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Old 04-28-2013, 10:21 AM
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Rod Bolt to Block Clearence

Hey guys I need to know what the minimum clearence I can have between my rod bolt and block. I did some measurements and right now I have AROUND .038 (maybe a little more but not less) of clearence when spinning the crank. I heard this somewhere else but dont remember and Im hoping someone knows who has built an engine before.

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Old 04-28-2013, 10:33 AM
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You need about .050", some use a long zip tie as a guide when grinding. Some ARP rod/bolt combinations will clear. Also check cam to rod clearance, you may need a small base circle cam. Again, depending on parts used.

Do a search in this forum for "rod bolt clearance", you'll find a lot of posts.
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Old 04-28-2013, 10:42 AM
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I'm building a 383 and all my research has said .060. Good luck!
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Old 04-28-2013, 11:34 AM
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Im using eagle rods and eagle arp thread in bolts that came with them. 5.7". Is it better to grind some of the rod or bolt or to grind some of the block?
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Old 04-28-2013, 02:37 PM
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I would only grind the bolt heads to clear the cam base circle, unless you can't take enough off the pan rails to get your clearance.
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Old 05-02-2013, 01:59 PM
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I took some off the bolt heads so know I can slide a zip tie in between. The pan rails wasnt the issue tho. A little lower was.
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Old 05-02-2013, 05:00 PM
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Originally Posted by ChevroletSS View Post
I took some off the bolt heads so know I can slide a zip tie in between. The pan rails wasnt the issue tho. A little lower was.
Got here too late! The simple solution for stroker clearance is to use the cap screw rod rather than the bolt and nut version. These almost always clear the block and cam without grinding, if grinding is required it is minor and in a less highly loaded area than the bolt head.

Grindeing on rod bolt heads gives me the shivers, I avoid it period. Although I know people who do it, but I can't.

Bogie
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Old 05-02-2013, 05:18 PM
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Grinding on rod bolt heads gives me the shivers, I avoid it period.
Never have, never will.
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Old 05-03-2013, 02:34 PM
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Cap screws are what Im using sorry guess i worded it different. I didnt have to take off much, Ill still be able to use a socket to get them off. It still seems close tho.
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Old 05-03-2013, 07:22 PM
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Cap screws are what Im using sorry guess i worded it different. I didnt have to take off much, Ill still be able to use a socket to get them off. It still seems close tho.
What do you mean by still able to use a socket to remove them? Normal practice is to remove material from the pan rail rather than the bolt head. Typically the upper part (shank) of a cap screw rod will clear the spigot extensions of the cylinder bore, but typically when a clearance issue is found here the bottom of the cylinder is clearanced. The only grinding on the rod or head of a conventional rod bolt (of bolt and nut design) is to clear the cam.

The clearance is usually pretty tight .050 inch is commonly used. One can see that if you loose a rod bearing, perhaps not even severe enough to do more to the rod than spin the bearing, the crankcase and cam are going to get hit.

Not that I think that taking a little material off the wrenching end of the cap screw's head is going to cause you problems other than getting a wrench socket on the bolt, but this isn't usually where material is deleted for clearance. At the other extreme one has to be careful about grinding on the pan rail or cylinder spigot as it's all to easy to discover coolant. To that extent the Vortec 880 block is somewhat easier to deal with because the cylinder wall so called spigot on the bottom does not extend as far into the crankcase as it does on other blocks. Because of this, the 880 block is better run with hypereutectic cast pistons, or if forged, the high silicon 4032 rather than the slightly stronger low silicon 2618. Because high silicon content pistons can be run with tighter skirt clearance so the thrust side reversal at BDC can't use the wider clearance of less thermally stable piston material to accelerate the piston to where the skirt gets cracked or snapped off.

Building an engine, even a simple engine, these days is not an easy task. Newer design elements for new materials have made several subtle but significant design changes to the Gen I and II SBC as well as the same kind of thing happening over at the Chrysler and Ford houses. So it's easy to stumble into previously unheard of problems simply by mixing parts from different years of technologies. Most of this stuff is not published and many engine building books out there are now many years behind the state of art that was incorporated into the last production years of the old SBC. When you arrive at the Gen III motor it’s a whole different world where in a lot of the ways you see the kind of kludged together ideas that show themselves in the Gen II LT1 an 4 of the 1990's become refined and defined in the extraordinary LS series engines of today.

Bogie
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Old 05-04-2013, 07:05 AM
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Humm.Not going back to re-read.Are ya using the short 400 rods??.

Believe it or don't,but what we found is the wire thickness of a standard paper clip is just about right for a number of different brand name rods for the pan rail clearances.
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Old 05-04-2013, 07:19 AM
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All I know is that what I took off wouldnt hurt anything but Ive been told by everyone that most guys use a zip tie and as long as I can put it between the block and the rod bolt head Im good so I took off a little on the bolt head cause I didnt need to remove much. I dont have any clearence issues with the cylinder at all so I should be good there. As far as my cam I havent decided which or what Im going with yet so still need to wait till I get it. All in all I hope im good with my clearence ill post some pictures later today
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