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crkoester · 09-07-2005, 02:16 AM

OK, it's not really new, but I'm proud to have it. Here's the engine that will be going into my 69 goat.

1970 455, code YH, #15 heads, 744 cam. It has about 6500 miles on a rebuild, but still runs strong (took a ride behind it last week). I'll run it as is for as long as it runs well and/or the go fast(er) bug hits me.

My first question (of many more to come) . . . .

I dropped the oil pan to take a peek, as I have been told that a few YH's left the factory with 4 bolt mains. Mine, of course, turned out to be only 2 bolts, but is drilled for 4.

Is adding bottom end strength as simple as adding bolts in the open holes? Is the block itself already drilled and tapped underneath?

Obviously in the engine's current form the 4 bolts would be overkill, but I'm thinking about the future.

Chris

quick67bird · 09-07-2005, 02:58 AM

If the block is drilled for the 4 bolt main caps it is already tapped. In order to add 4 bolt main caps you will have to have the block line honed. I have just completed adding 4 bolt main caps to an YH block and it can be quite spendy. I bought the billet four bolt main caps and then had to have all the machine work done which was around $400. Depending on what you are going to do with you engine you might not need 4 bolt main caps.

Robert

Half-Inch Stud · 09-07-2005, 07:20 AM

Leave it alone.

theoldone · 09-07-2005, 07:40 AM

Quote:

Originally Posted by crkoester

OK, it's not really new, but I'm proud to have it. Here's the engine that will be going into my 69 goat.

1970 455, code YH, #15 heads, 744 cam. It has about 6500 miles on a rebuild, but still runs strong (took a ride behind it last week). I'll run it as is for as long as it runs well and/or the go fast(er) bug hits me.

My first question (of many more to come) . . . .

I dropped the oil pan to take a peek, as I have been told that a few YH's left the factory with 4 bolt mains. Mine, of course, turned out to be only 2 bolts, but is drilled for 4.

Is adding bottom end strength as simple as adding bolts in the open holes? Is the block itself already drilled and tapped underneath?

Obviously in the engine's current form the 4 bolts would be overkill, but I'm thinking about the future.

Chris

you don't need 4-bolt mains for that level of HP on the street

good question....I converted my block from 2-bolt to 4-bolt, here's what was needed:

full set of original 4-bolt caps, including front/rear cap, from a 428- those cost me $50

the big surprise was, my original 2-bolt caps had smaller dowel pins- I had to pull all the dowel pins out, have the block dowel holes redrilled to the larger 4-bolt size dowel, then buy the pins, cut them to size, and press them in

then attach the caps, buy (6) outer main bolts, and have the block align honed

it's a lot of work and if you're not making over 600 HP, you don't need it.

your money would be better off spent on a new pair of heads or upgrading your present heads- the 15's were small valve low performance heads with pressed studs. You could put larger valves in those heads and have them ported, and pull the studs and tap the holes and put screw in studs in

Will · 09-07-2005, 08:35 AM

Agree with all of the above except that I have a '73 400 block that is drilled for 4-bolt mains but not tapped. Don't know if that's something Pontiac did as they phased out the drilling the outer holes or if that block is just a mistake, but after seeing that I don't assume anything about whether a hole is tapped or not.

In any case, under 600 horses the 4-bolt caps are definitely not necessary.

crkoester · 09-07-2005, 02:28 PM

Yeah guys, I fully understand I won't need 4 bolt mains unless I try to make a monster motor, and I don't intend to change it. I'm just trying to understand the difference a little better.

Looking at my caps it almost looks like there is a place on each end where another bolt could simply be placed. Obviously this is not the case, I'm just trying to figure out what I am looking at.

Can someone post a pic of what the bottom end of a 4-bolt main engine looks like? I guess the caps look entirely different?

I also still don't understand why any machine work is necessary? What is actually being done to the lower end other than just adding strength to the caps to keep the crank in place at higher energies/RPM's? Are some measurements or tolerances changed, or what?

Sorry for the stupid questions, but I don't know how else to understand this. I couldn't find "Pontiac 4-bolt mains for Dummies" at the bookstore.

Chris

mikeb · 09-07-2005, 04:02 PM

The main caps and the block were machined together at the factory. For this reason you can't just swap main caps, like you just can't swap rod caps (without machine work to ensure that the bore is round and straight). Each cap from block to block will be just a bit different than other caps from other blocks. Swapping them around from one block to another may result in misaligned bores or egg shaped bores. Then a line hone/bore would be required to make the bores round and straight again.

krisr · 09-07-2005, 06:21 PM

Quote:

Originally Posted by Half-Inch Stud

Leave it alone.

Yep, leave it.

Will · 09-07-2005, 06:25 PM

The holes you're seeing in your 2-bolt caps are for the locating dowels. The extra bolts on a 4-bolt engine go outboard of the dowel pins. If I had any time at all right now I'd go dig out a 4-bolt and 2-bolt cap and take a picture of it for you. Unfortunately, I only have a few minutes to goof off today and for the rest of this week...

thumper78 · 09-07-2005, 09:57 PM

Here's some pictures of 4 bolt main 455. 71 HO Service block.

The center 2 bolts on the 2nd and 4th cap are for the windage tray.

Hope this helps to answer your questions.

crkoester · 09-07-2005, 10:27 PM

Perfect explanation, and the pictures help a lot. I totally understand.

Now when the next guy I meet doesn't understand this, I can act like big shot, roll my eyes and explain it to him.

Thanks fellas...

Chris

crkoester · 09-07-2005, 10:48 PM

By the way, is it just the 3 mains in the middle that have the 4 bolts? From the pics it looks like the mains on either end don't have the outboard bolts??

Chris

thumper78 · 09-07-2005, 11:08 PM

Correct

4 bolts on center 3 caps only

P@blo · 09-10-2005, 01:09 PM

So 4 bolt mains would be a bonus to have but not needed for a street motor.....What would be the limmitations of a Two bolt compared to a Four bolt? ......I was considering getting 4 bolt caps for a mild street 455 but was reading that 2 bolt with studs are pleanty strong.......has anyone ever had engine falure that was the fault of the 2 bolt caps ?

Brian Baker · 09-10-2005, 01:18 PM

2-bolts with studs will hold up just fine up to 600-HP. I agree with 1/2"...leave it alone.

JohnnyC · 09-11-2005, 12:25 AM

If you are starting fresh and your block already is set from the factory lets say for 4-bolts, then it can't hurt to use them. My 455 that i'm currently building is a 4 bolt block, but only came with 2 bolt mains, which i assume was used by the last owner. I figured its already set up for 4 bolts, so it can't hurt to use them in a situation like this, but only be more security on the bottom end. C.A.T. makes aftermarket 4 bolt caps for a fair price too. So if you have a block already set up for 4bolts, why not use them for me stability?

P@blo · 09-11-2005, 01:39 AM

I too was considering switching to four bolt mains on a 455 but after reading that you have to install new main dowell pins along with god knows what machining i think i will stud my two bolt.......my block is also drilled for the 4 bolt caps but came with the 2 bolt so i guess mine is set up for only two bolt.........

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