About Us

head #96 · 05-09-2003, 03:03 PM

Just got motor back from machine shop was putting on the pan and discovered a crack in the #1 main cap. I won't be able to talk to my engine builder for a couple days. At least the crack is at the dowel pin hole. What do I do now is my new short block screwed? A friend told me I should not miss match main caps (one from a differant motor). Will it hurt it if I break the piece off and run it that way? Can it be fixed?

Here's a look at my horror

HELP!

Building a fast stock appearing street car.
homepage http://home.mchsi.com/~vroman6

head #96 · 05-09-2003, 03:03 PM

Just got motor back from machine shop was putting on the pan and discovered a crack in the #1 main cap. I won't be able to talk to my engine builder for a couple days. At least the crack is at the dowel pin hole. What do I do now is my new short block screwed? A friend told me I should not miss match main caps (one from a differant motor). Will it hurt it if I break the piece off and run it that way? Can it be fixed?

Here's a look at my horror

HELP!

Building a fast stock appearing street car.
homepage http://home.mchsi.com/~vroman6

Brian Baker · 05-09-2003, 03:06 PM

Gonna' need another cap, which means taking it apart again and align honing.

NOZZLENUT05 · 05-09-2003, 03:10 PM

96,
From my limited experience, I think(dangerous) you can get a new cap to replace the cracked one, BUT, I think you will need to get the block line honed. Let's see what others think.
Nozzlenut

head #96 · 05-09-2003, 03:15 PM

I do have another virgin 455 shortblock. But the good stuffs in this one.

I think I'm gona get sick.

Building a fast stock appearing street car.
homepage http://home.mchsi.com/~vroman6

Old Man Taylor · 05-09-2003, 03:29 PM

You can't run it that way, it is a time delayed hand grenade.

http://www.jimspontiac.homestead.com/Index.html

LouisianaGuy · 05-09-2003, 03:37 PM

Just get a new cap and have it line honed and put it back together no biggie

Mike

"Mike Kasparian · 05-09-2003, 04:33 PM

#96,i have got a couple factory front caps i'll give to you if you want to try them.you will have to diassemble the block and have it at least align honed.i am in indiana,good luck. mk

Robert Williams · 05-09-2003, 05:35 PM

I can also help you out with a front main cap, if you need it send me an e-mail. I will give you the cap, you pay the shipping.

Robert Williams

head #96 · 05-11-2003, 07:07 PM

Thanks everyone for the replys and the parts offers.
I spoke with my machinist yesterday and showed him the picture. He says that its just a locating dowel and will not affect the strength of the cap. He told me to remove the cracked end piece which I did.
My machinist as been in the buisness for 35+ years and built many race pontiacs, including motors for Arnie Beswick. He says he's seen this before, and will stand behind this engine 100% I don't have the extra 1000. it would take to go back though the motor, so I'm taking him up on his offer.
I just wanted everyone to know I'm not trying to undermine the advice of the board. This board has been a wealth of knowlege for me. I appreciate each and everyones information,and I will not come crying to the board if this motor eats it's self.

Thanks

Building a fast stock appearing street car.
homepage http://home.mchsi.com/~vroman6

SCOTT ESTERLE · 05-12-2003, 07:14 AM

I hope the cap doesn't walk very much back & forth.

jim brady · 05-12-2003, 07:23 AM

The clearences on Pontiac blocks are usually close. Get another cap put it on and check clearences. If it checks out just change caps. If your machinest didn't catch that I would be looking for another machinest!

wtakanabe · 05-12-2003, 07:37 AM

Ditto Jim Brady, just cuz Arnie and his machinist did it doesn't make it right. Arnie did ALOT of crazy s#%t in the ole days as a matter of necessity for the situation. Get another cap, check the diameter and align hone if necessary if you want that motor to live.

455Turbo · 05-12-2003, 09:26 AM

I have heard that this fracture is caused by the harmonic balancer not being torqued properly.

larry davis · 05-12-2003, 09:41 AM

One of my 68 428 block has the exact same problem.
I absolutely would not use it as is. I would buy a Program billet front cap and line bore/hone, re-asemble. Actually, if the center caps aren't 4 bolt, I would replace them w/ the Program units as well. Since you'll be re-boring/honing.
Assuming that your block is drilled for 4 bolts.

SECOND AMENDMENT: AMERICA'S ORIGINAL HOMELAND SECURITY.
I Misus Rash'!

GoatRider · 05-12-2003, 10:22 AM

Having not built many engines, I can only give you some "common sense" advice...

That crack appeared there for a REASON. Stresses on the crank trying to move that front cap either side-side, front-back or both off of that dowel pin made that cap crack there.

If you use it as is, there is going to be no real support to limit those forces in your new engine. I would think this will allow the cap to move even more, which is eventually going to make something, someplace else fail in an even more destructive manner.

Good luck no matter how you decide to proceed.

"Nothing Beats an Ol' Goat..."

Ron · 05-12-2003, 10:38 AM

Do it right. Replace the cap, align hone, assemble. You will be a happy person if you do it the right way.

Ron

sscherin · 05-12-2003, 11:02 AM

If he's willing to back it up then get it on paper with a picture and signed by him.

GURU: One who knows more jargon than you

Scott Schering
70 Firebird 455 12.34 @ 108.2
Http://www.pontiacs.org

PONTIAC DUDE · 05-12-2003, 06:24 PM

Funny how many miles motors have run with the caps broke off around the dowel hole and never tear up a crank before someone tears it down and sees it?

Funny that very few automotive blocks even use an alignment dowel at all. Except in the thrust main?

Funny the engines I have torn down with the pin hardly even sticking out into the cap to even be useful for anything.

I'll stick my neck out..........Depends on application and hp.

I feel that there is a point to being anal retentive. See the paragraph above.

Here come the hate mail. LOL. And I agree with the machinist, if ........ but, depends on application and usage.

Personally, I would countersink all the main caps into the block about a 1/8" for better control of walking, square the end of the cap, then line bore. But then a new can of worms for re-aligmnet of other items. Is it worth the cost for the minor gain?

Chioce #2: If the motor is fresh and not totally assembled, as it looks not to be. I see no resason you can't tear it apart at this stage to use another cap and line hone. That is the only cost incured as he should be willing to cover the cost of the galley plugs (to remove to clean) and possible the outer cam bearings/rear plug used to set up to hone. You would have had to replace the cap and hone anyway.

Build it fast, build it right, build a Pontiac.

http://PontiacDude.cc

[This message was edited by PONTIAC DUDE on May 12, 2003 at 09:37 PM.]

Malky · 05-12-2003, 06:48 PM

I agree with machinist. 100 ft-lb torque on cap bolt means it will take about 4000 lb sideways force to move this side of cap on block. This is at least as much as dowel can handle without yielding. Dowel is only for locating initially, not carrying side loads. This is typical for the industrial applicatiosn I am used to. But then it is not my engine. Good luck.

Menu

About Us