Block Assembly info
 

There is a very interesting discussion taking place over on the Speed talk site concerning block distortion and shift / changing clearances between assembling a block on a engine stand as compared to just on a work bench or having it supported the way it will need to be in the engine bay.

read the same deal,I can really see it on a long engine block like a inline 6 or 8.Tom

I guess anything can be over-thought.

Most V8s can easily be supported, and assembled, by the bell housing area, while on a stand.

Now if you only use like 1 or 2 bolts, it might cause some clearances differences, but duh, properly mount the dang thing.

So how much variance does one think can occur by the weight of the block on say for example, the crank clearances? I bet not enough to worry about. Even on a somewhat max-effort build even.

Still concerned? Widen the clearances slightly.

I've seen more issues/variances during assembly due to all the parts (and tools) not being at a stable temp than anything else. It's pretty common for folks to assemble in the winter, think about it. I used to have to run the heater in the garage for 2 days to get everything stable before I could assemble, and would use an IR gun just to get temp references before I started and along the way.

When it comes to forged/cast parts like cranks and rods, well, that's why cast parts generally have wider clearances.


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A little more on this. When you assemble, and you are pulling torque on bolts, the direction you pull can make a difference.

For example, if you're torquing a main bolt/stud, you always want the bolt/stud orientation to be 90 degrees to the floor, or length of the block. And when you pull, you stand at the rear of the stand, with a foot on one leg of the stand, and you pull along the plane that's front to rear. (if you get what I'm trying to say).

What you don't want to do, as an extreme example, is have the block oil pan rail 90 degrees up/down to the floor, and load the torque wrench where you pull down towards the floor. But that's IMO is a no-brainer.

I see people use torque wrenches incorrectly too. I've seen people do a pull somewhat fast, and once it clicks, give up. Not correct. You slowly draw the wrench, bringing up the 'value' in an even load, and evenly increasing, until it clicks. You can re-draw it too, and should, right at the point of where it clicks, can hold it even right at that point, and you will see you can get even another 1/16-1/8 of a turn on it before it clicks again. If it moves at all before it clicks, it's not to value.

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I have heard the engine stand/block distortion stories as well. Bob Glidden probably was most famous for this belief. see below:

I've been reading some of my old car magazines and in a 1980 Super Stock & Drag Illustrated they did a couple articles on BG and in one it said that in their very well equipped 7000 square foot shop one thing you don't see is a single engine stand. Glidden believes strongly that when an engine is mounted on a stand there is too much stress put on the bellhousing area and it causes the back four cylinders to elongate and in turn ruin the ring sealing. It has a photo of him working on a engine on the floor.

I've never heard anyone say that before, but you sure can't argue that he doesn't know every trick to get the most horsepower out of an engine.

So is there something to it? Possibly. Bob Glidden was very, very successful. If 1 or 2 HP will make or break your race program, I would take the time necessary to make instrumented measurements of cylinders with and without the stressed members bolted up. (engine mounts, bell housing, ball crank, front accessories). Then you will know for sure with your particular engine. My gut tell me 99.999% of the people racing would not see a measurable difference.

Of course for best assembly, you wouldn't blast the whole thing together with an air impact and air ratchet. But I have seen many, many put together just that way. A torque wrench was for those "egg head engineers", in the white coats.

Keep in mind that top fuel race blocks are lightweight, and not like a standard V8 block.

But, there are jigs for those engine blocks that do properly support them during assembly.

If you look at top fuel and funny car teams, the block stays in the chassis as they are rebuilt between rounds, so, those are properly supported.

I bet with low tension small pack rings, those things only last a few mins, so, sure, there could be some impact during assembly.

Bore distortion? Whew. Again, I doubt enough to worry about while it's in the chassis. But. Teams usually have several engines on the trailer that are in storage/moving boxes, so, I guess. Can't have all the engines in chassis all the time.


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I am not disagreeing with you. It amazes people when you tighten a main cap to specs and it changes it's size by .003". A torque plate vs no plate can change cylinder out of round and taper by over .002". So the castings do stretch and move around as you assemble and bolt things on to it. It makes sense. Some engine builders absolutely insist on installing freeze plugs, oil gallery plugs and bellhousing dowels before installing cam bearings because they say it distorts the cam bores. Some builders hone cylinders and line hone with this stuff installed. Some heat the 55 gallons of oil in the hone and run the hot oil through the block while honing to equalize temperatures and distortion. But then some customers whine and complain when their machine shop bill goes over $1000.00 to machine all this stuff using regular best practices. If you have hundreds of millions to burn like a formula 1 team or 25 million for a top fuel team a year, you can do all kinds of really cool things and find that little extra bit of ring seal that may be the difference between 1st and 4th place. 20 years ago, the cost of each additional 1 HP in Pro Stock drag racing was $40,000.00. I would love to build engines with that level of precision. It would be a learning experience.