Main Cap Girdle?

Originally Posted by donraye

I'm curious as to your opinion about cap walk.
Do you (or anyone?) think that cap walk is a problem in an engine like the one I'm building, which is about 550HP at the crank and has a hyd. roller cam so it will very rarely see RPM above 5,500-6,000? I know it's a problem in high RPM race application but what about a 6,000-6,500 RPM street motor like mine?
Don

From my understanding and experiences, cap walk is more related to tune and clamping force....or lack of it. Detonation (even slight) is a major cause of cap walk, thats for sure. Better fastener quality will help but don't think a girdle itself will stop it.
In saying that, I do run a girdle on our current drag only engine. I don't think it is really "doing" anything but it makes me feel better!!

The 302 Ford blocks are notorious for splitting at 500 - 550 hp

Do you know why?


The answer is simple! It is your intake manifold causing all of your problems along with cap walk. What happens is when you bolt up a 302 Ford manifold your bolts will go straight down into the block and what this does is puts a wedge into your blocks. When you start creating decent horsepower and your caps start moving inward they will egg-shape and cause the cap to lose its register. When this goes unattended for a period of time it will put stress on the hardware holding your cap in place. This will push the stud or main bolt over enough to crack the stud housing. (Main girdles are a waste of money! The only thing holding your caps in place is the hardware if your making enough power to push the caps off the block your main girdle is just going to go up with it also)






Once this occurs the wedge in your block that was put there by the intake manifold will automatically split the block in half because of the weak design. If you look at a small block Chevy the intake design is totally different. When they install the manifold the bolts go in at an angle putting a pre load into the block and pulling it together.

The Bessel Block support design puts a .003" pre-load in your block (basically pulling the block together like the small block Chevy does) and is held in position with dowel pins and cap screws. Simply put, the Bessel Block support system overwhelmingly increases the blocks stability. These are precision block supports which are designed from the center line of the camshaft. The supports must be installed with a bridge-port or CNC machine. Come with all hardware and instructions. (U.S. Patent Pending)

Or you can look into our Bessel Splayed Caps that lock into your block stopping cap chatter!

Those keyed main caps are slick. Best solution I've seen to prevent the cap from pulling away from the opposite register. A guy on one of the boost forums wanted to see how far he could push the block and welded the ends of the caps to the block - made nearly 800hp before splitting. I think your solution is better.

For the intake, we install the heads at only 10 ft/lb, then torque the manifold, and then finish the heads. This way the manifold acts as a girdle instead of a wedge.

What do you get for caps and machining - or just caps and we do our own whittling? Any track tests to zero-in on the general improvement?

David

Does anyone have a picture of main caps that have walked with a main girdle properly installed?

Main Cap Girdles aren't useful 99.9% of the time, when your engine isn't detonating. They come into play when a part of the crankshaft is pushed with the extreme force generated by the high pressure shockwave in the combustion chamber. The crank bucks, and a couple of the main caps are pushed a lot harder than the others. Normally, the bolts stretch elastically in the axial direction and push the caps back down with a decent amount of force. A main cap girdle adds its lateral elasticity to the axial restoration force of the bolt.

Since the crankshaft journals are located 45 degrees from eachother, there is little chance that all of the main caps will experience a bucking force simultaneously.

Here is a good example of my block and caps when using a stud girdle. I contribute this to using the bolts that came with the girdle. I had ARP studs but they were too short when I installed the girdle so like a dummy I used the bolts supplied. Luckily my bottom end didn't come apart. Build 'em, blow 'em up, and learn.

I will be using the stud girdle once again because it has a windage tray. I did order a set of ARP studs. I will also be using this valley girdle up top. Probably a gimmick but my buddy bought it for me.

HorsepowerSales.net and Valley Girdle Pro

Originally Posted by valleyfirearms

Here is a good example of my block and caps when using a stud girdle. ...

Excellent example of fretting and brinelling there. Thanks for sharing! It appears by the bearing spalling that you also had some det in cylinder #2. I feel strongly that any girdle start with high quality studs that will maintain clamping force, and they also need to have the nut and hardened washer directly against the cap (no spacer or above the girdle) to help prevent the cap walk and distortion. Then you can add spacers, girdles, windage trays, etc. above the solidly clamped foundation.

One more thought to stir the pot - if you're running enough power to need this sort of hardware, I think you should also consider running front and rear motor plates instead of mounts to reduce block distortion, or possibly keyed caps, or lastly a stronger block.

David

You are right David. I should be running a Dart block and I know there is one specific person who is going to say "I told you so." My next build will be a big windsor using a Dart block. I just wanted to get my 347 back together only to find out I could have bought a Dart block after all the machine shop expenses.

I know what you're saying, but a Dart block might cure the issue. What I'm saying is that you have a distortion problem. The block hasn't split, so it's strong enough that way. If you can isolate the root of your distortion problem (perhaps just the det), you can likely run a stock block indefinitely at your power level. Or, maybe not - I don't know how close you are to ripping that puppy apart.

You may want to consider (assuming a good tune, no det like it shows, and no pre-ig) that a partial block fill, the best studs or 4-bolt 2-3-4 mains, or keyed caps, and a valley girdle, or, or... could keep you running hard. Unless you're running over 550ish HP, you should be able to make it live. Over 600 at 6000+ is on borrowed time even with the best tune. Boosted power is much easier on a block than NA power - if done well. Even a Dart block won't hold any pre-ig or extended det.

Didn't you lose a top land on this one? If so, the det that overheated and seized the top ring and spalled your bearings may also be your only gremlin. If that's all it was then you're probably good to go with a better complete tune. The Dart sure is nice, though...

David

Good advice. It was the top lands on two JE pistons that broke. Thanks!