Breather between Block and Head - Sealing?

[perksy]

Hi All

So the TC is now coming together and the next job is to fit the cylinder head to the block

With regards the small stubby breather that sandwiches in between the head and the block, Do you need to use any sealer at either end or does it just rely on a dry fit?

Thanks

[ericbushby]

Hi Perksy
I used Wellseal as recommended by Brian Buckland (I think)
Eric in Burnley
1967 S3SE DHC

[Baggy2]

Hi
FWIW Miles Wilkins book says RTV
Cheers
Baggy

[perksy]

Thanks both for your answers

[pharriso]

I’d highly recommend the Lotus Marques aluminum drain tube. Seals with an o ring at the top… buy, fit & forget.

Search on here for info…

[MACCA.GLM]

Hi
I use hylomar and as long as the rubber is clean and dry as well as the head I've had no problems yet.

I don't like silicone as it can get in the oil ways and we all know what that can do.

cheers g

[2cams70]

Regarding sealants:
Wellseal and Hylomar are designed to seal between solid surfaces not rubber. If you want to help seal an elastomer like rubber then using something that is an elastomer itself (i.e silicone RTV) makes much better sense.

A lot of rubbish get written about RTV silicone. Most if not all of the issues are due to the numb nut applying it - i.e they apply it incorrectly, use it in the wrong application, or use the incorrect grade (they aren't all the same).

Regarding the head drain tube:
In my humble opinion the Lotus Marques aluminium tube is the best. There's a lot of needlessly complicated contraptions out there to try and do the same thing but they aren't as good. Yes you have to lift the head to fit it but once fitted it will never leak. In particular the bottom of the tube is a light interference fit in the block and sealed with Loctite retaining compound (eg. 641). It will NEVER leak as there is no rubber seal to leak. Yes the upper O-ring seal does need a little silicone RTV to assist the seal because the internal hole in the head has quite a rough surface having never been originally designed to accept an O-ring. Use some Threebond 1217H RTV here. Threebond sealants (of the correct grade) are what a lot of OEMs use when building new engines.

[andyelan]

Hi there.

I agree that there's nothing wrong with RTV providing the correct grade is used, not bathroom sealant for example.
I use engineering grade Hylosil 300 series which I find very good.

One problem I have found with the original rubber pipe is that it shrinks over time reducing the bore diameter and ruining the fit in the block and head. It should always be replaced with a new one if the heads been off and never reused. I haven't tried the aluminium tube design but it does sounds like a good idea.

Regards
Andy

[HCA]

I wonder, has anyone fitted the Elantrikbits drain tube and has any comments - other than the block needs to be milled to accept the tube..?

[reb53]

I used a high temp silicone when replacing mine a few years back.

I'm surprised to see people suggesting the head needs to be removed to do so.
I found several minutes in boiling water made the tube more than flexible enough to wriggle into place.
I may have pulled the carbs to improve access, can't remember, but I'd much rather do that than pull the head.

Ralph.

[rgh0]

There are two slightly different diameters of the drain hole into the block so you need to know what you have before buying an aluminium breather / drain tube thats a press fit into the block.

cheers
Rohan

[billwill]

As mentioned a couple of times above, it is not a breather tube, it is an oil drain that lets the oil pumped to the cams, drain back into the sump.

The real breather comes out of the side of the head near the back, on early models, oil simply ran slowly down a slanting pipe and dripped onto the road. In later models the breather hole is connected by a short pipe containing a wire (wool ?) filter, back to the air intake box, where the condensed oil gets sucked into cylinder4 and burned.

The head contains an enclosed chamber at the back, with the drain tube at the front end of that chamber. The chamber is there (I think) so that any oil vapour has a chance to condense back into a liquid and drain back into the sump. There would be room for a 1 or 2mm pool of oil in the bottom of the condensing chamber before it started flowing out of the breather hole.

If you look at photos of a cross-flow engine (from which the block is used in the twin cam) you will see that they have the condensing chamber as an external "Tin Can" connected at its top to their breather outlet on the head.

[2cams70]

There are two slightly different diameters of the drain hole into the block so you need to know what you have before buying an aluminium breather / drain tube thats a press fit into the block.

cheers
Rohan

There's two main sizes but it's not something that's all that accurately machined. Mine was such a case but Steve supplied another one that was around 0.001" to 0.002" larger in diameter where it fits into the block.
That clearance would have been small enough to be taken up by just the retaining compound but I preferred that it be a light press fit.

Note from memory I used a weaker grade of retaining compound than in Steve's instructions because I wanted the tube as easy as possible to remove should this be required in future. Those retaining compounds sure stick things solidly. Heat helps to remove of course.