[GTO]

I lost about 30psi oil pressure in Norwalk this year. I changed the filter and oil pump at the track but still only had about 40psi so I threw it in the trailer and watched. Lucky I did, I just pulled it apart and saw the damage. Looks like it's cracked right into the cam tunnel. I measured the outer holes for the bolts and they're plenty deep, nothing bottomed out. Thrust looks good and clearance was there. Rod bearings are like new. Mains look like they transferred a little metal on #2 and #3 but that was probably because I was down to about 5-10psi on the return road after a run and she was a little hot. What could have made this happen? It's an IA II, please no bashing, it's about 4yrs old and was freshened once before.

[mike leech]

what rpm?
I see that it is 6 weights
how was balance done?

[GTOGEORGE]

Originally Posted by GTO

I lost about 30psi oil pressure in Norwalk this year. I changed the filter and oil pump at the track but still only had about 40psi so I threw it in the trailer and watched. Lucky I did, I just pulled it apart and saw the damage. Looks like it's cracked right into the cam tunnel. I measured the outer holes for the bolts and they're plenty deep, nothing bottomed out. Thrust looks good and clearance was there. Rod bearings are like new. Mains look like they transferred a little metal on #2 and #3 but that was probably because I was down to about 5-10psi on the return road after a run and she was a little hot. What could have made this happen? It's an IA II, please no bashing, it's about 4yrs old and was freshened once before.

That SUCKS.........sorry!


GTO George

[cosgrove]

When I saw it was an IA II, I said "son of a bi**h".

[johnta1]

Sorry to hear that.


Glad you didn't keep running it and scatter everywhere.

[shaker455]

Originally Posted by GTO

I lost about 30psi oil pressure in Norwalk this year. I changed the filter and oil pump at the track but still only had about 40psi so I threw it in the trailer and watched. Lucky I did, I just pulled it apart and saw the damage. Looks like it's cracked right into the cam tunnel. I measured the outer holes for the bolts and they're plenty deep, nothing bottomed out. Thrust looks good and clearance was there. Rod bearings are like new. Mains look like they transferred a little metal on #2 and #3 but that was probably because I was down to about 5-10psi on the return road after a run and she was a little hot. What could have made this happen? It's an IA II, please no bashing, it's about 4yrs old and was freshened once before.

Well that sucks but that's racing!...everything is prone to failure...good thing you caught it!

Could have been much worse.

Hope you get your new block together soon.

[David Holmberg]

Sorry Eric, man that has to hurt.

Talk to Bob and Frank, I'm sure they'll want to know what happened as well.

[ponjohn]

I was going to suggest detonation but not on alcohol.

[GTO]

Originally Posted by mike leech

what rpm?
I see that it is 6 weights
how was balance done?

I shift at 7200. It went close to 8000 the weekend before when I was trying to dial in my 'shift by time'. Short block was done by All Pontiac not sure how the balance was done. I did freshen it up about 2 seasons ago, everything was good.

[mysticmissle]

Happen to know Wht yr it was cast. That's an odd place. Gd catch hate to see that car get wadded up.

[LMSRACER]

It appears as though the crack follows along the sharp edge that remains when the cylinder was bored. The problem with the pontiac block's bore spacing is that whenever the cylinder is bored excessively, the Large "Undercut" created in the "Main Webbing" of the block actually weakens the block in that critical area. Therefore it is of utmost importance that any stress risers in that area be eliminated.
Obviously I'm making an assumption from a photograph, but would like to stress the importance of deburring the sharp edge that is left over form boring the cylinder.
Also, I can see signs of "Shiny Spots" in the cylinder walls at the very bottom edges of the bores. These edges also need to be deburred and actually rounded over slightly. Since the stroke is 4.500", the piston skirt is protruding out of the cylinder walls significantly at BDC. Therefore as the piston rocks in the bore, in relation to the changes in connecting rod angularity, the bottom edge of the bore is actually slightly gouging the piston's skirt.

Just a couple of thoughts.....
Hope that helps a little,
Larry S.

[Tom Vaught]

Originally Posted by LMSRACER

It appears as though the crack follows along the sharp edge that remains when the cylinder was bored. The problem with the pontiac block's bore spacing is that whenever the cylinder is bored excessively, the Large "Undercut" created in the "Main Webbing" of the block actually weakens the block in that critical area. Therefore it is of utmost importance that any stress risers in that area be eliminated.
Obviously I'm making an assumption from a photograph, but would like to stress the importance of deburring the sharp edge that is left over form boring the cylinder.
Also, I can see signs of "Shiny Spots" in the cylinder walls at the very bottom edges of the bores. These edges also need to be deburred and actually rounded over slightly. Since the stroke is 4.500", the piston skirt is protruding out of the cylinder walls significantly at BDC. Therefore as the piston rocks in the bore, in relation to the changes in connecting rod angularity, the bottom edge of the bore is actually slightly gouging the piston's skirt.

Just a couple of thoughts.....
Hope that helps a little,
Larry S.

X2 on the sharp edges on the bottom of the cylinder walls.

On a 4.5" stroke, the piston skirt comes out of the hole a long way and that puts a tremendous load on the lower edge of the cylinder walls.

With a 4.0" stroke the piston skirt (if 2.75" long comes out of the hole about .500" and a 4.5" stroke comes out about 1" so when the piston is at BDC the piston is hanging out of the block 36% of its total length. Imagine what kind of a diving board that deal is!
So if now you have a sharp edge on the block where that high load is you can create a stress fracture and once that starts it goes all over the block from that point.

Tom V.

ps Looking at Pontiac Blocks for 45+ years that is the first block failure I have seen at the #4 THRUST Location. Typically #2 or #3 will fail.

[GTO]

Originally Posted by mysticmissle

Happen to know Wht yr it was cast. That's an odd place. Gd catch hate to see that car get wadded up.

I picked it up in Sept. 2009. Awesome road trip! Might have to make another one.

[Elarson]

Any signs of detonation? Typically shows itself as a sandblasted area on the top of the piston, aluminum specs on the plugs, bits of the pistons missing.....

Eric

[GTO]

Originally Posted by Elarson

Any signs of detonation? Typically shows itself as a sandblasted area on the top of the piston, aluminum specs on the plugs, bits of the pistons missing.....

Eric

Piston tops look good to me, black and smooth. I'll clean them up and check but I'm running alcohol and only about 32-34 TIMING. Plugs were normal, clean. Never noticed any piston parts missing. Never took a real close look at them, kind of bummed when I found the crack.

[mgarblik]

Detonation is not impossible, even on alcohol. Just for kicks, check the ring side clearance very carefully on the top ring land all the way around. If the gap is opening up, there is mild to moderate detonation going on. Can't say if it would cause that crack though. That's a bit of a puzzler. Certainly have the crankshaft checked for cracks. I have seen many cracked shafts ruin a block. Sorry to hear about this happening, but you caught it in time to save many valuable parts for re-use. As a side note, I would strongly recommend using studs in the outboard cap holes when you put your new engine together. Studs can go 3/8"-1/2" deeper into the block than the cap screws you have in there.

[GTO]

Thanks for all the replies. Just came back in from my shop and found other probs. Rear main is cracked also, bolt hole and dowel hole. Dowel is in the cap. Damage on block is all on the pass. side. Driver side is OK. Took some pics. Funny metal movement on rear cap. Was it 'walking'? Thanks again, Eric.

[Tom Vaught]

Did you by chance drop the car from a tall wheel stand in the past?

Tom V

[johnta1]

Funny metal movement on rear cap. Was it 'walking'?

Probably from when the block cracked, it made the rear cap 'loose' and it was not tight.

Very, very, lucky I would say that you stopped when you did.

[tom s]

by chance engine plates or solid mounts?