Diference between center main bearings.

[SweetCars]

My center main bearing on my engine is the original VW which has a flat back and the oil hole is positioned directly in front of the hole on the bearing.
http://www.cbperformance.com/ProductDetails.asp?ProductCode=070-105-531

I bought a set of Metal Leve as you can see the back side has the strip for oil and the oil hole is positioned diferently.

http://i.ebayimg.com/11/!BeH(+8w!Wk~$(KGrHqQH-CwErfUh1,+SBK75gnlQ0Q~~_35.JPG

Some diference at the end or both lubricate well?

[esde]

This is a quote from SRP1's post a few years ago, which I had bookmarked.

"Ok here's the deal.
In the early 36hp, 40hp, and 1500cc engines the crankshafts where straight drilled for oiling. The straight drill design made the crank very strong, and those engines used the early KS internal oil groove center main bearing, the center main and groove feeds oil to #1 and #4 rod bearings at all 360* of crankshaft roatation.
Later on VW changed the crank design to a crossdrilled oiling set up in the crank, when they did so they also changed the center main to an external oiling groove. Now here's the key; when VW went to the crossdrilled crank they also incorporated that huge tear drop in the crank to increase oil pick up from the now small slot in the bearing (no longer 360*)

With the tear drop slot the #1 and #4 bearings are feed oil about 280* of crankshaft rotation, that's a pretty good amount of oil, at least enough IMO to keep the rods well oiled even in a big stroker engine, little lone a stock engine.

Now lets back up to the straight drilled crank, you know that little oiling hole in the main journal, but stronger by design (most all stroker cranks are drilled with straight shot oiling to increase crank strenght) When used with an external grooved bearing the rods are oiled about 90* of crankshaft rotation, before the hole in the crank passes past the slot in the bearing, the remaining 270* degree's of rotation the rod bearings are left out in the breeze so to speak for oil. We all know that as RPM increases, and centrifical forces increase, the oil is pushed (slung) forced outward faster, that increases the demand for oil at the rods. Add a short 90* fill time from the oiling galley to the rod, so at as low as even 4000rpm, and the next thing you know, BOOM.
At the very least your rod bearings are starving for oil.
I should touch just a little on what is called hydro dynamic wedge, that is the locked layer of oil trapped between the bearing and journal. FWIW I am also sure that VW was paying attention to this with the new bearing design and crossdrilled cranks. With the new design the oil galleys are closed so to speak when the piston is at TDC and BDC. With the galley blocked off it does increase the strenght of the wedge as the oil can not creap back into the galley as the piston is loaded and forces the rod into the crank journal. With the 360* slot that effect is there, just not as strong so to speak. However I have never seen any adverse effect from it in the VW engines. Just something to include in this.

You have to keep oil running through the center main, bottom line. That journal feeds not 1, but 2 rod journals, clearence is also key too, but I won't go into that here.

Now someone mentioned the lack of internal groove bearings, that's true it's is a problem now. You can get KS bearings, but your up against using the aluminum backed bearing vs the steel back.
I noticed this oiling issue many many years ago, and I did not always have a set of KS bearings to use. So what I have done many times in the past is I cut an internal groove into the external groove bearing, but only a steel back bearing, never aluminum back. I don't think the aluminum back has the strenght to handle this mod, I know for a fact that the steel back does, I have done to many of them to be concered about failure with this mod, it works.
The other mod out there for those who have one (yamaducci is one of them) is to cut a 360* groove in the center main of the crankshaft. That mod
works, but worries me in high HP applications, because it gives the crank a place to flex. I have seen those cranks beat out the center main pretty bad, like I said, I believe that this is a high HP based problem. Yamaducci's crank I believe is a full circle unit, that one should hold up fine??? We'll see I guess as time is the mother of all tests for that one.
Last FWIW I have also grooved the bearings in all out effort engines for the #2 and #3 rods also, even though they will live a good life without it. This is due to the fact that the oiling galley and main bearing for that particular journal is only feeding one rod.
If you groove the main bearings at all the journal positions (skip the little bearing at the pulley) the bearing life increases 10 fold, and you will also see a drop in oil temp due to the ability of the oiling system to increase flow.

I hope this sheds some light on this subject, I'm sure there will be the naysayers that don't understand or have an engine that "run's just fine"
That's ok, no need to reply, I know more than I need to about this subject already. Everything I post on this site comes from years of experience, countless engine builds, and miles of R & D. I hope someone can learn from all this.

SRP1"

[SweetCars]

So what i understand is better i get the original VW steel backed main bearing which as a inner groove and straight oil hole?

Im going to give back the metal leve one to the store and buy myself the original VW ones.

[esde]

I sent my Silverline bearings to SRP1 and he machined the inner groove. Search and read "main bearing groove" and there is more info and opinion to help you decide. There is some debate as to wether the groove is better to provide more oil, or no groove for more surface area to support the crankshaft..

[SweetCars]

The original VW set which is steel backed on CB is Out Of Order.

I am going to order the KS German kit on CIP1
http://www2.cip1.com/ProductDetails.asp?ProductCode=C24-111-198-461

My engine is not High performance, is totally stock and if VW decided in 1997 to put that type of bearing in the engine, should be for a reason.

What do you think?? Good choice?

[SweetCars]

I took a look to my bearings again. It's my first time rebuilding a bug engine.

I saw that the other 2 main bearings (beside the little one) as the same type of lubrication with an outside groove and 2 smaller holes.
It is only the 2 piece main bearing that i can see 2 types: inside groove vs outside groove.

Is the 2 others are working well with the outside groove, i guess this 2 pieced main bearing should work well also.

Now tell me about quality. Learning about backed steel and aluminium. Which is better?

[vwracerdave]

the KS main bearing from CIP1 are not the steel backed bearings. They are the newer aluminum backed bearings.
_________________
2017 Street Comp Champion - Thunder Valley Raceway Park - Noble, OK
2010 Sportsman ET Champion - Mid-America Dragway - Arkansas City, KS
1997 Sportsman ET Champion - Thunder Valley Raceway Park - Noble ,OK

[SweetCars]

which brand does steel backed yet??

[vwracerdave]

Silverline are currently the only steel backed bearing you can get however they are the external oil groove. I'm not sure about the Bugpack racing main bearing set ACN has listed.
_________________
2017 Street Comp Champion - Thunder Valley Raceway Park - Noble, OK
2010 Sportsman ET Champion - Mid-America Dragway - Arkansas City, KS
1997 Sportsman ET Champion - Thunder Valley Raceway Park - Noble ,OK