Rod Knock - What to expect on tear down

[terminal_crazy]

95 LT1 Z28 M6 49k miles

Hiya
OK I'm pretty sure it's a rod bearing that's let go. It would explain the UNfalse knock i was getting whilst tuning my cam :-(
It Originally sounded like a cracked piston but is now ringing it's brains out, I know this is BAD.

I've dropped the oil & filtered it, Found a _few_ very small flakes.
Filtered the oil still in the filter... again a _few_ very small flakes.
Cut the filter... Hardly anything visible at all.
Nothing visible at all in the lifter valley, lifters or heads.

Which way round does the oil flow in/out of the Filter ?

My next move is to drop the motor which i've been avoiding by pretending it wasn't really bad.

I'm not really sure at this stage what do. Just looking for ideas/suggestions. What rebuild kits are available etc.
I'm hoping, fingers crossed, that i might get away with a freshen up, bearing & rings.
If the crank is buggered, do I regrind the crank OR instead rebore the block +30 and put new internals in for not much more money (383 etc) ??

Thoughts & ideas please.

Thanks
Mitrch

[ShowNoMercy]

I would doubt you managed to mess up the crank enough that a .010 undercut won't fix it.

Plan for a stock rebuild, or plan for a budget 383, but don't try to do one on the others budget.

I would pull it out, take apart the engine, and then clean it all up for a machine shop to look at. Honestly, you could get away with stock bores, but again, let the guys at the machine shop steer you on that one.

[Dynamic396]

You'll likely find a spun rod bearing, with both bearing halves stacked up in the rod side of the journal. This effectively makes the rod longer so the piston hits the bottom of the head. Due to the weak factory rods, bolts and heavy pistons, the big end of the rod stretches and relaxes its "grip" on the bearings at high rpm and eventually you'll spin one. I've seen this many, many times! It's one of the reasons many of us preach against huge cams on a stock bottom end. If you spin the motor up to where that big cam begins to work, this kind of stuff happens.

My money is on the #8 cylinder...

You'll likely need a crank and at least one rod, so I'd definitely look hard at the 383. It makes a lot of sense if you have to buy that stuff anyway.

[cardo0]

U need a shop manual to at least help dianose the noise and definatly overhaul whats needed. A Chiltons is like 20 bucks and every auto parts store has one for sale on the shelf. Heck try your library too.

Good luck,
cardo

[Dynamic396]

I'm not sure how a manual is going to help with noise diagnosis, but it may come in handy for reference during the rebuild process...

[terminal_crazy]

Originally Posted by Dynamic396

You'll likely find a spun rod bearing, with both bearing halves stacked up in the rod side of the journal. This effectively makes the rod longer so the piston hits the bottom of the head. Due to the weak factory rods, bolts and heavy pistons, the big end of the rod stretches and relaxes its "grip" on the bearings at high rpm and eventually you'll spin one. I've seen this many, many times! It's one of the reasons many of us preach against huge cams on a stock bottom end. If you spin the motor up to where that big cam begins to work, this kind of stuff happens.

My money is on the #8 cylinder...

You'll likely need a crank and at least one rod, so I'd definitely look hard at the 383. It makes a lot of sense if you have to buy that stuff anyway.

I am tempted to go 383
What kits/suppliers get recommendations and what sort of RPM's will they stay together. I'm not looking for a race motor, just something that will stay together

Thanks
Mitch

[cardo0]

How much u want to spend is critical. With rod knock u will most likely need new crank or at least grind. Let your experience guide u. If never done overhaul before limit your efforts and $$$ - there are enough junk $5,000 rebuilds to read about. U will need to use measuring tools like bore gauges if your machine shop can't for you, feeler gauges, torque wrenches and plastigauge.
U may just want to go for a budget crate motor and use your core to learn on. Alot of engine shops are looking for business this time of year and will overhaul your engine at reasonable price to get u back on the road - look in your local yellow pages. Ops, your in England - i don't know what kind of machine work to expect there.
For rotating assemblies try flatlander racing: Flatlander Racing - High Performance and Custom Engine Parts. But to England shipping will kill the deal. To save u will need a local machine shop that can grind cranks to SAE units. Then all u need is the correct size overhaul kit - pistons, rings, bearings, gaskets.

Hope this helps,
cardo

[KW Baraka]

Originally Posted by terminal_crazy

I am tempted to go 383......I'm not looking for a race motor, just something that will stay together.....

Fresh Rebuilt, Forged LT1/4 383ci Short Block

Of course.....with you being in Engaland, you'd have to arrainge for shipment/delivery.

KW

[Dynamic396]

Buy KW's engine... Problem solved!

[terminal_crazy]

Originally Posted by Dynamic396

You'll likely find a spun rod bearing, with both bearing halves stacked up in the rod side of the journal. This effectively makes the rod longer so the piston hits the bottom of the head. Due to the weak factory rods, bolts and heavy pistons, the big end of the rod stretches and relaxes its "grip" on the bearings at high rpm and eventually you'll spin one. I've seen this many, many times! It's one of the reasons many of us preach against huge cams on a stock bottom end. If you spin the motor up to where that big cam begins to work, this kind of stuff happens.

My money is on the #8 cylinder...

You'll likely need a crank and at least one rod, so I'd definitely look hard at the 383. It makes a lot of sense if you have to buy that stuff anyway.

Close... No 6 Rod :-)
Other Rod bearing/journals seem ok
No 6 bearings are chewed up at the ends and curved up on the rear face. no markings left on rear face.

Crank itself doesn't look too hideous. Rod looks alright at first glance

All the Cap inserts were very loose in the caps though.

Bearings stamped with:
GM-45
18021941
341 B 41
would they be std size ?

Still toying with options atm.

Thanks
Mitch

[Scoobie]

I just broke a Rod... # 6 ! any one else? It will complete the cycle 66_

[Dynamic396]

Originally Posted by terminal_crazy

Close... No 6 Rod :-)
Other Rod bearing/journals seem ok
No 6 bearings are chewed up at the ends and curved up on the rear face. no markings left on rear face.

Crank itself doesn't look too hideous. Rod looks alright at first glance

All the Cap inserts were very loose in the caps though.

Bearings stamped with:
GM-45
18021941
341 B 41
would they be std size ?

Still toying with options atm.

Thanks
Mitch

You'll have to measure the crank to know for sure, but if it's got factory GM bearings in it, they're most likely standard.

That rod is not OK...!! You can't spin a bearing and have the big end of the rod still measure OK. I'd recommend replacing the rods. Stock LT1 rods are nothing to write home about.