The Veg wrote:The WSM says .0014 max between the follower and sleeve; my thinnest feeler gauge is .0015 and it would not go into the gap on any of them and they all feel nice and smooth and free of wiggle when I slide them in or out.
The chances of accurately measuring a 0.0015" or less arc'd gap (cylindrical, not flat) with feeler gauges is pretty much nil. You would have better luck accurately measuring the tappet OD with a micrometer, and the bore ID with a bore gauge, then subtracting. For reference, typical household kitchen aluminum foil is about 0.001" thick. But you would be hard pressed to use a narrow strip of it as a feeler gauge. It would be like pushing on a rope.
The Veg wrote:That said, the wear-pattern on the follower in the picture is typical of what I've seen on all of them. To my novice eye it looks like their motion hasn't been completely free of tipping but I understand that a tiny amount will happen with even the smallest gap. Does it look OK or suspicious? How much difference in diamater should I see between the worn areas near the edges and the unworn central area?
The original Lotus tappets were chilled cast iron. Okay for street-stock, but not really up to the task with aggressive high lift cams and high rpm. In 1988, Lotus switched to steel tappets, and discontinued the cast iron version.
A026E0024Z, 0.218" thick crown, 22mm skirt, Pre-1988, Chilled Cast Iron.
B920E0017Z, 0.224" thick crown, 21mm skirt, 1988 on, Steel.
The iron tappets had a 22mm skirt length, and the newer steel ones were a millimeter shorter, at 21mm. Neither was particularly generous with skirt length, and the tappet could be more inclined to cock in the bore with aggressive high lift cams. When the tappet is prone to cocking in the bore, bands of wear marks and scoring near the top and bottom are typical. Such wear/ roughness is not a good thing, and to my eye, the tappet in your photo should be replaced. Lotus later issued a TSB advising that their steel short skirt tappets should not be used with aggressive high lift cams.
If you shop around with independent Lotus specialists, you'll find that most carry non-Lotus steel tappets that have both longer skirts and a lower price.
The last time I checked with Garry Kemp in the UK, he offered two steel tappet options.
0.220" thick / 23mm skirt = Near stock, but a longer skirt.
0.240" thick / 25mm skirt = Thick Crown for re-ground cams, and long skirts so a tappet that must extend further out of the bore to follow a smaller, reground cam lobe won't run into issues with insufficient bore engagement.
And the last time I checked with JAE
0.240" thick / 23mm skirt,0.220" thick / 23mm skirt,
0.200" thick / 23mm skirt,
0.180" thick / 23mm skirt,
0.140" thick / 23mm skirt,
Steel, Hi-performance/ race upgrade tappets for Twin Cam, also fits the Lotus 9XX engines.
It's been quite a while since I checked with them, and what either company offered seem to be in flux over time. If interested, call and ask what is currently available before making any plans.
Stay safe,
Tim Engel