Engine build questions

backfocus

Member

Sep 3, 2004

254

3

18

Little Rock, AR

Apr 6, 2011

#1

• Apr 6, 2011

• #1

Of those that have built a 331, did you have to clearance the cylinder skirts, or anything else? Also what is the correct clearance for the crank and rods from the block?

Third question, I knew my current crank had been ground down before, but I recently had it checked and the machine shop confirmed it is a 20/20. I think that means the crank was ground down .020? Does that also mean the mains where .020 as well? If that is the case if I get a 331 kit do I need different bearings than what comes with the kit?

 

RangerJoe

I leave the horn on while driving

15 Year Member

Apr 26, 2010

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Georgia

Apr 7, 2011

#2

• Apr 7, 2011

• #2

I used the scat 331 kit to do my build early this year. It had I beam rods and they were no where near hitting the piston skirt. However, if you use h beams, you may have to clearance them.

Yes, your crank was turned .020, but your main caps should not be effected. Thicker bearings should have been used to make up the difference. Standard bearing sizes that come with your kit should work. Measure to make sure...should have .020 to .030 clearance on rod and main bearings.

Good luck.

 

FastDriver

I was uncomfortably high & wearing a helmet

SN Certified Technician

Sep 5, 2001

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Vass, NC

Apr 7, 2011

#3

• Apr 7, 2011

• #3

What are you asking about in terms of clearance? I'm not sure I follow what you mean. Are you talking about ensuring that your rods don't hit the cylinder skirt? If so, then there's no magic number. You just need to notch the skirt so that there is no contact between the rod and skirt.

 

backfocus

Member

Sep 3, 2004

254

3

18

Little Rock, AR

Apr 7, 2011

#4

• Apr 7, 2011

• #4

Thanks for the reply RangerJoe, that is what I was looking for mostly.

FastDriver, I was looking at the clearance between the skirt and the rods. I have heard that there is a safe number for the clearance, meaning as the bearings wear, it still gives safe clearance without causing major problems. Anyway after looking at numerous posts, some people say .060 and other say .10. I am probably over thinking it but I already have the motor back from the machine shop and was going to go back to the 306, but now have decided to go 331, but I will need to notch it I think, we will see when I order the rotating assembly. I was just looking to seem what other people did or have experienced.

 

FastDriver

I was uncomfortably high & wearing a helmet

SN Certified Technician

Sep 5, 2001

6,104

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Vass, NC

Apr 7, 2011

#5

• Apr 7, 2011

• #5

Cool. I can't give you number, but it sounds like you're on the right track. Maybe Rick91GT will chime in. He's probably got a preference.

 

Rick 91GT

Mustang Master

Nov 29, 1999

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PA

Apr 7, 2011

#6

• Apr 7, 2011

• #6

I like to see .060"-.080" on a quality steel rod motor.

If your stock crank was 20/20 then both rods and main journals were turned. You will need to check the main clearance with the new crank and bearings, it may vary and you may need to hone to get the proper clearance.

 

90 lx convert

Stanger

Founding Member

Aug 13, 1999

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18

Falling Waters Wv.

Apr 8, 2011

#7

• Apr 8, 2011

• #7

I noticed you said you already have the motor back from the machine shop. The best time to clearance the block is before it goes to the shop that way when they tank it all the debris from the clearancing will be removed. Don't forget to debur the cylinder notches after you're done. Make sure you scrub the heck out of the block once you're finished. Just a little bit of metal left in there will make the bearings very unhappy. Mike