Lotus Elan and Lotus Elan Plus 2 Forums

Now I know this forum is the font of all knowledge Elan wise, but I'm hoping that some of this is transposes to a Mk1 Lotus Cortina, since it's basically the same engine/gearbox (or there's enough cross over in interest to find some Cortina experts here). My brother in law has a very nice restored example that he's somewhat frustrated with. There's a funny noise. His description:

Metallic noise very easily heard but only in top gear but only between 3000 and 2,500 rpm on overrun. If the clutch is dipped or the lightest throttle load applied the noise disappears.
In summary car bought as a restoration project. Engine, gearbox and axle rebuilt by Lotus specialists. Three different diffs and propshafts have been tried. Two complete rear axles been used, drums balanced and half shafts swapped out and numerous thrust release bearings and carriers tried.

Hope that helps and thanks for your assistance.

As you can see, he's tried lots of things to fix it - any body got any other suggestions as to what it could be?

Thanks in advance

Steve

Worn engine mountings allowing something to " touch "?

John

Thanks John

I'm forgetting what else has been done, but I'm fairly confident we've tried exerting force on the engine front/back/up/down/sideways and it remains. There's no obvious fouling either - the car is basically concours, so we'd see any telltale in the engine bay/underneath

Second guess..

Gearlever ( or part of it ) catching on bodywork ?

John

Loose/broken springs in clutch disc ?

May be a sympathetic or a harmonic vibration, does the Cortina suffer any known prop shaft resonance?

Check the dog teeth on the transmission input gear. I've pulled apart many gearboxes where the side of the dogs that is loaded under power have been quite visibly worn. It's a weak point of the 3 rail box. These dogs are transmitting power only in top gear. Under load either on over run or drive the slack is taken up but under coast conditions it's possible for the dogs in the synchro hub and on the input gear to rattle together. The input gear dog teeth seem to wear much more than the dog teeth on the other gears.

Check the laygear end float too. In top gear the laygear is not under load and free to float

Definitely gearbox related; possibly missing a layshaft thrust washer or worn, the sycnroniser hub teeth also a possibilty, I would try the vehicle with a thicker transmission o?l (what is he running?) to see if it changes the noise.

Possibly related to the centre bearing on the split propshaft?

I was just wondering if the car had the split prop shaft. Does it? Have you tried a one piece shaft instead, just to see if it makes any difference to the noise?

I had a similar issue with an MG TD many years ago, only on overrun. I think it had something to do w/ the remote housing, but we're talking almost 50 years ago. How time flies!

Roger

The OP says he has tried 2 different diffs and propshafts so it's doubtful there is a problem with these components.

A mate has Jim Clark's old road going Lotus Cortina, the one with the Elan rear suspension, and that had a similar problem. After rebuilding the rear end, playing around with diff positions, it turned out to be just part of the exhaust touching the bodywork on overrun. You could see it was close, but couldn't make it touch when the car wasn't moving.

You haven't mentioned which variant the car is. If it's an early car with a torpedo propshaft it will be worth getting it finely balanced, as these were prone to setting up all sorts of strange vibrations and noises when only slightly out of balance....hence the move to a split propshaft.

Mark Kempson

Thanks for all the answers so far. Comments from brother in law:

Comments relating to the gearbox would I hope have been found during the rebuilds. I need to get another gearbox to try but I will check engine mounts etc again

If anybody else has any other suggestions, please add them. If we get a solution I'll post an update.

Thanks again

You know , you wouldn't get help like this on any other forum , they'd tell you to Pi** off and ask the Lotus Cortina Forum.

John

john.p.clegg wrote:You know , you wouldn't get help like this on any other forum , they'd tell you to Pi** off and ask the Lotus Cortina Forum.

John

I just did that as well