Conclusion to work and Exhaust "height" on Sprint

[olr159w]

After a couple of months of disjointed work I now have the car back together pending final front suspension seat height adjustment. The engine and gearbox are sitting on new mounts with the former no longer vibrating against the steering rack. The front brakes are rebuilt and the car started and running well. It probably needs a tune and for sure the tracking needs looking at.

There remains one issue. There is still some vibration which seems to primarily exist at idle.

Yesterday I jacked up the rear of the car and started it to see if I could then identify the source. I was pretty sure it was the exhaust and sure enough after gently applying a jack under the downpipe/first pipe area I could make the periodic vibration/knock go away.

I have a theory. It seems fairly likely that the previous OS engine mount was both stuffed and upside down potentially causing the engine to be perhaps lower on the OS and slightly higher on the NS. This would have raised the exhaust relative to the sub frame by a small amount. The downpipe on the car is wider than standard and (disappointingly) it was beaten into a flat on one side when it was fitted to get it to avoid the subframe. Kinda negated the point of the wider pipe anyway but .........

I can't get far enough under the car the way it is sitting at the moment so I thought I'd ask. Is there a way to adjust the height that the exhaust sits at? If I could raise it closer to the gearbox I reckon it would be enough to stop the knocking.

Failing that I either put up with it at idle - and its only really noticeable inside the car - or I find some bespoke exhaust expert and get a properly fitted custom downpipe

cheers

[gmsclassics]

There should be a triangular bracket at the rear of the overdrive that when clamped correctly to the exhaust system will both correctly locate the exhaust and hold the exhaust system and downpipe firmly in place and unable to move relative to the engine/gearbox. If your new engine and gearbox mounts are reducing the movement correctly, then if the downpipe is hitting anything (subframe etc) then it probably needs replacing or bending by an exhaust specialist.

I do find at idle that I can minimise engine vibration by getting the carb balancing / tuning spot on. Takes time to get it right and often needs redoing frequently. A very smooth idle usually gets rid of any exhaust rattle.

Geoff

Just another thought, are the heat shields loose or is it the downpipe touching these?

[Toledo Man]

I second what Geoff has said about the exhaust. The gearbox bracket should stop the vibrating. I've had the same problem with my 1850 and fitting a bracket solved the problem so it is well worth doing.

[olr159w]

It seems like a no-win with the exhaust. I’m almost certain that is what’s causing the knocking sound. When I got under the car at the weekend – and bearing in mind this is a straight S/S exhaust, not an original – I found the triangular bracket, additional right angle mini bracket and the exhaust clamp configuration. There was something of a slot in the mini bracket so I tightened everything back up in the highest position. If anything it made things a little worse.

It’s always hard to identify cause and effect. In the first place I suspect the OS engine mount was put in upside down by somebody leading to the engine being rotated slightly clockwise thereby lifting the exhaust slightly. Given the downpipe had a depression beaten into it to go around the subframe I reckon that is now insufficient hence the knocking. But you would have thought raising the next clamp along would help. On the other hand I now wonder whether raising that has caused a leverage/pivot type effect that actually works to apply downward force at the problem zone.

Likely grasping at straws. I think I may have to accept that its reached the point where it needs to get a custom downpipe fitted that properly clears everything without a recess being bashed into it