I have a few machining questions that have been bugging me for a long time.

RODS

1. When a rod is rebuilt, material is cut off both the cap and the rod, correct?

2. If material is cut off the rod, then the rod length is shortened slightly. That bothers me. Can that be corrected by bushing and boring the small end?

3. If the rods and caps are cut at a slight angle, how tight are the bolts when the big end is honed?

4. Is it better to cut straight or at an angle?


BLOCKS

5. Before a block is align bored, the caps are removed and cut. Are they cut straight or at an angle?

6. Is the block cut at all? If it isn't, the crank centerline would be up in the block, and the plane of the split between the block and the caps would not intersect the crank centerline. That doesn't seem optimal.

I'll have more questions later, but let's just start with these.

 

Usually off just one surface.


If the rods aren't bushed already yeah, if not its a lot of work and you have a weaker rod.... usually it's cheaper to get new rods. Hell I know I replace Eagle H beams rather than fix them

you TQ them down to final spec, or stretch.

straight

Straight... at least perpendicular to the vertical... this gives you a true thrust face, which if that is off the thrust goes all to hell... Believe me this is a problem. I blueprint rear main caps based off the thrust surface, first making the sides of the cap parrallel to the thrust surface, then the bottom perpendicular to the sides, then the top washer face parallel with the bottom.

When you cut the caps you re line bore the block so the caps and block split the mains in the center of them, then you line hone to size.

When you cut the cap you raise the centerline of the mains in the block, this throws off the bores, decks and cam to crank centerline. Which means you have to bore, hone and deck the block relative to the NEW crank centerline and usually run a different timing chain to tighten up the slack of the chain, or a timing chain tensioner.

Bret

 

Really? Then when you hone the big end, is any material removed from the rod?

More questions...

Rods
So if the bolts are tightened to the final specs, why do people think that it's good to angle cut the caps? So that the bolts are straight when the big end ovals at high RPM?

Block
OK, so we've trued the caps to their bolt/stud holes and align bored and honed the mains. The crank centerline has been moved up (toward the cam) a few thousandths into the block, so we will use a reduced center-to-center timing chain. But no material has been removed from the block at the cap mating surface. This means that the plane of the split between the block and caps will not intersect the new crank centerline, right? So the bearing half that goes in the cap will actually protrude out of the cap a few thousandths of an inch. Does that have any impact on bearing crush?

Oh, and how is the block registered during the align boring/honing of the mains? Off the cam?

 

lol... notice what time I answered this the first time?

Whenever you bore or hone the new hole in something and you cut the cap, you will now have made the axis perpendicular to the split smaller, so to do this correctly you will cut equal amounts out of both ends to bring it back out to size, one reason why you bore the new journals in for shape then hone to size....

Yes the split will occur in the lower half of the bore... but it doesn't change the clearance and bearing crush since only the bearings touch each other.

Yep you support it thru the cam journals.

Bret

 

Do you you know whether or not, the block actually NEEDS align boring/honing?

AFAIC, is is faulty reasoning to ASSUME the block main bores need reconditioning, unless the block was 'tramatized' in some way. Unless you are assembling an 8000 grand engine, a tenth here or there, would not really matter. Better have a competent performance engine block establishment check/measure/evaluate the condition of the block. Then let their expertise decide if the block actually needs that work. If they lack the common sense here, and insist the block will automatically need the main bore work, consider another shop.

 

No. I have a block, but it won't be machined for quite some time; I'm just curious about this stuff. The main concern is that all the main bores should be concentric with each other, right?

To summarize the hypothetical situation, we've had the block hot-tanked, mag'd, pressure tested, and sonic checked to make sure it can take the overbore we want. It's been align bored and honed so our caps are right-on and the crank CL is dead parallel with the cam CL. What's the next step in ultimate block prep? Decking, boring, or something else?

 

You dont need an align-bore unless you are changing to a splayed cap that requires it.

Clean & Mag
De-burr block
ARP main studs with line hone
Bore/hone w/ torque plate
Deck for proper piston recession
convert oil galley's to screw-in pipe plugs

 

So now it's time to bore the cylinders. Does it require a special machine to bore them where they're supposed to be, or can any boring machine be set up to do that?

 

Boring machines index off the main journals and pan rails, which are used to index in all the original machining from the factory...the boring bar self-aligns withen the bore and make a concentric larger bore in the same place...you are over-engineering the job, it's just a street motor, any performance machine shop should be able to take care of you.

 

It's not a street motor, it's a hypothetical race block. So again, does it require a special machine to bore the cylinders where they're supposed to be, or can any boring machine be set up to do that?

 

It depends on how accurate you want your engine to be, and how much you are willing to spend on the block. You could have the bores centered exactly on the main journals and indexed exactly at 90 degrees, but as MachinistOne indicated, the normal method is to enlarge the existing bore where it is. It can cost a lot to reloacte the bores if they are off a few thousandths or a fraction of a degree.

You are probably going to get into correcting the alignment and bushing the lifter bores next, right? That might be as important, or maybe more so than correcting any bore mislocation, because lifter bore mis-orientation effects valve timing. All of this is costing many hundreds of $. If you are building for the last few % of power, go for it, but the cost-benefit ratio is terrible.

Personally, unless I just HAD to use an LT1 block, I'd buy a new CNC SBC raceblock to start with. It would be accurate and a s-pot stronger that any LT1 block, no matter what you spent on the LT block.

FWIW: If you are going to have someone build your engine, thoroughly discuss with the builder all the stuff you think you want done . He may agree or disagree with you, and if he disagrees with what you want to do and how to do it, find someone else...if you can. Make sure you understand what it will cost, and be prepared for some unexpected costs and a fairly long lead time. Make sure the builder has done blocks this way previously...you don't want to be his first shot at this extreme type of prep. I've watched this procedure, and sometimes getting it right is not easy. You really have to trust your builder, because you aren't going to be able to personally verify if it was done correctly. Standing over his shoulder micromanaging will double or triple your cost. You know the story: $35/hr base rate; $65/hr if you watch; $100/hr if you help.

You might read some books on race block prep. Vizard, Smokey, John Baechtel, Wadell Wilson, Bill Fischer & Bob Waar and others have done stories/books. I recall and article on how Hendricks prepares blocks in some mag. Search around.

Good luck!

 

Yup, that was going to be my next question, and then I was going to wrap it up with oil system modifications.

What about big blocks? Do you prefer either Dart's Big M or World's Merlin II over the other? (As I'm sure you know, the Big M has splayed mains and the extra lifter valley head bolt bosses, and the Merlin II has straight main bolts and no lifter valley head bolt bosses.)

Thanks, I'll do that.

 

I reguarly trip over a new GMPP P/N 24502500 block around the shop. If you read about it, it might interest you. It ain't cheap; with freight there is not much change from 3 large. It'll go to 4.600 x 4.600 (612) and still be plenty strong.

http://69.20.110.81/index.asp?PageAc...D&ProdID=22943

 

Yes, it's quite interesting. One thing I noticed is that the main caps are made of the same material as the block, so I'm guessing they're not billet. Some people love billet caps, but it seems to me that it would be best to have the caps and the block share the same expansion coefficient.

"The intermediate caps also feature 16 splayed outer bolts..." I don't understand that. There are 5 caps total, and I would consider either the middle 3 or maybe the front 4 caps to be "intermediate." I don't understand how there can be 16 splayed bolts, but I don't quite dare suggest it's a typo.

I like the priority main oiling system with the galley along side the cam, but there are some potential problems with the Gen VI design as well: I'm not certain, but I don't think the GM block has a mechanical fuel pump boss. Also, timing covers and oil pans for Gen VI blocks are not as common and cost quite a bit more than Mark IV components. Does the Gen VI GM block have a drilled and tapped hole for the block side ball stud needed in manual trans applications?

Also, World claims their Merlin II block weighs approximately 270lbs, and Dart lists their 4.500" bore Big M as 260lbs. I wonder what block GM was thinking of when they mentioned aftermarket imitation Bow Tie blocks that weigh 290 lbs?

Please understand that I'm not bashing the GM block, I'm just explaining my slightly/barely-educated, unexperienced concerns and opinions about it. I'm just trying to learn!

 

There is a reason that the best engineered SBC and BBC blocks use 8620 BILLET caps on a cast iron block, because they are the strongest.... I really get sick of the BS about cast iron caps being the best because they are the same material as the block, that's just being ignorant. (not pointing the finger at you here man, it's the marketing people that I'm pissed at) BTW I think the 245XXXXX PN Chevy Bowtie blocks are about the best you can get.

The outer bolts are the splayed ones! the 16 is talking about 16°! Not the amount of splayed bolts.

Bret