Sludge trap

[geo3]

Hi everyone,
I am currently rebuilding a 1957 BSA A10 engine and have the crankshaft completely stripped down to clean out the sludge trap.
It is a genuine small journal (SJ) crankshaft featuring the 6-bolt axial flywheel layout. I have removed the two identical 5/8" flat end plugs (Part No. 65-0615) from either side of the crank webs.
Before I begin aggressively scraping out the fossilised sludge and running a brush through it, I want to clarify a detail about the internal architecture. Is the internal oilway tunnel drilled completely straight-through as a uniform 5/8" parallel bore from end-to-end, or is there an intentional factory-machined step or shoulder inside?
I can feel a distinct lip/restriction inside the cavity right now, but I want to confirm if this is simply decades of rock-hard, centripetal-packed sludge forming a ridge around the rod oil-feed holes, or if it is an actual physical feature of the crank forging.
Also, when I reassemble with new hex-head plugs and Loctite 243, is it absolutely critical to keep them perfectly flush with the outer face of the crank web to prevent them from traveling too deep and blocking the oil transfer holes?
Any insights or tips on safely shifting a stubborn internal sludge ridge on these specific 6-bolt SJ cranks would be greatly appreciated!
Thanks in advance,

[berger]

don't worry you won't hurt it, there are two bore sizes yes to keep the flow of oil good to the drive side, don't take the flywheel bolts out they are not to be obtained they sell you crap set screws . use a vernier to find the depth of the oil feed hole from the crank web and measure your new plugs  when they are fully home , i ended up filing  a groove in the plug when it was fully home to make sure the big ends had full flow of oil.

[geo3]

thanks for your reply and interesting read particularly the groove comment -just to clarify the two bore sizes where can I find more info on this? I have scrolled for days trying but can't find anything ? Any advice appreciated.

[JulianS]

Service sheet 202 shows a cutaway with the small journal crank. You can just about see the smaller drilling.

[Swarfcut]

 The small journal crank does not have a true "Sludge Trap"..... this is found on the later big journal crank with the three radial bolts locating the flywheel.
  No, the hole is not the same size bore across this earlier crank.
 The cavities each side revealed when the plugs are removed is where the majority of sludge collects. These are connected by a relatively narrow oilway running along the crank axis, the reduction in diameter being what you can feel. Explore with a small drill bit for starters.

 Usual practice is to replace the plugs flush with the web face, but some aftermarket plugs are too thick and will obstruct the oilway running from the timing side journal up to the big end when tightened into place. This is a problem bergs found, fortunately avoiding another disaster with a bit of clever fettling. Aim for the plug fitted flush and that oil way clear. some examples may need a fair bit of material removing from the back face of the plug.

 Plenty on the Forum about cranks, Service Sheet 207 gives regrind detail.

Swarfy

[geo3]

thanks for the info - the sludge trap was completely blocked up particularly on the T/S with not sludge but metal fused solid mass - unable to shift with methods previously mentioned so to avoid damage to crank I was hoping to find detailed info on diameters and depth etc ?