| Author | Message | ||
     Benoit Leus Prolific User Username: benoitleus Post Number: 122 Registered: 6-2009 |
The gasket between the carbs and inlet manifold had blown after less than 1000 miles. I suspected I might have damaged it during installation so I installed a new one. Now after less than 600 miles it has blown again. The gasket is build up of multiple layers and it is one of the middle layers that's blown out. I only noticed it because, when cold, it was idling very rough. Front of the carbs :  Rear of the carbs :  What could cause this ? Poor quality gasket ? Faulty installation ? Benoit | ||
| Chris Browne Prolific User Username: chrisb Post Number: 124 Registered: 2-2010 |
Hello Benoit, I am a little puzzled by your problem. The gasket in your photographs looks like thick paper or card when the correct gasket is about 8mm thick and is made in one layer which cannot come apart.  Here is a photograph of the one on my car before I cleaned and serviced the carbs. There are two register pins in the gasket into which two locating pegs fit and it is all held together by the long central bolt. Has a thick paper gasket been fitted in error so the two register pins are not able to seat in their holes in the casting? It would still be possible to tighten the long centre bolt but it would mean that the thin gasket would not form a seal and would be leaking all the time. Could this be the reason why the gasket appears to blow? Kind regards, Chris | ||
| Benoit Leus Prolific User Username: benoitleus Post Number: 123 Registered: 6-2009 |
Hi Chris, the gasket is indeed about 8mm thick and has the two register pins. However, the gasket in your picture looks different as indeed it doesn't seem to be built up from different layers. On my gasket you can clearly see the different layers on the side, which seem to be held in place by a thin layer of tansparent glue. I bought the gasket from a well known company in the UK. Benoit | ||
| Chris Browne Prolific User Username: chrisb Post Number: 125 Registered: 2-2010 |
Hello Benoit, I can only assume there is a fault in the manufacture of the gaskets. I can't understand why or how the gasket can come apart like that when it is clamped between the carburettor body and the inlet manifold by the long bolt. Have you contacted the supplier to see if they have had any other complaints? I think the one on my car is original and it seems to be made of compressed fibre which is not layered. The other strange thing is I would not have thought much pressure was passing through the gasket in use to cause it to burst. Very strange! Kind regards, Chris | ||
| Bob Reynolds Frequent User Username: bobreynolds Post Number: 57 Registered: 8-2012 |
That chamber contains the manifold vacuum, so how can the gasket 'blow out'? Is the engine backfiring through the carbs? If it's happened more than once I would check the inlet valves. | ||
| Benoit Leus Prolific User Username: benoitleus Post Number: 124 Registered: 6-2009 |
The engine doesn't backfire at all. I can imagine it would be quite a big backfire for the gasket to blow. What is clear is that both times the gasket seemed to be soaked. It is as if the sides of the gasket absorb fuel and this starts the delaminating process. Benoit | ||
| Jan Forrest Grand Master Username: got_one Post Number: 517 Registered: 1-2008 |
This problem is touched upon in the latest issue of T-One Topics (issue 97, page 1322). Although no cause has been attributed a possible cure is indicated by the use of longer 'registration pins' on reassembly. From the front/rear location of the pins it seems to me that this is where your gasket assembly has failed. Hope this helps. | ||
| Benoit Leus Prolific User Username: benoitleus Post Number: 125 Registered: 6-2009 |
Hi Jan, thanks for the tip. I wil check this on my car. Benoit | ||
| Benoit Leus Prolific User Username: benoitleus Post Number: 126 Registered: 6-2009 |
I removed the gasket today and examined it. It is soaked through with petrol. I don't know if this caused the gasket to delaminate and blow or if it blew and because of this the fuel could soak in. Could it be I overtightend it and this caused the gasket to blow ? Anyway,I'll replace it and see what happens. Benoit   | ||
| Jan Forrest Grand Master Username: got_one Post Number: 518 Registered: 1-2008 |
Have you checked for distortion of the mating surfaces with a straight edge? | ||
| Benoit Leus Prolific User Username: benoitleus Post Number: 127 Registered: 6-2009 |
Yes, I checked them but luckily they are OK. I have the new gasket and will install it carefully, taking care no to overtighten it. I coated the sides of the gasket with Loctite fuel resistant silicone and immediately wiped it of again. This leaves a small film that is soaked up in the gasket. Hopefully this should reinforce the gasket. | ||
| Chris Browne Prolific User Username: chrisb Post Number: 126 Registered: 2-2010 |
Hello Benoit, Just a thought. Why don't you try fitting the gasket dry, without silicone sealant, especially as this is the second one which has failed on you? Perhaps something in the sealant is reacting with the gasket and causing it to fail? I have removed the carburettor assembly on two Shadows and on both occasions refitted the gasket without sealant (and without future gasket failure). I always assumed that the long central bolt would apply sufficient pressure on the gasket without the need to apply sealant. Kind regards, Chris | ||
| Benoit Leus Prolific User Username: benoitleus Post Number: 128 Registered: 6-2009 |
Hi Chris, I fitted the previuous gasket without sealant so I guess that can't be the problem. I'm still planning on installing it without the sealant on the surfaces, only the slight coat on the sides. What I noticed is that the 2 pieces that had been blown out were totally dry, which might indicate that the gasket only got soaked with fuel after this happened. Benoit | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 878 Registered: 9-2004 |
A possible likly cause can be when the engine sneezes due to a cylinder backfire due to air leaks or ignition timing issues. Stale petrol can now also be more of a common cause here in the uk with the addition of ethanol added,not good if the vehicles are left unused for months on end through out the winter months. |
