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Discussion Starter #1
I pulled the heads off the 307. I discovered why the nova had slowed from 14 flat @ 99 mph to 14.7 @ 89.

:(:(:(

Three piston skirts are.... missing! A few of the rings look a little funky too. I'll take pics when I go back home, but the damage is considerable. I wonder if the pistons were damaged when my water pump gasket blew last fall. The motor got fairly hot before I realized it and shut her down. Well, a sad day for a fairly strong little motor. Two and a half years of hard service, around 40-50 quarter mile runs, 35,000 miles and dealing with a young kid with a pretty heavy right foot, it stood up as well as a stock bottom ended boat anchor could be asked to.

Today, we salute you 307. Rest in pieces.

Kev
 

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you should contact GM this has to be the most durable 307 they ever built. Possibly they might want to study it just to see what they did right:rolleyes: :D But seriously that motor really served you well Kev it didnt owe you a dime...:)
 

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Kev, generally broken skirts are the result of too much piston to bore clearance and the over revving didn't help. All that slapping back and forth was too much for the cast pistons. Keep that in mind with the new engine.
 

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Discussion Starter #4
Maybe... it never saw the north side of 6000 rpm though. I suppose that's enough to break stock parts though.

Who knows how many miles were on it when I got it too. There's a lot of things that could have happened in the meantime.

Kev
 

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sixtyII said:
For some reason I think Paul is trying to tell you something here. Maybe really important too.

yes he is....that the new motor will spin to 7+k nooooo problem:rolleyes: :D ;) :)
 

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Discussion Starter #8
Don't over rev my beautiful new claimer motor? Yah, I think I get the message.

It was kinda hard to play too nice with the 307 knowing that Paul was working diligently on the 350. I also have another vehicle for transportation now with the little *** car.

I think the amazing thing was that the skirts dissolved on the 307 and the motor didn't make any funny noises or implode. An interesting situation. The valves didn't even look beat up in the heads. Could the pieces have found their way out the exhaust or down the crankcase? I wonder when I pull the motor down if the bearings are going to be completely wiped. The oil pressure was awfully low at idle...

Kev
 

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i'm sure the skirts will be found.........likley mangled in the pan somewhere..:)

is the pan still on the motor?
 

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Discussion Starter #10
Pan and shortblock are still together. I'm pulling the motor when I get a chance in the next few weeks.

Kev
 

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novaboy009 said:
Maybe... it never saw the north side of 6000 rpm though. I suppose that's enough to break stock parts though.

Who knows how many miles were on it when I got it too. There's a lot of things that could have happened in the meantime.

Kev

I think you hit the nail on the head. The 307 had what, 220,000 miles on it?
What made you think that 6,000 rpm which might be ok for a NEW engine would be ok for a high mileage engine. I know it's 20/20 hindsight but 5,000 rpm might have actually been the upper limit.

I think if you measured the bores in the thrust direction you may find the clearance is excessive. All that slapping back and forth weakens the skirts and they eventually break. 6,000 rpm is an excessive red line if there's too much clearance. I recall Jeff (StockZ/28) had a post on that very subject somewhere. In fact I think it's in your mile long budget 350 thread, because we were discussing piston fit and what's too much clearance.

The other interesting thing you learned was there might not be obvious clues to internal damage. People often assume when an engine "blows up" it's spectacular. In my experience it's often un-remarkable. The engine just quits and won't restart. I'm amazed your 307 still ran despite being mortally wounded.

Ok, You've got two boat anchors under your belt. Let's try to keep the 350 alive for awhile.

Please remember it's not going to be as good as if we went .030" over and installed lightweight forged pistons.
 

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Discussion Starter #12
I don't know how many miles were on the 307. It was "rebuilt" in the early 90's by the previous owner of dad's '75. I'd imagine it had plenty though.

Yah, maybe 5000 rpm would have been better, but it seemed to run fairly happily up to 6000 time and time and time again. Alas, that is the end of the 307. Hopefully we'll keep the 350 alive for quite a bit longer. It helps that this motor won't be seeing a bazillion street driven miles too.

Kev
 

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novaboy009 said:
I don't know how many miles were on the 307. It was "rebuilt" in the early 90's by the previous owner of dad's '75. I'd imagine it had plenty though.

Yah, maybe 5000 rpm would have been better, but it seemed to run fairly happily up to 6000 time and time and time again. Alas, that is the end of the 307. Hopefully we'll keep the 350 alive for quite a bit longer. It helps that this motor won't be seeing a bazillion street driven miles too.

Kev
Mrs. Romeo is running a 305 in her blue Ventura now (the 350 blew up the other week) and she's still running 13.80s!!!
 

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novaboy009 said:
It was "rebuilt" in the early 90's by the previous owner of dad's '75.
Kev
Well check the bore size and see if there are markings on the pistons.
If the pistons are original std bore 307 pistons then it wasn't rebuilt in my book. It might have been re-ringed and reassembled. Putting new rings on worn pistons is a temporary fix. Honing a worn bore is only going to make the piston to bore clearance worse.

DriveWFO said:
Mrs. Romeo is running a 305 in her blue Ventura now (the 350 blew up the other week) and she's still running 13.80s!!!
Geez, and I have an old 305 I could have given Kev!

I suppose now I have to make sure this budget 350 can beat Mrs. Romeo's 305 and Dave's blue light special or I'll never be able to show my mug here again?
 

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Discussion Starter #15
I have some pretty interesting pics from todays 307 tear down session. I'll post pics of the carnage tonight!

Long story short, all the main bearings were wiped, all the rod bearings were wiped and scored, piston pieces were in the pan, and two rods/pistons looked burnt (very copper/brownish colored). The pistons were .030 but they had excessive clearances. I could litererally shove a screwdriver down the side of the pistons. Also, the rods had a TON of play on the crank. So much play that they were scoring the edge of the block and crank throws. The rod bolts were pretty much finger tight on the rod caps. I think they were very very close to letting go for good. It's ugly!

Off to the scrap yard now...

Kev
 

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The good news is the Chinese are buying up all the scrap metal we can ship.
Ferrous scrap was $80 a ton when I unloaded a bunch of junk.
 

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Discussion Starter #17
Here we go....

1) Disassembly in progress



2) Empty engine bay... give it a weekend or two, it's getting a revamp:)



3) Tough to see in this pic, but it's the best I have. Notice the nasty vertical scores on cylinder number 8? How about the little piece missing on the right side of number 4. There's also a crack on the bottom of number 6.



4) Here's the telling one. Look at that color!!!!!!!!!!!!



Kev
 

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Kev, i have ta say... that poor Lil' Engine looks as if ya wrung ALL the fun out of it ya could have... remerkable isn't it ??? that with all the fun (abuse at track) ya put on it... it held together and actually served ya Very well...

i'm looking forward, as i'm sure everyone is, ta hearing Great News when you, Paul and Dave get yer car hooked up again... i've been enjoying the PW thread a lot, except for the bad news parts :( i hope it's 10 times more than ya expected and hope everything works out the best it can.


KICK SOME A$$ Kev !!!! you deserve it !!! :D :D :D


and keep up the good job at school !!! ;)
 

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This is where be began:
novaboy009 said:
I can get a set of L98 Corvette heads for my 307 for $400. This would resolve my oil usage problem and be a significant upgrade to my current mismatched powerpack/267 head. They are 56 cc's, so my compression will come up a good bit. The aluminum is nice too. Sound like a good deal?

Kev
And here we are. It doesn't look like the engine was rebuilt. Maybe re-ringed and bearings. No rebore and crank grind. It's amazing it suffered and lasted so long. Might be a lesson that shouldn't be repeated. Have you thought about a crate short block?

btw, check your subframe bushings while the engine is out.
 

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Discussion Starter #20
It was rebored! The pistons are .030 over. But obviously the guys just slapped the thing together and prayed it ran. It ran, but the tolerances must have been very very very loose. I'm sure the machining was less than amazing as well...

Kev
 
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