I did a mockup of my 406 today, but i don't have a timing chain yet. When i put everything in and cycle the crank and the cam by hand, at certain points the rods (there are 2 of them that hit, but at different times) hit the lobes on the cam. Now, I'm fairly certain that this would not happen with a timing chain on, and will certainly test that when I get the chance, but the question is, is this semi-normal to happen with large cams in 400s with 5.7 rods, or should I grind the rods to clear the cam no matter what (as in, in case the timing chain breaks and its free spinning).

The rods that I have in there are Ohio Cranks H-Beam 5.7 rods and the cam is a comp xs-290s
COMP Cams Xtreme Energy Camshafts: CCA-12-679-5 - summitracing.com

Thanks

 

Yes it is normal.

The rod length makes NO DIFFERENCE. The rods inhabit the cylinder of the cam, regardless, even in a stock 400.

What DOES make a difference, as far as the rods are concerned, is that 400-specific rods have slightly shorter rod bolts, with a corner shaved off, also; even stock 5.565" 400 rods are like that. If your rods AREN'T 400 specific rods, you WILL have trouble. But that has nothing to do with their length, as such; only whether they're SPECIFICALLY MADE, or at least adapted, for going in a 400. Or, if they use cap screws, instead of bolts and nuts. That kind usually has ALOT less material at the points of interference.

In fact, even with a stock 400, you can't remove or install the cam unless the crank is turned appropriately.

Having a "big" cam usually improves the situation; since the tips of the lobes are ALWAYS as big as they can make them and the cam still install through the bearings, a "smaller" cam actually has larger diameter lobes.

 

acidpad,

That's one "agressive" cam there! Is it mostly a strip car? I just put a roller cam in mine, but not quite that much duration or lift, and it's a lopey idle for sure. But mine's 90% street.

I'm using 5.7 Eagle sir rods and I got a small base circle cam. Unless you can grind the rods you have a bit and not upset the balance too much, or find different rods (and re-balance the whole thing)....or get a cam with a small base circle (best bet).....maybe someone else knows??

But honestly, I'm not sure if my rods would've cleared or not on a standard size base circled cam...

 

A meaningless check until you actually have the chain installed (exactly as it will be on the final assembly- including degreeing the cam to it's final position). As was stated above, unless those rods were built for stroker applications you're likely to have contact. It may not be much- little enough you can grind a bit of the rod and rod bolt "shoulder" off to gain the clearance you need. Or contact could be extreme, in which case you'll be thinking long and hard bout either a small base circle cam or different rods (or both).

 

check it once you get the timing chain and degree the cam in. i doubt you will have any issues with that cam and rods. if they hit just grind the corners slightly to clear.

 

Some info here, look down the page for a picture:

Chevy 406ci Small-Block Build - Tech Article - Chevy High Performance Magazine

 

Hey,

Thanks for the replies. The Ohio Crank H-Beams use cap screws so they are suppose to be some of the best you can get for clearence in these type situations. There is not much material hitting, and it is definitely only when it is out of time, so is it even worth grinding the rods to clear this situation, or just put the timing chain on and verify 100% that it wont hit in time ?

Basically, is it going to be worth the extra money, or should I even consider grinding and have the whole thing balanced to clearence the setup for a situation that SHOULD never happen.


As far as switching cam or rods, thats not going to happen. I'm not going to find another rod that going to give me that much more clearence, and I really like my cam. It's not going to be mostly track, but basically a street toy that I can take out and wallop on when I'm in the mood. aka, never going to see rain or much traffic, and definitely not a daily.

 

I would have the grind/balance done for just-in-case. Rather safe than sorry, esp. if a lot of money and time/work has gone into it.

 

BINGO! YES DO THAT! .....I didn't catch the fact that you DID NOT have a chain on it and aligned on your first post when it was touching. Get a chain, try it and let us know. Done deal.

-And if it hits, get another cam. I have a Comp cam, and it didn't cost me anymore than a standard grind. You can get one with the same specs as the cam you have now...except it'll be ground on a small base circle.

I only like cams that work myself! lol.

 

If it doesn't hit when the motor has the timing chain on, then you're fine.

Leaving it this way essentially makes it an interference motor. (except WRT to rods and cam, not pistons and valves, but same end result really).

Many many motors have been made that way by the factory, since timing belts/chains rarely just "fly apart" assuming regular replacement.

 

Easiest thing to do would be to lay one of your rods on top of a stock 400 rod, and see what the difference in clearance is. If yours have less material than stock ones right up at the very corner where the rod bolt head is in the stockers, then it'll be fine.

UNDER NO CIRCUMSTANCES would I grind on the rods, except as a VERY LAST resort, after ALL OTHER options had been exhausted. Which means, a custom cam, BEFORE grinding on rods.