View single post by Esprit2
 Posted: 03-22-2015 06:43 am
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Esprit2

 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 289
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The 907 is not supposed to have valve guide seals. The engine is designed for high rpm operation, and that requires adequate lubrication for the valves. If the guides are worn, installing seals might stop the smoking, but it also gives up the lubrication the valves need. If you're going to granny drive it to get groceries, go with the seals. If you wish to drive it as it was intended to be driven, fix the root cause problem... the valve guides and/or the valves (worn stems).

190 psi compression pressure is very good, so I suspect the rings and valve seats are sealing very well. Jensen-Healey specified checking the compression cold, and Lotus specified hot. For the same engine, hot produces higher pressure readings than cold does.

8.4:1 cr = 7.58 - 8.96 bar (110 - 130 psi) COLD = Jensen-Healey spec
8.4:1 cr = 10.2 - 11.6 bar (150 - 170 psi) HOT = Lotus spec
9.5:1 cr = 11.2 - 12.6 bar (165 - 185 psi) Hot
9.44:1 cr = 11.2 - 12.6 bar (165 - 185 psi) Hot
10.9:1 cr = 11.5 - 13.0 bar (170 - 190 psi) Hot

Are the cylinder liners iron or Nikasil coated aluminum? The 190 psi implies the engine is a 1985-92 912HC, which is a Nikasil liner engine. If so, then the 10.9:1 compression, 180 Hp, and 166 Lbs-ft of torque would be a nice bump over the stock J-H 907.

Regards,
Tim Engel

Last edited on 03-23-2015 04:35 pm by Esprit2