Seems to be a controversial subject. Some books recommend align honing others favor align boring.

jon

Jon,
I presume that i would go align boring when wear is a problem, but sometimes honing would be sufficient.... I'm no automotive engineer. Would you be so kind to elaborate on pros & cons of honing vs boring?

Klox

I would seem to be inclinded to decide after determining the amount of ovality in the bores. If just a light skim-cut is needed, I'd probably go with a hone, if you have some serious ovality, probably be best to bore it.

Just my 2 cents

Speaking of the bottom end, I live next to a race engine building shop. Known the owner for years, he builds high-dollar, high horsepower engines only. Very successful at what he does. They race a couple of cars of their own. At the track, I was helping spot him one day, and thought I was seeing things, watching the tach through the back window as he launched, he left the line at about 11,000 RPM!. This car has a 331 chevy in it. (327). I asked him how in the hell it stayed together.....he just grinned. A few weeks later I was helping him clean up the shop one day...noticed a 2-bolt chevy small block with some oddness going on on the main caps. He had machined the bottom of the main caps, and made blocks that added about 3/4-1" of material to the bottom of the main cap. The bolts had been replaced with studs, and there was a hand-made stud girdle laying beside of it. I asked him about it, he laughed, then said 'you have to do something to hold it together at 13,000. Ingenuity at work....hehe.

Boy would I like to see that! I work in a race shop where we make all kinds of high performance engines, including 2500 horse Pro Mod dragsters. My job is to design and make. The current project is a 500 cubic inch forged aluminium block for a supercharged alcohol Pro Mod, (no coolant).

I have never seen a small block spin at over 10,000 and stay in one piece. We get 9500 in races regularly, but that's as far as we push. Perhaps your neighbor would be interested in licensing his technology? I smell an opportunity!!!!

Let me know....

Fish

Originally posted by Klox
Jon,
I presume that i would go align boring when wear is a problem, but sometimes honing would be sufficient.... I'm no automotive engineer. Would you be so kind to elaborate on pros & cons of honing vs boring?

Klox

Hi Klox,

I took sometime this afternoon to call and talk with BHJ
Products who make tools and fixtures for automotive
machinists. Because the subject of align boring and align
honing is not properly covered in the five books I presently
have on automotive engine machining, I felt I needed to do
this. The books I own all deal with the small block Chevy V8.

http://www.bhjinc.com

What most people now do is align hone the main journals as a
first step. In the past they use to align bore them. The
problem is that most shops don't go the extra step and align
bore and align hone the camshaft tunnel to make sure the
camshaft tunnel is square and parallel with the mains. BHJ
makes a very expensive fixture that does allow one to do
this on a Bridgeport type mill.

As far as your question goes, align honing allows, from what
I read in Smokey Yunick's Power Secrets book, a higher crush
on the bearings which in turn allows more heat to be carried
away from the back of the bearing to the main webs of the
cylinder block.

I have been doing a tremendous amount of reading in order to
really understand performance racing engines and it took
a call to BHJ to realize that none of the books that I have
give the subject adequate coverage. The books I have also
do not have much to say about cam roller bearings, just cam babbitt bearings.

jon

Hey David,

Another thought on the high revving small block. In my experience, revs on pushrod engines have always been limited by valve train more so than the bottom end. How does your next door guy deal with that?

As far as align honing is concerned, it is usually performed to round out mains that have been beaten out of round. The object is to align the bore with the journals on the crank so that you don't have any high spots in the crankshaft and bearing contact faces. If you look at the main caps on a high performance engine, you'll notice that after time, the caps tend to deform along the cylinder axis, where the piston was at the bottom of it's travel. Makes sense right?

Fish

Jon,
thanx for the info! As fish pointed out the bearing caps goes out of round along the cylinder axis (make sense to me!).
If an engine is line bored/honed, is it necessary to go to standerd (?) oversized bearings? Do these bearings come in certain oversizes?
On the canshaft issue, i know that some motor engineering firms does not want or know how to hone or bore the camshaft cavity.

See you,

Klox

I was an automotive machinist for 8 years and built quit a few performance and stock engines. Generaly the main caps are cut on the mating faces before boring or honing to make the bore smaller for resizing. On an engine that still has the original caps and not worn badly the only thing needed is honing. If the caps are replaced with aftermarket caps you must align bore before honing due to the additional material left in the new caps. As a general rule align honing is alot faster than boring and usually has a better finish. Align honing may take 30 minutes or so and align boring could take several hours depending on the amount of material to be removed.

As a related point to this discussion, Honda used (uses?) oval shaped cylinders in some of its motorcycles, cylinders with about half the diameter accross the cylinder as they do in the other direction...I'll see if I can find a pic