172 cup, knocking noise and high revs

[Flood]

I started getting a dull knocking noise in the first two gears, up around 5-6000 revs, google told me it was probably worn engine mounts causing the exhaust to touch the chassis. So I took it to the garage for a second opinion, they told me the engine mounts looked fine and their money would be on worn cv joints, advising I leave it and see if it got worse. Left it for a while and it quickly worsened, the cars only done 60k with the vast majority being on the motorway, so ruled out the cv joints, decided to trust the internet and had the engine and gearbox mounts fixed earlier this week.

Its about 90% better, but I'm still getting a low single knock at the top of the rev range, theories:

Suspension top mounts, it feels like it knocks just as the tyres are starting to lose traction, also seems to happen more with some steering lock on or over pot holes, there's no noise when hitting bumps at lower revs though. I've jacked it up and there doesnt seem to be any play in the suspension.

Exhaust loose, though I've had a prod around and nothing seems to be obviously loose.

Exhaust popping, though I think this only tends to happen as you lift off the accelerator right?

Cv joints?

If anyone has any other ideas it'd be appreciated.

[exgtt]

Sorry Flood its one of those problems that could be a number of things as you know.

Get it to a specialist asap, i wouldnt waste your time chasing diagnosis on the internet.

[sean19]

Did you have the dogleg mount changed?

[PetrolHeadSeb]

sean19 said:

Did you have the dogleg mount changed?

+1

I had the same problem in my old 172. The standard mounts aren't that great, so are often worn even when they look OK. A Powerflex uprated mount is a good modification worth considering.

[Flood]

Think so... would I be right thinking the dog leg is the mount at the bottom passenger side of the engine? Pretty sure all the engine and gearbox mounts were replaced.

Tried to replace all my exhaust mounts this week as a precaution, the rubber bushing in the rear most one was especially knackered, but when I go to loosen it though the bolts just spin. Feels like the thread boss that it screws into has broken away from the chassis and obviously theres no access to grip the back side of the bolts.

Real love/hate relationship with this car.

[Acehood]

Speak to Fred at BTM Performance

http://www.btmperformance.com/