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[edit: below is the original post...turning down the bearings has been scrapped in favor of pursuing a different 50mm rod bearing option...more of this discussion is on the 2nd page, but we're not giving away any details yet, so nanny nanny nanny ]

What do you think?
Scat forged crank with 50mm journals turned down to 48mm? That's about a 0.080" cut. Certainly larger than the 46mm Rabbit journals, but smaller than the 50mm 2L journals that nobody loves.

Too much crank flex? This is a Scat forged CW'd 78mm crank that should never see more than 7000 rpm.

Comments please

What is the point? Do you have a burnt up Scat crank? Where are you going to find rods? Is the crank Buick (Chevy) 2" journal or ??? Or this a custom crank you want to have made?

stealth67vw wrote:Is the crank Buick (Chevy) 2" journal or ???

Stripped66 wrote:Scat forged crank with 50mm journals...

That, in itself, should provide enough motive for me to ask the question.

But it doesn't answer the (very good) question John asked.
What good is it if there are no rods that'll fit it?

Ordinarily one has a crank turned down to a new rod journal diameter in order to alter the stroke...but the new size is one for which rods of the desired length and bearings are available.

Marc wrote: What good is it if there are no rods that'll fit it?

I have several rod options I'm pursuing...they both use 48mm journals.

Right now I am asking about the implications of turning the rod journals down 2mm.

Personally I think a 48 mm rod journal on that much stroke would be pushing it.
- In the 80ies and early 90ies Eurorace and some Swedish/Finnish T4 tuners turned their 66 stroke cranks to 46 mm Rabbit rod size, getting 74,6 mm stroke. It worked OK off the hook, when light balanced rods etc. were used, but when they were reved past approx. 5700 rpms on a regular basis, the rod bearings wore out in about a season. (5-7K miles) And the cases showed a lot of stress marks in the bearing saddles.
I have seen the inside of ONE engine (74 X 96mm Volvo pistons) that had done about 50K miles and actually still looked pretty good inside. It was equipped with a 270 degr. Eurorace cam "S" heads and dual 40 IDF. It was always driven "with respect" and resided in a 1303S.
About 5 yrs ago I saw a similar engine that came out of a bay bus, that had been sitting for a number of years in a backyard. According to the owner, he had it built for more hill power and for towing his camper. Well, 10.000 miles later the engine was toasted. And I mean crank, rods, case, cam, pistons and cylinders. Heads were reusable.

OTOH, IF you go through all the proceedures to help strengthening the crank, such as f.i nitriding, cryo treatment, a.o. you might get away with it in a light car.
T

With a journal that small the bearing used and the oiling passages in the journal are of UTMOST importance.

That's just it...I know the 46mm Rabbit journals are junk. The 48mm journals will give me two rod and bearing options, both of which have excellent bearings.

I'm just looking for feedback on how this may affect the crank. The 46mm Rabbit journals have a reputation based on experience...they weaken the crank; the 2L journals have a reputation based on the uber-poor quality bearings (and nothing else from what I've read).

See my question? There's a bit of dogma floating around that the Chevy journals are as small as you'd want to go. So, that means that the 50mm 2L journals are too small, right? Nobody can answer that because all 1st hand reports are that the 2L rod bearings are shite...crappy rod bearings cannot speak for the strength of a crank with smaller journals.

So...it looks like I am at a cross-road here. Either take a risk and do something that nobody has done (or that somebody has done but won't divulge any info on it), or weld the journals up to Chevy diameter, or sell it.

Stripped66 wrote:........or weld the journals up to Chevy diameter, or sell it.

AHA! NOW we know what you are up to!

You are trying to salvage a worn out crank!

Save yourself the headache, send it to be welded uop, it won't
cost much more than what you are gonna hvae to pay anyway.

Trust me, I have a $400 crank with type 4 journals, I've researched
ALL this before. My options are run the type 4 rods, or buy a new crank.


Don

dstar wrote:
You are trying to salvage a worn out crank!

Did you even read the first post? It's a Scat crank with 50mm (2L) journals. It needs to be salvaged for the same reason your does, not because it is worn out, but because it has 2L journals.

On another note, however, I *may* not have to go down to 48mm journals. I've located some Clevites (tri-metal) for an application that has 50mm journals (and I can buy the bearings all day long at Checker for $8 ); the rod width is very close, but I still need to research the bearing width.

Don, fire me an e-mail with the info you've found. I don't know if we've run into the same info, or if I've found a plausible option. Believe me, I would prefer not to touch the crank, if possible. I think I have an option that will only require existing rods to be modified. (and by *existing*, I mean rods that are currently in production).

Done... check your PMs.

Don

Well, come on now guys...
Why hold out???
Give us the Who and Where!

No.

...

Stripped66 wrote: the 2L journals have a reputation based on the uber-poor quality bearings (and nothing else from what I've read).

See my question? There's a bit of dogma floating around that the Chevy journals are as small as you'd want to go. So, that means that the 50mm 2L journals are too small, right? Nobody can answer that because all 1st hand reports are that the 2L rod bearings are shite...crappy rod bearings cannot speak for the strength of a crank with smaller journals.

Well, I dunno bout that. It seems an overly strong statement.
As long as Russ Fellows runs 400-450-ish Hp on those same stock rods and rod yournals and countless 2,0 ltr engines have done way over 100,000 miles with one rod bearing set, I wouldn't go to any length to change the size from 50.00 to 50.80 mm (that is the chevy size in 'mm'). The size isn't the issue imho.
Also remember that the type 4 rod is quite a bit wider - so it has more bearing surface (!) - than a 'buick' rod yournal.

Only when you want/need a longer rod, than the change is justified, again, just my opinion.
The Clevite chevy bearing is probably a lot better, and I don't know what you are building, but you may ask yourself if you would notice the difference when you are using a good synthetic oil, again largely depending on what you are building.

Best regards,
Walter