Lotus Elan and Lotus Elan Plus 2 Forums

Since restoration of my 1969 S4 SE i have noticed and whirring (can't explain any other way) from under bonnet.
I have always suspected alternator, but having recently slackened the fan belt, noise still exists, when listening under bonnet as revs increased.
Noise is noticeable when getting 2k and above revs as changing through gears.
Could this be timing chain? is it too tight?

Yes, most likely the timing chain is too tight.

Thanks for info. Still unwell with covid so will check in a few days (hopefully)

I agree w/ Greg.

Roger

Hi

I rebuilt my twincam in 2022 and found a whirring sound that I could not get to the bottom of until I noticed the chain was not sitting fully into the teeth. Once I got the tensioner out (possible without head removal) i could compare it with another original Formoco pully and the inside radius had been machined incorrectly. The supplier was one of our UK usual suppliers. I obtained another (from different UK supplier) and the radius not exactly the same an original but cut back sufficient for chain clearance.

Maybe worth a close look at yours.

thanks for info. Off to spain for few weeks tomorrow.
Will check on my return.

TrevorJones wrote:Hi

I rebuilt my twincam in 2022 and found a whirring sound that I could not get to the bottom of until I noticed the chain was not sitting fully into the teeth. Once I got the tensioner out (possible without head removal) i could compare it with another original Formoco pully and the inside radius had been machined incorrectly. The supplier was one of our UK usual suppliers. I obtained another (from different UK supplier) and the radius not exactly the same an original but cut back sufficient for chain clearance.

Maybe worth a close look at yours.

Thanks for posting as this is the kind of helpful information that we all need. It's not obvious to me from the pictures however what the issue is. Are you saying that the depth of the teeth on the new sprocket was not enough?

I wouldn't be shy with mentioning the supplier by the way.

The teeth appear to be too wide causing the chain to rub on the sides of the teeth. i must go and measure up some of my tensioner sprockets

cheers
Rohan

I agee wih Rohan, the teeth on the sprocket on the right appear wider nearer the tip. It wasn't clear but
is the aftermarket sprocket the one on the right?

Hi

The chain has been sitting on the radiused side of the sprocket because there is not enough relief on the radius. This has caused the links on one side of the chain to tip slightly wearing one side of the tooth. If the chain cannot sit flat between the links it will cause noise wear and possible chain snap.Check the chain is sitting correct against the bottom radius of the teeth and not against the side or sides as it shows in the pics.
If I were you I would change the timing chain also if that snaps it curtains

Cheers
G

Hi

I also forgot to mention what looks like a poor repair on fig 2 as there is centre dotting around the periphery of the bronze bore and shaft of sprocket .If that has come loose that will cause the sprocket to tip over as well with disastrous consequences.

Cheers G

Hi all

MACCA.GLM you are correct in that the radius on the new Sprocket is a larger diameter and is too great a radius and does not give sufficient clearance for the chain to seat correctly and the whirring was caused by the cheek plates of the chain trying to wear its own clearance (the flats can be clearly seen on figure 2). As already mentioned this discovery required a new chain and another rebuild.

It is also worth checking the chain that has been fitted, as I also found the chain I was supplied with would not mesh correctly and would click as you roll the sprocket along the chain! Thankfully I eventually found a matching sprocket and chain and all is good.

The center pops shown on figure 2 are the original way the sprocket boss is secured from unscrewing in service, the center pop is made into the threaded gap to disrupt the thread.

Hi

Glad you sorted it out