BSA B21 Deluxe

[Group Leader]

The cylinder head on my B21 leaks somewhat and I've been reading up on the dismantling / reassembly process.   Apart from not being able to quite get my head around those weird head bolts, I'm unclear as to the need for a cylinder head gasket.    Looking at the parts list and the Haycraft instructions it appears that there isn't one (my interpretation of the statement "metal to metal" in Haycroft and the apparent lack of an entry in the parts list).   

Although still in one piece at the moment my engine definitely has a copper head gasket in place.   Might this have been desperation on the behalf of a previous owner to prevent leakage from a warped or damaged head joint I wonder?   If this is the case presumably I would need to get the head and possibly the top of the barrel skimmed?

Any informed thoughts and/or advice would be most welcome!

Alan

[Group Leader]

Well the answer appears to be that a PO obviously thought there should be a gasket so hand whittled one from what appears to be hard or half-hard brass sheet (well that's not going to work then ...).    Gasket removed and the fit of the protruding liner to the cylinder head recess was checked as best as I was able using a black permanent marker as a substitute for Engineer's Blue.   There appears to be one very small high spot close to one of the head bolts and if I get desperate I think you can lap the two together, although I'm not sure how you prevent lapping past escaping down the bore which wouldn't be too clever.

Anyway, I re-assembled it as is and it seems to be much better now, at least it doesn't make wheezing and farting noises when it starts now!

One thing I have noticed is that the instructions for setting the tappets in the Haycroft manual are not appropriate and woolly in their description of the process.  They are inappropriate because the gap between the tappet and the push rod is not in the adjustment window it's up the push rod tube.  Good luck with finding the gap let alone putting a feeler gauge in.   Fortunately I found a much better description of the "Special" method of setting BSA cam positions to set the clearances which includes diagrams and an explanation which seems entirely logical.   Anyway, armed with that and a clock complete with a ball end sitting in the little cup on the rocker arm above the push rod the clearances have been set(ish).   "Setish" because the clearance changes as you rotate the tappet to an extent and also due to side play in the guide-way so I went with what seemed like the best compromise.

Alan

[Hairy Gee]

No gasket is fitted head should be lapped to cylinder

[Group Leader]

Thanks HG.   

Having given the engine another test, there is a very slight leak as demonstrated by a slight oil bubble blowing out of the gap although it's no where near as bad as it was.

Looks like I'll have do some lapping!

Alan

[Hairy Gee]

 what year is your B21 out of interest ?

[Group Leader]

It's a 1939 De Luxe

Or at least, that's how it started out although it's had some updates along the years apparently.

Alan

[Bess]

Hi Alan,
            Try a mixture of linseed oil and graphite, brush sparingly on the face to face joint. Its used on steam turbine face to face joints with great success, lower temperature areas shellac is used.

Best wishes...

[Group Leader]

Try a mixture of linseed oil and graphite, brush sparingly on the face to face joint. Its used on steam turbine face to face joints with great success, lower temperature areas shellac is used.

As a form of sealant as it's only a minor leak?   

Thanks 

Alan

[Hairy Gee]

my copy of book of the bsa says a thin smear of hermatite

[Bess]

Hi Alan,
            Yes as a sealant, its tried and tested as a high temperature face to face jointing solution. Many engineers still put the graphite on gaskets, to fill the grooves, keep them supple and as a realease agent.

https://my.rs-online.com/web/p/pipe-thread-sealants/0692700/

Hermetite (Red) was the sealant of choice in the olden days, I remember spending hours cleaning mating faces and reapplying the same. I dont think you can get the original Hermetite but I believe Hylotyte could be the substitute. There are better choices on the market now, again use what you feel comfortable with.

Best wishes...

[Y13 Alan G]

Hi Alan. I have a 1937 BSA Annual which states that the front chain size is 1/2 inch x .305 inch. the rear chain is also  1/2 inch x .305 inch.
I wouldn't recommend running chains on wrong size sprockets. If to tight the chain could rub and overheat and break.
Hope this helps. Alan G.

[Group Leader]

Hi Alan. I have a 1937 BSA Annual which states that the front chain size is 1/2 inch x .305 inch. the rear chain is also  1/2 inch x .305 inch.
I wouldn't recommend running chains on wrong size sprockets. If to tight the chain could rub and overheat and break.
Hope this helps. Alan G.

Me thinks this landed on the wrong thread! 

Alan

[Group Leader]

Hi Alan,
            Yes as a sealant, its tried and tested as a high temperature face to face jointing solution. Many engineers still put the graphite on gaskets, to fill the grooves, keep them supple and as a realease agent.

https://my.rs-online.com/web/p/pipe-thread-sealants/0692700/

Hermetite (Red) was the sealant of choice in the olden days, I remember spending hours cleaning mating faces and reapplying the same. I dont think you can get the original Hermetite but I believe Hylotyte could be the substitute. There are better choices on the market now, again use what you feel comfortable with.

Thanks, I remember using Red Hermetite years ago (probably on an old Mini).    Went on well, was a PITA to get off later I seem to remember   

I'll try and track down some of that graphite jointing compound and give that a go.

Thanks,

Alan

[Group Leader]

So, Steamseal tracked down, head joint lapped, engine re-assembled using Steamseal on the head and Wellseal elswhere and tested.   Seems to have worked very nicely so many thanks for the advice.

I've done about 150 miles on the little B21 and I have to say I rather like it, even if the ride is rather bouncy thanks to the rigid back end and the sprung saddle!

https://youtu.be/I66WoldxITw

Alan