oil filters and sludge traps

[DAVE BRADY]

Oil filters and sludge traps.

Are both necessary?

The sludge traps built in to the cranks of BSAs are designed to take sludge out of the oil.  They work but they need to be cleaned out regularly.  How many engines have met a premature death or need for a rebuild due to the sludge trap being at least restricted or at worst blocked?  The disposable cartridge filter that many of us now fit to our BSAs must be at least as good as a sludge trap but more likely very much better.
Combine this with a detergent oil and our engines are kept much cleaner than BSA could ever have imagined.
So would it be a mistake to not bother fitting the sludge trap tube, especially if it means buying a new one?

Dave.

[chaz]

well, most modern bikes dont use the sludge traps but do use filters. the majority of servicing, I would say 999/1000 or even higher 9999/10000 only ever change the canister filter. owners probably dont know there is also a filter screen in the sump, which obviously requires removing the sump and a new gasket. on the other hand, having pulled apart a few British motors the sludge traps are often full of solid carbon.
regarding the detergent,I would go with oil without detergent as it can clean too much.
how many times do you strip the sludge trap out? once each rebuild, so why worry. the thought of laying under the bike trying to undo the sludge trap and then peening it back tight at every service would fill me with fear as to doing it up tight enough, I prefer the hex head not the slotted sludge plugs.

[DAVE BRADY]

Hi,

Cleaning the sludge trap at each rebuild is essential and from what I have read over the years even some 'professionals' omit this vital task.  Although there are many variables, when is a rebuild considered necessary?  High mileage, rattly engine, poor performance, high oil consumption.....  I suppose high mileage contributes to the rest. 
Would using detergent oil, mono or multigrade, by keeping the engine cleaner and being filtered extend the life of an engine?  What is the average life expectancy of a reasonable quality rebuild?

Dave.

[DAVE BRADY]

The image attached is of a small journal crank that had covered about 50,000 miles.  The small journal did not have a tube so the sludge just accumulated in the oil way.  The sludge in the foreground is what accumulated just behind the plug where there is a bit of a cavity but some has been deposited along the oil gallery.  This engine was run from rebuild with a filter on the return to the tank and using a full detergent 20/50 oil.  So even though using the ideal way to keep an engine clean sludge will build up.  I wonder what it would have been like with no filter and a non-detergent oil???  Incidentally the engine, with an end feed conversion, was stripped to replace a worn out cam.  The big ends were perfect and left undisturbed and the engine has now covered over 100,000 miles.

Dave.

[ChrisG]

I always retain the sludge trap and use a cartridge filter. Yes, the sludge trap will fill up again but the rate should be much reduced as the big bits are taken out by the cartridge filter (and the bigger bits by the gauze in the sump). I would not take the engine apart just to clean out the sludge trap but always clean it if the engine has to come apart.

I have recently cleaned out the sludge trap and fitted a cartridge filter to my A50. Bearing in mind the mileage I expect to do on it, say an average of 2000 per year, I doubt I will need to split the cases for at least 10 years and only then if something goes awry. However, if I do, I will measure how much of a build up there is in the sludge trap and let everyone know. Don't hold your breath though.

Re detergent oils, I'm just going to carry on using 20/50 as BSA intended and I wont be losing sleep over whether it can cause problems etc. I will just enjoy carefree rides on the bike!!