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| Joined: | 08-01-2005 |
| Location: | Minneapolis MN |
| Posts: | 122 |
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"The OLD, measured numbers I gave you back in ~2005
0.484" / 31/64” / 12.281 mm Diameter, concentric about the oil passage.
0.075" / ~5/64” / 1.905 mm Depth
However, I have since struck up an email friendship with an engineer at Lotus Engineering, and he's been very helpful about digging through the archives and finding old info for me. One of the tidbits I asked for was the design dimensions for the O-ring c'bore. The most notable dfference is that the spec depth is less than I measured on both of my engines (I don't know why... Quality Control??). Too deep means the O-ring isn't sufficiently compressed to seal as well as it could. Too shallow over-compresses the O-ring and crushes it.
FYI... the numbers I got from Brian at Lotus are:
O-Ring Counterbore Details:
.......... SPEC METRIC / Calc'd Inch Decimal / approx inch fraction
Dia. 12.30 -12.44 mm / 0.48425" - 0.48976" / ~31/64" (.484375")
Depth 1.20 - 1.30 mm / 0.04724" - 0.51181" / ~3/64" (.046875")
The factory service tool back in the day was a 31/64" cutter with a 11/32" pilot drill and a T-handle. With that you could hand cut the c-bore (forget it, the OEM tool is now imposible to find). Without that, any competent machine shop can cut a proper c’bore for you... as you have found."