I've done 500 miles now since a complete engine/bike rebuild and changed the oil a couple of times. On draining the sump just 50 miles after the last oil change I was slightly alarmed to find how dirty it has become – no bits in it just dirty – see photo new oil v 50 mile oil.
If it wasn't for wet sumping and my practice of draining off before a run I would probably be blissfully unaware of the situation – as I was in my youth when I hadn't heard of wet sumping. The engine and oil tank were meticulously cleaned on rebuild but maybe the rings, particularly the oil ring are not fully bedded in yet. Your opinions welcome.
Sorry I am a bit dense first thing .Is that 450 miles between the two samples shown ?
If the engine is still running in, the oil is likely to get quite dirty, partly from rough metal worn off plain bearing surfaces (including the bore) but also from carbon on the cylinder walls not being pushed back up into the combustion chamber and then eventually out of the exhaust. Normally, you change the oil after 500 miles after which it will hopefully stay a bit cleaner?
Hi,
Just out of interest, if you do not have a magnetic sump plate, put a magnet in the container of dirty oil to see just how much ferrous material is in there. Put some cling film over the magnet first to make it easier to clean.
Dave.
The idea is for the oil to hold contaminants in suspension as well as lubrication. Old engines like ours are dirty inside due to larger clearances.
Hi,
Looking more closely at the photo, the 'dirty' oil is not thick with contaminants as the bottom of the container can be seen. As Idie says the oil will carry material in suspension until removed by a sludge trap or a filter but even then some remains in the oil.
Dave.
Thank you for those replies which are quite reassuring - which I suppose is what I was hoping for.
In response to some of the comments:
I was imprecise about the oil changes - I think there were probably three upto 450 miles and the sample shown is 50 miles after the last change.
I do have a magnetic sump plug fitted and there was a small amount of black gunge attached to it after the last 50 miles which must be ferrous but I am reassured that the consensus is that these are quite dirty engines, particularly when running in. I will be changing the oil quite often and may see some improvement after a few more miles.
Several decades after my last B31, and more recently being more familiar with FireBlades and R1's, I find myself constantly having to recalibrate my expectations of B31 engineering and performance!