View single post by Esprit2
 Posted: 03-17-2020 08:18 pm
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Esprit2

 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 536
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The spec valve clearances are stated as a range, typcially two thousandths wide. Lotus specs the clearances as:

0.005"-0.007" Intake
0.010"-0.012" Exhaust

The clearances always close-up (get smaller) with use/ wear, and the lower spec value is the 'Wear Limit', or 'Service Limit'.

Shim to the top of the range in order to enjoy the most drive-time before having to re-shim the clearances.

If you shim to the bottom of the range, you're technically within spec. The only value in that is being able to say "I did it correctly" in some pedantic, argumentative sense. The reality is that if you shim to the bottom of the range, then by the time you drive out of the shop, you're due for a re-shim. You could keep yourself really busy that way.

I'm not certain of the J-H service interval without looking, but Lotus specified 'checking' the valve clearances every 6000 miles, and only adjusting as necessary (ie, at or below the lower limit). If you shim to the top of the range, you can probably expect to get 18,000 miles before needing to shim again. But don't lock-onto any mileage as the limit. Check the valve clearances, and re-shim when they reach the bottom of the spec range.

Too-tight clearances put the valves at risk of being burned, negativelly affect how well the engine runs, and causes elevated exhaust emissions. If the car must pass an annual emissions inspection where you are, and it has started failing lately, one of the items to check is the valve clearances.

Regards,
Tim Engel

Last edited on 03-18-2020 11:13 pm by Esprit2