Lotus Elan and Lotus Elan Plus 2 Forums

This week I replaced the exhaust system on my S3. Following the usual procedure of removing the left side engine mount and rocking the engine to the right for clearance for the manifold, we completed the job and restarted the engine. There is now (for the first time ever) a loud "snapping" sound which disappears when the No. 1 spark plug lead is disconnected. Has anyone experienced anything like this? I'm wondering whether the distributor cap could have been damaged allowing a short to earth but haven't had a chance to check it since returning home. The car ran ok for about seven miles or so back to my home but it obviously isn't right. Any other ideas?

You could have a leak at the newly installed No.1 cylinder exhaust gasket. An exhaust leak hear can make a sharp knocking noise that would go away if you disconnected the plug on No.1.

cheers
Rohan

Poor exhaust gasket seal on No. 1.

Thanks, guys. I'll check it this week.

Sounds are difficult to describe, do you mean a sharp crack of a sound? If so, it could be an HT spark from the lead/plug to the head or another earth point from a poor lead. Easy to spot in the dark! Try swapping the leads over to see whether the fault goes with the lead, if so a new lead is an easy fix.

Mike

mikealdren wrote:Sounds are difficult to describe, do you mean a sharp crack of a sound? If so, it could be an HT spark from the lead/plug to the head or another earth point from a poor lead. Easy to spot in the dark! Try swapping the leads over to see whether the fault goes with the lead, if so a new lead is an easy fix.

Mike

That's exactly what it sounds like. It was dusk when we fired it up but there was no visual evidence of sparking, just the sound. It had been a really long day and I had taken enough of others' time so I drove home and parked. That's why I suggested the possibility that we had damaged the distributor cap as there was no evidence near the spark plug. I'll check out both scenarios when I have a chance.

Sounds like Rohan and Roger are on the right track.
Grab a short length of garden hose, hold one end to your ear and poke it around the exhaust flanges etc. until you locate the noise. It's as good as any stethoscope!
Dr. Alan P (Doctor of motors)

Got it fired up for the first time since the winter. Once it was warmed up I popped the bonnet, grabbed a length of tubing and put one end in my ear while exploring the manifold to head joints. I did notice what looked like a carbon stain at the number one cylinder and listening through the tube seems to confirm a leak there. I tightened the nuts some more and will try it again when I have a bit more time, The car badly needs a wash as well after sitting outdoors all winter! Thanks, guys, for all your help.

Just a question. There is still a small audible exhaust leak at cylinder no. 1. I don't have access to a garage and don't really want to take everything apart again unless it's absolutely necessary. Would a bit of exhaust sealer be worth a try at filling the small gap? I have already tightened the brass nuts and don't want to put too much load on them. Opinions -preferrably backed by relevant experience - please. Thank you.

I like to use a 1/4" drive and socket on the manifold nuts which makes easy access to nuts.
I think i would loosen off all nuts on all flanges to pull complet manifold from head still hanging on studs.
Squirt some sealant between n?1 flange and head. Retighten all manifold nuts.
I know it sounds a bit of a bodge but it's easier than removing the manifold to reface the flange.
Alan

alan.barker wrote:I like to use a 1/4" drive and socket on the manifold nuts which makes easy access to nuts.
I think i would loosen off all nuts on all flanges to pull complet manifold from head still hanging on studs.
Squirt some sealant between n?1 flange and head. Retighten all manifold nuts.
I know it sounds a bit of a bodge but it's easier than removing the manifold to reface the flange.
Alan

Thanks, Alan. I think I'll try that.

If as it sounds like, you havn't actually driven it and are just revving up the engine off load then all your faffing around has been a waste of time.

As soon as you accelerate under load you will have no doubts as to whether there is an exhaust flange leak and it will be many magnitudes louder.

I use high temperature silicone on the head to manifold exhaust gaskets, this should seal better and be easier to get in the gap than conventional exhaust gasket cement . The exhaust at this point is cool enough because of cooling from the head. Further down the exhaust its to hot to use silicone.

cheers
Rohan

Chancer wrote:If as it sounds like, you havn't actually driven it and are just revving up the engine off load then all your faffing around has been a waste of time.

As soon as you accelerate under load you will have no doubts as to whether there is an exhaust flange leak and it will be many magnitudes louder.

I drove the car home about seven miles after we replaced the exhaust so I know without doubt that there is a leak - and I know where it is after using the tubing-in-the-ear trick to confirm the location. I tightened the nuts but it hasn't completely stopped the leak so I'm going to try the suggestions made here.

rgh0 wrote:I use high temperature silicone on the head to manifold exhaust gaskets, this should seal better and be easier to get in the gap than conventional exhaust gasket cement . The exhaust at this point is cool enough because of cooling from the head. Further down the exhaust its to hot to use silicone.

cheers
Rohan

Thanks, Rohan. What is the temperature range of the sealant you are using? Is it made by one of the major brands? Thanks again.