when are 3/4 grooved main bearings needed for bbc ?

[Little Mouse]

Those damn idiot chrysler engineers, why in the hell did they not make there main bearings different on the 426 hemi that showed the other manufacturers how to run at 7600 rpm for several hours in nascar and win, not just blow up engines.

I hope your not praising the fully grooved main bearing era! Lol

Lol I don't know those dummies at chrysler won a lot of endurance races, have you ever picked up the weight of a half inch rod bolt hemi nascar rod 6.8 long and that heavy dome hemi piston. They kept all that in check with there full groves mains.

[Little Mouse]

Those damn idiot chrysler engineers, why in the hell did they not make there main bearings different on the 426 hemi that showed the other manufacturers how to run at 7600 rpm for several hours in nascar and win, not just blow up engines.

I hope your not praising the fully grooved main bearing era! Lol

Lol I don't know those dummies at chrysler won a lot of endurance races, have you ever picked up the weight of a half inch rod bolt hemi nascar rod 6.8 long and that heavy dome hemi piston. They kept all that in check with there full groved mains.

[Little Mouse]

Those damn idiot chrysler engineers, why in the hell did they not make there main bearings different on the 426 hemi that showed the other manufacturers how to run at 7600 rpm for several hours in nascar and win, not just blow up engines.

I hope your not praising the fully grooved main bearing era! Lol

Lol I don't know those dummies at chrysler won a lot of endurance races, have you ever picked up the weight of a half inch rod bolt hemi nascar rod 6.8 long and that heavy dome hemi piston. They kept all that in check with there full groves mains. Pretty good evidence the full gloved mains hurt nothing for them.

[modok]

Can someone explain to me, like to a fifth grader, what oiling problems can fully grooved main bearings fix? Too small crank oil passages, too large rod bearing clearances, mains not cross drilled in a low rpm application, or what?

a full groove gets you slightly more oil flow through the Rods AND the mains, at the expense of main bearing area. That's usually a good thing, tho not always.

"Not enough flow" is ultimately the most common problem to have with a bearing, tho usually caused by some other problem.


personally I like the combo of a full groove and a single drilled crank for the sake of simplicity, tho it is not the BEST.
A lot of things are not ideal but they are good enough.
When it comes to the cooling and oil systems "simple" often wins over more ideal but complex designs.

Example..... those korean cars.....can't think of the name,
they had a problem with burrs in the crank oil passages inside the crank where the drillings intersect, like "hanging chad" if you remember that election. Oops. OOPS

[engineguyBill]

180 degree groove main bearing results in superior performance as compared to 3/4 and fully-grooved main bearings. 180 degree groove delivers the oil to the exact location that it is needed - at the parting line - which insures that sufficient oil is available to form the oil "wedge" between the bearing shell and the crankshaft journal. Extending the oil groove beyond 180 degrees does not result in any performance gain whatsoever.

[Little Mouse]

So lets see you design, build a race engine specifically to win at nascar at 7600 rpm for several hours time, you have super heavy rod and piston weight. So seems like making damn sure for 360 degrees the rod bearings are getting oil, makes sense to me. I guess some engine at just a few seconds down a drag strip then not as important.

[modok]

i wonder if the "IDEAL" would be to have two 90 degree grooves on the sides, each fed with it's own oil passage, and then you would want the crank drilled at two places 90 degrees apart, so inside the crank you have three or four holes come together in the right spot.....sounds tough.
I haven't seen that tried, but if it was I bet it would be German design.

[engineguyBill]

The 360 degree grooved main bearing does not allow for the very necessary oil wedge to form between the bearing shell and crankshaft journal, which will allow the crankshaft to come into contact with the bearing surface. Not a good scenario and will lead to failure ultimately.

[modok]

Ideally a plain bearing would be about as wide as it's diameter, to be most efficient, but with the reality of a crankshaft that's not what you end up with.
Especially when the crank is twisting and bending a lot the actual contact is near the edges of the bearings anyway, the middle may not be doing a lot so losing it isn't hurting you.

What do they do in Nascar 5 years ago?
I don't actually know, but, for awhile they were going hard to reduce bearing friction, I bet things were tried.

[Little Mouse]

Most people have problems spinning rod bearings far more then main bearing problems.

[modok]

Especially when the crank is twisting and bending a lot the actual contact is near the edges of the bearings anyway,

I just realized that....at least on what I consider good designs, the cap probably will flex to match the crank (giving full contact), while the block may not. Very interesting. Possible reason for the grooved upper.

[engineguyBill]

Chrysler engineers spent a ton of money and many man-hours trying to develop rollerized rod and main bearings for the 426 HEMI back in the late 60's, eatly 70's. The project was ultimately abandoned as the project illustrated the importance of the oil wedge in automotive crankshaft bearing design. The roller bearings just did not have sufficient strength to survive in this enviornment. Oil wedge formation is a very basic and simple concept but it is extremely important when insert type bearings are used.

[ClassAct]

Can someone explain to me, like to a fifth grader, what oiling problems can fully grooved main bearings fix? Too small crank oil passages, too large rod bearing clearances, mains not cross drilled in a low rpm application, or what?

Someone already said it. Oil timing.

[GARY C]

The 360 degree grooved main bearing does not allow for the very necessary oil wedge to form between the bearing shell and crankshaft journal, which will allow the crankshaft to come into contact with the bearing surface. Not a good scenario and will lead to failure ultimately.

Makes one wonder why an upper shell that has a grove never suffers damage even on high rpm engines?

[cgarb]

I have been trying for some time now to set my oil timing...can someone explain that? Do I need a dial back timing light or will a standard one work?