Big problem :(

[78' Silverado]

Well we started puttig the cam in today. Came into a big problem. first off were runing a Summit 383 Crank, 6 in. Scat Rods, and a Comp cam .630 lft cam. Well the first 3 lobes on hte cam are hitting the the #1 and #2 connectings rods. Is that b/c of the crank having to much stroke? Wat would the problem be? The cam spins freely but when spined w/ the crank it hits. Now thats at top dead center on number. Will adv. and/or ret. the timing get rid of this clearence problem. Or would it have to the with the cam to crank center line? Right now we 4 1/2 in. Center line from cam to crank. I have no clue wat so ever on wat the problem is. I figured, it would slid in no problem wat so ever. But, wat yalls advice on this problem? Is the cam to big, is my Crank, rod to cam combo wrong. The block is outa of an 86 Burb, and its a 1 piece rear main. Help me guys!! Thx

Tyler

[Captkaos]

You need a small base circle cam.

[TwinTurbo]

Maybe you can get away just radiusing the bolt heads and a small section of the big ends on those rods,from what i remember (and i have never used Scat rods so I may be wrong) they have quite a bit of meat there and can be radiused just fine. If not, do as captkaos says and get a small base circle cam.

[78' Silverado]

Originally Posted by Captkaos

You need a small base circle cam.

Wats a small base cirle cam? never ehard of that. Wanan fill me in please

[TwinTurbo]

Don't you know what the base circle of the cam is? It's the circle of the cam where there's no lobe, so the section the lifter rides when the valve is closed. A small base circle cam has, as the name iimplies, a smaller circle allowing more clearance. Lift is still the same as it's just the amount the lobe lifts from the base circle.

This should clarify it a bit:

[78' Silverado]

Originally Posted by TwinTurbo

Don't you know what the base circle of the cam is? It's the circle of the cam where there's no lobe, so the section the lifter rides when the valve is closed. A small base circle cam has, as the name iimplies, a smaller circle allowing more clearance. Lift is still the same as it's just the amount the lobe lifts from the base circle.

This should clarify it a bit:

Ahhh thx so much TiwnTurbo, Still learning, rmemeber this is my first hotrod engine lol. I called Summit, and talked to a tech up there. Umm, yea they said yea u need a small base cirle cam. They got one same as this one same lift same duration and wat not but smaller. So were buying that one w/ new lifters. So you mgiht see this old cam and lifters in the for sale forum along with roller rockers as well Thx guys!! Yall helped alot!

Tyler

[TwinTurbo]

Because of the smaller base you will most likely need longer pushrods, be sure to check valvetrain geometry.

[78' Silverado]

Originally Posted by TwinTurbo

Because of the smaller base you will most likely need longer pushrods, be sure to check valvetrain geometry.

Yea thats wat I figured. I'v never done that before and have no clue. I'm gunna ask a good firned of mine that knows all this. Now that I think about it, we'll need a new Sprocket/cam bolt set and new timing chain haha. Oh well haha. I jsut ordered the new cma and lifters. Lifters be in, in about a week, and the cam is special order and wont be here for a month but oh well. Thx agagin for the info!!

Tyler

[TwinTurbo]

First of all you will need a pushrod lenght checker tool. The geometry is easily checked, you can do it for 1 valve or all if you want to be real precise. Just watch the rocker tip (or roller if you are using that) and see if it starts out at the inboard side of the valve stem and travels to the outboard side without getting close to or on the edge in both extremes of travel (valve open & closed), that's all.

Why do you need a new cam drive setup?

[low 84]

with that size cam there is a chance that you still will have to clearence the rods even with a the new small base circle cam

[78' Silverado]

Originally Posted by TwinTurbo

First of all you will need a pushrod lenght checker tool. The geometry is easily checked, you can do it for 1 valve or all if you want to be real precise. Just watch the rocker tip (or roller if you are using that) and see if it starts out at the inboard side of the valve stem and travels to the outboard side without getting close to or on the edge in both extremes of travel (valve open & closed), that's all.

Why do you need a new cam drive setup?

I was being an idiot and wasnt thinking right. 69 that statement lol.

[1FaastC10]

Tyler, what heads are you running on that engine?

[78' Silverado]

Brodix, Dont have the specs rdy at the time I'll post them up later. They are fully cnc ported but not polished. And they have been on a flow bench and I'll post that up as well.