Advice - Fitting Cat bypass

[chrism964]

Hi all,

Can anyone give me advice regarding the practicalities of fitting the cat section of the exhaust?

My car was designated M150 from the factory (i.e factory cat delete) but my OEM exhaust is holed at the cat section and the MOT expired (because I could not get the parts) before I could drive to someone to throw money at.

I have therefore gone DIY..........

I have removed my OEM section of exhaust (and found the flange on the heat exchanger is corroded at the bolt holes (another job to get done at some point [:'(]) but when dry fitting the new exhaust section(a straight through pipe) have found that it is a little tight to get the new gasket etc in place.

My question : Do I just need to release the primary silencer (across the rear PU) a bit? If so, how do I do this? Do I just ease the strap around it on the cat side?

Many thanks in advance.

Chris

 

[Steve Brookes]

Yes they are a tight fit and the aftermarket decats are not made to the same tolerance as orignal. I would loosen both straps on the primary to give you some wiggle room and tighten them up when you're done.

 

[chrism964]

Cheers Steve.

I just wanted to make sure with someone before I undid even more bolts.

I will have to get to it tomorrow now. I have my 6 and 4 year olds to entertain.............

Will report back on success (or abject failure and the car transporter of shame to the specialist[])

 

[Dekker]

Make sure you have spare bolts and a gasket ready for the job.

 

[chrism964]

Sage advice. My OCD ensured I had acquired new fixings before embarking on this (also a quick eyeball of the old suggested I would be lucky if I didn't need to dremel them off/split the nuts to remove them.)

So, an update.

Bypass pipe is in secured to the heat exchanger/manifold. However, on loosening the straps for the primary silencer it dropped down on the passenger side and would not move. Investigation of this suggested that the reason for this was that the connection of the primary to the secondary silencer was at an angle. I tried to move the primary silencer back into position but it was very difficult. The only way to get it to move was with a piece of wood on top of a trolley jack to move it back up under the bumper. So, decided to disconnect primary silencer from secondary silencer.

So currently, primary silencer is removed and I am going to refit it on Thursday. Just need to get a new clamp bolt to for primary to secondary connection (dremelled in half as so very rusty the nut and bolt head became dust!)

Last piece of advice sort.

Should I connect all the exhaust up - with assembly paste - then tighten the primary silencer location straps before tightening both the exhaust clamps? (From the cat bypass to the primary and from primary to secondary silencer)

Or tighten the connection clamps and then strap the silencer up into place? It would appear this might have been the issue in the first instance that caused the primary to drop and become stuck.

Thanks

 

[Steve Brookes]

The cat and secondary are pretty much fixed when bolted to the engine - the cat bolted to the heat exchanger flange and the secondary to its bracket. I would make sure those two are bolted on and then attach the primary to the cat and secondary. You don't need any compounds as the 'olives' do the sealing when you tighten the clamps round the joints. Then you can tighten up the straps on the primary.

Nb. You'll want to remove the tailpipe from the secondary so that you've got good access when joining the primary to it. This will also enable you to adjust the tail pipe so that it sits nicely in the bumper crescent.

 

[Dekker]

I agree with Steve, the only "paste" I use is a light smear of engine oil on the olives so they rotate and align well before clamping. The primary support strap bolts have them unwound as much possible to give yourself maximum movement.
I always work from the heat exchanger towards the tailpipe as the secondary has lots of movement whereas the cat to primary hasn't.

 

[Steve Brookes]

I like that tip about the engine oil on the olives. []

 

[vitesse]

Makes for an interesting party []

 

[chrism964]

Thank you.[]

There is evidence that assembly paste was used on olives and exhaust connections from prior installation. Have cleaned them all up and will see if it seals without.

Just need to get another clamp through bolt, washers and nut for the clamp on the primary to the secondary silencers (not in my plans to have to dremel this away). My secondary silencer is pretty mobile. Will fiddle with the tail pipe when I can be bothered(unless it looks horrific) as this requires further dremel action and bolts.

Had hoped to get this done this weekend as the MOT expired on Friday (25th) and the Tax is also due Tomorrow.

Looks like a Halfrauds MOT. I wonder whether they'll try to offer to service it..........................

 

[Dekker]

I always use Never Seeze by Bostick on high temp threads. Much like copper slip but made with aluminium instead.

 

[chrism964]

Thank you again for the advice.

I think the quality of the fixings used for the clamps was the main issue. The nuts/bolts themselves just disintegrated on touch, let alone with the use of a wrench. Definitely not stainless and definitely not treated with anything to aid resistance to corrosion. Heat, wet and road-salt = corrosion/total annihilation.


Anyway. Quick update - 1st attempt at assembly - gas leaks at clamps. Will loosen everything off again and attempt to get the exhausts and olives to fit 'snugger'. I think part of the issue is the aftermarket bypass - it would appear that the olive needs to be really snugged in at one point (as the flaring is a little wide here - may resort to paste).

Who would think it could be so exciting to fit your own exhaust - I mean it - I will be well chuffed if I succeed!

 

[Steve Brookes]

Good point about the aftermarket cat being more difficult to snug up. Also, I've found that you need to really lean on the clamp bolts to get them tight. To do that you need quality bolts and spacer washers rather than normal washers because normal ones just bend and cut. i.e. you need something like this:

http://www.ebay.co.uk/itm/Stainless-M8-Extra-Thick-Spacer-Washers-Choose-Your-Quantity-/371039634289?var=640216566265&_trksid=p2054897.l5664

Nb. the above are M8 (from memory that's the correct size).

 

[Dekker]

I read some time ago that SS bolts & nuts were not a good idea on the exhaust/turbo/cat area because the high temp and the expansion and contraction always distorts the threads and makes them hard to get off, usually needing a grinder.
Brass nuts on mild steel bolts is what used to be used on other car makes in the past.

As for centring the olives, when all pushed together you should only see the centre seem of the olive with about 1-2mm either side showing. Well it's like that on my car and I fitted a C cup last week.

 

[chrism964]

Yes. Cat bypass is attached with mild steel bolts and copper/brass nuts.

It's all in the olives!

Even when just pressing the olive in to just one side of the exhaust connection I can not get it (the olive) to sit with only 2mm either side of the centre line.

Anyway. 'Tis done now. I have used assembly paste (read grey sticky mess that goes rock solid with heat) to take up the slack around the aftermarket cat bypass and have fired up with no leaks.

I shall go see if the MOT is passed.

If so, these guys are pretty local http://www.pdgough.com . I shall ask them to see if they can sort the disintegrating flange (on the heat exchanger) and maybe they will modify the flaring of the pipe for the olive.

 

[chrism964]

Thread finisher.

MOT passed after headlight adjusted and both steering bellows replaced. Given that the geometry will have been messed with I will now have an excuse to book into Center Gravity for a proper set up.

Exhaust is fine - quite a bit noisier than I expected but quiet by cup bypass or g-pipe standards.