Disassembling Crankshaft?

Given all of the input here, perhaps I should go from the "leave well enough alone" mentality to the "better safe than sorry" mindset. I'll dismantle the crank, clean the sludge trap and have the main bearing journals magna fluxed.
 
Dan1950 said:
Given all of the input here, perhaps I should go from the "leave well enough alone" mentality to the "better safe than sorry" mindset. I'll dismantle the crank, clean the sludge trap and have the main bearing journals magna fluxed.
Click to expand...
Money and time well spent 👍
 
Dan1950 said:
Given all of the input here, perhaps I should go from the "leave well enough alone" mentality to the "better safe than sorry" mindset. I'll dismantle the crank, clean the sludge trap and have the main bearing journals magna fluxed.
Click to expand...
Yes. Sorry to rain on your parade but I was very surprised and disappointed when I found the crack in my crankshaft. I was sure it was going to be OK and it looked in perfect shape on the original grind.
 
70 crank separated to find a buildup of very hard grey matter/sludge to remove first with a chisel then solvent final outdoors in a pan .
73 828 separated to find no sludge whatsoever . Solvent clean only .
75 828 separated to find no sludge . Solvent clean only .
All 3 bikes had a layer of black thick oil goo in bottom of oil tanks .
 
Dan1950 said:
Given all of the input here, perhaps I should go from the "leave well enough alone" mentality to the "better safe than sorry" mindset. I'll dismantle the crank, clean the sludge trap and have the main bearing journals magna fluxed.
Click to expand...
One other thing to check. The engine I'm working on right now had 3 of the four journal holes properly drilled and chamfered. The fourth hole was not chamfered and the drill was not run all the way in - the inside of the hole had ragged metal like the tip of the drill just broke through. Not positive how important the chamfer is, but I'm sure it would have been bad if those metal flakes had come lose; and, the hole was only partly open so the shells were not getting all the oil they should.
 
Torontonian said:
70 crank separated to find a buildup of very hard grey matter/sludge to remove first with a chisel then solvent final outdoors in a pan .
73 828 separated to find no sludge whatsoever . Solvent clean only .
75 828 separated to find no sludge . Solvent clean only .
All 3 bikes had a layer of black thick oil goo in bottom of oil tanks .
Click to expand...

My error in thinking the sludge could be flushed out was in thinking it was like the gunk we used to find in the sump before the advent of detergent oils. I had no idea a chisel is needed.

Lots of good input here from those in the know, proving the value of this Forum.

Slick
 
My present in pieces crank was so filled with hard gunk that it partially blocked oil to drive side bearing. LH side so worn that it needed grinding. RH side within std tolerances. So a .010 grind done on both sides. Will put it together next week.
 
Mike40M said:
My present in pieces crank was so filled with hard gunk that it partially blocked oil to drive side bearing. LH side so worn that it needed grinding. RH side within std tolerances. So a .010 grind done on both sides. Will put it together next week.
Click to expand...


Is your bike an earlier unfiltered model ? The later filtered ones seem to be having better luck on sludgetrap buildup.
 
Last edited by a moderator:
If you do decide to disassemble... don't listen to those that tell you the "tab" washers are unnecessary.
Their function is not to lock the nuts as some believe (loctite and punching the threads do that) but rather to ensure the dowels don't fall out.
A dowel might be initially tight but during the life of the crank and numerous heat cycles could possible work loose.
Do not omit these items.
 
Fast Eddie said:
Yes, IF the bike has always been run with a good clean filter, and IF it has always been run with modern high detergent oils, the crank will likely be as clean as a whistle inside.

Trouble is, you simply do not know unless you look.
Click to expand...
And if you you know the bikes history IE it's not unusual for the bottom mount on the oil tank to break,so the oil tank could have been swapped for one half full of debris
And don't forget the oil filter is on the return to the oil tank not the feed to the crank
 
Disassembling Crankshaft?
1971 750 sludge trap
 
Just talked to a mate who has been building these engines for decades. Successfully- including lots for racing.

He said that if you have the engine that far down your an ***** if you don't check the crank. Excuse the *****.

Unless your the original owner and treated it properly all its life you don't know what's there. He has rebuilt many US imports and said even with a proper filter half the American owners just full up the oil and never replace a filter. So 12,000 mile bikes with solid packed trap.. Two cranks he did recently had the wrong bolts in them. One had loose nuts. He also said to fit the locking plate because as Robb SS said they keep the dowels in place. He loctites the bolts and turns up the lock tabs but doesn't punch the threads. New genuine hardware from Andover. There are imitations out there. And check for cracks.
 
baz said:
Wow
That's the cleanest I've seen!
How many miles has the bike done?
Click to expand...
There's 8000 mi showing on the clock but TMU.

Crank journals STD mic'ed at 1.750. Plasti-gaged at .002 with the original inserts.

No measurable wear in the cylinders. STD bore, but they seem glazed like maybe someone replaced rings without honing.

Fitting . 020 over graphite coated JS pistons.
 
Dan1950 said:
There's 8000 mi showing on the clock but TMU.

Crank journals STD mic'ed at 1.750. Plasti-gaged at .002 with the original inserts.

No measurable wear in the cylinders. STD bore, but they seem glazed like maybe someone replaced rings without honing.

Fitting . 020 over graphite coated JS pistons.
Click to expand...
Did the crack testing check out? My crank looked perfect but failed.
 

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