Thread: furthest under for crank/rods on a blown motor; 10/10 10/20 20/10???

Tweet

Hello Everyone, what is the most that is acceptable on a blown motor in regards to the crank/rods being turned down??? {392 Hemi, street/strip, 6:71}. 10/20, 20/10, 20/20 or ??? Thanks & have a great week-end! :-) Bill

Two items of concern---crank journal harness will be ground thru

Bearing choices are limited in undersizes---
However , it was ( and is ) common to offset grind jounals down to stroke a crank and use bearings from another application---

Being that its a 392 you can offset gring it to pick up an extra .100 stroke

Choices for replacement cranks are limited

If only scuffed some you can have it hard chromed to standard size

Hope this helps


Jerry

...Thank You Jerry, I read something somewhere r/e it's not good to have the crank & rods ground down to much in a blown motor {oh, I know nothing about this topic, other than what I read a while back}. Well, I called PAW in regards to ordering one of their 392 Hemi kits on Friday. When I asked about what the crank/rods were ground down to he said sometimes 10/20, sometimes 20/10, sometimes 20/20 & then stated that lately most of their kits have been purchaced from out of the county & that no one even asks that question. That they have sold quite a few kits lately and that the pickings where pretty slim. The guy said he'd check to see what is available & call me back.... I then called my engine builder & asked him what he thought. He said that 10/10 was fine, that 10/20 was fine but that 20/20 or more really wasn't that good. Because the bearings have to be to thick {especially if the bearings aren't solid steel, if they have used other materials to make up the thickness difference}.... When PAW called back I missed the call & by the time I saw they called they were closed.... So I will call PAW back on Monday morning to see what cranks/rods that they have available. But before I talked to them I wanted to know what you guys thought. I DON'T want to buy something that PAW says is a good kit & then have my engine builder say "that's un-exceptable tolerences". Then I'm stuck between a rock & a hard place! PAW says if something is wrong that they will replace it but being as it's a 50 year old motor who knows what could happen! PAW says it's a good kit, my engine builder says it's not, I'm in the middle, when I go to exchange it PAW says "all we have left are 354 kits, no money back", etc, etc, etc..... So a couple of questions; 1) how much grinding does it take to go through the hardness? 2) At what point {20/20, 20/30, etc} is an engine kit un-exceptable? THANKS Bill

As far as rod sizes---they can be ground down to standard chevy sizes, either bbc or sbc(Nascar now uses Honda size)
Mains---mostly bearing choices--severe undersizes don't have top level bearing materials
Hardness of crank needn't be worryed about---the steel crank is harder than most cast cranks anyway
Whats wrong with the crank you have????if you have one---

Depending on budjet there are lots of choices

In one that I'm building for myself ( 33 roadster) I am going to offset grind the rod journals down to 2.2 bbc size and run billet rods on it

The smaller rod diameter lessens the clearance grinding necessary in the bottom of the block also

Jerry

PS----I'm looking for a mag Cragar blower manifold and an Enderle barndoor injector so I can build it like the engines from my dragracing days( and nights)

Thanks Jerry, I talked to PAW again this morning & the block they have is already bored .060 over & the cylenders aren't in good shape so they were going to sleve it back to standard bore. The best crank/rods that they had were 20/30 under & my engine builder said don't get it.... So back to square one....... Bill