What does an "n bolt main" mean, where n is usuall

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robroy
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What does an "n bolt main" mean, where n is usuall

Post by robroy »

Good morning,

I've heard guys saying for years that their engine has an "n bolt main," where n seems to be three or four most of the time.

What does this mean? Why is it a noteworthy spec of an engine, and what's the best number of bolts on the "main" to have? And what's the "main?"

Thanks very much for answering my basic question,
-Robroy
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Post by robroy »

Sorry about the truncated subject line; it looks like I need to restrict myself to typing 49 characters and no more.

My original subject line was, 'What does an "n bolt main" mean, where n is usually 3 or 4?"

Thanks!
-Robroy
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re: What does an "n bolt main" mean, where n is us

Post by DuckRyder »

This is most commonly used to refer to those off brand motors (Chevy/GM).

Generally you see 2 bolt and 4 bolt mains, some 4 bolts are splayed. 4 bolts are better than 2 and 4 bolts splayed are better than 4 bolts.

Since you are building an FE, the equivalent of a "4 bolt" is a cross bolted block which were 427's and 406's (some, not all)

The main is the main crankshaft journal or more specifically the main cap, and the number of bolts refers to how many bolts secure it to the block. 4 bolt mains have step shaped main caps which have one long set of bolts nearest the crankshaft and 2 somewhat shorter ones further out, splayed only means that the outer bolts are placed at an angle. Crossbolted mains have bolts through the blocks skirt into the mains at a 90 degree angle to the main bolts.

Since I know you are having an FE built at about 400 hp, the stock FE 2 bolt main is plenty strong, you builder might use main studs instead of bolts, but at that power level on an FE any quality bolts will be fine.

Worry more about a quality oil pan, at least factory cobra jet spec, and windage tray.

Stand by and I will try to dig up a picture..
Robert
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re: What does an "n bolt main" mean, where n is us

Post by DuckRyder »

This post includes some good pictures of a crossbolt set up conversion on a 390. There are kits to do this, but as I said, it isn't required at your power level.

http://www.customdesignperformance.com/ ... sbolt.html

(thats not a reccomendation of that particular company either)

Still working on GM 2 and 4 bolt mains...
Robert
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re: What does an "n bolt main" mean, where n is us

Post by DuckRyder »

Scroll down on this page and there is a good picture of a 4 bolt main (Lima Motor)

http://www.ve3sy.com/scj/2006-start.htm

Here includes a picture of splayed 4 bolt mains:

http://www.gmhightechperformance.com/te ... to_10.html

a google image search of "4 bolt mains" turns up many more.

Hope this helps.

Oh, and the reason for them is increased strength, however the FE has a skirted block and it is quite rigid and strong with very stout main caps and bolts thus is really much less of an issue.
Robert
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re: What does an "n bolt main" mean, where n is us

Post by seattle67 »

Fantastic info DuckRyder, thanks!
Dan

"I plan to start procastinating immediately"

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Post by robroy »

Good morning Robert!

Thanks very much for your detailed response! I've read it several times and will follow all the links to learn more.

I'd be curious to hear more about your thoughts on oil pans and windage trays. Is the windage tray that thin piece of sheet metal that sits under the intake manifold to collect debris from the oil?

Steve and Doug at Proformanceunlimited are putting on an aftermarket Moroso oil pan (since I didn't like the chrome one that planned to use), but I don't know much about this. Maybe its specs need to be investigated?

Thanks again very much Robert!
-Robroy
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re: What does an "n bolt main" mean, where n is us

Post by DuckRyder »

Oil Pans:

What you want your oil pan and windage tray to do is keep the oil where the pickup can get it.

The stock car and truck front sump pan does have a baffle in it, but for some reason there is an opening that allows the oil to escape from the sump on hard acceleration.

The Cobra Jet pan has a better baffle and when used with a Cobra Jet windage tray seems to alleviate oil starvation on hard acceleration. perfectly adequate for anything except an all out drag car.

I suppose the baffle under the intake is a windage tray of shorts, but it is actually called a valley pan most of the time. a windage tray is below the crankshaft and helps to control and direct oil splash. The FE is a bit atypical again in that since the block has skirts and oil pan rails that extend below the crank shaft the windage tray is a pretty simple metal baffle that sandwiched between the pan and block using an additional gasket.

Ford Racing still sells the windage tray, and Milodon makes a good pan. I am sure Moroso has a good pan for it but am unfamiliar with their specific offerings.

You want one with baffling more like the 69-70 pan on this link, which also includes the windage tray photographs.

http://www.428cobrajet.org/id-oilpan.html

HTH
Robert
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Re: re: What does an "n bolt main" mean, where n is us

Post by Ranger72 »

DuckRyder wrote:This post includes some good pictures of a crossbolt set up conversion on a 390. There are kits to do this, but as I said, it isn't required at your power level.

http://www.customdesignperformance.com/ ... sbolt.html

(thats not a reccomendation of that particular company either)

Still working on GM 2 and 4 bolt mains...
Wow!

Not that I know a performance engine from my ass, but I didn't even know that kind of thing was possible. :eek:
Steve
1972 F-250 Camper Special
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