'Oil feed' grooves on K&B crankshaft.

Hi guys,

I've been racing 3.5 and 7.5 OB tunnels since 2006 and have not used any K&B engines to date. (I've been running OS, Rossi and Novarossi engines). I've recently started to build a new 7.5 tunnel for my son and have managed to source three used K&B OB engines (two Redheads and a Goldhead), that I will be 'rejuvenating' with some new parts that I managed to get from Joe Monohan in LA. In the process of taking these engines apart to clean them, I noticed that all three crankshafts have what appears to be 'oil feeding' grooves running from the intake-port forward towards the front bearing. All three the grooves look identical so I assume that they were machined onto the cranks by the K&B factory.

I remembered many years ago when racing 3.5cc on-road RC cars, we used a thin Dremel disc to grind such 'oil feeding' grooves onto the cranks of all our engines in order to 'push' lubrication to the front bearing.

If these grooves that I noticed on my three K&B cranks are in fact intended to also 'push' lubrication to the front (upper) bearing, then the grooves have been machined incorrectly! As they are at the moment, they will 'pull' any fuel/oil mixture back into the crank intake port away from the front bearing.

I've attached a photo of one of these three cranks which clearly show the groove I'm referring to, and shows the direction of the groove itself.

I know there are a number of OB K&B guru's on this forum and would appreciate your comments on this matter.

Thanks in advance.

Wennie,

The grooves work!!!...

Hello Ron,

Thanks for your response and I know the grooves work ! The problem is that they work in the wrong direction !!! Have a close look at everything I've explained and you will see the problem. The 'coil' of the groove has been machined 'in reverse' ! As it is, it will work correctly for an anti-clockwize-rotating (airplane or car or inboard-boat) engine, but it's wrong for an OB engine such as the K&B !!!!

Yes, that groove direction is the same as shown on the k&b pro diagram shown at the link posted below. I will try to find one of mine to confirm its the same. I understand what you are saying in theory. You would think the groove would start on the crank induction window opening trailing side and spiral up to the front bearing, instead of the leading side. Maybe what many of us have thought to be an oil groove to oil the front bearing may actually be an oil groove to help limit crankcase pressure leaking through the front bearing as the clockwise rotation auger as shown would constantly be pulling in instead of drawing out???? Never really studied it as close as you obviously have. It will be interesting to hear from others.......

http://www.mecoa.com/kb/48/7500-exp.pdf

I think you will find that it might be a labyrinth groove to keep the oil in.

I read somewhere that K&B and Fox and some others developed shallow spiral grooves on the crankshaft to reduce the oil oozing out of the front bearing.

I have many outboards with the spiral rotation the same as attached picture of crank Wennie.

Thanks

Ross

Hello Ron and Ross,

Thanks again for your input and as per my comment on the photo that I attached, I accepted that the groove might not have been an 'oil-feeding' groove, and that it may have been placed there for another reason, such as to prevent oil oozing out of the front bearing.

However, with the OB engine sitting with the crank in a vertical position, any oil getting to the top/front bearing should surely have been seen as a positive. I suppose we are past the point where someone at MECOA could provide a definitive answer on a production step that stopped many years ago?

Thanks again,

Wennie,

K&B added an oil hole to the front housing near where the front bearing rests. This was added to give us an opportunity to give that front bearing a shot of oil before each run. Oiling that front bearing any way possible will greatly improve the life of the front bearing on all outboard powerheads.

Hi Ron and Wennie

I e-mailed Mecoa to get the correct reason for the groove and this is the reply as below.

It's not to oil the bearing, it's to keep the fuel/air from pouring out the front bearing from the crankcase pressure.

Thanks

Ross

Ross Petersen said:

Hi Ron and Wennie

I e-mailed Mecoa to get the correct reason for the groove and this is the reply as below.

It's not to oil the bearing, it's to keep the fuel/air from pouring out the front bearing from the crankcase pressure.

Thanks

Ross

Click to expand...

Thats what I thought as it augers back into the engine when turning clockwise. Thanks for the verification Ross!!