Rod side clearance

[ekacpuc]

Working on collecting parts for a 2332. There’s not a “real” vw machinist in town and I’m on a remote island in Alaska so everything gets shipped out. Trying to decrease the chance of having to send parts out to be machined. Looks like I’ll go with a DPR crank, seems to be less of a chance of something being wrong with them. I have access to a machine shop so I can use all sorts of precision measuring tools and will check everything..


So I realize nothing is known until you measure what you have. However I have noticed trends, the CB rod side clearance is typically on the loose side. Scats seem to be tight. I’ve seen this on a couple motors I’ve built, the CB side clearance is around .020” on my last motor. I wanted to notch the rods but didn’t because I don’t think with that much clearance it would do anything..

Any idea what other brands seem to be? Like AA H-beams or even empi? I do like that the scats have a 3/8” bolts though.. I’ll seek out a rod with ARP bolts and have seen there’s fakes out there..

I agree with having the side clearance on the loose end is better than too tight... the scats I have are super tight, almost scary. I’d have to remeasure as it’s been years since I built the motor (was a 2007cc with scat Ibeams, I just dug the rotating assembly out of storage).

[modok]

I'd like to have about .015" on a high powered engine, but .020 is a lot better than too tight.
On the one hand I don't LIKE how CB is making the rods too narrow, (I can do that myself perfectly well) but then again I know it's not something worth being overly concerned about.

Putting the oil groove in the rods is still a good idea, IF the cheeks of the crank actually cover the rod. A lot of older welded cranks they don't.
Have a look at that, maybe you did a lot of overthinking over nothing.

[ekacpuc]

[67rustavenger]

I can't help much here.
But the AA "H" beams are on the rather loose side of things too. Like you found, 0.020"
Have you considered the newer EMPI "I": beams? They appear to pretty stout!
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[ekacpuc]

[modok]

Nobody really knows what postition the rod will actually assume under what conditions.
You can't really go wrong with putting some grooves in the sides.
If it is rod is thrust against one side then the groove will help, if it isn't then the groove will not hurt.

[esde]

I have scat h beams on a DPR crank, and it’s not loose.
If you don’t have a machine shop, have dpr fit everything and balance it...
One stop shopping, he can get you the bearings too, and check your rod clearances
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[Ohio Tom]

Side clearance is really a Non-issue. It just allows the rod to float to wherever it wants to live. Has zero effect on oil flow or oil pressure.


As for notching: You can do it, but it doesn't really do anything.
The oil is squirting from the rod bearings 360deg all around and getting flung everywhere by centrifugal forces (mighty strong ones too).
Little notches cannot overcome the forces slinging it all over.

[c77owen]

[Dan Ruddock]

Greg, go DPR and VW or Porsche journals. Tom is right, don't bother with notching. I like having the rod ends drilled like in this pic. The drilling is an extra $100. Dan

[Dan Ruddock]

Here is a mind blower for you. Joel Mohr told me about a engine he built with a 40hp crank and 1600 rods. Had a ton of side clearance, like .090" and he said it made no noise and ran many miles.

[txoval]

Dan, out of curiosity, what is the purpose of the hole on the rod end? Weight reduction or oiling?

[Dan Ruddock]

[mark tucker]

I would be happy with .010~.012" and If I wanted more thats a eazy fix.

[txoval]

With my Scat 4340 forged crank and CB H-beam rods I have exactly .015” on each rod. Maybe a coincidence

When I used the CB Uni-tech rods they were .016-.018”

[Alstrup]

It also depends on how high you wanna rev.
On a 8000 rpm engine I wouldnt assemble anything less than 0,015"
Factory specs on a stock engine is 0,1 mm (0,0039") But I have found (from disassembling loads of especially aftermarket rebuilds and VEGE engines, that that is on the low side. Those ALWAYS have cranks that are blued. So for that reason I do not assemble even a std plus engine with less than 0,008" (020 mm)
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[ekacpuc]

Thanks for the answers.


Dan I Honestly was just going Chevy for the better selection of rod bearings. I want to run clevite bi metal rod bearings. They don’t seem to make them for a VW journal. Motor won’t have a huge amount of HP so I doubt overlap will hurt. Porsche stuff is expensive..

Saw VW released a bulletin about notching T4 rods. I don’t see it doing anything with an excessive side clearance though.

The bearing is the restriction so I wouldn’t think side clearance would effect oil pressure. I do think if you wanted “squirters” it would affect that.

Doesn’t seem worth the time..


Thanks again.

[Dan Ruddock]

[ekacpuc]

[Dan Ruddock]

Greg those rods are for T4 engines. Take a look at my ads.