Chris`s85Z28

I`m trying to polish a 67 302 crank and need the specs for it. I really don`t want to cut it since it`s a forged 302 crank so I`m trying to save it by polishing it.

rskrause

What do you by specs? You mean journal size, or what? These were "large journal" cranks, I am pretty sure with 2.10" 2.450" journals. Of course, you need to measure anyway to determine the correct bearing to use, so I am not sure how the "spec" matters?

Rich

damnyankee36

The 67's used the small journal crank, the same size as the 283. 2.00" rods, and 2.30" mains.

angel71rs

1967 302 was of the small journal variety, 2.30 mains, 2.00 rods.

Exact spec for mains is listed as:

1 2.2984-2.2993
2-4 2.2983-2.2993
5 2.2978-2.2988

rods 1.999-2.000

damnyankee36

I've always wondered why the clearances are different on Chevy engines. I'm surprised the factory could keep within these tolerances. Look at the difference between the #1 journal and journals #2-4. There is only .0001" difference between the two sizes!

Chris`s85Z28

thanks angel71rs thats the specs I wanted can anyone tell me how much undersized the rod and main journals can go .001", .002" ?? after I polished it the most undersized journal was .0025" under

markinkc69z

You can usually get .001" under bearings. Small journal stuff should be available from Clevite. You need to make sure the journals are round though. Be sure to mike it. There is nothing wrong with turning the crank undersize btw. I dare you to break a 302 crank, the leverage just isn't there. BTW I run a 302 in my '69. I used the 5.94 PM rods from Gm and ARP bolts. This allows you to use a 350 piston which is much lighter and of course there is a large selection. Its seen 7800 numerous times, just don't expect a synchronized transmission to shift up there.

Clevite bearing numbers:
Rods CB745H1
Mains MS429H1

H series is a harder bearing only suitable for use with a steel crank. The embedabilty is lower and you may experience more crankshaft scratching if it is subjected to a dirty environment. The bearings may still be available in a V series which is the old Vandervel cast copper lead indium bearing. These are excellent for all around high performance use, but availability is spotty. V series are like the Childs and Albert bearings.
.001" under is not available in P series for this application

angel71rs

Factory 302 cranks were tufftrided, so if you do turn it, you lose the surface hardening.

markinkc69z

So. If you polish off .001" its gone as well. Its a surface treatment. You're not going to break a 3" forged steel crank under high performance use. Ford guys run blowers all of the time on a cast iron lightweight casting. There aren't many harder environments than that, and they run them with much success.

angel71rs

I think surface hardness goes down 2-3 thou. At least it does for most forms of surface hardening. Won't decrease strenght to remove it, but surface is less resistant to wear.

markinkc69z

I agree angel71RS, but he mentioned that he had taken off .0025 already by wear/polishing. I don't remember my DZ crank being black like some 427 cranks I have seen. I have always turned my cranks because I wanted them to be round and indexed which usually requires a .020" under grind. I have never had any kind of crankshaft failure. I think many people are scared of turned cranks for high performance use without merit. His small journal 302 crank is essentially a 283 crank, but with a slightly different balance for the heavier 4" bore piston. There was no special treatment given to 283's and all small journal blocks are 2 bolt, which shouldn't give him any trouble especially if he uses studs. I shouldn't have made the comment about .001" taking it off, but usually if you have a surface treatment once you start abrading it, you're going to go through it in spots.

http://www.wallworkht.com/HeatTreatm...ufftriding.asp