Main cap walking

What are you guys thoughts on main caps walking, is it more due to not correctly torquing the caps or is it beating up on the cylinders from too much timing or too lean and that causes the cap to walk. BB Chrysler Iron block with 1/2 inch studs torques to 85 ft lbs, with Torco assembly lube on the threads. On a blown engine. 20 lbs boost. Any thoughts would be much appreciated. Cheers. Post here or PM me.

 

I am on that too.....but i pushed too hard on the engine....cylinder walls with too much marks.....not have a pre-ignition yet.....

too hi rpm can cause cap walk?

and how to fix cap walk?

 

85 ft/lbs seems a little bit lite on for a half inch stud, if its a good quality arp stud with the supplied moly i would pull them down to 100-110 ft/lbs
hope this helps

 

Main caps

Detonation causes the main caps to "walk" and transfer metal..............

 

I would second this. 85 not enough

 

When I ran an iron block, I would contersink all the high tork treads so i had a 1/8 in deep hole befor the tread started, when you tork a bolt with the tread all the way up it distorts the mateing surface. (pulls the tread)just my two cents. P/S counter sink should be same size as bolt in this case 1/2 in. so your not takeing any meat from around the hole.

 

I've never heard about what Gene suggested but it makes a lot of sense. Cap walk is just an unfortunate fact of life with an iron big block Mopar from 550-600HP on up. Not sure why, since the block seems to have enough beef in it. Aluminum caps can minimize the effect a little bit since they soak up some of the harmonics. I've had pretty good luck with them although some people like the Pro-Gram billet steel caps. The NASCAR guys (probably fuel guys too)used to put 9/16th studs in the Hemi blocks back in the day, the extra torque seemed to help, but caps would still walk and transfer metal, even with the cross-bolts. I think there is enough meat in a wedge block if you wanted to try 9/16 studs somewhere down the line, think they can reduce it but don't think you'll ever get rid of it completely, especially if you're running boost.

 

Thanks to everyone who has either posted here or sent a pm. Your help is much appreciated. Thanks. John

 

Back then, 60's early 70's I ran a 354 or 392 hemi, Milidon made a ,what was called a girdel for the block, it mounted on the oil pan rails and put pressur on the three center caps, if i rember right it had .003 crush on the caps, you had to have this on a blown applacation or the crank would blow out the bottom of the engine, the only BIG draw back was that it was heavy, about 30 lb. i'm realy not sure about the weight. i'm sure if you check googel you will find it and see what it looked like, and mybe you could make one, it was made out of 1/2 in. steel .

 

Cap walk

We had problems with main cap walk on our BB Chrysler also. I used the Pro-gram caps and increased the torque on the mains to 110ft lbs (40-ft lbs on side bolts of Program caps). I also tall filled the block to increase strength. These modifications helped but never solved the problem.

The car weighed 2100lbs at the time and would run 7.60's with 20-lbs of boost.

After 2-seasons, the block broke near #2 cylinder lifter bores.

We have since stepped up to a Stage-6 KB dry block that we re-drilled for Indy wedge heads and have not had any problems with cap walk.

Hope this helps,

 

Beware of the desire to go up to 9/16ths studs!!! The original 1/2 inch thread is 13 TPI and the 9/16ths thread is 12 TPI. Tap drill size for the
9/16ths is .484, and the threads will cross one and another as you tap the new thread, leaving you with a less than desired and weakened thread, perhaps not as strong as the original 1/2X13 was. Your option would be to go deeper in the block to reach virgin material, but there probably isn't that much material available to go deeper. Just a word to the wise...
Also the idea of counterboring the existing bolt holes down .125 is very valid, as Gene said, it keeps the top thread from pulling up to interfere with the sealing and clamping force.
Henry

 

Good points Henry, I never had actually done this mod, and really hadn't thought about the thread depth and pitch. I had a couple of old Nascar Hemi blocks that had the big studs already in them, and since its been a while, it's hard to remember how much more meat is in the Hemi main area than the wedge block. I do remember on the Moparchat site about two years ago, someone was marketing a new billet girdle that basically mirrored the oil pan rail, similar to the old Milodon girdle like Gene was talking about, but supported all five mains instead of the middle three. Seemed like a pretty neat deal if you had to run an iron block, but I think in the long run, you're better off investing in a KB.

 

Here is a link to one of the girdle systems, but the one I'm thinking of was about 3/4" thick. I'm still looking for the link to that one.

http://gearsandrears.com/girdle.html

 

This one looks a lot more promising.
http://www.bcrproducts.com/caps_and_girdle_system.html