383 Con Rod Bolt Doesn't Clearance Cam Nooo :(!!!

So I put my cam into the 383 SBC I'm building with 6 inch rods, put the valve timing at 0 degrees and gues what........... THE RODS HIT THE CAM LOBES!!!!!!!!!!! I was told by the tech guy i talked to on the phone that this would NOT happen with 6 inch rods but obviously HE IS WRONG!! I have a fairly radical cam in there (0.50" lift) by Lunati Voodo. I really do not feel like taking the whole bottom end apart again since I have had to about 4 times already so my question are: #1- Can I buy a small base circle cam, from where and how much are they (if lunati even makes them??) #2- If I HAVE to grind material off the con rod then I guess I will grind, could somebody please tell me where I have to grind this since I can't get a very good look at that portion when it hits. #3- Can I do this grinding without removing the pistons only removing the rod caps and ENSURING I COMPLETELY COVER THE ENGINE OFCOURSE!! Any and ALL help would be very kind from anybody becuase I did not expect to be in this dilemna.

Thanks alot,
Keith.


Register now (free) or login to remove ads

Hey, when you put it together did you also install the timing chain so that they rotate together? They will definately hit if you roll them seperatley.

yes I did :'( I rolled them seperately before putting the chain on but I was hoping when I lined them up at 0 degress they wouldn't hit, well.... they do. Could you help me with any of the questions I had in the previous post?? Thanks alot,
Keith.

you sure it hits the cam .
never saw that
have seen them hit the block

That's why they make small base circle cams! LOL Rods hit.

Yes, you could get a small base-circle cam, but its not a garuanteed fix. It will definately help, but like i said not a garuanteed fix-all. Im not sure how much more expensive they are, or if Lunati makes them, but i know Comp has them. If they dont have the exact one you want, they'll make one for you! No joke. Oh yeah, small base-circle will effect pushrod lenght requirements. No big deal, just a FYI, in case you didnt already know.

Ok, now the grinding. First, get a little mirror or something to see exactly where they're hitting and then make clearances (.050" is enough). Id have the balance checked after all the clearancing is made.

I know its all a pain in the rump and can get pricey, but all-that streetable torquey power is worth it. Always better to do it right the first time!

Good luck buddy

Most of them that I see like this only hit a small portion of the rod and rod bolt. If you do decide to clearance the rods, make sure you polish out any grinding marks. This will help prevent a rod failure. Small base circle cams require longer pushrods.

Where can I buy a small base circle cam though........ Jegs only has like 2 of them for SBC............. not even hydraulic cams either.

Jeg's or summit or any of those guys don't even show 1/4 of all of the stuff out there. They just show the most commonly sold and new items. Check out the actual cam company sites. Use their online catalogs to find what exactly you need. Comp, Crane, Lunati, etc. If you dont know the web sites, just google search the names and youll be able to find the official sites.

The rods only hit on 2 cyls, i think 5 & 3 or something, But you must grind all the rod bolts , dont forget, the crank will deflect under load. A small base circle cam is a band aid on a chainsaw wound there, What about the push rod length? A small base circle cam and .200 long pushrods are going to set you back alot more than 2 hours labour to remove the rods. Use a belt sander ( the one you did your cabinets with will not work ) not a grinding wheel and DONT super heat the rod bolts while doing it or else you will have reverse heat treated rod bolts or as they commonly reffered to, Scrap. You grind the side of the rod 1/4 below the head of the bolt to no more than halfway through the center of the bolt head. Unless you are really handy you should not attemt this. You can buy 383 and 400 rods pre clearanced for this application, They would be a good idea before you get grinding. And you wont like this but if you have nicked the cam and you can feel it with your fingernail, it should not be used, this will wipe a lobe fast.

The Rod bolt heads are on the bottom of the rod caps unlike the stock bolts which place the bolt heads in the upper rod cap. I got the special 12-point ARP small head bolts just for this reason and figured they would clear but they don't on only a couple cylinders. I am going to grind rather than buy a small base circle cam because I have been told not to go this route. My question now is should I grind all the caps even the ones that do not require clearancing so it will remain balanced?? (it has already been internally balanced) My other question is a few of you guys said that the bolt HEAD needs grinding or mentioned the bolt head, how the hell can I grind the bolt head and expect to fit a socket onto half a bolt head???? I have been told that if I take roughly the same amount of material off of each rod at the same place I can maintain the balance fairly well, is this true?? Anyways thanks for the help with all these questions.

Keith

You would just grind it so it was shorter not at an angle. Still retaining the 6 points or 12 points but it would not stick out so far from the rods. This is for clearing the block though not the cam. This is one way that aftermarket rods are better because they don't stick out through the top of the rod which makes more room between the rod and cam.

Change the weight by 1 gram on any or all of the rods and you have just ruined your balance job. It won't matter how much you take off because when the crank is balanced they weigh everything (pistons, rods, rod bearings, piston rings) and then they make them all weigh the same (950 grams for example) then they apply the appropriate balance for that weight. As soon as you change that by increasing or decreasing weight your motor will be out of balance.

it could vibrate all the time or it might only vibrate at certain RPM's but you will not know that until you start it or have it rebalanced. It might even be so little that you won't notice it. Or It might feel like the whole vehicle is shaking. You just never know.

And the balancing "BS" machine sounds like it's about to fire up. Don't worry about it, you will be removing at the most five grams from each rod. Oil entrainment in the crankcase of a running engine amounts to more than that!--and it's CONSTANTLY changing with rpm and g-force Sounds like you are referring to a capscrew style rod and not a bolt and nut style rod, correct? Just grind on the rod "shoulder" where it interferes with the cam.

Do you mean you have cap screw bolts, like if you unscrew the bolts they are in your hand not in the rod? Or bolts with nuts? The side 180 from the bearing tang at the top above the parting line should be where the contact is. You can make a simple jig to ensure you only remove so much on each rod. Most balancing shops use a +or- 2gram, so dont worry about exact.