Lotus Elan Tech Session – March 26 at Mike Mullan’s

Summary –

A small group of LOOPies met at the Mullan residence to check out a Lotus Elan which Mike’s daughter Ann had acquired about a year ago and which was suffering from “performance problems”. David B. led an informal, hands-on checkout and analysis of Ann’s Elan to determine what the cause of performance/compression problems might be.

Thanks to Dave Mott for arranging for the event and David Barnett for leading the session. Many thanks to Mike and Ann Mullan for their hospitality and to Edd Brady for his photos.

The Order of Battle –

The starting point was a check to ensure that there wasn’t something wrong with the ignition set-up or fuel delivery. The Lotus Twin-Cam engine has a couple “eccentricities” that need to be considered when you are doing work especially if the car hasn’t been run in a while. First – the distributor is located under the fuel delivery system with the fuel lines passing right over the top of the distributor cap. The fuel lines should be checked regularly for any possible leaks. Second – the intake manifold is situated such that carburetor flooding will likely result in raw fuel draining back into one or more of the combustion chambers. See more below!

1. Check that distributor and ignition wires were connected in the proper firing order – we checked these and labeled them appropriately.

2. Start engine – after some amount of cranking (mechanical fuel pump) the engine started but immediately flooded – we could see fuel dripping from the velocity stacks. Shut off engine!

3. We removed the covers from the Weber float chambers and discovered that the float needles were sticking and not closing off the fuel flow. Cleaning out the float needle chamber w/ air and little fine sandpaper on the needle got them working again.

4. We were about to re-start the engine, but the starter seemed jammed – Edd B made a diving catch here – realizing that there was likely to be fuel in the combustion chamber. We pulled all plugs, cranked the starter and saw fuel blowing out the top of at least one chamber! Take a break and let the chambers air out

5. Re-seat plugs and re-start engine to listen to how it runs – nothing obvious – at least to me! The engine seemed to idle relatively smoothly, but was extremely rough (trying to shake itself off of the motor mounts) as soon as any throttle was applied. Removal of each spark plug wire in turn indicated that the no 4 cylinder was not contributing anything significant to the “party” above idle.

6. Pull plugs and set up to do an “audible leak-down” test, i.e. applying air pressure to each cylinder listen for air escaping from the chamber. This requires getting each cylinder in turn into position with its piston at Top Dead Center (TDC) of the compression stroke when both intake and exhaust valves are closed. The position of the cam lobes can tell when your close you are on TDC at the completion of the compression stroke, as required, versus TDC at the completion of the exhaust stroke where both valves are open. When lobes are perfectly opposed – 180 degree separation – piston should be at TDC. (for an example of TDC Compression, see photo XX with both cylinder no 1 cam lobes pointing horizontally away from the center of the engine).

a. We Put the car in 4th gear and move it forward or backward as necessary to get each piston into position. A firmly attached dial indicator or a thin tube, like a soda straw can help checking the piston movement. This can take some patience, special equipment or at least two people- with one watchful eye on the piston to show when it is stopped for a few degrees of revolution of the crank at TDC.

b. When TDC is achieved, put car in 1st gear and have someone keep a foot on the brake; screw pressure adaptor into plug hole and apply air pressure and listen/feel for air escaping from intake manifold or exhaust system or use a leakdown tester (which, if you have one of these, would probably mean you are only reading this to see if we made any mistakes)

c. Do each cylinder in succession

What we found –

After getting our routine down and re-checking a couple chambers we found that all valves were seating appropriately and all escaping air was leaking into the crankcase. The low compression doesn’t seem to be related to the valve train - Sorry Mike and Ann!

We didn’t have time to pursue this, but I’m concerned that the aft Weber carb is not functioning properly. We had a prior report of low compression on all cylinders (which might be influenced by not being able to run the motor until warm and normal) plus a much lower pressure on cylinder no 4. If the aft carb has an internal fuel leak (a not uncommon Weber occurrence), it might explain why the engine idled relatively smoothly yet the no 4 cylinder went dead as soon as throttle was applied.

There is an upside here however – this is likely to require another tech session when the engine gets pulled from the Elan! Stay tuned LOOPies

ps – thanks also go to Jeff Taylor for getting us off our collective duffs and doing some fun/instructive stuff – Thanks Jeff!