Gentlemen. I am building a sbc 383 using a 1989 two bolt roller 350 block . I’m using the scat assembly with flat top pistons. The assembly rotates fine but the cylinders will need to be ground for a little more clearance ans the rod bolt is close . Any idea how much I should have for clearance? Are there any other areas I should look at using this assembly before taking it back to the machine shop. Thanks.

 

.050" is the usual. I use a medium sized wire tie as a gauge.

Pay particular attention to the camshaft. The rod bolts come REAL close to it.

 

thanks, that’s what I’m worried about. I have ground the cylinders for the rod bolt clearance however the machine shop didn’t want to install the cam bearings because of metal in the block from grinding. I can see what you’re talking about with the camshaft as I can see the rod does come into the camshaft hole. The assembly does need to be balanced as well . I’m wondering if I should just chance it and look at it when I assemble the engine ???

 

These ^^^^ two phrases do not belong in the same sentence.

 

This thread ended up getting hi jacked after a few good responses. Here’s the deal. The machine shop didn’t want to install the cam bearings as I would be clearancing the block . So checking the cam clearance in the assembly was sent for balance wasn’t practical. I had to clearance the cylinders on one side of the block a little more . The assembly rotated but was close. The cam I have chosen is a GM 383 cam 528 is the high on the lift . The assembly is all scat I have read good things about clearances using this assembly. That said I’ll send it all back to the machine shop for block finishing and balancing . I’ll do the assembly and check the cam clearance myself. I’ll report back and let everyone know how it goes. I believe that since this build is so popular there shouldn’t be many issues that are difficult to resolve. Thanks

 

Max lift has relatively little effect on this issue.

First, THIMK about "lift" for a minute. Cams are generally made with the "nose" (the part that's active at max lift) about as tall as it can be and still fit through the bearings. Then, "lift" is THE DIFFERENCE BETWEEN the height (outer radius) of the "heel", and that of the "nose". They actually grind the "heel" down SMALLER to give higher lift. Meaning, that a cam with MORE lift, is actually more likely to give enough clearance, than one with lower lift.

OTOH, the 2 points during the cam's rotation at which the rod adjacent to it, can come up and hit it, vary from cyl to cyl. I can never remember which cyls and which valve and what 2 points of the cam cycle it is. Unless someone else can come up with that info, you'll just have to check.

Obviously you don't have to grind on the block anymore once you get the bottom of the cyls clearanced. At that point in your operation you can clean up the block at the quarter car wash to get rid of shavings (keeping in mind that the vat or the oven DO NOT dissolve metal), install the cam bearings, and put in the cam & timing set; and check CAREFULLY for clearance. If you find a clearance problem you have 3 choices: get a small base circle cam (often the grinders will custom-fab whatever cam you have chosen that way); or grind on whatever part of the rod interferes, which is usually the head of the bolt and/or that corner; or replace the rod bolts with ones that give more clearance such as 400 ones. Since you have an "assembly" that was created as part of a stroker setup, you might not have trouble with this, butt the only way to know is to check.

Wait to get the assy balanced until after you make this check and are finished taking care of whatever you find that needs it.

If the rods are cap screw type, rather than bolt & nut, they'll probably be OK. This photo shows why and potentially how much, compared to stock "X" rods.



This is an Eagle rod, butt the principle is more or less independent of the mfr.

 

thank you this certainly makes sense I’ll do this !,

 

You probably don't even really have to use the cam you're going to run, for the clearance checking. An old stock one would probably be adequate, although if you're planning on running a roller, I'd use an old aftermarket roller just to be safe, since the lobes are a different shape on those from any stock one for SBC. Just make sure you leave a bit more than "the bare minimum" and most likely it will work with any cam.