Crankshaft cleaning
 

Evening all

So I have my S2 engine apart for a refresh, seals, rings, rod bearings etc. Pistons, bores and crank all in spec and crank in really good nick only needing a polish. Everything will be getting a really good clean, but question is, does one have to clean out the galleries in the crank, if so to what extent? Seems there are through drillings on the big ends but blind on the mains?? Can't find any coverage on the topic in the WSM or search Rennlist.


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David
'85 Euro S2

FWIW the sludge traps will also collect the polishing media from the polishing event.
The only for sure way to remove this residue is to drill out the galley plugs and put a bore brush through the holes.
Then you could tap the holes and insert cap plugs with green loctite,
you might want to check the crank balance.

NOTE the polishing compound if its not fully removed can rinse out with the engine oil and then it will destroy the bearings.

I would suggest that if the crank looks good (the 928 cranks are very well made) then dont take the crank to the polisher,
just flush it with carb cleaner then install it.
\
NOTE something else to consider you can buy the extra reach red spray straws, these are about 18 inches long
these will let you spray the carb or brake cleaner all the way to the bottom of each oil passage way.
you will use a lot of cans the spray.

NOTE straws are also useful for oiling the window arm pivots .

One of the most important steps in a rebuild. Seldom addressed by the "home mechanic."

Once the crankshaft is removed and stood on end, you need to get every little chunk of that hardened sludge out of the sludge traps or you will end up with bearing failure. Not doing this, is the leading cause of 928 "rebuilt engine" failure. It is possible to get it all out without drilling out the stock plugs and installing threaded plugs (which sucks), but it takes hours and hours to get a crank completely clean....you need to bring a sack lunch with a side of patience. I made a custom air nozzle that blows air 90 degrees (out the side) so that I can blow into the 90 degree drillings, which helps. Alternating blowing through the passages, plugging the other side of the main bearing and then releasing, blowing through the drilling with 90 degree air will get the sludge out. (I'm in California and we are not allowed to have any decent spray chemicals, which probably helps.)

Most automotive machine shops will use a thin specialized belt sander (made for polishing crankshafts) with a Scotch Brite belt....not polishing compound, so that isn't usually an issue. (If they want to use a super fine sanding belt, that works, too.)

Clean, reclean, when you think there is nothing left, clean more. You will feel the chunks of hardened sludge hit you in the hands and face. Once the chunks quit hitting you in the face and getting all over your clothes....you are getting close!

Thanks MrMerlin , Greg and Slate blue, I kinda figured this car was going to drag me down the rabitthole but all good as I still have another 928 to drive thank god!...
I will see how I get on with cleaning, do any of you have a diagram of the drilling scheme to understand the angles?

D

you should be able to figure out the oil passages by looking at how the plugs are drilled into the sealing ports,
you should get some of the long red straws to fully direct the spray cleaner into the bottom of each passage

If I never took the crank out of the block during my partial rebuild will not doing this pose any issues?

This has me worried...

No, unless the the rebuild was needed for a blown engine and resultant debris.

Stan sent me down an Amazon rabbit hole:
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Getting a "straw" to make a 90 degree turn 25mm into an 8mm hole is a tough task.

Impossible to clean a crank when it is still captive in the main bearings...must be removed to clean.

Sludge build-up in the blind drillings is a real.problem in 928 engines, because they tend to run for many miles/years, allowing huge amounts of sludge to collect. I've seen crankshafts where these passages are completely packed full of sludge. Fortunately, this is a very stable situation and the sludge just stays there when not disturbed.

The answer to your question can go either way.

If the sludge was left undisturbed....you simply removed the rods, kept things clean, and didn't blow through the passages....the sludge should stay where it was.

Disturbing the sludge, in any way, can break it loose and the hard chunks will proceed immediately to the rod bearings, on start-up, resulting in damage.

Bearing fauiure, after "rebuilding" 928 engines has always been a huge problem. Hundreds of these engines have failed in very short periods of time....it is, unfortunately extremely common.

Bearing clearance issues have been discussed, at length, on this Forum. I just have never seen any discussion about crank cleaning and sludge removal, which probably causes as many failures as inadequate bearing clearance.

I'm not trying to increase paranoia, just passing on "tricks of the trade".

Going to try to access the galleries. Not much on the web but found a video of someone cleaning and X19 crank. Not sure if our cars are "same"/similar but will have a go. Looks straight forward and well worth the effort based on what emerges...

See link: - UPDATE - Greg points out in post #14 below that the gallery plugs are not the same as the type in the video/removal method. If viewing, do so on the basis of seeing what might be inside a crank.


Seems the function of the galleries are to trap sludge (and presumably retain unless disturbed), assuming the same is the case in our engines. Watch this space...

D

It would be really nice if the oil galley plugs were like those. Of course, they are not.....no such luck.

If you are going to try and remove them, clean the crank, and install new plugs, I'd seriously recommend that you find a junk crankshaft to "play" with....and not use that beautiful crank you have to attempt this.

I'm just saying....The "learning curve" is crazy steep!

If I took out the crank it would have found its way to Engine Supply very quickly. I found out that bribing them with cookies works very well ;)

I wouldn't risk damaging something like that myself and have people that have done it numerous times do it instead.

As you stated Greg, the learning curve is steep...