I know this has probably been covered a blue gazillion times. I even searched the board for an answer but can't seem to find one that satisfies my mind. I just received my cam a CC306 (not a small base circle) from a fellow board member. I lubed it up, slipped it into my 383 block nice and smooth, lined up the cam and crank pullies straight up, tightened the cam pully, and started to slowly rotate the assembly. Well surprise (NOT!!) it won't rotate freely. The number 2 and number 7 rod shoulder appears to be catching on the cam lobes. Now here comes the questions. It appears that the rod shoulder needs to be ground about .125 to .175" to clearance the lobes. since this assembly was already balanced will I need to have it rebalanced again or can I just grind the same amount from each rod? these are the scat 6" forged rods that my machinist said he had to recondition(?). I can't for the life of me figure out why he did'nt clearance the rods when he did the block clearancing, and assembly. Since there is no nut on the rod shoulder (these rods are threaded) how much can i safely remove and how do i check the clearance. One last question: how much clearance should i have between the rods and cam to allow for thermal expansion.

 

He didn't clearance the rods becuase you didn't give him the cam along with the rest of the bottom end. Every cam and every set of rods will have slightly different clearance issues when used together with eachother in a stroker. Some combos require a lot of grinding, some require none!

I think it's grind and rebalance time. Grinding down all the rods the same amount? I'm not sure that will work. Just keeping things even might work for reciprocating parts like pistons and wrist pins but I'm not sure it does for rotating parts like the big end of the rod.

It might be worth it at this point to look into a cam with a smaller base circle (along with appropriate length pushrods) and recoup part of the money you spend on it by selling off your current cam. Probably no less costly than having the bottom end rebalanced but it saves a trip to the machine shop.

 

Thanks for the reply Damon, However my questions are still not answered, I can balance the assembly myself, The checking clearance is what i am not sure of.

 

Are you asking how much clearance you need? The old rule of thumb is fifty thousanths (0.050"). Race engine builders like Bret may use a closer tolerance. As far as "is this too much to remove from the rods?" goes, probably not, though there is no hard and fast rule. Must it be rebalanced? Depends how much you remove I guess. It's easy enogh to remove the same weight (IOW just match the rods after gross clearancing). Will this throw off the crank/rod+piston balance? Well, the big end is less of an issue than the small end, but since you said you have balancing capability yourself, why take a chance?

All IMHO. Maybe Bret will chime in.

Rich Krause

 

Thanks Rich, The clearance ROT is solved now on to how to check the clearance, I would assume that a plastic feeler gauge could be used to check for clearance. Since the amount of material to be removed is considerably small, My balancing would consist of weight of rod before vs. weight of rod after grinding then removal of the same amount of material from each rod. would that work? I am trying to avoid a 50 mile drive and a rental truck to haul the whole assembly to my builder. On a separate note, the use of a small base circle cam keeps popping into my head, however I do not understand how that would help me in this case. My understanding is that a small base circle cam would still have the same amount of lift on the lobes, which is where the rod shoulder is contacting the cam. I have searched for an answer in the tech sections but can't seem to find what exactly a small base circle does to a cam. Methinks its just .200" smaller off the lift area of the lobe or should i say 180 deg. off of maximum lift area?. Correct me please if I am wrong!!!

 

Although my setup is completely different, I had to do the same thing.

I called up Powerhouse (who I bought the stroker kit from) and they said a minimum of .020 clearance from rod to camshaft. So I tried to be safe and ground all the bolts down so I have .030 clearance on every rod They also said grinding a little off each rod bolt won't hurt the balancing (they had previously balanced it)

My rods are the ones with the caps on them, good thing I didn't get a larger cam becuase I would have probably needed different rods

Like I said although our setups are different, at least this gives you a little more info on your buildup.

Good luck

 

Are these I-beam or H-beam rods?

 

They are I-beam rods, and I have them clearanced, I ended up grinding about 2.5 grams off each rod and a little of the bolt threads as well.

 

On a small base circle cam, the peak of the lobe is just as far from the base, but the base is smaller. So there is more clearance but the same amount of lift (the distance between the base and the peak). Make sense?

Rich Krause

 

Ahhhh i see said the blind man, makes a world of sense, then you would use a little bit longer push rod. ie .200" or so right

 

By George, I think he's got it!

Rich Krause

 

The clearance can be .020-.030, but there really is not need to run it that tight.

One thing to do when you do a I beam setup in a 383 buy the Scat I beam Dowel Pin cap rods. They are about $250 and have bushed pins and are already clearanced for the stroker. Also being Forged 4340 they are a great low cost rod for a under 600hp motor.

Bret

 

I don't think you need to get rebalenced unless you are taking some un godly amount out of the rod. Which you don't need that much. I bought a rotating assembly that came balenced and had to do this on 2 of the motors I built. They ran fine with no problems or troubles. Make sure you check all the rods, 1,7 and I believe it was one more that might be close or may even hit. I wanna say it was #6, but maybe someone that has built more of them will chime in.

 

I have a CC306 (non-small base circle) in my 383 and have no clearance problems with my SCAT 6" I-beam rods. At the time my engine was built the builder didn't have the CC306, he just made sure the rods cleared my hotcam that I was using at the time and as far as I know he didn't do any grinding on the rods. Wonder why yours doesn't clear and mine does?

 

He may have already ground enough off your rods to make sure they wouldn't hit with whatever you put in there.. I didn't have to grind the ones I put in either b/c the guy wanted to use his stock cam, but I told him I would grind them anyway incase he wanted to install a bigger cam later.