Can anybody tell me on thr threaded stub that goes into the head, should there be any sealer/thread tape or gasket on the castellated lock nut to prevent air leaks ? I can’t see anything on the parts list
Thanks barney
inlet stub gaskets ???
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morini_tom
- Posts: 1042
- Joined: 05 May 2006 13:47
- Location: Northampton
Re: inlet stub gaskets ???
As you mention the castellated nut I am taking it that you mean the first series metal intake manifolds.
The biggest problem you’ll probably find is not air leaks down the threads but the whole assembly loosening off and then you’ll definitely have air leaks!
To improve (I’ll never say solve) this problem, here’s what I do:
1) make sure that the length of the stub tube that screws into the head is such that it bottoms out in the head in the correct position. If it doesn’t, you can remove some material from the stub tube or add thin shims below it as appropriate. This will go a long way to stopping it undoing itself.
2) the triangular flanges are more often than not warped and an excellent source of unwanted air. Flat them down on a glass plate with some grinding paste or some wet and dry paper or suchlike. Ensure that you keep them flat and perpendicular to the bolt holes or you might make it worse!
3) when reassembling I use a ptfe pipe thread liquid sealant (loctite 572 or the like) on the thread in the head and threadlock on the castellated nut (but do the nut up last, once the carbs are fitted and in place)
4) ensure the integrity of the black insulator which goes between the metal stubs. These often crack. Again, make sure they are flat, that the o rings are in good condition and reassemble with new paper gaskets and a smear of hylomar on all faces. Threadlock on the three bolts wouldn’t do any harm but these haven’t been the problem area on my bike.
5) fit the carb. It can be incredibly tight on the stub tube. Once you are happy with the orientation, tighten the carb mounting clip and finally with a dab of thread lock on the castellated nut, nip it up with a decent fitting castellated spanner.
If on final assembly you find the carb can’t be made to sit in the correct orientation then sadly you for step 1 wrong
Having taken the time to carefully do the above, my sport does not shake its manifolds off anymore and runs much better, which begs the question why the process had seemingly not been done in the last 50 years
The biggest problem you’ll probably find is not air leaks down the threads but the whole assembly loosening off and then you’ll definitely have air leaks!
To improve (I’ll never say solve) this problem, here’s what I do:
1) make sure that the length of the stub tube that screws into the head is such that it bottoms out in the head in the correct position. If it doesn’t, you can remove some material from the stub tube or add thin shims below it as appropriate. This will go a long way to stopping it undoing itself.
2) the triangular flanges are more often than not warped and an excellent source of unwanted air. Flat them down on a glass plate with some grinding paste or some wet and dry paper or suchlike. Ensure that you keep them flat and perpendicular to the bolt holes or you might make it worse!
3) when reassembling I use a ptfe pipe thread liquid sealant (loctite 572 or the like) on the thread in the head and threadlock on the castellated nut (but do the nut up last, once the carbs are fitted and in place)
4) ensure the integrity of the black insulator which goes between the metal stubs. These often crack. Again, make sure they are flat, that the o rings are in good condition and reassemble with new paper gaskets and a smear of hylomar on all faces. Threadlock on the three bolts wouldn’t do any harm but these haven’t been the problem area on my bike.
5) fit the carb. It can be incredibly tight on the stub tube. Once you are happy with the orientation, tighten the carb mounting clip and finally with a dab of thread lock on the castellated nut, nip it up with a decent fitting castellated spanner.
If on final assembly you find the carb can’t be made to sit in the correct orientation then sadly you for step 1 wrong
Having taken the time to carefully do the above, my sport does not shake its manifolds off anymore and runs much better, which begs the question why the process had seemingly not been done in the last 50 years
Re: inlet stub gaskets ???
Thanks Tom, very informative, a slightly long winded job but worth doing.
I never had a problem with air leaks before but having cleaned everything off new rings, valve seats cut and valve faces ground I thought I would ask.
They had been moved at sometime because the inlet rubber never fitted properly and someone previous to me had even tried siliconing it in which obviously didn’t work and it was the stubs not lined up correctly, so as you say I will do a dry assembly first and go from there,
Thanks you very much for detailed reply
barney
I never had a problem with air leaks before but having cleaned everything off new rings, valve seats cut and valve faces ground I thought I would ask.
They had been moved at sometime because the inlet rubber never fitted properly and someone previous to me had even tried siliconing it in which obviously didn’t work and it was the stubs not lined up correctly, so as you say I will do a dry assembly first and go from there,
Thanks you very much for detailed reply
barney