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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: Sticklebrick on April 30, 2026, 05:15:46 PM
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On my 1985 K100 RS, is it possible to remove and replace the lower crank case with the engine still in the frame?
I have stripped the bike from the back to the gearbox and I'm now at the point of beginning to remove the clutch.
According to the wizard AI the lower crankcase cannot be removed without first removing the engine from the frame. Is this correct ?
I have the bike on its side and have the opportunity to remove the clutch and then the lower crankcase however I am worried about "splitting the engine" as the AI says and having to put it back together again "in a balanced manner".
All of this work is necessary as a result of a bolt on the timing cover breaking inside, and falling into the sump... at least this is what I think happened. When I started the bike after replacing the cover gasket there was an almighty bang followed by an oil leak of equal and continuous pressure around the edge of the lower crankcase where it mates with the upper part of the engine.
I have a replacement lower crankcase housing, although it may just be the seal that has gone as a result of impact from the sheared cover bolt, from what I have read in my searches on here and elsewhere, the crankcase could be cracked so I have the replacement lower crankcase here in case it is.
This is the first time I have done this in 25 years of owning K bikes.
So to sum up my question ... as I need to remove the lower crankcase to inspect, do I need to remove the engine to do this or can it be done with the bike supported upright or on its side?
Any advice gratefully received.
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When I started the bike after replacing the cover gasket there was an almighty bang followed by an oil leak of equal and continuous pressure around the edge of the lower crankcase where it mates with the upper part of the engine.
So to sum up my question ... as I need to remove the lower crankcase to inspect, do I need to remove the engine to do this or can it be done with the bike supported upright or on its side?
That sounds like a tall order, but you're in a position to try it and update the forum. But you might not have to remove the lower crankcase for inspection. You might find the problem by removing the crank cover (or the cam cover, depending on which bolt broke) or the base plate of the sump.
Good luck, it's not sounding very good, an almighty bang and leak. You might be lucky, you might not need to dismantle it, hopefully it's something simple.
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What work—besides replacing the cover gasket—had you completed before this happened?
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Excellent question... I removed the cover to replace the weeping gasket but can't think of any other work I had done on the engine. I over-tightened that cover bolt but didn't hear anything drop, I just heard the bang. Should have used a torque wrench
Be advised everyone... those bolts snap off quite quietly and can cause disaster.
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Thanks for the reply. Are you referring to the Hall sensor cover gasket? It could be too early to diagnose a broken screw shaft to be at fault, given your description of the timeline between starting and the banging. A short screw shaft fallen to the floor of the sump probably would stay on the floor, especially when the motorcycle isn't being ridden. Like daveson implies, it would be easier to remove just the crankcase cover and sump for a diagnosis.
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Sorry I should have made it clear, it was the right hand crankcase cover that I removed to replace the gasket. It was the top left pesky bolt on that cover, when I remove the sump cover I hope I'll find it!
My theory is it was whipped up by the flywheel and whacked the side of the crankcase housing, causing a shockwave that broke the gasket seal and maybe worse. But any damage done should be confined to the lower crankcase housing (which I have a replacement for).
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Timing cover = Crankcase cover. Got it! :laughing4-giggles:
However likely that might be a widely accept translation, I still can't visualize how a fastener with 8Nm of torque requirement mounted through a rubber bushing can be broken—unless it was a victim of 'roid-rage—then fall into the oil sump of the engine and follow up by causing an ominous bang, but I will admit I don't have much imagination. Others are sure to chime in with clarification. Please keep us in the loop and try to provide photos as you go.
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Are we talking about the crankcase/crankshaft cover bolts?
If I remember correctly they go into a blind hole in the crankcase and no way it should end up inside the engine.
The engine serial number is stamped into the lower crankcase/oil sump and is a matched set with the upper crankcase and may not match up correctly.
Frank