Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board Where does sludge in the sludge trap come from?om

If from new the oil was changed as the book said, the sludge trap would not fill
before the normal engine strip at 25-30k miles. Most of the time either blokes
did not change the oil and just topped it up or didn't bother doing the job when .
the engine overhaul was performed.
The centrifugal filter is an excellent device although inconvenient to service.

Thanks all for the Whitworth guidance! I ordered a set of 1/2" drive Whitworth sockets, 3/16 W through 5/8 W; eight sockets in all. They were on Ebay U.S. from a company named AB Tools in Stoke, UK. $30 and change with free shipping; how they will ever ship and sell at that price is beyond me. The sockets were chromium-vanadium and made in I don't know where. Taiwan has a lifetime of experience making tools and my Taiwan sockets hold up OK. Just crushed a 22 mm black oxide deep well Taiwan a few days back standing on the trusty 30" breaker bar trying to loosen my Ford van rear wheel bolts. The PA state inspection station failed the rear brakes and air gunned the wheel nuts back on to over 300 ft-lb estimated. Lucked out and had another abused off brand beat up 22 mm deep well to finish.

Here's a pick of the crank hole as the trap cap was pulled. Yup, the flywheel bolt tit is there.


Concluded that the trap will have to stay in place, a fait accompli.

If you are filtering on the pump suction line successfully, its not due to the filter manufacturer's design for a pump suction side application.

"Concluded that the trap will have to stay in place, a fait accompli."

Do you mean that you won't be removing it to clean it out? If so, why not?

"If you are filtering on the pump suction line successfully, its not due to the filter manufacturer's design for a pump suction side application."

No comprende Bill. The only filtering that should be added is on the return side. Maybe or maybe not mentioned above, one good feature about the sludge trap is that it does not restrict feed side oil flow, as would a filter. Hey, is that the '71 FBS engine?

One nice thing about tools for motorcycles is that they don't incur the amount of stress that automobiles sometimes impose. So even reasonably good quality wrenches tend to last "forever".

Hey, Bustednuk,

Better check (and maybe replace) those wheel studs. There are specific torque ratings for wheel studs, and 300 ft. pounds isn't it.

Some "cowboy mechanic" over-torqued those on one of my trucks sometime in it's former life, and the first time I did a tire rotation, several of them broke.
I decided to punch all of them out and pull in new ones.

The last thing I wanted was to have more of them break if I had to change a tire alongside the road.

If your not going to remove the trap, you might as well just put the plug back in and run it as it stands. If you try and wash it out and not remove the trap, you'll just create a fine grinding paste which will screw your engine up very quickly.

If the bolt wont go, apply some heat. It should be hot enough to make spit sizzle. If your worried about the bolt, sets of the correct spec are available. It might seem over kill but having a heavy flywheel that spins round at 7000 revs is enough to make me want to be sure it stays attached.

I agree; that bolt is not likely to break. Clamp the flywheel in a vise and get some leverage on the wrench. I would not be afraid to use a breaker bar.

Yeah you don't want to push any grit into the exit holes to the journals.

Applying heat to the side of the flywheel adjacent to the threaded bolt hole IS A MUST. These bolts are supposed to be installed using Red Loctite.

They are hardened steel and quite brittle. You can break them. Especially if you don't release the Loctite with heat (and the surfaces were clean when assembled and it worked like it is supposed to). Old Loctite wasn't tollerant of oil covered surfaces) THEY DO BREAK!

Breaking them is a confounded nuisance. You will not be able to easily remove broken part from the crankshaft. It will also be difficult, if not imposible, to remove the flywheel from the crankshaft to make the removal easier. Best way is to have it removed by EDM.

Where does all of the sludge come from? Carbon created by combustion by-passing the rings. If your piston and head is covered with carbon chances are your sludge tube contains a lot of this carbon also. The carbon is so small that oil filters do little to keep it out of the sludge tube. Oil filters are good, but routine oil changes are a must in one of these engines.

The bolt on the flywheel will be removed, and the sludge tube removed for cleaning and inspection The crank oil lines. will be cleaned and flushed. The flywheel balanced, yada yada. Hopefully, the AB Tool Company in Stoke, UK has my Whitworth socket set shipped by now by rocket express.

Mark, lets talk.
Me: "If you are filtering on the pump suction line successfully, its not due to the filter manufacturer's design for a pump suction side application." -By that I meant to comment that oil filters are designed to be pressure fed.

You "No comprende Bill. The only filtering that should be added is on the return side. Maybe or maybe not mentioned above, one good feature about the sludge trap is that it does not restrict feed side oil flow, as would a filter. Hey, is that the '71 FBS engine?"
- I don't believe knowledgeable people would have any objection about adding a filter to the return side. But what about the supply side to the pump? Unconventional, yes. A manufacturing or engineering acceptance signature, no. Informal thought about why this might be done and why it can work, yes. Britbike members successfully filtering on the suction side of the pump, yes.

Also, Mark, yes its the "71 FBS. A diamond in the rough basket case since the crank mains are nice as well as the rods. The TS bush is also good. I have new pistons, rings and rod bearings. Hey, I have a ColorTune you can have. Let me know. Your motor goes in my "71 FBS:



Part of the reason I started the thread was to elicit thoughts about oil filtration since IMHO the factory screens are inadequate and the trap is a misapplication.

Irish Swede,
We took this photo of my 160 pounds bouncing with a cheater bar to get the wheel lugs off the rear of my Ford van in case there was damage to tell the judge if need be. NTB did this once to my daughter's Benz which had alloy wheel studs recessed in the wheels It was towed to my place and had to grind them off. NTB settled.

I don’t know much about BSAs but have run a Charlie’s filter in a triumph for decades.

However early OIF bikes had a different oil system from later and a Charlie’s won’t fit early frames without work.
Then you have the choice of a Trident style or Norton on the return

A filter on the return line isn’t on the suction side, it’s on the pressure side
Of the return feed. There is a difference. Your not sucking through the filter your pushing oil through it, as the filter fills it
Pushes the clean oil back to the tank… it is under pressure.



Oh no I didn’t mean that, my fault I should have elaborated. All bolts have a specific torque calculation, at 5/16” a rough guide for me Would be 25ft/lb. At that point I would say “it won’t go” (that’s my personal preference) I’ve had flywheel bolts undo with that level of effort, most likely they have been out before in that case.

Again, call me over cautious but I replace these bolts each time
I do an engine. If it’s my engine I’ll most likely be revving the nuts off it, if
It’s someone else’s then I don’t want it to bite me in my ass so I go with caution.

Breaking a bolt; If you have access to a welder then welding a nut onto a snapped stud will heat the outer part sufficiently and give the chance to get a socket on the hex to wind it out.

Breaker bars should be limited to undoing axel nuts/wheel nuts and an impact wrench is ideal for clutch centre and primary drive side crank nuts (or winding things off once they are not under load).

As said above, warm the crank centre with a gas torch if they are solid in there.
You must get the tube out to clean the cavity properly. The job is not a 5 minute one.

Sorry Bill and everyone else for suggesting going King Kong on the flywheel bolts. The bolts on both of my A65s came loose without using heat; maybe they were apart before and the PO didn't use Loctite, or maybe I was just lucky. I dread the thought of having encouraged anyone to break a bolt, especially one of those!

The 71 WSM has 45 lb.ft. as the torque on the flywheel bolts, 0.38 ( 3/8) B.S.C. 26 tpi.
Not 25 lb.ft., not 5/16".

You guys are lucky I keep the WSM by the PC.

Reprints of the Factory WSm are on e bay and worth every penny/cent. Theres info in there you wont find anywhere else.

A norton type cartridge filter can be mounted using a U clamp to the lower frame spine section, off set to the TS so it clears the back tyre, plumb it into the return line. As well as doing a fine job keeping the oil clean it also adds useful oil volume, never a bad thing.

In the UK Paul Goff sells a suitable kit, heres a link, http://www.norbsa02.freeuk.com/goffyoil.htm

should be
fairly easy to fit an aftermarket filter kit " Charley's type" in place of the
inlet oil screen , even on an early 71 frame , like yours that has the engine oil feed
from that small tube near the bottom on the oil reservoir tube .
( especially at this stage of the game , where the engine is out )

This real filter will give you filtered oil on the inlet side , with a proven setup ,
that only alittle of a hassle to change when it comes time to change .

to do it ,
the small oil tube inside the frame gets sawed-off and the outside of the tube gets capped off .
Conversion is complete
the after market filter will now fit more deeply inside where the
Original shorter strainer , with top hole , fit ...
and new oil feed is taken off the bottom of the bolt-on bottom-plate filter- assembly

(oil tube , to be disabled . can be seen here , timing side , bottom of oil Reservoir tube)

I used 5/16" as an example (intentionally pointing out that you don't want to use the power of Thor to undo the bolts), I didn't have a set of bolts or a manual to hand for propper sizes and torque.


It does help a lot. I would usually refer to the WSM etc collection on my laptop, however the wifi card has failed and I haven't had the time to fix it.



My version of this: its still in prototype status, I don't really like a 3" U clamp going around the frame, but will fabricate a "nicer" bracket and utilise the rear footrest mount as additional support. Though so far it seems to hold up ok.

Whilst the engine is out of the frame I'd look at fixing the centre stand so the bike stands up propperly then address the front brake adjustment.

You mean something like this?

If you do not want to make the 90 degree bends with the hoses the bracket could be extended and rotate the filter 90 degrees similar to your steel bar and U-clamp.

quinten, I enjoy how you call the Charley filter "a real filter". LOL. I really want a real filter, but am naturally reluctant to place a hack filter setup on the suction side of the oil pump without others having tested the waters so to speak. And apparently there are plenty of guys running this setup.

Since I'm such a chicken maybe I should just put a return line oil filter in. But that leaves me wondering about the OIF oil space in the frame. Over decades of dead storage won't that frame have rust chunks way up in the frame? For that matter wouldn't a well maintained machine have that same high space in the frame where this same rust would form?. In either case as long as the rust chunk is filtered by the mesh then your good to go. Better to have a "real filter" at the bottom of the OIF oil storage tube or similar.

On the B.S.C. flywheel bolts with the 3/8" bolt and the 5/16 W hexhead (if I got that right) and might be still Red loctited into the crank, thanks all for the discussion. Doubtful I would bust this, but who knows. My Whitworth socket set ordered from AB Tools in Stoke, UK is near the Gatwick airport with Langley Royal Mail. So, no rocket express delivery, but that's cool. Looking closer at the bolts situation seems that the crank and not the flywheel might be the ultimate spot to heat if forced to that situation since the threads are in the crank with the flywheel simply an unthreaded hole.. Hopefully, it just comes out nice and easy, but if not then heating the hexhead to "spit sizzle" (LOL)would be the first choice to give it some torque. John Healey's warning that if the bolt breaks you may have no clearance to do much of anything and the flywheel may be stuck there is easy for me to envision. EDM (Electrical Discharge Machining) sounds like a chunk of change. Might as well shop for a crank/flywheel!!!

Gavin, searched Ebay US and UK for WSM and only got a BSA rifle scope and ladies lingerie. What does WSM stand for? Might help the search. Still really a BSA nimrod here. Lucky to have the guidance fer sure!!!

Come to think of it, Allen, can I change my user name to Nimrod? It has a nice Brit resonance and gives other more expert members an idea who they may be communicating with or miscommunicating with as the case may be. Plain Dumbass is too pejorative.

WSM =Work Shop manual. Link to e bay seller. https://www.ebay.co.uk/itm/284227417618?hash=item422d463612:g:7U0AAOSwexddTIw8

or https://lmgtfy.app/#gsc.tab=0&gsc.q=1971%20BSA%20A65%20work%20shop%20manual

Burtons Bike Bits in the UK stock them. https://www.britishbikebits.com/workshop-manual-bsa-a65-1971-72

Although the haynes manual is better than no manual, the 71 factory manual has useful stuff like wiring diagrams ans chassis info that haynes do not cover.

To clean your oil spine, fill to the top with a citric acid solution, use bottle brushes. A power washer might be a good thing for a final clean.
The WSM tells you how to pressure test it , watch for cracks around the rear motor mounts, do all this before thinking about paint. My frame was cracked at the top weld of the timing side motor mount, fixed it 40 years ago and its been OK since.
In service the oil spine does not rust internally, when the motor runs the top air space is full of oil mist. Thats why the filler cap is where it is , originally it was meant to be up near the headstock ,during development it was moved to the current location to allow space for expansion and oil mist. I have on occasions slightly overfilled mine, result , mess from the frame breather. Incidentally the WSM states the motor oil volume is 5 pints, and it would be if the filler was in the original position, as it is the frame barely holds 3 pints with the lowered filler cap, one of the reasons why adding an external filter is a good thing , it adds an extra 1/2 pint or so of oil to the system.
re the Charlies filter on the suction side, it is a neat idea, but a major PIA to change compared with the easy access to a cartridge filter in the return line.
D Madigans mount looks like the answer to the maidens prayer . I have something similar that was made by Anglo Bike many moons ago, sadly no longer available. You can pad the U clamp with rubber strips to prevent paint damage.

FWIW, Chilton's "BSA Repair and Tune-Up Guide" also lists the flywheel bolts torque for twins as 45 lb.ft." (Kind of irrelevant since that book is long out of print.)

Bill, 5/16 W is the correct wrench size for those 3/8" bolts, also 3/8 BS. (Whitworth bolts had one size-larger head size for a given bolt diameter, so those are not actually Whitworth bolts.)

"FWIW, Chilton's "BSA Repair and Tune-Up Guide" also lists the flywheel bolts torque for twins as 45 lb.ft." (Kind of irrelevant since that book is long out of print.)

Bill, 5/16 W is the correct wrench size for those 3/8" bolts, also 3/8 BS. (Whitworth bolts had one size-larger head size for a given bolt diameter, so those are not actually Whitworth bolts.)"
- by Mark

Thanks Mark and all the other guys too!

My W socket set is still with Royal Mail. No problemo.

"Now let's all go and have a beer"- Alan G