V12 crankshaft grooved bearings

I am ready to put the crankshaft into my 5.3L v12 and wonder why the centre bearings are smooth or do you run one grooved one in the rear one in the centre cheers Richard

There is a caution in one of my manuals regarding them. Rear mains have groove, centre bearings are plain.
Don’t know why but it has been that way all way back to 70’s.

Interesting. I would be very interested in seeing the Jag manual and understanding why they are suggesting that.

In the engine I stripped, it had grooved shells in the top (block side) and plain in the caps (sump side).

I was told that the grooved go in the top and the plain go in the cap, but then the guy who told me might have built that engine.

On a more scientific basis, the groove is to assist lubrication where the lack of bearing surface is not critical on the upper side of the crank journal. Whereas the lower side is where all the action is and requires full support.

I also have 2 sets of KINGS bearings, and I am pretty certain they come 50:50 with half having grooves and half plain. That is the C29313-1 bearing shell. I always assume the grooved half would go in the block.

Quote from Kings Technical Guide. “Design of Oil Goove for High Performance Bearings”

“The oil groove is commonly made in the upper shell where the oil hole is located. A180º groove is sufficient for providing the required amount of oil to the connecting rod bearing, which it reaches by flowing through passageways within the crankshaft.The lower main shell has no groove. Therefore its effective area is greater than that of the upper grooved bearing. This design allows distributing the load applied to the lower shell over a greater area, reducing the specific load acting on the bearing material. Since the lower bearing shell is generally loaded heavier than the upper, the specific loads of the two are balanced.”

It then goes on to analyse an improved groove design for high performance engines, but always assumes the upper shell is grooved.

In saying all that, there were definitely issues with the rear bearing in the Jag V12, so maybe Jaguar were trying to improve lubrication to that bearing, and also control crank flex with a full centre bearing.

Kind regards

This particular manual is for series 2 XJ12 but l am sure similar in other model specific workshop manuals.

When I put mine together my kit came with two of each. so I put the grooved ones block side and flat ones cap side for both the centre and rear. I believe that is how mine came from the factory.

Shouldn’t have been! Possibly a Friday afternoon build?

Maybe. its all together now so too late to change it.

I looked at the king bearing online catalog. It list two different sets of bearings for V12 5.3. One set has bearing which appear to be “grooved” on both the top and bottom shell, for positions 1,2,3,5,6 & a larger (wider) shell in position 7. Position 4 has no grooves.
The other set (connecting rods?) has no grooves in any location.
Is the MB792 CP set the correct set for our HE V12 5.3?

king bearing set.pdf (118.0 KB)

Rods generally never have grooves.

many years(early 60s) back i would have on the main bearing journals a .060 deep groove ground into the center of steel journals , and polished to reduce possible fractures!
that way rod bearings would get a continuous oil flow!
not the hit and miss factory designs!
never had any problems with them, most problems occured with the top ends making to much power,!

So it looks like I may have put them in incorrectly then. I guess we will find out if it really matters.

The king bearings list are unobtainable, dont know if all manufacturers followed their design illustrated in their catalog.The king offering seems to have both upper and lower shells with grooves. When only one shell has the groove does oil feed to connecting rod come into discussion, IDK, sorry. I thought that the king offering was in stock, but may be long gone

Terrific to get help,my engineering company that ground the crank, checked everything as I haven’t the tools or skill to do so assembled the mains without the crank to measure line and size etc and had one of each in the middle and the rear. I had read that the middle has the two plain and asked why they assembled one of each, that was their decision based on experience for other motors. Two reasons came up, the rear main gets hot without the extra oil and the centre main bearing oil feed only feeds the main and does not have to also supply a conrod journal, ultimately I have gone with the Jaguar manual.

It’s not massively important, don’t worry.


another way of getting oil to the crankshaft , was in the top half of cylinder block, was to carefully grind a slot starting from the enlarged center oil hole/feed, but NOT all the way to parting line!
then on top shell with the factory groove, drill and chamfer 4 oil holes leading into the groove!
that way more oil will get to rod bearings!! I hope??
actually some Diesel engines came that way from factory, that is where i copied from!
I specialized in Diesel engine rebuilding for 40 yrs, but my love was HI- performance Gas/petrol engines , but many good ideas came from the experiance!
if all else fails, put a bigger oil pump in along with more pressure/volume!

like Nige says , the factory is probably good enough anyway!
when done properly!

Beach some useless trivia, about King bearings, they got there start , when GM was down sizing, and sold off lot of bearing manufacturing stuff, along with proppritary engineering patents realating to bear manufacture!
most was GM/ MORAINE Corvette race car bearings of the Moraine 300/ 400/ and hard as steel 500 series,(good for one race only),some years back!
today i try to use King bearings , i have used them in Turbo Buicks, many chevy stuff, also in some Turbo 4 cyl. Nissan,!
my opinion is they are top quality stuff if available, like any modern companies , a product is not selling well, they drop it, its called good business!

In theory, a non-grooved shell can handle roughly 4X the load that a grooved shell can carry. AFAIK, the only reason a grooved shell is used is to channel oil into a port in the crank itself.