Main cap dowels
 

Looking for some advice here. Helping a friend with his 455 build and noticed the main caps are loose on the dowels. On some caps torquing and retorquing don't yield the same measurements, a few are .0025 out at the parting line. The vertical clearance is on the front cap is .0005 over the big end of the spec. too. We are wanting to line hone the block back to the low spec. but i figure we are wasting our time unless we fix the dowels first. He talked to some local "Geru" and was told, "They are all that way, don't worry about it". Does anyone have suggestions on how to do a proper fix? Not looking for answers like beat the hole shut or other cob jobs.

There are oversized dowells available from some people like the Butlers, Spotts, Kauffmans, or Pontiac Dude. If they don't have the pieces they know where to find them.

Course if you really wanted expensive pieces you could have a shop like the one I deal with take some 4340 steel, grind it to your rough size, heat treat it, centerless grind it to the exact size you want then you ream the block and caps to that size. A lot of effort though vs having the guys get you real close with other parts.

Tom V.

thanks for the info Tom. I had considered the oversize dowel route, but wasn't sure if they were avalable.

Any industrial-supply place will have dowel pins in nominal size (5/16") plus .0005" or plus .001" or plus .002". I've heard of some engines originally having dowels that were a couple thou undersize, in which case a standard 5/16" dowel might suffice. Of course you'll need a corresponding-size reamer.
If you need to make up more than .003" or so, you'll need to go up to 3/8" (or fabricate custom-size dowels, as Tom V said). There's plenty of "meat" to go up to 3/8" with no worries- I've done it a few times.

I was looking through the Fastenal catalog.... noticed they have 8mm X 34mm dowels listed. That is .0025 bigger than the original dowels and long enough to come flush with the hole in the cap. Gonna give 'em a call Monday.

Also have to order a couple reamers. Would .001 interference be okay for fit in the block?

You don't really want .001" interference fit in the block. A "light press fit" is called for, which means very close to a "zero" fit. Usually the first 1/4" or so of a reamer is slightly undersize (some fraction of .001") and gives the fit you want.
You also don't want a 34mm long dowel- more like 5/8"-3/4", with more than half of it into the block. You could shorten them with a cut-off wheel, then grind a little chamfer on the cut end.

By the way is there an easy way getting those *&$#@^! dowels out? I have a pin puller but that good Pontiac fit and steel laughed at the collets trying to grip it. Finally got one out so I could measure the hole depth in the block. I'm not looking forward to removing 9 more.

I don't know a good way to pull them. I just fight them with Visegrips, with a thin hard washer over them to protect the block. Seems like I remember playing the torch near some really stubborn ones. I've heard of people making something like a crude slide-hammer that they welded to the end of the pin, but I've never needed to try that.
Do all ten need replacing? I wonder why?

Jack,
Every cap has some looseness, figured if going to the trouble, I'd like to fix them all.

I would drill a hole in the center and tap it to the hole to 1/4". Use a bolt and some washers for a puller or make a spacer to fit over the stud. Should work fine.

5/16 Valvestems make super Main Cap dowels. :ranger: HIS

"5/16 Valvestems make super Main Cap dowels. HIS"

HIS, Just by chance I have some used ford 5/16 valves laying around. Mic'ed them, .03112, too small for what I need. However I have a bunch of used 11/32 valves and have reamers that size... thanks for the suggestion.

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I would drill a hole in the center and tap it to the hole to 1/4". Use a bolt and some washers for a puller or make a spacer to fit over the stud. Should work fine.

Jim, Great idea, going to try that tomorrow night, probably will try a smaller threaded hole. At 1/4 if I'm off a smidgen it would get into the block or even worse if I broke a dowel pulling it, the end might be worse than the beginning.

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I just fight them with Visegrips,

Jack, I tried the visegrips, there is only 1/4" of dowel sticking out, they just kept popping off.


Thanks for all the suggestions, I appreciate them all.

I don't know the hardness of original Pontiac main dowels. But if ViseGrips "pop" off them without marking them, I'm guessing they're nearly as hard as SAE dowels- in the range of 55 Rockwell C. If so, it would not be possible to drill and tap them.

Advice: 2-piece Ram Air III valves makes the best Main Cap dowel stock.

Professional Dowel Puller Collets are MOST effective on these unchamfered dowels.

Basic: Throw away ViseGrips - only good as welding Clamps

Ditto on the 11/32" valve stems. They make excellent dowels, and most shops have the correct sized reamers laying around (sometimes literally). We use "bent" race valves from the small block crowd. Good stainless, and workable.

Try some heat on the dowels. Using acetylene, heat them 'til they're red, allow to cool just enough to "lose" the glow, and hit them with some canning wax. You may have a fighting chance for the dowel tool to get them out. Work quickly. You're relying on the cooling process to "shrink" the dowel more quickly than the hole.

Jim

Last night I tried drilling holes in the dowels, they are hard but will drill with a new bit. This weekend might set the block up on a mill to drill them. Before then will try the heat and wax method. I've had great results getting gallery plugs out that way, good chance it could work here too.

Thanks for the help

I had the same problem with loose dowel pins in the caps. Although it wasn't found until after an engine freshen and took out the main bearings. This was after a fresh line hone also. I can tell you that loose dowel pins is not a good thing. I also had problems removing the dowel pins from the block. I drilled and tapped the dowels 8-32 or 10-32 (can't remember which) and put a screw in a slide hammer and pulled them right out.

Tim C

All this Dowel Pin Register stuff is sooo much better than a Step-Resgister Cap. :ranger: HIS

Oink 1 Dowel removal trick
 

Cover block with wet towel with a hole in it to access dowel, place grade 8 nut over dowel, click on vise grips that are laying flat on block. With a long clamp, hold the vise grips in position. Weld nut to dowel with a NICKEL rod.
When it just stops glowing red, turn vise grips back and forth while lifting up, stubborn dowles, place a pry bar under v-grips while turning. Works every time !!

Pontiac Gregg

I used to thing those stepped registers were the best idea ever, but then I fooled around with some BBC stuff and they are almost all loose as they can be. Then what do you do? At least with the pontiac stuff, we can drill them out, put bigger ones in, and make the block good as new. I guess you could always install Pontiac pins in the BBC stuff when it gets too loose.:D