Stainless Steel Bolts Not Good For Exhausts.

[Konrad C]

I hand to change the stainless steel bolts holding the front down pipe and the catalytic converter.

Every time near the end of a motorway run, the exhaust resonates and is slightly louder.

Last year when I first installed the whole exhaust system, I had issues with the bolts on the joint between the cat' and the mid/rear section. The nut and bolts had welded themselves together (galling), so you could not undo or tighten them. This was after 3 days! A friend from Kwikfit gave me a set nuts and bolts, grade 8.8 zinc plated steel and no issues.

I left the remaining nut and bolts on the front to cat' joint as they seemed fine. The problem is they were loosening and threads showed signs of damage. All the stainless steel nuts and bolts are A2-70 grade.

Hopefully with 8.8 bolts on all the joints there should be no more problems.

It seems I have learnt a bit of science with practical experience on metal fasteners. The test continues.

Konrad

[Konrad C]

Further on from changing the bolts, I examined the rear back box because of the resonance. I thought it may have blown already plus the sound was loud inside the car as well as outside. I rocked the rear silencer and heard a rubbing sound. It was the under body shield that was touching the silencer. The shield had a bit of rust close to the rear wheel.

I got some tools and forced the shield away from the silencer and checked the clearance to make sure no more contact. The shape of the silence was more oblong than oval, plus it is slightly larger. This is a Klarius from Euro Car Part. I have heard that EuroFlo do have a similar product, and pictures I have seen shows it to looks exactly like the Walker that my car left the factory with. I am looking for somebody who can cut and replace short rusty piece that forced me to change the exhaust in the first place.

As mentioned in the forum, replacements are not the same as the originals. Lots of fettling is needed to get it to fit correctly, and the washers, nuts and bolts need to be suitable for the job.

I don't mind doing it myself, because this has given me more knowledge, plus it is done better than some garages who throw it on and some owners who except poorly installed systems.

The car is nearly as quiet and smooth as the original. I am fussy.

[Cyker]

Funnily enough, I was talking to a guy about stainless steel exhausts at a car show on the weekend and some of the downsides he mentioned was the risk of galvanic corrosion/welding and the different rates of thermal expansion which can cause it to loosen or creep over time, allowing it to rattle and leak if it's not checked.

[fastbob72]

Coincidentally I've been having a similar if not exactly related issue with replacement stainless steel bolts.

When I did my brakes I rebuilt 3 calipers and had to buy one new for the rear. I can't remember what happened to the original carrier to caliper bolts but I had to replace them so I bought stainless steel ones.

After thr m. o. t there was a constant rattle from the rear that took me a little time and head scratching to trace.Originally I thought I'd not tightened the rear bumper down properly when i refitted it but I quickly discovered the rattle went quiet when braking so it had to be connected to the brakes but everything felt solid and sure.

Eventually I traced it to the rear caliper bolts being ever so slightly loose, I mean maybe ond turn or two. It wasn't enough to feel by hand when I tried the caliper for any play originallly and even at the time the movement was probably at most 0.5 mm but that was enough to cause an annoying rattle.

Out with the ratchet, tighten it home again problem cured or for around 3 weeks or a month till it started to rattle again for the same reason. Same cure tighten it to the correct torque, although it probably requires a different yorque setting being stainless stell..... alls well until the rattle returned this week.

So I bought some loctite threadlock,have always found it does the job in the past so am hoping in will now.

She just clocked over 3000 miles since the m.o.t so I've been sitting here waiting for the rain to ease off so I can change the oil and filter......luckily i can get about half the car in the garage so i'll be finishing my tea and putting the front end in for the oil change then backing out and reversing in to do the caliper bolt :)

[Konrad C]

The exhaust has settled down since I replaced the bolts. Motorway journeys are very smooth and hardly any resonance at most speeds apart from 60 mph where there is a slight boom.

The zinc plated steel bolts are perfect compare to the stainless steel bolts and the bolts were checked and pinched up. Hardly need any more tightening.

I can definitely say, don't use stainless steel bolts on exhausts!

The other source of the resonance is the back box, which is a different shape to the original, and this is turn put it close to under body shield. They were touching so I had to make some adjustments.

Much happier now, but not perfect. The sound of the exhaust with the windows down is 'sporting'.