B25: Refitting the head and barrel. Oil filter swap and sump

Having restored all the threads on these studs 26 tpi BSF and BSC on the 1/4 inch and 26, 22 tpi on the 5/16 I fitted all studs back into the head. I have decided to use the second head as this one hasn't been skimmed at all and so has more life ahead of it.

Steel studs going into ally should (I believe)  always be lubricated- either with oil, or in this case Loctite threadseal 2701. I applied this to all threads and then screwed the BSF threaded ends into the head. I used the stud remover to tighten all to firm hand tightness, they will grip through the upward tug of the nuts when these are tightened rather than the twist of the steel stud in the head and so studs don't need a lot of torque into the head itself.

I found that I was lacking one of the longest 1/4 inch studs and made a spare one using 1/4 inch stainless steel rod.- Note from experience - don't try threading stainless unless you have HSS taps/dies! I simply blunted the carbon steel cheapo versions that I had and needed to order  the real-deal kit.

Head steady in place- two washers underneath each side to act as spacers

I ended up making three new studs but the rocker box went on fine after that, tightening small nuts to 7 and larger ones to 10 ftlb respectively. I had been concerned about the state of the cylinder base gasket and was also worried that taking the head off might have disturbed it anyway so I decided to renew it as well.

The barrel pulled off easily, here using wood strips to stop the piston flapping about and getting damaged.

Bottom of barrel- signs of base gasket having leaked- I recall it was a bit oily about here so definitely a good idea to pull the barrel. Bore looks good- some original honing visible and no sign of a ridge at the top.

Bottom of barrel cleaned...

... and the top

Barrel cleaned up nicely with brass wire brush on the Dremmel, careful to get the burnt on carbon off the top cylinder spigot and around the liner base

Given the evidence of leakage I decided to take a leaf out of the Lotus book and use a gasket sealant - in this case Wellseal. Lotus use this on all gaskets and I think its a good idea here. If its good enough for Mr Chapman its got to be way good enough for the likes of me! Paint it on to the barrel and then apply the gasket

Gasket bedded into Wellseal

Then paint the other side of the gasket...

... and check that the oil holes are not obstructed.

It was at this point that the best laid plans etc etc -anyway they came unstuck: In order to install the barrel I needed to compress the rings. If you are gifted with a rock hard grip and insensitive calloused fingertips you can probably do this by hand- I wanted to use a ring compressor. I have the Laser 5066 Universal motorcycle piston ring compressor kit which should cover this piston size... and it does... but unfortunately the position of the studs means that the clamp cant be fitted!!! Much swearing and aborted attempts later (all the while with my Wellseal going off) there was no alternative but to remove the front stud to gain access and refit it later.

Front stud removed

 The ring compressor then fitted a treat BUT... the stud is wider at its base than than at the top and cannot be inserted downwards through the barrel so fit the compressor and insert the stud as you lower the barrel down...

Compressor in place- just need to...

 Feed the stud in (coarse thread down) from the bottom of the barrel and slip it into alignment with the hole in the crankcase before...

 Lowering the barrel- with the compressor in place its now a doddle

 Remove compressor, lower fully and lastly tighten the stud back down into the crankcase (oiled thread)

Push rods on tappets and angle for their respective rockers.

 Fit push rods into the tappets - intake is at the front- don't mix them up. Apparently the exhaust should have a red top- mine was marked but poorly. Fit a new head gasket - I think these can be reused- there seem to be a lot of used ones on Ebay anyway, but I think they would need annealing. I just bought a new engine set so I would have everything I might need.
 Lower on the head- you need to fit this at first positioned on top of the push rods but facing out to the left of the bike. Then you can swivel it back around the push rods and line it up on the studs. Note new head gasket in place.

 Check the rockers engage on the pushrods as the head comes down- here the inlet...

...and here the exhaust. You will need some form of hook tool to position the push rods as the head comes down, I used a pipe cleaner. This job would be easier with three hands and slender fingers but it can be done. You can get some movement on the rockers by depressing them with a finger through the rocker cap and then lowering them back onto the top of the push rods before the head is fully down- might be best to make a wooden spacer about 1-2 cms thick to support the head while the rockers and push rods are in this "sweet zone" where there is just sufficient vertical room to lift the rockers enough to let you move the push rods underneath, but tight enough that lowering the rocker then engages the rod top and holds it in place while you do the other, and of course lastly remove the spacer and lower the head.

BUT- all this fiddling about can cause the base of the push rods to jump out of the tappet/cam follower at the bottom- and as this is now invisible the only way to check is to fit the head loosely hand tight is good enough  (don't need to torque down) and rotate the motor to check both valves operate and in the expected sequence. On my first attempt I had somehow dislodged the inlet so it is worth checking.

Finally torque down the head- as I suspected during dis-assembly, it is impossible to torque the two 5/15 nuts on the studs recessed below the rocker box... even with a crowfoot spanner. I torqued down what I could and just made sure these seemed to be "as tight"

You can make a compound torque wrench like this using a socket adapter to attach a combination spanner to the torque wrench and the C end to slip onto the nut- no good for tightening really but just to check final torque. I still think this idea has a lot going for it but as the torque is now measured some 15 cm from the actual nut head I suspect the reading I'm looking for would differ- the maths of this defeated me so I just went for "tight".
Before I could finish the bike, I needed to sort out the leaking tank. This has a filter socket combined with a banjo union at its base. The banjo is sealed by two washers - I had expected copper but they are specified as "fibre" in the parts list (The Starfire shown)

Banjo washers are shown with different numbers but they have the identical BSA part number so in fact are the same.

 The washers should be the same, but in my case there were two different washers fitted of different thicknesses.

Note different washers and hole in filter gauze

 There is also a hole in the filter at the base- this would let any crud straight through so the filter will need changing. It is possible just to get the gauze filter (RGM Norton have one that should fit) but this is about half the cost of a new unit and still needs soldering on in a neat and tight fashion- it seems easier just to replace the lot.

Thread in base of oil tank

...and here is the rub! The filter unit can only screw into the base of the tank so far- eventually it screws up hard against the end of the threads. At this point the banjo section is left protruding but the washers have to seal tight before you run out of thread- and in my case they hadn't. What this means is that the thickness of the washers is critical- anything too thin will never be able to seal - and this seems to be my problem.

I ordered a new filter plug and two new fibre washers- however I also found a metal replacement washer pair on offer which are apparently reusable with care so I ordered two of those as well.

I

Nub of the problem old washer right- thinner than new (left) either from new or through over-compression. New washers were 2.6mm, the old ones 1.4 and so that's 2.4 mm of thread saved on the filter plug fitting

New filter plug in position with fibre washers.

The "metal washers" turned out to be two large Dowty washers with a gratifyingly thick rim. I havent fitted these as yet as the fibre ones arrived first but I may do so later.

It seemed churlish to have come this far and not checked the sump so I undid the 4 x 3/16 WW bolts holding it and allowed the oil to drain into a container.

sump retained by 4 x 3/16 bolts. Bit nasty and a couple of gouges.

Sump removed, lots of gunk trapped around the edge of the gauze and gasket 

Remove gasket - note crud around gauze and...

Clean up the filter mesh. I used my sonicating bath and it loosened the crud very nicely.

 The sump is obviously on the bottom of the motor and so the plate and the bolts are a prime candidates to collect grit- and I found quite a lot worked into the threads of both bolts and bolt holes. This will wear them in time so I cleaned all the bolts and washers in the sonicator and cleaned out the threaded holes in the crankcase with carb cleaner spray and a pipe cleaner

The underside of the plate had obviously been scraped at some point resulting in some grooves and ridges. I filed these as smooth as I could get them and then treated the sump plate to a new coat of VHT alloy effect paint. I refitted it with a fresh gasket, using copaslip on the bolts.

The rest of the reassembly went gratifyingly well: I used copper RTV silicone gasket to help seal the exhaust into the head. Even the problematic right footrest turned out to be no problem- it was a taper fit not a splined fit and after cleaning both tapers and the bolts it reassembled without play.