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Ron Mau Member
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I have decided that my restoration project would loan it's engine to my other car. No $ for a major rebuild. After a compression check(# 2 cylinder @ 80psi all the others @ 135psi) and the #4 cylinder has had the spark plug cross threaded. A trip to the machine shop is in order. Now I need some help. This is my first trip to a machine shop and the first major engine work I have ever done, But I'm jumpimg in with both feet.What needs and should be done to the head. Questions from the machine shop. Valve legnths (installed height) after they lap the valves and seats. Spring rates? TIA for all your help, Ron Mau |
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Judson Manning Member 
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Ron, One school of thought is to send your head to a Lotus expert like West Coast Racing Cylinder Heads and let Richard work some magic...like a $1,500.00 porting job...if you've got the budget! Alternatively, if you know how to talk to your local machinist, you can have good results for less money. Start by assembling parts: You'll need a new set of valve guides and valves which will cost you ~$250.00. If you want to spend another $100.00 on competition valve springs from Delta, feel free. Personally, I've yet to have any of my machinists come back to me and say that any of my springs needed to be replaced due to sag. The next trick is to find a machinist. I usually walk in w/ the head and parts and ask the guy behind the counter if he can do a valve job on it. Do NOT go walking up and say 'you guys ever see a Lotus'. If they ask, I usually tell them it's a GM Quad4 head, then after I've broken the ice, I fess-up about it being a Lotus. All you are basically needing is a standard valve job. With the proliferation of Import Drag and such, 16-valve heads aren't so exotic anymore. My current machinist is a younger guy who came from Toyota, he does great work (when I can get him!). I usually request my machinist to remove ~0.010" from each Intake valve stem and 0.020" from each exhaust stem. This is usually enough to account for removing the cardboard gasket and to account for the seat recess). You can casually mention that the shimming process is a PITA and it would be nice if each valve had a similar height off the deck. The exact height is hard to report because I've noticed that heads and cam towers have differing flange thicknesses throughout the years. It's really not that hard of a procedure, finding someone who will listen to you is usually the hardest part. Best of Luck, Judson |
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Ron Earp Member 
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Having gone through this now a number of times I can second Judson's advice. Find a good shop that does reasonable volume and knows Honda, BMW, etc. 4 valve cylinder heads. They won't think anything of it and it'll be done for not too much cash. The first time I did not have them set the valves to all the same height. The second time I did, and it really makes shimming a pleasure. Get a guy you can talk to and trust and you'll be fine. R |
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Brian Kelly Member
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In addition to the above I’d consider having all four spark plug threads heli-coiled with stainless coils. Doesn’t cost much and you will never have to worry about those weak aluminum threads again. Also replace the rear frost plug (or all frost plugs) since it can only be gotten to with the head off. Nothing like getting it all back together, engine back in, only to find out that you’ve got coolant leaking from the rear frost plug. Been there – done that! Once Head is done with valves installed perform a simple leak test by laying the head on its side and fill the ports with mineral spirits. If the valves and seats are ground properly you should see no leakage past the valve-seat interface. Hope this helps, Brian |
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Mark Rosenbaum Member 
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Rather than Helicoils, you might wish to consider threaded inserts -- same basic idea but solid metal bushings rather than spiral coils that might be a bit more likely to leak. or, worse, shatter on the combustion chamber end and fall into the engine. See http://www.timesert.com/index.html for further information. Usual disclaimers, haven't tried these myself, etc. |
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pbahr Member 
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I'll go along with Judson, and recommend West Coast Cylinder Heads for a first class job, Richard Reyman is an expert in heads, and knows the JH Lotus inside and out. Get a quote from local shop and Richard also, and Richard is within a few hundred of your local shop, spend the extra $ - you won't be sorry!!! Pete |
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Jensen Healey Super Moderator 
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I went to my local machine shop that happened to be next door to the British Car repair shop. They didn't flinch when I told them it was a Lotus but asked me to find the parts. I supplied the valve guides and he called and said that 4 or 5 valves were not re-useable. I stripped a spare head and brought in the box of parts from which he selected the needed valves. Total cost was $275 for the machine work and about $40 for the guides, and that's in expensive California. Let's face it, the stock head breathes really well for a street machine. If you are in the quest for more power the usual bolt-ons, (cams, carbs, and HC pistons) will give you an impressive boost. Kurt |
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Judson Manning Member
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Kurt, The only thing I'd add is what Garry Kemp pointed out to me years ago, and that was the early 907 intake ports are fairly tiny. I posted a photo comparing early and later castings at: http://shorpac.com/v-web/gallery/album08/907Intake_comparison Esprit intake ports are even larger...but they're pushing 300hp. If someone goes to the trouble (and expense) of bolting on cams and Dellorto's, I would always recommend an "Improved Touring" legal porting job. This type of porting job is more appropriately referred to "gasket matching". In the case of the 907, the runners are fairly short and "legally" matching the head runners to the intake manifold 1" in either direction can really help those bigger cams and carbs bring the engine to life. This type of "porting job" isn't very aggressive and generally does not cause the low-end losses common with "full blown" porting jobs (it also won't net you 40hp like one of Richard's jobs either). As a compromise solution it's something I suggest because it's fairly easy and inexpensive for almost any machinist to do. Judson |
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