Jump to content


Photo
- - - - -

Exhaust Blow


  • Please log in to reply
13 replies to this topic

#1 jime17

jime17

    One Carb Or Two?

  • Members
  • PipPipPipPipPipPipPip
  • 923 posts
  • Location: Bury lancs via E. London
  • Local Club: None

Posted 09 February 2019 - 03:58 PM

Hi gang...

I CANNOT get the exhaust clamp to seal for more than 38 nano seconds.

I've tried all 3 types of clamp. All sorts of sealing goo. Foil tape and goo.

In all the years I've owned this car and the one nearly 30 years ago they've blown here.

Has anyone had any success with cutting a few inches off the exhaust pipe between the gearbox clamp and the flared end and fitting a universal flexi?

Is there enough room for this?

Am I living in dream land as usual?

Is there a 100% way of obtaining a proper seal without hare brained schemes?

I'm trying to resolve a persistent misfire and I'm running out of the usual suspects to change...


Thanks as always

Ps. 1990 998 hs4 waxstat aac needle etc

#2 Homersimpson

Homersimpson

    Speeding Along Now

  • Members
  • PipPipPipPipPip
  • 352 posts
  • Location: Redditch

Posted 09 February 2019 - 04:06 PM

Are you sure its blowing and if it is are you sure its from the joint and not some other minor hole/crack/damage?

 

Are you allowing the exhaust sealant to dry before starting it?

 

If you having major problems its either something your doing or what you are repairing isn't actually the cause of the leak.



#3 jime17

jime17

    One Carb Or Two?

  • Members
  • PipPipPipPipPipPipPip
  • 923 posts
  • Location: Bury lancs via E. London
  • Local Club: None

Posted 09 February 2019 - 04:30 PM

It seals at first as I can stall the engine with my hand over the tail pipe.

Maybe 38 nano seconds was an exaggeration but after a few weeks blocking it has no discernable effect which is where I am at now.

I left the paste a couple of hours as per the blurb on the tube.

I couldn't be certain there is no damage but the fact it seals initially suggests not?

#4 panky

panky

    One Carb Or Two?

  • Members
  • PipPipPipPipPipPipPip
  • 1,377 posts
  • Location: Cheshire
  • Local Club: Northwest Casual Classics

Posted 09 February 2019 - 04:44 PM

Have you got a steady bracket from the exhaust to one of the gearbox bolts. The joint wont last long if there isn't one fitted - just a thought.



#5 jime17

jime17

    One Carb Or Two?

  • Members
  • PipPipPipPipPipPipPip
  • 923 posts
  • Location: Bury lancs via E. London
  • Local Club: None

Posted 09 February 2019 - 04:53 PM

Have you got a steady bracket from the exhaust to one of the gearbox bolts. The joint wont last long if there isn't one fitted - just a thought.


Yes got one.

The engine mounts and steady bushes are new too.

#6 Homersimpson

Homersimpson

    Speeding Along Now

  • Members
  • PipPipPipPipPip
  • 352 posts
  • Location: Redditch

Posted 09 February 2019 - 05:19 PM

Ah now thats a bit different, if it lasts for a while then check your engine stabilisers and mounts, if the engine is moving around it will keep cracking the joint.

 

You should have one stabiliser on the drivers side of the engine to the bulkhead and the one on the underside from the gearbox to the subframe (generally by the oil drain plug but there are other positions).



#7 jime17

jime17

    One Carb Or Two?

  • Members
  • PipPipPipPipPipPipPip
  • 923 posts
  • Location: Bury lancs via E. London
  • Local Club: None

Posted 09 February 2019 - 08:05 PM


You should have one stabiliser on the drivers side of the engine to the bulkhead and the one on the underside from the gearbox to the subframe (generally by the oil drain plug but there are other positions).


I've the usual block to bulkhead steady at the top and bottom one on the same side which if I recall bolts to diff case and rearward onto the subframe.

#8 unburntfuelinthemorning

unburntfuelinthemorning

    One Carb Or Two?

  • TMF+ Member
  • PipPipPipPipPipPipPip
  • 923 posts
  • Location: Bedfordshire

Posted 09 February 2019 - 10:38 PM

They can be a nuisance to get right but if they keep blowing there's a reason for it, they should last for years if done right.

 

As said already make sure the engine stabiliser bushes are in good condition.  Also make sure the gearbox clamp can be properly tightened to eliminate all movement of the exhaust pipe.  I've found the manifold clamps with two fasteners are better than the single fastener type. 

 

I find it easier with the front wheels up on ramps or the front of the vehicle supported on axle stands. 

 

Make sure the flare on the downpipe is a good condition.  Clean the mating faces with abrasive paper.

 

With the gearbox bracket disconnected jack up the exhaust gently until it meets the manifold. 

 

Make sure it aligns perfectly, you shouldn't need to pull the downpipe sideways at all to achieve the correct position, if you do then loosen the rear exhaust brackets and adjust the pipe as necessary. 

 

Lower the exhaust pipe and apply sealant to the downpipe and manifold mating faces, a decent layer but nothing ridiculous.  Holts Firegum is good but others work well too.

 

Jack exhaust up as before.  Fit the gearbox bracket and nip up so the exhaust can still just move.  Fit the downpipe to manifold clamp and nip up.  Now tighten everything firmly - don't go mad though.  Remove jack.  Start engine (no need to wait hours) but don't rev it - just let it fast idle until the exhaust is properly hot.

 

This is my method and it works.



#9 jime17

jime17

    One Carb Or Two?

  • Members
  • PipPipPipPipPipPipPip
  • 923 posts
  • Location: Bury lancs via E. London
  • Local Club: None

Posted 10 February 2019 - 09:41 AM

I'm wondering if the clamp at the gearbox isn't gripping the pipe tightly enough and allowing the manifold and exhaust to move independently rather than as one unit.

Back to the drawing board.

Thanks all.

#10 panky

panky

    One Carb Or Two?

  • Members
  • PipPipPipPipPipPipPip
  • 1,377 posts
  • Location: Cheshire
  • Local Club: Northwest Casual Classics

Posted 10 February 2019 - 10:44 AM

Could it be that the manifold that's fitted is a bigger bore than the exhaust. Pretty sure the 1098 manifold used a slightly bigger outlet than the smaller bore engines. After a bit of digging it looks like the 12G3538 is the largest.



#11 jime17

jime17

    One Carb Or Two?

  • Members
  • PipPipPipPipPipPipPip
  • 923 posts
  • Location: Bury lancs via E. London
  • Local Club: None

Posted 10 February 2019 - 02:32 PM

I'd think it's more due to my ineptness but anything's possible on cars this age.

#12 Homersimpson

Homersimpson

    Speeding Along Now

  • Members
  • PipPipPipPipPip
  • 352 posts
  • Location: Redditch

Posted 10 February 2019 - 03:48 PM

 

 

Make sure it aligns perfectly, you shouldn't need to pull the downpipe sideways at all to achieve the correct position, if you do then loosen the rear exhaust brackets and adjust the pipe as necessary. 

 

 

If all the engine mounts and steadies are in good condition then this is the most likely problem.  We used to start by loosely hanging the exhaust on the mounts, getting the front right(sit it on a jack to hold it in the right position)m fit the clamp with sealant and then working front to back tighten all the mounts (adjust them as necessary so the exhaust fits nicely and is not under strain.

 

If you really get stuck then there used to be a piece with a new flange on it with a flexible section you could cut the end off and weld on.



#13 Cooperman

Cooperman

    Uncle Cooperman, Voted Mr TMF 2011

  • Mini Docs
  • PipPipPipPipPipPipPipPipPipPipPip
  • 21,324 posts
  • Location: Cambs.
  • Local Club: MCR, HAMOC, Chelmsford M.C.

Posted 10 February 2019 - 04:20 PM

In the 1960' there was an aftermarket dhort downpipe which sleeved over the standard pipe. It had a flexible metal hose about 3" long with aflanged top to mate with the manifold. All you had to do was cut about 5" off the standard pipe and slide the repair piece on, then fit a small clamp at the bottom.
It was a great improvement.
Anyone remember this?

#14 Homersimpson

Homersimpson

    Speeding Along Now

  • Members
  • PipPipPipPipPip
  • 352 posts
  • Location: Redditch

Posted 10 February 2019 - 04:51 PM

Like this:

 

https://www.ebay.co....WDKI:rk:43:pf:0






0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users

Mini Spares