Late Exhaust Backbox - flow direction?

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StuM
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Late Exhaust Backbox - flow direction?

Post by StuM »

Hi All,

I'm swapping my early system for a late one - managed to get a light-use late system and could not find anywhere that had early systems in stock. I have a late engine mount bar and back-box saddles to go on too.

Despite being sold to me as NOS, the back-box I have has been cut off at one end so that all three bolts are rusted in the holes. I will try to drill them out, but figured that if this is the tailpipe end, it doesn't matter as much.

With this in mind.... Does it matter which direction the back-box goes on, or should flow only be one way?

Thanks,
Stu
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California Dreamin
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Re: Late Exhaust Backbox - flow direction?

Post by California Dreamin »

Isn't one flange loose (the one that attaches to the intermediate pipe) and the other fixed (for the tail pipe). Tail pipe side with captive threads, intermediate side drilled through with nut/bolt.

Martin
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StuM
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Re: Late Exhaust Backbox - flow direction?

Post by StuM »

Thanks Martin. Both sides of the silencer are rigid. This is what it looks like:

http://www.ebay.co.uk/itm/400623362404?redirect=mobile" onclick="window.open(this.href);return false;

From what you've said I think that it's the tailpipe end at issue where the bolts were stuck in the captive threads and have been chopped off flush with the joining face.

I'll go take a closer look...
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itchyfeet
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Re: Late Exhaust Backbox - flow direction?

Post by itchyfeet »

I think the pcd of the flanges are very slightly different, you need different gaskets too, very similar you have to wonder if this was deliberate to stop you getting it wrong
do you have an old backbox for sale or is it shot?
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itchyfeet
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Re: Late Exhaust Backbox - flow direction?

Post by itchyfeet »

Just remembered if its a stock backbox the flange is closer to the silencer on the tail pipe end than it is on the engine end
Also tailpipe end has tapped holes in the flange, once you drill them out you need to fit nuts, its so close to the silencer its fiddly but just possible
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StuM
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Re: Late Exhaust Backbox - flow direction?

Post by StuM »

Thanks for that. You're right - tapped holes one end and wider holes (non threaded) the other. That is good - means the end with the intermediate pipe end is clean. Looks like drill out tomorrow!

I think it might be a Timax silencer.

Not sure of the condition of the existing silencer - if it's solid I'll keep hold and let you know. I'm not doing the work - van is going in to a garage for MOT prep and some other bits and bobs on Friday.

Cheers
Stu
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itchyfeet
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Re: Late Exhaust Backbox - flow direction?

Post by itchyfeet »

Ok cheers :ok
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Re: Late Exhaust Backbox - flow direction?

Post by Cruz »

Doesn't the late system need the back box supports which the early engine mounting bracket doesn't have the necessary flanges for fitting them to?

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Re: Late Exhaust Backbox - flow direction?

Post by StuM »

Hey Cruz.

I have those - bought a while back in preparation having read your posts :ok

That is another question though. How big a job is swapping the engine mount bar?
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itchyfeet
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Re: Late Exhaust Backbox - flow direction?

Post by itchyfeet »

Fairly easy to swap the mount, i did have one recently where the bolt was siesed into the mount by corrossion and the head snapped off, had to cut the bar in half with a hacksaw to get it off, but thats no problem as you dont need the old one but if it happens you would need a new bolt, the contact of aluminium to steel is so long i dont think plus gas would have released it
engine mounts can be a bitch to align if you dont leave them loose until all bolts are in then tighten, you may take the opertunity to replace them
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StuM
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Re: Late Exhaust Backbox - flow direction?

Post by StuM »

itchyfeet wrote:Fairly easy to swap the mount, i did have one recently where the bolt was siesed into the mount by corrossion and the head snapped off, had to cut the bar in half with a hacksaw to get it off, but thats no problem as you dont need the old one but if it happens you would need a new bolt, the contact of aluminium to steel is so long i dont think plus gas would have released it
engine mounts can be a bitch to align if you dont leave them loose until all bolts are in then tighten, you may take the opertunity to replace them

Many thanks for that. :ok
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Re: Late Exhaust Backbox - flow direction?

Post by StuM »

Here it is in all its glory ready to go on*...

Image


Has anyone got a photo of how the rear bracket attaches to the engine mount block? Yes, the front bracket is missing :-(



* I've no idea why I rested the tailpipe that way round!
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itchyfeet
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Re: Late Exhaust Backbox - flow direction?

Post by itchyfeet »

Not sure what you mean , these any good...

reccomend all stainless steel bolts, you can get them cheap enough these days

Image

Image

Image

Image

Image
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Re: Late Exhaust Backbox - flow direction?

Post by Cruz »

I could eat my dinner off that engine.

Where's the 30 year oil spray? Where's the oxidising engine bar? :lol:

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itchyfeet
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Re: Late Exhaust Backbox - flow direction?

Post by itchyfeet »

Thanks, they were pics after the engine had been out, cleaned, heads off and replaced with plenty of bits changed, also its an 88 so its only 26, still a youngster :lol:
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