Sealing a blowing exhaust?

[MiketheBike]

On a ferret, there is a y-piece that joins to an elbow attached to the hull via a short length of pipe.

This short length of pipe is loose, and the exhaust is blowing badly. I think this may be part of the cause of my backfiring on over-run (I read another post about that on this forum).

 

I tried sealing it with clear RTV sealant (which is Ok up to 250C), but this very quickly (like 10 minutes after warming up) dried, cracked and fell out.

 

What would you use to seal these joints? I assume they have to move a small amount, so would need to remain flexible, but also be resistant to the exhaust pressure?

 

Thanks,

 

Mick

[john fox]

Mick

 

this has been discussed many times on the "other" :whistle: forum and there is no real cure other than a rebuild using flexible exhaust pipe which has been remodelled (eg. cut and welded) to fit tightly - you are quite correct that it is important to ensure there is movement to avoid manifolds or the hull elbow cracking due to engine movement relative to the hull

 

If your mileage is low and you are happy to risk cracks then fitting metal shim between the swaging on the short pipes and the rim of the elbows provides a temp fix - shim held in place with jubilee clips around the short pipes. The metal will of course rust away and is renewed with more shim (try brass if you can but watch out for differential thermal expansion by using non ferrous metal). I'll reiterate that such action does of course produce a solid pipe - you have been warned.

 

in the past I have seen others post about a flue sealant which you can apparently buy in plumbers (not builders) merchants. Not sure I remember the name correctly but was something like "plumb flue" - it was claimed this never sets and is designed for sealing joints between a metal flue lining (which moves with heat expansion) and the brickwork of a chimney etc.

 

That said no one ever posted whether they had actually used it and if it was successful. Gun gum and other "exhaust sealants" sold in motor factors set hard and are certainly no use. You might try exhaust bandage and hold it in place with jubilees but the gap would have to be big for that to fit in the first place.

 

I myself have done the rigid fix using 4 thou shim but am currently in the process of replacing it with flex exhaust pipe

 

on the "other" forum you will find that the consensus amongst the people who actually post (ie not the majority view) was that such leakage is normal and you have to live with it. The Australians pointing out that the temp in the engine bay can get the exhaust pipe up to red heat whereupon expansion seals all leaks - but we don't have their sort of ambient temperatures so I personally take this with a pinch of salt.

 

I'll be interested to see what others say

[sirhc]

They will all leak when cold, but they should seal up when the exhaust gets up to temperature and the tubes expand.

 

Mine was leaking quite a bit so I took it all apart, and found that the elbow casting which bolts on to the inside of the hull had worn due to the tubes rattling. The holes were enlarged and the pipes were no longer a good fit. I put a new one on and it's been much better since. Worth checking.

 

Chris

[snowtracdave]

Not come across Plumb Flue but I would guess what you are talking about is fire cement which is what we used to use (when we did things like that) to seal flue pipes to stoves & where they penetrate register plates . Don't think it would work well in this application , it sets very hard when it goes off and is not flexible . I would guess that it would crack & blow out with the movement but it might be worth a try as an experiment .

DM

[MiketheBike]

John,

 

Sounds like having a solid joint is not good....I am doing a few miles.

 

maybe I have another option:

700F Xtra Copper RTV Silicone Sealant

 

Sounds like it stays flexible, and can cope with temps up to 390c.

Other option is these I guess:

 

or something like:

 

http://cgi.ebay.co.uk/Universal-Exhaust-Repair-Flex-small-medium-large_W0QQitemZ160157615183QQihZ006QQcategoryZ9886QQrdZ1QQssPageNameZWD1VQQcmdZViewItem

 

 

Chris,

 

yes, the pipes are really loose, and do not come anywhere near sealing when hot. I wonder if its the short pipes or the Y and elbow that is worn?

It may be that a elbow and tubes may be the way to go and keep it original. Maybe I will see what Marcus Glenn charges...he seems to have them in stock.

 

Mick

 

[Tony B]

1 get a bean tin open both ends. 2 cut slots and bed round Y 3 smear librally with exhaust repair paste. 4 Clamp firmly in place. this is a metal to metal repair and acceptable by MOT. I had an old Montego that went on for years with the odd replacement tin.

[Simon Daymond]

when I used to paint boats, I noticed that in the engine bay the exhaust was wrapped in a heat proof special bandage lagging affair (great description I know), I think the purpose was to protect you from the heat but also to stop any leaks entering the boat.

Try a chandlers near you, it might be just the job. Failing that, or as well if it's any good, lengths of flexible exhaust are not that dear, unless you go to Halfords etc, so could you not buy a good lengh for stock, and some decent exhaust clamps, then you can refit a new section easily as the better commercial clamps are intended to be re-used several times. You can also get stainless flex exhaust which does last a lot longer than the noraml steel.

We use commercial motor factors, such as Partco, HS Atec etc, I don't know where you live so I don't know what your local firms are. Perhaps try searching for them on Yell.com ?

[sirhc]

I thought I'd post a picture of the exhaust so everyone knows what we're talking about. With the Ferret exhaust some of these ideas will not work! Items 3 and 4 are the 2 interconnecting pipes which usually leak.

 

Chris

[Tony B]

No way of getting a flexible mount in at the junction 9? I see the problem, the whole system seems to swing on that point. Can you get an etra rubber support mount in there some where?

[sirhc]

Tony,

Item 9 is a gasket. The exhaust passes through the hull at this point and the gaskets are for either side of the hull.

 

Chris

[abn deuce]

That diagram explains why its such a difficult problem , so each time the engine revs the first 4 parts of the system can sleeve in and out slightly or simple engine vibration in time wear's out the exhaust tubes , and no ones come up with a better coupling . Doesn't look like it would be a very easy repair either, Likely you pull out the engine to work on it ?

 

[Simon Daymond]

thanks for the diagram, see what you mean now. On our Scania coaches, there is a pipe similar between the manifold and the downpipe, it seals with what looks very much like a piston compression ring at each end. Would something like that work?

There is a groove on the pipe for the ring to sit in, but it goes together dry (ie without any pastes etc) and allows for movement, and doesn't leak at all.

Perhaps it's an idea for the future?

 

Also I'm sure there is a similar joint on the Gardner engine exhaust manifold, I'll investigate. Hopefully you've got something missing/worn out? As I can't see that it would be simply pushed together, it does look like the short pipes 3 & 4 are designed to move slightly on their respective seats, if so, surely there must be something inserted in the joint to keep a seal, but something flexible.

[N.O.S.]

See your problem......... :shake: Only on British PW kit ...:banghead:

 

Quite a job to re-engineer with flexi, but as Simon suggests, go for the stainless stuff EVERY TIME.

 

If ever there was a case for product upgrade to something like a Cummins 4B..... :naughty:

[sirhc]

There's nothing wrong with the engineering, it's a prefectly good solution to the problem. As for changing the engine, you've obviously not spent enough time listening to a B60 or driving a Ferret... If you swapped the engine you'd be taking away the best part!

 

Chris

[N.O.S.]

Point taken! :died:

 

[N.O.S.]

You are of course quite correct - I have zero Ferret experience.

 

Does the engine installation have any resilient / flexible mounts?

Is it mounted remote or direct to transmission?

[Richard Farrant]

Does the engine installation have any resilient / flexible mounts?

Is it mounted remote or direct to transmission?

 

 

Tony,

 

To answer your question, yes, there are silentbloc type mounts on the transfer box.

 

There was an earlier type of elbow and tubes but were superceded to these current type which are relatively thin tube with swaged ends. In service there was no problem, if there was a lot of play in the tubes, either tubes and or elbows were renewed. Any slight blow was disregarded by the Examiners as it was not a great issue. The tube tends to suffer more as being thin steel, it scales and flakes. I did once build a set up with braze around the swaging, knowing that this would be more reliable, and filing it until it was a nice sliding fit with no lateral movement. If really bad, the elbows can be worn inside where the tube has been rattling.

[MiketheBike]

I am waiting for Marcus Glenn to get back to, they are closed until Monday, with prices for the long and short intermediates, the two elbows and the casting that goes against the hull.

 

I did think of using exhaust heat wrap, wrapped around the intermediates and snugged up against the castings, using the stainless tie-wraps for the heat wrap...I am guessing it would resolve most of the blowing but I am not sure how resistant it is the wear...but at only £10 for 5metres (1 inch wide) it may be worth a shot just to see how it goes? At least it would not be a solid joint.

[Tony B]

If you have room try a sleeve of loose sheet metal wrapped round that can flex. Ah la bean tin, as you say if it burns through dirt cheap to replace.