Technical SBC Rod Bearing - No Oil Slot

I guess I'm out of touch but it's only been a couple years since I rebuilt a SBC. Today I was ***embling a 283 and noticed there was no oil slot in the rod bearing shells to match up with the slot in the rod cap. I always understood it's purpose was to direct oil to the cam and lifters.

I called the fellow who did my machine work and he said that the slot in rod bearings was discontinued years ago. The bearings I'm using are Mahle, so they're not some garbage, no-name bearings. Even looked at Mahle rod bearings online and the photo shows no oil slot. I trust my machinist, since he does race engines that will rev a lot tighter than my 283 probably ever will, and he said there's enough oil "sling" off the sides of the rods to oil the cam, lifters and cylinder bores. I thought the rod bearing shells I put in a SBC just 2 or 3 years ago had the slot in at least one bearing half per rod. Maybe they weren't in those bearings either and my memory is worse than I thought. Learn something every day I guess.

Does make me wonder though....is the lack of the "extra" oil squirting out of the rod cap slot toward the cam contributing to cams going flat so often? Hmmm.

Lynn

 

I’ve put together many SB Chevys w/o slots in the connecting rod bearings & they’re still running strong with no problems.


Sent from my iPhone using H.A.M.B.

 

At one time the split oil hole bearing and a “slot” on the cap side were stock. I my opinion when they were eliminated camshafts started wearing lobes. Dealers got more business as I saw it.
At idle these “spit holes” as I heard them called made sure oil was on the cams and cylinder walls. A few engines I rebuilt had the holes in the bearing but no slot on the rod cap so I filed one in.
Today on the race engines I ***emble I have a lot more side play in the rods so I don’t worry about it.
I also believe the hydraulic lifters which never relax on the cam lobe to the lifter helped with the failures. A solid lifter cam had a better chance of oiling along with the rollers used today.

 

Thanks for the replies. About how long ago did "non-slotted" rod bearings become normal? Do some bearing manufacturers still put the slots in the bearings that the bearing I used a couple years ago might have still had them? I don't recall 100% but I think the bearings a couple years ago were either King or Clevite. One last thought/question and that is wouldn't the bearing face almost have to be grooved in the center to really get oil to the slot? If at least one bearing shell per rod didn't have a groove to carry oil to the slot it doesn't seem it could possibly get enough oil to even "squirt".

FWIW...I'll probably just carry on with ***embly, but what I noticed did obviously raise some question.

Thanks!

Lynn

 

Well,,,,I think it would probably put a fair amount out .
Even with a small groove,,,,,,oil at 50-60 psi,,,,would put out a pretty decent stream,,,,I think .
Kind of like an old squirt pistol,,,,,,that little stream of water hits you in the face pretty good,,,,LoL .
More comes out than we realize ,,,,,and even at 800 or so idle rpm,,,,,that is a lot if spinning the crank is doing,,,,,slinging oil at every p*** .

And I’m with some others,,,,,,I think the cam lobes and cylinder walls need that extra lubrication,,,,at least at idle and low rpm .
Most modern cars are required to sit in traffic,,,,and get warmed up for extended periods .
Might be something to do with som3 of the new wear problems,,,,,and the oil I guess,,,,who knows ?

Tommy

 

@lake_harley

Having a slot in the upper rod bearing is bad engineering because this is the load bearing side when the cylinder fires at TDC.
Chevy designed [or timed] the oiling system so the oil feed hole in the rod journal was leading by approx 55-60 deg.
This left a trailing film of oil at the maximum load/pressure point.

 

You asked when the oiling port was omitted, it was a small journal thing so 68. If the lack of the slot in the shells concerns you just carefully file it in..i would. JW

 

That's a fair amount of " supposin' "

 

Think about how many millions of SBC have run successfully since the elimination of that oiling design ....

 

Those bits of info makes me realize I haven't been paying attention at all! I guess seeing the groove in the 283 rod cap but the lack of matching slot in the bearing had me thinking (incorrectly) that a recent change or mistake had been made. Thanks for the replies and education.

Lynn