Main studs & align hone.

[old blue 75]

A quick align hone ?. If I use main studs in place of the factory bolts, will the block
need to be align honed? Every one I have asked has said yes. But in Davids books
he writes that align honing is not needed most of the time.
The owner of the machine shop I use has told me that if you use studs and don't align hone the bores won't be round.
He also told me he has had customers try it and the crank will rub the bearings right by the studs. Is he correct? Or can it be done? This is sbc stuff if it matters

old blue 75

[Packard V8]

Machine shop owners are not in the business of talking themselves out of business. Think about it, if he says not to align hone, he loses the business. If you don't align hone it and there is any problem, he had said it would be OK and you'd blame him. Safest, most profitable course for him is to tell you to machine everything

FWIW, I agree with David. Think about it. The main caps are located by the broach in the block, not by the bolts or studs. Of course, you are asking about limp-wristed SBC iron, then anything could happen.

thnx, jack vines

[Lasse]

Originally Posted by old blue 75

A quick align hone ?. If I use main studs in place of the factory bolts, will the block
need to be align honed? Every one I have asked has said yes. But in Davids books
he writes that align honing is not needed most of the time.
The owner of the machine shop I use has told me that if you use studs and don't align hone the bores won't be round.
He also told me he has had customers try it and the crank will rub the bearings right by the studs. Is he correct? Or can it be done? This is sbc stuff if it matters

old blue 75

Why not just put studs in, torque main caps and measure with 2-point micrometer if they are (or not) out-of-round? Keep It Simple Stupid. My guess is you can't find difference in roundness between original bolts and studs, if they was originally round. In any case it is very good idea to check roundness and diameter of main cap bores.

[FlowSpecialist]

There's no reason why a different type of fixing should alter the alignment or roundness other than perhaps a minute amount from a different torque setting. Even so I don't believe that matters a jot or even that main bearing housing alignment is that important. The crank is flexing about like a palm tree in a gale anyway. Every time a piston hits TDC or BDC at high rpm there's a force of several tons acting on the crank. Anyone who thinks it ain't gonna bend to the very limit of the bearing clearance under that load is kidding himself. I doubt that the crank would really be that bothered if the block was bent as a banana.

If the crank turns over freely with the caps torqued up it's going to be fine.

On a similar principle I've seen cams installed in aluminium OHC heads that were warped to buggery because they'd overheated, been skimmed true on the gasket face but no one had stopped to think that the whole head is warped and therefore so are the cam bearing housings. Didn't seem to make a scrap of difference to the cam. It just bends to fit the head as the caps are torqued down and then runs quite happily like that bending again every revolution while the engine runs.

Engines are extraordinarily tolerant of some types of build error.

Dave

[mach9]

I put about 550 runs on a factory Ford 5.0 block 347 cu.in. before the block cracked. Studs in the mains with no align hone. Bearings always look like new. And that has to be about the wimpiest block out there. I've never understood why it should AUTOMATICALLY be nescessary. I think it's probably more of a CYA type thing. But, I'm willing to listen. MJ

[Lasse]

We have in our road racing car one sbc 350 block where main bores are out-of-round. Vertical diameter is ok, but horizontal diameter is 0.005" over. I think bores are machined over and corrected by lowering caps. At first we had problems with bearings, but when we lowered oil temp to 250F problems were gone. We have raced now 10 races without problems in engine. One race is about 15 miles.

[want-a-be]

I've owned a line hone, and the rest of the spped shop,... and was taught to hone with the fastener that was to be used in the combination. But to be hosest...I've not seen any difference that would make a difference. Actually, and I might get slapped for saying this, I think the same way with torque plates. But thats a different argument.

Don

WCRE/Ace Rod Shop

[Cammer]

Do not take David's book out of context as each engine build may require specific machining.

Faith in your machinist is important. Communication must be open and honest.

Your machinist is giving you the benefit of his experience regarding this matter. If I felt align honing was necessary I would not do the job without it!

None of us can say with certainty that your engine does or does not need align honed!

There is no simple yes or no answer.

Best of luck with your engine build!

[Cammer]

David Vizard has this to say about align honing:

How to Build and Modify Chevrolet ... - Google Book Search

David's thoughts are in line with mine and pretty much all the automotive machinists I know. Without accurate main bores you will not be able to accurately machine the rest of your block. Many block dimensions are referenced to the mains. Used blocks regularly exhibit mains that are way out of blueprint specifications.

[DavidVizard-GFN]

Flow Specialist, Cammer, Want-a-be, Mach 9 and Lasse,

My guess here is that in spite of sounding contradictory you are all right!

I like to have all my reference surfaces accurate so I know where I am. This means at some point of the game you do know what the hell is going on. But the truth of the matter is that under the heavy loads seen in a high output race engine things move - and they move a lot more than you may suppose.

Here are some examples: While working with some of my racer friends in UK some years back (about 89) we had occasion to rebuild an 850 A Series Mini Crosser race motor. This engine powered a car that was kicking butt at almost every meeting so won the regional championship and qualified to run in the final. No good being second here it was all or nothing. So my friends rebuild the engine and during the rebuild found that the center main was almost 0.003 thousandths out. The guy that built the engine had not checked for this at the time of the original build and it is doubtful that the block, which was well seasoned, could have moved that much in a six month period. Anyway the block problem was fixed and the engine rebuilt to the exact same spec. On the dyno the rebuilt power curve virtually overlaid the original. No extra power was seen.

A similar case was some tests that my friend, Paul Ivey, one of UK's most famous Mini engine builders did with the factory. They progressively bent the crank until a power drop was seen. It took just over 0.003 bend in the crank to show a drop in power on a 28 hp engine.

I also heard, but cannot confirm, that Cosworth did some experiments here on the old and highly successful DFV F1 engine. So the story goes, they measured the block distortion of an engine running WOT at near max rpm. They then machined each main bearing housing off by that amount reversed so that, in theory; all the main bearings would be inline at 10,000 rpm. It made no difference to the output!

You may ask why - well here is at least some insight to this. Let us assume that the bearing, when supported by oil, has no friction. This means that there is no torque lost due to bearing friction (load times friction coefficient). At this point let us push the main bearings out of line by say 0.004. That is enough to bind them up during the build. But an oil film is incredibly stiff and can support a very sizable load. This oil film picks the journal off the main bearings. Under these conditions the friction torque would be the load - we will say 15,000 lbs per bearing times zero answer frictional torque loss = zero. Ok that may be an over simplification but it does make the point. I have line honed blocks which were a little out (0.0015 max) and seen no measurable gain on the dyno.

Does all this mean I put together motors without due consideration to the mains alignment - certainly not. If the mains are at all suspect I have them honed at a trustworthy shop. However If the build is a low buck street deal and the crank rotates like it's on ice and all the clearances are right I don't bother. The money otherwise used can be spent on better parts elsewhere.

At the end of the day it really is a question of knowing where to draw the line (unless you work for a cup car team that is!)

DV