[NeighborsComplaint]

Originally Posted by GTOEARL

Read every entry in this blog. Very interesting information and very unfortunate for you. I hope it’s an easy fix. Obviously you’ve heard from a lot of people and a lot of different scenarios of what might’ve happened. Hopefully it’s a spun bearing that allowed the crank to move just a bit to kiss those spark plugs.. The very best of luck for you in solving this issue..

How does the crank move with a spun rod bearing? It's upward travel is limited to the normal stroke plus the main bearing clearance which is restrained by the main cap. Even with a single main bearing failure, the unsupported part of the crank between adjacent bearings does not deflect enough to allow a piston to contact the combustion chamber.

As regards theory that a flat top piston can hit the spark plugs, try this at home: Screw a spark plug into a cylinder head. Turn the cylinder head upside down and and place a flat top piston on the deck. What does it do? It sits nice and flat on the deck without getting anywhere neat the sparkplug.

My current 455 motor was drag raced and had 670 heads with Venolia pop-up piston domes. The motor had repeatedly spun a rod bearings and the owner gave up and had the motor disassembled. Every piston had a ding in the corner of the dome from contacting the edge of the combustion chamber due to interference as a result of the block being decked too severely. Even with spun bearings and an interference fit with the chambers, the piston domes were not hitting the spark plugs.

The pistons (3) hitting the sparkplugs and no piston to valve contact is a good story, but it doesn't add up with "no other damage other than a spun bearing and sheared cam gear keyway.

[HWYSTR455]

Aside from the plugs, the timing gear and pump shaft appear to have obvious damage.

If the crank came to a sudden stop, so would the cam, which is why I'm thinking it was the other way around, the cam came to a dead stop, crank kept moving (some), and that damaged the timing gear & pump driveshaft.

It's kind of moot, since it needs to be completely torn down, and once that happens, it will most likely be obvious what the root cause was.


.

[mgarblik]

Originally Posted by wbnapier

Yes, but a very light line hone. Just a touch.

For seating the thrust bearing, I used a dead blow hammer and gave a couple of whacks from both sides. My machinist didn't think this was necessary and gave me an explanation of why, but I forget the details.

Yes, I measured endplay and it was withing spec, but I am at work and don't have the notes.

I am guessing your machinist said bonking the crank for and aft on a Pontiac doesn't really do anything because the main caps locate on pins, not a block register. He would be right. Many people do it on a Pontiac, but unless you have a loose sloppy fit on the pins, it doesn't really do anything.

[RWS]

My guess is that the timing chain broke, which meant that a number of pistons hit open valves.

That happened to me long ago at about 50 k miles, and it required a total rebuild (albeit with no damage to the block, crank, or rods).

[wbnapier]

You're right! That's what he said. I still gave a couple moderate whacks though. I figured it wouldn't hurt.

As a side note, I purchased and used those extra long dowell pins made by Precision Automotive Specialists. Both mains and head dowels were from them.

[SRR]

How was the block cleaned before final assembly? I got a block back from a machine shop once and was told "Just put it together" I elected to clean all the oil passages with brake clean and brushes. Lot's of dark gritty stuff came out. I did have a new engine once develop a rod knock after only a few miles and when I pulled the pan there was a pile of black gritty stuff in a small pile under the bad rod...expensive lesson on final cleaning.

The only reason I ask is because I think I see some black debris in your oil pan?

[wbnapier]

Hot, soapy water. Acetone, mineral spirits, etc... I had one of those engine brush cleaning kits, Maybe a missed something. We'll find out.

The first oil filter was really clean after initial start and the second oil filter was pretty clean after failure.

[hgerhardt]

And none of the recent posts address the rotated/spun main bearing that we already know of. My guess is he installed that bearing with the oil hole down which caused that bearing to run dry and seize. With only light load, the rod bearings could have been OK since the rods share common crank pins and would have gotten some oil from the mains that did get oil.

[mrennie]

Originally Posted by hgerhardt

And none of the recent posts address the rotated/spun main bearing that we already know of. My guess is he installed that bearing with the oil hole down which caused that bearing to run dry and seize. With only light load, the rod bearings could have been OK since the rods share common crank pins and would have gotten some oil from the mains that did get oil.

Depends what brand of bearings...the last set of Clevites I bought came with a thrust bearing with 2x upper shells (with holes and grooves), rather than one with a hole and groove and one plain with no hole/groove. Apparently this was a change to simplify production and packaging.

[Brian Baker]

Originally Posted by NeighborsComplaint

How does the crank move with a spun rod bearing? It's upward travel is limited to the normal stroke plus the main bearing clearance which is restrained by the main cap. Even with a single main bearing failure, the unsupported part of the crank between adjacent bearings does not deflect enough to allow a piston to contact the combustion chamber.

Think of it like this. The lower rod bearing half gets under or on top of the upper rod bearing half, decreasing the deck height. It's still possible for the pistons to kiss the ground electrode but unless they were extended plugs I think it would kiss the head first like you said.

[chiphead]

Originally Posted by wbnapier

You're right! That's what he said. I still gave a couple moderate whacks though. I figured it wouldn't hurt.

As a side note, I purchased and used those extra long dowell pins made by Precision Automotive Specialists. Both mains and head dowels were from them.

Were the block's housing bore diameters checked after the line hone? My motor ended up dangerously loose (.0015" over max spec) after I swapped those same pins and had a shop line hone it. Shop said "It's fine". I said "It's not". I had to have them shave the caps again to tighten it up, to get enough main bearing crush. There is a long ugly thread about it on here.
Loose housing bores will let a bearing turn, even if the bolts are torqued to spec and the journal clearance looks OK. A turned main bearing is trying to tell you something!

[hgiv]

That was my thought. If had some head work maybe there was stuff in there which didn't initially come through. Maybe once hot or higher RPM? Then it almost instantly knocked out 3 plugs and all sorts of trouble happened. Of course I have no idea if 3 bad cylinders could then cause the other damage or things to seize? I mean... a bad electrical situation could cause the same thing. That wouldn't kill everything.

Also we don't know that it's seized... it just won't turn. Not same thing.

[wbnapier]

Unknown. I assume so. The machinist did the light hone because I switched to ARP studs.

[tekuhn]

Any possibility you forgot to torque the #4 main cap? With the visible gap between the cap and block it seems like you would have heard something if it broke enough to have that much gap with it fully torqued. That or perhaps the cap hung on the alignment stud or something was trapped underneath? All just guesses, of course. Sure sounds like you did everything right and it's certainly a high quality build overall. It sure sounds like you knew what you were doing. I hope the mystery gets solved. I think you'll regret selling the car down the road, so don't rush into that decision. Hang in there...

[HWYSTR455]

I don't think there's a gap there, think it's an illusion, due to a slight build up of oil at the parting line.


.

[tekuhn]

Originally Posted by HWYSTR455

I don't think there's a gap there, think it's an illusion, due to a slight build up of oil at the parting line.

I wondered about that and hope you're right.

[lust4speed]

Were the dowel pins put in prior to the line hone?

[NeighborsComplaint]

Originally Posted by Brian Baker

Think of it like this. The lower rod bearing half gets under or on top of the upper rod bearing half, decreasing the deck height. It's still possible for the pistons to kiss the ground electrode but unless they were extended plugs I think it would kiss the head first like you said.

You missed the point of my post. The crankshaft does not cause the stroke to increase due to a rod bearing issue of any kind. What you refer to is "throwing a rod" meaning the crankshaft "threw" the rod away from the cap as a result of a rod bolt failure , The excessive clearance lets the bearing rotate and then partially "nest" one half atop the other. Nowadays, "throwing a rod" can mean any connecting rod failure, breakage or otherwise.

Again, for this to happen, a rod bolt has to fail or a bearing has to be worn through down into the shell the corresponding depth of the head gasket thickness plus deck height to allow the piston to hit the cylinder head and the plugs would still be untouched (extended tip plugs a maybe) none of which applies to the OP's motor.

[tekuhn]

Originally Posted by NeighborsComplaint

.....Again, for this to happen, a rod bolt has to fail or a bearing has to be worn through down into the shell the corresponding depth of the head gasket thickness plus deck height to allow the piston to hit the cylinder head and the plugs would still be untouched (extended tip plugs a maybe) none of which applies to the OP's motor.

Yep. In other words, if the bearing shells were to double stack, and nothing else was compromised, the maximum the piston and rod could travel further into the chamber toward the head is the thickness of the single bearing shell. I assume there might be additional clearance created by the distortion of the rod cap, but pretty minimal in the absence of catastrophic failure. Yet, clearly something closed the gap on three plugs.

[tom s]

I dont think anyone has pointed out what the issue might be yet!Tom