My machine shop wants $100 to drill/tap the splayed caps in. I have them bolted down in place and THINK i can do it myself. I have all the necessary tools and what not so thats not an issue. All thats keeping me from doing it right now is...

when I was on the phone with the shop, he mentioned something about there needs to be .003" clearance somewhere or something.....no idea what hes talkiing about. The fit like a glove in the steps and lay flat on the rail so the only issue now is drilling/tapping them in as far as I can tell.

Anybody know anything more about this than I do?

Also I do not know how far to go to not hit the water jacket (if its even possible) They included two bolts and the bushing with the caps so im assuming you are just suposed to drill them in as deep as these bolts would go in.

help please. thanks

Jon

 

"I have them bolted down in place and THINK i can do it myself. I have all the necessary tools and what not so thats not an issue."

If you have a mill I might consider it. The other thing is all the knowledge and machining skills to pull it off properly.

I have torn down a motor where the outer holes were not put in right (out of placement by .015) and because of that the main cap broke in half! So it's really critical to do the holes right or you will waste a lot of time and money.

The bushings are the only way to go to do it properly.

"when I was on the phone with the shop, he mentioned something about there needs to be .003" clearance somewhere or something.....no idea what hes talkiing about. The fit like a glove in the steps and lay flat on the rail so the only issue now is drilling/tapping them in as far as I can tell."

.003 is needed between the step in the cap and the outer part of the cap. Measure the step on the block with a depth mic and the step on the cap, you should get .003-.005 difference which is what you are looking for. This is one reason why I like a 4 bolt replacement cap, no gap betweem the cap and the block and no bending of the cap once everything is TQ'ed down. Seems that's a good way to prevent cap walk.


As for the water, no real chance on the block when you put main caps in. You will most likely drill deep enough so the tap can FULLY thread the holes enough for the bolts, you don't go far enough you will get false readings and then the hole 4 bolt thing was worthless.


I'm guessing the caps are Milodon? Nice caps but they are going to cause a issue with the dipstick. One reason why a factory 4 bolt style cap or a Pro Gram cap works better in a LT1 motor.

Hope that all helps. I might consider letting them do it for $100, because they can fix it for free if they screw it up you can't.

Bret

 

Is this the Milodon "drill your own 4-bolt" kit? Careful man, replacing a block will be a big ol PITA.

I was curious about this myself, but I'm wussing out and having the shop splay them for me.

Make sure you let us know how it goes.

 

Well, Bret, you scared me out of doing it. They are eagle caps, still cant figure out why no one likes them for $78, they ARE billet steel, their ESP material, Im sure theyre good for what I want out of them.

Is that .003" clearance the MAX, or MIN. Cuz when I bolted them down I had to keep them level or they wouldnt fit in the step, so Id assume there is .00000001 clearance between them.

Bret, if I have the bushing and they are bolted down into place fine can I screw anything up? Ill 99% chance just let them do it, but Im curious more about what CAN go wrong. And why do you say a mill is needed?

 

Is this gap due to heat expansion differences between cast iron and billet steel? Or is this solely to ensure there's no "U" shaped bending going on when the bolts/studs are torqued down?

The step you reffering to is the cap register right? I'm looking for a set of 4-bolt caps myself and assumed they were all spec'd the same from a fitment point of view. What "4 bolt replacement cap" has no gap? is this GM's straight-4-bolt caps you refer to? would all straight-4 caps share this property? (and all splay'd would most likely have clearance requirements to prevent problems with the angle-load?)


<snip>

Pro Gram caps are straight-4-bolt as well?

 

I'm not Bret, but the idea of drilling an angled hole into cast iron without skipping around on the surface, or keeping the hole at the exact angle nesseasry for the bolt... and then doing it 6 times in a row with no practise just scared the crap outta me. Hand-drilling this bad boy just doesn't seem like a great idea.

 

Do the Oliver main caps have the same dipstick interference issues? I may just go with factory 4-bolt caps anyway.

To the original poster: I realize we're all looking to save $$ where we can, but this is just something IMO that's not worth trying if you haven't done it before. It could be an economically devastating experience.

 

I am one of the few who prefer the straight "replacement type" caps, for the reasons Bret mentioned. The set I got this year were from Callies, but they look suspiciously like the Pro Gram pieces. Very easy to fit and I am sure they will be strong enough as the last ones I had were GM nodular iron straight 4-bolt caps and they held up fine. I would have used the same ones again, but they are out of production.

Rich Krause

 

Good things to think about.

Yeah the mill makes it easier because it prevents what you are saying plus you will want to center drill the hole first and take the hole up in a few cuts before you run the tap down in there with the mill.


Bret

 

I'm actually not sure why there is a clearance there, I'm thinking that it's critically important that the lower (inner) studs have the most clamping force on the cap since they are the closest. This would probably be best answered by one of the resident experienced ME's on the forum. (Just a hint)

Bret

 

There are such little heat expansion differences in billet steel vs cast iron that I doubt it's that. Again the reasoning for it I leave the old man to ponder about.

Yeah the factory 4-bolt caps are not steped and not splayed. On a big power setup like a blown or N2O (or BOTH like Rich) I like the Oliver 4 bolt replacement caps. That bad thing is that you have to mill the block registers perfect to use them. The fit of the caps is within .0005 and they have to be centered. Yeah it's a pretty fun thing to do. Most 4 bolts caps don't need this because they fit into the block register that is already there (stepped for a 2 bolt)


Depends on the PN but Pro Gram has a 4 bolt replacement cap.

Pro Grams Site list of center caps

You can see that there are a lot of choices....

1. Stepped with angle bolts for a 2 bolt block with stock register.
2. Stepped with angle bolts for 4 bolt blocks with stock register.
3. Flat Bottom with angle bolts for 2 or 4 bolt blocks (the block register has to be increased).
4. Stepped for 2 bolt blocks with straight bolt holes and stock register.
5. Direct replacement for the stock 4 bolt cap

So lots of choices. Oliver has a lot of the same caps.

#1 is the standard LT1 choice and for a NA motor is the easiest way to go.
#5 is what I preffer for big power blown or dope fed motors with a front main cap too.

Bret

 

The 4 bolt replacement caps are pretty good about the dipstick.

As I said cutting the block for this is a BIG DEAL!

Bret

 

Ah..I didnt realize shops did this on a mill, thought it was done by hand. Haha, forget I even asked then.

Think I should pick up a billet front cap? Right now I just have the middle three and stock front. From anyones experience is it worth the $ to pick up that front cap? If so who sells them and where do I get just one?

 

So the factory 4-bolt caps use a larger register and flat-bottom caps?

Ahhh... With all the talk of converting 2-bolt ot a 4-bolt design, I just assumed the registers were the same size.

Thanks Bret, guess I'll need to talk to my machine shop about the cost difference between drilling for a step-ed 4-bolt conversion, and machining the register (and drilling) for a flat-bottom cap.

 

I know Oliver sells billet front and rear caps... and I imagine Pro Grams does as well (the Oliver stuff looks suspiciously like Pro Gram's units.. even the bolt angels are the same when I last checked ).

I don't know if it's nessesary, but it sure wouldn't hurt I imagine. The front cap usually gets some wierd forces on it if a blower is run (due to the extra belt having more leverage and tension on the bearing than the stock belt would).

I'd wager this, like a 4-bolt conversion, really comes down to budget and engine specs (redline, operating rpm, belt tension, torque levels).