaust only, and 910 Intake & Exhaust.
1988-92 Esprit Service Notes (ie, Lotus Workshop Manual),
Section EB Engine, Addendum 1: Two Liter '920' Turbo Engine, page 58:
"Tappets:
"Steel tappet buckets are used (previously cast iron), and will be communized on all 910 engines. Because the steel tappets have a 1mm shorter skirt (21mm Vs 22mm), they must "NOT" be used on engines with the high lift '104' cam (912HC), where the greater skirt length is needed to resist tappet rocking." Similarly, they must "NOT" be used with 107 cams that have the VERY AGGRESSIVE opening and closing ramps.
*~*~*~*~*~*~*
JAE aftermarket STEEL tappets:
Hi-performance/ race upgrade tappets for the Lotus Twin Cam and 9XX Series engines.
Available in 0.216", 0.200", 0.180" and 0.1401" thick crowns.
All skirts are 23mm skirt.
Garry Kemp Hi-Performance Engines (UK), aftermarket STEEL tappets:
0.220" thick crown / 23mm skirt = Near stock.
0.240" thick crown / 25mm skirt = Thick Crown for re-ground cams (smaller base circle requires thicker shims, crowns, or both).
The above aftermarket tappets are both steel for strength and long-skirt for stability in the bore with more aggressive cams.
Also, re-ground cams have a smaller base circle diameter, which requires the tappet to ride higher up out of it's bore. A longer skirt preserves the required bore engagement.
Tappets have unique crown thicknesses, like valve shims. If you change tappets, then measure and consider each tappet's crown thickness just like you would the thickness of a valve shim. Include it in the "valve clearance" math.
Regards,
Tim Engel