Lotus Elan

Engine Re-build Advise

PostPost by: nico506 » Mon Jun 21, 2004 12:01 pm

Dear all,
I :huh: :) am currently overhauling and rebuilding my lotus twin cam engine for Elan S3 1968 with webers and require some feedback on what people have done and expereinced to get the best out of the engine when carrying out such work.
Mine is a 79,000 miler which has had a tough life.
The valve stems show signs of wear and there is barelt perceptable play in the guides.The seats are all polished-but not pitted.
What I want to know is:
What sort of play is permissble in respect of valve guide wear?
What signs do i look for in respect of the need to fit new valve seats-other than pitting?
With respect to the camshaft- the cams are okay in terms of minimal wear- but the bearings are lightly scored- can I get away with new bearings and fit these to the existing cams?
Is there any value in having the ports cleaned and polished?
Any other useful advise that helps me to decide on the best course of action other than as a last resort spending hundreds on unecesscary work.

Thanks in anticipation of your help and replies :)
nico506
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PostPost by: rgh0 » Mon Jun 21, 2004 1:11 pm

Nico

What you should do depends on the intended use for the engine. The comments I have put below in response to your specific questions are based on the assumption that the car will be used for typical low milage road use that most Elans see today. If building an engine for more than standard HP or competition or high mileage road use a lot of other things possible and desirable


1. Check the guides with a internal bore gauge, measure your valve stem diameters and calculate the running clearance. Check that the guides are not worn in a barrel shape by checking top middle and bottom diameters. You need to have the inlet guides running clearance at the bottom of the specification range and the exhaust guides around the middle of the range if you are going to avoid a smoky engine. If the inlets are in the top half of the specification range or the exhaust in the top 25% of the specification range I would replace them.

2. If the seats are not badly recessed and you have acceptable shim thicknesses to get the correct clearance then just reseat the valves by lapping in.

3. If the scoring on the cam jornals is only minor and there is no roughness on the surface of the journals that will chew up the bearings then you could reuse. If in doubt get the journals built up by spray welding and reground to size. Any competent cam rebuilding / grinding place should be able to do this.

4. You should have the head including the ports totally cleaned before reassembly. A hot solvent clean followed by a soda blast clean to remove solid carbon deposits in the ports is the procedure I use. Otherwise hand solvent cleaning and careful hand scraping does the same job just takes more time. This then enables proper inspection of the head for cracks or other problems.

5. No reason to polish the ports unless you are doing porting and aiming to get more than standard HP out of the engine.

A thousand other things to check and do to ensure a good engine rebuild, if you have not got the Miles Wilkins book on the Twin Cam get it and follow its guidelines.

Rohan
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