Main cap walk?

[Garys1969RR]

Looking at the main bearing cap mounts on this 496 Block. Never seen cap walk before, but is there any sign of that here?

 

[Hemirunner]

Appears to be material transfer due to “cap walk”...

 

[Garys1969RR]

Yea I was thinking that. Do you prevent that by using studs instead of main cap bolts?

 

[zyzzyx]

I see it on the surface that you circled in yellow, but not the other one! Point loading and heat did that.
Never saw it before, but understand the cause. ARP main studs torqued @ 110Ft/lbs aughta fix dat!

 

[Hemirunner]

Yea I was thinking that. Do you prevent that by using studs instead of main cap bolts?

Studs will help as they are high strength and have increased clamping force. Girdles will also help stabilize the entire assembly and aluminum main caps can be added as well. Using a center counterweight crank will help if it’s a high RPM application. Lower reciprocating weight and a good balance job help. Simple things you can do, such as keeping the tune clean, and not detonating the engine are also key.

 

[rumblefish360]

IMO, also use a superior cap.

 

[Challenger340]

The "Load" is right behind #5.... which #5 itself is too close, so it acts as the "fulcrum" in the teeter-totter and then #4 gets walloped.
As mentioned... if you can move a slight over-balance on a center counterweight crank it helps alot !

 

[miller]

The main caps...do they just fall in place, or do you have to tap them in, before they fully seat? Should be the later.
Yeah, agree studs would be better way to go, as long as no ill fitting caps.

Or, full blown, and get the thing line bored, getting the mating surfaces cleaned up.

 

[Badvert65]

I have heard from my fellow racers that when you get into the 600+ HP range, cap walk becomes an issue with Big block Mopars. It happens with steel and aluminum main caps. A stud girdle or cross-bolt mains is the only effective cure.

 

[dvw]

That is next to nothing compared to mine when I got it. Almost 1/2 the mating surface on #1 had transferred material. Cleaned it up and ran it. Been that way for 525 passes making close to 900hp. Block is a Mega Block with studs. On the stuff we really beat on #4 main is always the one that takes it the most.
Doug

 

[Garys1969RR]

Thanks dvw! May go to studs for the mains. That increases clamping force, right? This is a 13 to 1 motor, and I've heard hi compression engines are more prone to cap walk.

 

[dvw]

Keep it

Thanks dvw! May go to studs for the mains. That increases clamping force, right? This is a 13 to 1 motor, and I've heard hi compression engines are more prone to cap walk.

Sure studs are best. What happens is the caps bounce. Keeping it out of detonation is the best thing you can do. Mine is 15-1. My bet is you should be running 112 or E85 fuel (I run 114). To much timing is a killer. Mine runs best at 32°. Even backing it down to 26° doesn't kill .10 in ET.
Doug

 

[Garys1969RR]

Oh, ok. I'm at 5400 feet, running 13 to 1 and 100 LL. I'll try backing off to 34 from 38 advance. See what that does.

 

[Hemirunner]

Oh, ok. I'm at 5400 feet, running 13 to 1 and 100 LL. I'll try backing off to 34 from 38 advance. See what that does.

You must be used to the BBC chamber that needs 38-40 degrees NA. Damn! If you got a good cylinder head on that you’ll pick up some power even at that altitude.