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Dools, don't be overly concerned about the bypass spring having little tension.
We discussed this issue at depth on the forum and the consensus was that differential pressure was the reason the ball would stay in place with a low spring pressure, as long as the oil filter was in good condition.
The spring, ball and retaining plug are all available through Southbank BMW, quite cheap.
The best thing to do is check the ball is in place at every filter change.

My brother found his spring broken about 6 months ago. Although he reckons he accounted for all the pieces, he is now having oil pressure issues!
It only takes a piece of spring 2-3mm long to do the damage.

I'd like to know where a bottom end could be got for free. Not in this neck of the woods.
It would need to be in pieces anyways to know it was in good repair.

It is a good idea to pull the gallery plugs and be sure the gallerys are clear, given your circumstances. You may need some heat to get the little bastards out. (3)
I didn't use loctite on my plugs, but others may insist on using it.

If you have had chunks of powder coating or paint going through, I would take a look for oil pump cavity/housing damage. If it is really trashed, a different bottom end might be the best way to go.
I just finished a crank replacement and looked at five of them before finding a really nice one. Many people selling them will tell you they are good, without really knowing. The problem with two of those I looked at, was some well intended person polished out the roundness trying to remove scratches.

Thanks guys! Yes I did consider a cheap complete bottom end, but I love the bike and really want to have a crack at rebuilding it myself. Besides, then I'll know that the jobs right without potentiallly inheriting someone elses headaches!! I'll replace the crakcase plugs with loctite after inspection and cleaning, The oil pump housing is a little 'marked' but it looks like machining marks to me and the oil pump rotor appears to have side clearance within spec!! Jeff I'll go with the spring/detent as is but check it often after rebuild!! Is it worthwhlie replacing the rods? I'll check /measure the big ends for ovality (hey,there was some serious thashing about and clunking going on in there!!) but what's the current thinking!!? Cheers, Hools.

Perhaps get the rods checked for twist, they can be straightened a little if need be.
Get 'em weight balanced too while yer at it.
With new big end shells, you could check for fit/ovalness with plastigauge. Repco sells it I think. Or let an engine reconditioner check it for you.
I didn't worry with my crank, just new bearings all round and away we went.
I'm still wenting 2 years and lots of rpm later.
If all the oil pump rotor clearances are all good, good!
They pump more oil than is needed anyway.

Duane Ausherman wrote:Why fix it? You can get a good used lower end for cheap/nothing.

Major Softie wrote:That's the most economically practical solution, but some people really care about maintaining "matching numbers." For them, replacing the whole lower end is an absolute last resort.

For others, rebuilding will be the only recourse to guarantee the quality of an engine.
For them, disassembly, inspection, and rebuilding as necessary
would also be the proper course of action for that "good used lower end for cheap" as well –
Untouched, it's condition can only be an unknown quantity and an unsubstantiated risk.

vanzen@rockerboxer.com wrote:For others, rebuilding will be the only recourse to guarantee the quality of an engine.
For them, disassembly, inspection, and rebuilding as necessary
would also be the proper course of action for that "good used lower end for cheap" as well –
Untouched, it's condition can only be an unknown quantity and an unsubstantiated risk.

Yep, also a good point.