Grooved main journal

[buguy]

I'm going to buy a new 82mm crank for a 2276. I see the Scat crank has grooved main journals. Any benefit to that? They are about $100 over the standard 4340 non grooved journal.

[modok]

Groove good? groove bad?
...eh,
I feel completely indifferent about it.

I do like the oiling to the rods, (single drilled)

[evanfrucht]

My grooved Empi was $260 from Car Craft VW... just btw. I have a hunch the same factory oversees is making them for both Scat and Empi but don't take my word for it, or flame me for presuming so

Spend less, get the "premium" option... Win, win as they say. Atleast that's what my cheap ass did

As far as the grooved crank. My thoughts are... you either want the bearings grooved, the crank grooved, and/or a cross drilled crank like stock. They all accomplish more or less the same thing, making sure enough oil gets to the main bearing surfaces.

Some people say grooving the crank theoretically makes it weaker, therefor grooved bearings are better. Yes probably, but... enough to matter? I haven't lost any sleep over it yet.

I didn't even know my crank would show up grooved, so how's that for indifference?
_________________
1967 Bug ( the daily rod )
1964 Fury Wagon ( the pavement shredder )

[buguy]

Interesting. I have an Empi crank in my current engine and i don't remember it being grooved. Went through my pics and i don't have one of it without bearings, so i really don't know.
Car craft is where i saw the Scat grooved, but the pic of the empi doesn't show it grooved.

[evanfrucht]

[modok]

Yep the new empi cranks look great.
Just recently changed, year or two ago?

[Pruneman99]

I think EMPI started grooving them right around the time Evan bought his.

[Dan Ruddock]

I bought mine before Evan did, looks the same but without the grooves.

[Dan Ruddock]

I bought mine before Evan did, looks the same but without the grooves.

[Pruneman99]

[kangaboy]

[buguy]

I don't believe my empi crank has grooves. Been only a few months on mine though. I actually built it over a year ago but i broke an axle. I had a new trans built and did a semi restoration at the same time. Been fighting trying to get a clutch to hold so it's been in and out a few times lately too. So not many miles. Seems fine so far to about 300hp.
Next engine will be more serious though so if the grooves are better...

[Brian_e]

I dug this up from a long time ago, and I think it should be re-posted here once in a while. This was written by Steve Reeder (SRP1). He use to post here frequently, but unfortunately he hasn't in quite a while. Steve has forgotten more about building HP VW's then most of us will ever know. He is a very successful engine builder in the off-road/desert community. He has done the research, and real life hard testing, to back up everything he says. I have talked with him on the phone and bought parts from him. Amazing guy who loves to share solid info.

Brian




Quote from SRP1

"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 rotation.
Later on VW changed the crank design to a cross-drilled 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 cross-drilled 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 strength) 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 centrifugal 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 cross-drilled 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 strength of the wedge as the oil can not creep 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, clearance 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 strength to handle this mod, I know for a fact that the steel back does, I have done to many of them to be concerned 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"
_________________
www.type-emotorsports.com

[esde]

Brian, thanks for posting that, it's a shame SRP1 isn't around here anymore. Back around 2010 he was advertising custom grooved bearings and explained the need to me exactly this way. And since then every single engine has gotten internally grooved bearings. I know the grooved cranks are supposed to be strong, (I've never seen a crank broken in the center of the center main) but it still feels sketchy to groove the crank right next to where they like to break.
_________________
modok wrote:
Bent cranks are silent but gather no moss. I mean, ah, something like that.

[modok]

The "downside" to grooving the crank is pretty much the same downside as grooving the bearing; narrower loaded zones, decreasing the oil film thickness.

But it turns out that in the real world....most times when the bearing is loaded heavily, there is also enough crank deflection so the bearing isn't evenly loaded anyway. The edges of the bearing are where it's "at" no matter how you look at it so grooveing the center is not really losing bearing area where it counts.

Is it weaker?.... not really. The middle of a main journal is not a weak point... except for the oil hole, and IMO the groove has no impact on that.

I believe as a general idea, that the bearing should have all the oiling details and the crank should be simple as possible, BUT, a groove in the center may make the crank easier to grind or polish accurately if you know what your doing, so I really 100% feel completely indifferent about it. Pros and cons equal.

[Brian_e]

[sled]

I wonder how many big-stroke cranks SCAT has sold, and how many have broken through the oil groove?

_________________
drive your split.

[jeff68]

Interesting discussion in this post with good information. If you'd like to read other thoughts / opinions on grooved VW crank main journals I encourage you to read the Berg information on this.

[Paul Jr]

I would be interested to read his findings but don’t have a book. Anyway someone can post up what his thoughts were on it?

[buguy]

Thanks for all the information guys. Hoping to find a decent black Friday deal on the remainder of my parts.