main cap walk

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J

Jbarker

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I recently tore down my 383 --> 489 stroker and found evidence of cap walk on every main cap. For that engine, I had the crankshaft gun drilled to lighten it up. Engine was probably just shy of 500 hp. The block was line honed before the build. It was a 440 source stroker kit, balanced by them. I used arp main studs (it was line honed with these in place) and stock main caps. On tear down, the main bearings all showed signs of wear, with a little copper showing on 2 of them. Rod bearings were all mint. This motor saw 6,000 rpm regularly over the course of about 12,000 miles, but I really didn't expect to see cap walk with this relatively mild build, especially with main studs and a fairly light rotating assembly. Going by ear, and looking at pistons and plugs, there was no sign of detonation ever.
The new build will probably be roughy 100 more hp. So the question is what to do to keep from blowing it up. Just run it and forget it? Girdle? Aluminum main caps? Blame it on the balance job on the crank and get it re-balanced? Was it the cheap 440 source fluid damper I used?
I'm leaning toward a 440 source girdle with my stock main caps as cheap insurance. And just like any other insurance, I'm not sure it will help lol! Aftermarket block isn't really in the budget, but from what I've read I shouldn't need one for 600 hp. Let me know what you think. Thanks!
-Jay
 
A BB MoPar just basically does that. A friend I built a 440 for who sprays nitrous got greedy and burned a piston, so we pulled it to inspect/freshen it. It had years and many passes on it, with a midrange bobweight, and the juice flowing on it most of the time. The pistons looked great (except the one that burned) and so did the rods/rod bearings (which I reused), but the #4 main was in the copper and no longer fit snug in the block or cap. My machinist said we got extremely lucky, he gauged the main bore and it was perfect and polished the crank. We had used needle-bearing rockers, so I attributed the #4 wear to oil starvation somehow via the valvetrain oiling. I converted it to full time (lifter galley fed) rocker shaft oiling with a restrictor in the head rocker stand, and put a new set of main bearings in. There was uniform cap walk, even with ARP fasteners, so I just slammed it back together. SO far no problems with it, still blasting the laughing gas and turning the number. Another friend has a 440 in a Super Street bracket Duster that ran for years, with a Herb McCandless setup (ultra-light Venolia dykes-rings pistons, polished/lightened LY rods, bridgeported combustion chambers to clear the pistons, etc.) and he ran nothing but VP112 in it and launched with a transbrake at 5000rpm. Used ARP main studs, and STILL had cap walk (worse than the 440 I built for spray, with heavier components). I think they just do it (cap walk), but make sure you don't starve the #4 main for oil with needle bearing rockers!!!
 
Thanks man. That makes me feel better. Your post also reminded me of one piece of information I neglected to include. The main caps were definitely all still tight in their registers, which I suppose is a good sign.
 
No problem. My stock main-capped 340/416 stroker with light ESP Eagle rods and lightweight Diamond dished pistons had cap walk too, but I suspect it had some detonation issues on pump gas (89-91) and street driving. Used ARP studs on it as well. Zero main bearing wear issues and I was able to reuse the rod AND main bearings upon inspection/freshening. Mild cap walk, but discernible.
 
I have concerns with the Source balancing, and also with the gun drilling a mid-price-point crank. If the crank is flexing you might have a bigger problem. What balancer is on it?
 
I'm using 440 source's off brand fluid damper.
The crank is the one part that I'm not really worried about. I think that piece can handle a lot more power than what my engine is throwing at it.
 
Jbarker said:
I'm using 440 source's off brand fluid damper.
The crank is the one part that I'm not really worried about. I think that piece can handle a lot more power than what my engine is throwing at it.
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I think u will help it w/ a girdle. I run a 440 source fluid damper and like it. I think it`s about impossible to totally stop cap walk. My approx. 600 horse sbc 406 had splayed 4 bolt mains and it had as bad a capwalk as I`ve seen. By comparison, the s.s. type hemi we used to run didn`t have hardly any, but still had a small amount. A girdle will definitely help a r/ b in my opinion.
 
famous bob said:
I think u will help it w/ a girdle. I run a 440 source fluid damper and like it. I think it`s about impossible to totally stop cap walk. My approx. 600 horse sbc 406 had splayed 4 bolt mains and it had as bad a capwalk as I`ve seen. By comparison, the s.s. type hemi we used to run didn`t have hardly any, but still had a small amount. A girdle will definitely help a r/ b in my opinion.
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But opinions are like--------, everybodies got one. WELL , MOST EVERYBODY !
 
What do the backs of the rod bearings look like? What about the tops of the pistons?
 
Have the rotating assembly balanced at a reputable shop and install a Hughes girdle. No need for aluminum main caps. I would also install a good balancer. I prefer to use Fluid dampners. Don’t forget to have the clutch/flywheel or flexate balanced also. You should have no cap walk after that.
 
440dartsport said:
Have the rotating assembly balanced at a reputable shop and install a Hughes girdle. No need for aluminum main caps. I would also install a good balancer. I prefer to use Fluid dampners. Don’t forget to have the clutch/flywheel or flexate balanced also. You should have no cap walk after that.
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There's also no need for a girdle. Especially the thin pieces of metal that just basically sit there, like most of these speed shops sell. You can't convince me they do anything to actually improve the structural integrity of the block. Snake oil for people to spend their money on... All the necessary machine work done well, with studs throughout combined with a correct tune is all you need, from my experience.
 
My opinion and I like and use 440source stuff I wouldn’t use that damper if someone gave it to me. I cheaper out once and bought a Summit damper and it spun. You didn’t give much info such as compression and type of heads on your build but if you are down to the copper after only 12,000 miles you have some issues going on. Everyone wants to jump on the girdle bandwagon but I’ve run lots of 8 second passes without one and will do it again. No concrete either. I save that for swimming pools.
 
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