Sump Off - Crank/Rod Bearings

[paul_GB]

Gents, this topic sort of follows on from where I left off in my previous thread... http://www.sl113.org/forums/index.php?topic=22913.msg163770#msg163770

With the sump off and engine upside down (cyl head still installed) I decided to do what I said I wouldn't do and check the Crank and Rod bearings. I replaced the timing chain (using the SL groups excellent step by step guide) and was set to button everything up but thought 'whilst here' delve a little further. I believe the engine essentially is in good order and appears to have had a rebuild not long ago. I can see the pistons look newish and bores are unmarked.

I popped off 3 accessible bearing caps and removed the half shell of each bearing (the front bearing cap is currently obscured by the oil pump). The shells appear to be not too badly worn, but I'd appreciate a second opinion from you guys if thats ok.. i.e. does the wear indicate there would be benefit changing the shells (without having a re-polish of the crank itself). Trying to avoid fully pulling out the crank/pistons or removing the head if possible. The crankshaft journals show no obvious signs of wear, scores or burning. So... my thought is to change the shells whilst its apart. The current ones are marked 0.50 UST and 72-0314.. assume this refers to 0.5mm undersize (i.e. 59.50mm dia). With the engine upside down I am hoping to raise the crank very slightly to get enough clearance to swap out the crank bearings fully. Hope all this makes sense...

I also removed just one half of one rod bearing.. it looks hardly worn but as Ive come this far might be worth changing the set. The number on the outside of the shell is 127 06 10 KZ   0914   11-08. There is no mention of size so can I assume these are standard size?

Photos of the bearings attached

Any thoughts appreciated..

Paul

[paul_GB]

.. engine is currently on a stand :

Cheers
Paul

[ja17]

Looks fine, be careful not to mix anything up.

[Shvegel]

I agree with Joe.  The lower shells suffer the lion's share of the wear as the crank is always trying to get out the bottom of the engine. No dirt and minimal wear so I wouldn't think twice about reusing them.  If you want to have fun you could always check the clearances with some Plastigauge.

[paul_GB]

Thanks guys.. sounds like the light wear on the crank bearing is acceptable. The rod bearings look almost new to me. I will leave all alone then .. saves me money for spending elsewhere . Ive had my car for 25 years now.. I know there will be other 'opportunities' to spend money! Eagerly awaiting my car to come back from respray this weekend.. its been gone 3 months 

[Benz Dr.]

Replacing rod bearings usually requires that the big ends get re-sized. At the very least you would want them checked which means pulling everything apart. Not common to find one bad bearing but it does happen.

[Shvegel]

Just wanted to make sure you are looking at both halves of the rod bearings.  The same forces that load the lower half of the main bearings also loads the upper half of the rod bearings. The lower half almost never sees wear while the center of the upper shell can be worn right to the base metal.

[paul_GB]

Sound advice. Given I've gone this far I thought best to buy plastigauge and check bearing clearances (as suggested by Shvegel). Ive never used them, this is new territory for me. I'm methodically checking each one.. I'm about half way, so far clearances are within spec and the 'spread' across each journal fairly linear. That said I've found the front crank bearing has a score, but the journal surface is unblemished. I've ordered a new set of mains!

Re determining the size of the rod shells.. does anyone recognise the stamped no 127 06 10KZ, also 0914 and 11-08 ? Cheers