View single post by Jim Sohl
 Posted: 03-23-2007 05:33 pm
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Jim Sohl


Joined: 03-26-2005
Location: Chandler, Arizona USA
Posts: 39
Well... some warning signs seem to be present.  If, as you say, the stem is visually higher than the others, then something has allowed that valve to recede into the seat.  You state that the engine 'ran fine'.  A compression check might suggest otherwise, or better still, a leak-down test.  It will be very important to follow up on your wayward valve for several reasons: 1) valve trouble is always important; 2) 907's are difficult to work on (you know that first-hand) and owners (of course I mean po's) often neglect proper valve care; 3) 907's have a history of 'burning' exhaust valves; and 4) numbers one, two, and three sound like your engine.  'Sounds like off-with-the-head to me.  Conceivably, some weird coincidence of warped castings could produce your symptoms, but I doubt it given that receding exhaust valves are relatively common in 907's and most 9xx Lotus engines for that matter.  My advice then is double check and triple check the symptoms to try and find a cause that may suggest that a burned valve is not the problem.  If you do have to remove the head, check the stem to guide clearance on all valves.  If the valves wiggle around more than a few thousandths (with the springs off), it is highly indicative that a general overhaul is in your future.  Also, assuming you do have a burned valve, the seat may be too far gone to rehabilitate.  This will require close examination for the reason that 907 seats don't grow on trees.  Try the usual suspects, DMS, Dave Bean, etc.  Hopefully, you will be able to get things right without removing the head, but obviously, don't trust to luck with an engine that is expensive/difficult to repair even when the 'normal' repairs are indicated.  It is my belief that a 907 properly used means high output at high RPM, things that stress valves and pretty much everything else more than your average street engine.
Good luck!

p.s. I have '73, '74' & '79 907's and an '84 910.  All are high mileage and all have valve issues of one sort or another.