Are main caps subject to "cap walk" without locators?

[Twincam]

Will A series main caps exhibit cap walk or other ill if their location feature is not used (e.g. hollow dowels, enlarged diameter on bolt or stud)? I've found several examples in the Big Block American V8 world were they are not used, even in some pretty high powered drag racers. Some people say absolutely required, some say not needed if - with caveats about using high quality fasteners. (Seems it would be worse with a V8 since power forces are more inline with the cap/block interface than is the case with an inline 4, but I realize a V8 is different than a 3 main bearing, crank whipping 4 cylinder)

Because of the popularity of ARP fasteners, I'm wondering if anyone has used the ARP for 1300 stud kit in an S block? That combination would eliminate the location feature. I'd like to find out if they regretted it or can say there's no issues.

[mk1]

Not something I have heard of. Personally I can't see the point in not using the dowels or whatever location mechanism the caps have.

[woodypup59]

Perhaps the Yanks use big "dowel bolts" fitting into tightly controlled holes in both cap and block.

[Exminiman]

why would you not use the dowels, if they are available, surly they can only e a good thing ?

They do wear also, so might be worth checking or replacing.......

[mk1]

why would you not use the dowels, if they are available, surly they can only e a good thing ?

They do wear also, so might be worth checking or replacing.......

Couldn't agree more.

[Twincam]

I agree with all of your responses too, and if I could use locators I would, but I can't.

Let me parse that a little. I originally posted a topic trying to identify a 1071 block that had conflicting features. One of the respondents was able to figure out my block had main caps from a different engine, basically an early bolt style block with later stud style caps. They were supplied to me as unassembled parts without bolts or studs so i hadn't noticed the discrepancy.

I believe S blocks don't have room for sleeve locators. I think that's the reason 1300's have cap bolt spacing set wider than studs on S blocks. If you were to install sleeve locators in an S block, the sleeves would breakout or near breakout into the shell region.

I'm currently exploring match boring the block to match the S style stud locator and using S studs but I wanted to explore the general concept of going without locators.

That's why I asked whether anyone has real life experience, good or bad, running an A series without locators.

[Oneball]

How can you gaurantee the main cap location with your set up?

US V8s without dowels locate their main caps either with the bolt or because the main cap is inset in to the block. They don’t just float around. Main cap walk when it occurs is very slight and just the tolerance in the locating surfaces or often because the clamping force isn’t correct. The usual solution is 4 bolt mains.

[Twincam]

I realize you can't guarantee location other than rough centrality by the crank. Maybe I've misinterpreted some American V8 forum posts incorrectly. Some of the posts mention cap "registration" in addition to the presence or absence or dowels so they may be suggesting dowels are not needed if the caps are nested into the block. I seem to remember Triumph used that method.

Yes, I imagine cap walk is similar to fretting corrosion in which micro movements promotes micro-welds that break and wear the surface.

I know of one bolt style 1071 that was built with just ARP studs without locators and it was fine but I don't have knowledge of its true longevity and it was probably babied for the most part. I was thinking that with the lack of new supply 1071 bolt, there may have been other builds using just studs that would provide some real world data.

What would your thought be of positioning using solid dowels, which engage using half their diameter into the ends of the cap, followed by align bore.

The reason I might go this way instead of going with Cooper S studs is that the primary location that must be maintained is the crank bore match between the cap and block to allow for needed align bore. If the cap stud locator pockets are not then inline with the block's threading, then the transferred bore that will accept the S stud's locator may not be concentric with the threads in the block causing binding when installing the stud. That's why I'm thinking ahead about using external dowels. Boy, that was hard to explain!

Thoughts?

[Spider]

The Caps may walk - you only need look at the mating faces and dowels to see if they have been trying.

The main function of the dowels though, is for precision alignment on assembly. Sue, you can likely run without them, but how do you assemble it spot on in the first place ?

[Twincam]

For my situation, the use of non-locating ARP studs is an approach I was thinking of using. I don't have any parts that are in that configuration that I could look at to see evidence of walking. That's why I'm asking others if they have experience with cap walking when locators are not used.

But...

I can agree a location feature is an absolute necessity for alignment. So..... if it's not possible to use original bolts, original studs or hollow dowels as a means of achieving alignment.....would solid dowels, we'll say 5/16" diameter, planted in the block at opposite ends of the cap, engaging by half their diameter into half moon cutouts at outer ends of that cap, be suitable location devices?

The 5/16" dowel I picked out of the air seems like a good compromise between area of contact for alignment and minimal size (less than the 7/16 used for 4 bolt mains).

[251 ENG]

Get some ARP cooper s main studs

Machine the lower half of the location diameter down to suit block

Fit 1275 caps and get block line bored

[Twincam]

Get some ARP cooper s main studs

Machine the lower half of the location diameter down to suit block

Fit 1275 caps and get block line bored

Thanks.

That is a way I had been originally thinking. I was concerned the bolt pattern and crank bore might not be the same for cap and block. If crank bore ended up looking like 2 half moons that slid off each other, it means the cap would have to be shaved further to achieve a full cut during the align bore. Guess there's plenty of meat there that it shouldn't' be a worry.

By the way, as far as I know, the only main studs that ARP makes are straight shafted 7/16" studs meant only for non-S 1300's There's no location diameter to cut down. Please let me know a part number if I'm mistaken. In any case the same suggestion would work with the non-ARP studs that are available.

Edit: Found the ARP ones at MiniSport. They must have an exclusive cause other suppliers don't list them.