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Just recently rebuilt my 5.7L LS1 1999. Heads reconditioned, block bored out 10 thou, new pistons, rings, pushrods, new high flow water pump, new cam, crank and conrod bearings.
First time started noticed a slight squeak and ticking noise coming from the engine. Assumed it was just the rings bedding in so wasn't so concerned. Ran it twice for about 15~20 mins each time, varying the RPMs to ensure good bedding in. Third time I started it, very loud clanking noise evident. Shut it down straight away.
Removed the valve covers, everthing looked fine. No sign of spring or rocker damage. Can't see any bent pushrods (only pulled one out to inspect and it looked fine). But I can rotate the others and they don't appear to be bent.
Then I tried to rotate the crank by hand with a breaker bar and socket to turn the crankshaft bolt. It would only rotate about half a turn and then stop. Its not stopping due to compression (I have removed all the spark plugs) as it is an abrupt stop. Usually if its due to compression you can apply more force and it will start to 'give' and then turn. This is a sudden stop and more force doesn't seem to move it any further. I can also move the crankshaft back half a turn but then it will also come to a sudden halt.
You can see the rockers moving as I turn the crankshaft so pretty sure its not an issue with the camshaft, lifters or cam chain. I loosened all the rockers so all the valves are fully up, but still the crankshaft won't turn a full revolution. So pretty sure the pistons are not being fouled by bent valves, etc.
Coming to the conclusion its a bottom end problem. Maybe a spun bearing or broken conrod? Would appreciate any advice......
I think your assumption is correct. There are a few things that do come to mind. Bearing clearances weren’t correct, oil starvation, something wasnt tighten down to spec, a bad part but it all points in you needing to tear down that engine again. You’re not really going to get anywhere unless you pull the engine. I know that’s not what you want to hear but it’s inevitable regardless of what we tell you here.
Did you have good oil pressure both times you started it?
Before I started it I cranked it a couple of times (without the plugs installed) to check the oil pressure. It was reading 0 psi. I then primed the oil pump by pumping oil into tthe port on the side of the block. That seemed to do the trick, as when I started it I had around 50psi which after it warmed up settled at around 25psi. Revving the engine would take it back to around 50psi. This seemed to align with the pressures I was getting before I did the work on it, so I don't think it is an oil pressure issue.
Regarding the bearing clearances, I installed standard bearings. I didn't specifically check the clearance as I assumed STD would be ok. (maybe a wrong assumption?) I also installed a double row timing chain which when I put it in seemed a little tight to me. I checked with the engine shop where I got the head and block work done, and they said it should be ok as it should loosen up after running the engine.
So looks like I will need to pull the engine again which I didn't want to do as its in a custom car and a really tight fit. I can't pull it out with the tranny attached as there is just no room to get them out together. Not sure how I can get the bolts out between the flywheel and torque converter? I'll have to remove the oil pan and see if I can free up what ever is stopping the crankshaft from turning so I can remove the three bolts.
Not gonna beat you up but you need to always check bearing clearances regardless. Keep us posted. Maybe once you get the pan off you might be able to see something.
Pulled the oil pan off today and found a bent conrod! (see photo).
Not sure how or why it bent ???? I can’t see any others that are bent. Incidentally, it’s in the same cylinder that had some bad pitting marks that were bored out (cylinder 7). But I doubt it’s the same conrod as I didn’t keep track of them and just put them back in at random.
I will replace all the conrods (it has new pistons, rings and gudgeon pins already; the conrods were about the only parts I reused).
Regarding the crankshaft getting stuck half-way, there is a large semi-circular projection that juts out from the crankshaft – this is hitting the top of the bent conrod – this is why it won’t move past that point.
The question remains – why did it bend in the first place?
You have an injector problem. Your injector leaked down, practically/partially filling the cylinder with gas. Gas, as a liquid, is not compressible, and something had to give. So the rod either bends or breaks. Fortunately fir you here it bent. If it would have broke, you’d be gathering parts for a new engine build. This is a fairly common issue. I did a swap a few months back for a friend in his Silverado…same exact scenario. Bent rod from a dirty/faulty injector. I then rebuilt the engine with the bent rod, and sold it to another friend for his turbo truck, after finding a good set of rods.
Ah, ok. That explains it. Would also explain the cause of the original problem. It was running very roughly when it warmed up. I thought it was a problem with sticking valves, that's why I got the heads reconditioned. Once I took the heads off, I found one of the cylinders was badly pitted, hence the rebore and rebuild.
So as well as a new set of conrods, looks like a new set of injectors. However, one thing still puzzles me. I put a borescope down the cylinder with the bent rod, and it looked normal - no sign of any fuel in there. Just a little oil sitting on the top of the piston which I assume came off the cylinder wall that I had prelubricated. Would the fuel have leaked away? Or maybe it was detonated by the spark plug? (see photo below)
BTW, any recommendations on a good set of injectors?
Ah, ok. That explains it. Would also explain the cause of the original problem. It was running very roughly when it warmed up. I thought it was a problem with sticking valves, that's why I got the heads reconditioned. Once I took the heads off, I found one of the cylinders was badly pitted, hence the rebore and rebuild.
So as well as a new set of conrods, looks like a new set of injectors. However, one thing still puzzles me. I put a borescope down the cylinder with the bent rod, and it looked normal - no sign of any fuel in there. Just a little oil sitting on the top of the piston which I assume came off the cylinder wall that I had prelubricated. Would the fuel have leaked away? Or maybe it was detonated by the spark plug? (see photo below)
BTW, any recommendations on a good set of injectors?
Cheers,
Greg
The fuel has evaporated in that cylinder. What looks like oil on the piston, possibly could be fuel residue…pump gas is just plain nasty stuff. As far as injectors go, you can send your off and have them cleaned at any injector shop. That way your tune is still good. If you change injectors, you’ll have to re-tune from scratch.
I believe they are the original stock injectors. Probably time for a complete new set as I was told the motor had done around 190,000kms when I bought it.
This is what that piston looked like when I first took the head off to rebuild the engine. It had a brown coloured coating on it as opposed tothe others pistons which had a black/dark grey coating on them. Not sure of the significance of that......
Brown makes me think. You find that in the back of the piston and usually caused by combustion heat oxidizing a portion of the crankcase oil. Do you think that there might have been some oil getting into that piston?
O2*C5 looks like you were right! Tested the injector and it is leaking. I fed it via a tube filled with fuel and it just started dripping fuel without any voltage applied.
Under pressure, it would be spraying out fuel continuously I would think.
I've attached a video of the test I carried out. Thanks for your tip. You were spot on!
Pulled the oil pan off today and found a bent conrod! (see photo).
Not sure how or why it bent ???? I can’t see any others that are bent. Incidentally, it’s in the same cylinder that had some bad pitting marks that were bored out (cylinder 7). But I doubt it’s the same conrod as I didn’t keep track of them and just put them back in at random.
I will replace all the conrods (it has new pistons, rings and gudgeon pins already; the conrods were about the only parts I reused).
Regarding the crankshaft getting stuck half-way, there is a large semi-circular projection that juts out from the crankshaft – this is hitting the top of the bent conrod – this is why it won’t move past that point.
The question remains – why did it bend in the first place?
Cheers,
Greg
Looks like the bottom of the piston is hitting the crank throw. I agree with Che70velle, you had either a leaky injector dump fuel in there, or you have coolant entering the cylinder from above. Either way, non compressible liquid kicked the rods ***.....
Yes, Che70velle was correct about the leaking injector. Thanks for that.
I've just pulled the head, and doesn't seem to be any coolant leaks evident. So pretty confident it was the leaking injector that caused the bent rod. I think it has been leaking for some time as it was running roughly before I rebuilt it. Actually boring the cylinders and replacing the pistons and rings probably agrivated the problem as the fuel had no where to go when it was compressed - the old rings and cylinder pitting would have let some of the fuel escape past the piston during the compression stroke.
About to pull the piston and rod. Hopefully I don't discover any further damage......
I've pulled the piston out and everything looks good. Cylinder wall is smooth with no scratches evident. Piston looks unmarked, rings seem fine. Can't see any damage to the underside of the head or the valves. The only minor issue is some scratching on the bearing halves.
The conrod seems stuck on the gudgeon pin. Not sure if it will press off. May have to cut the pin either side of the conrod and then just press the ends in.
Greg, that’s a pressed-in piston pin. You’ll have to have a shop press it off, and press the pin back on the new rod. Most shops have a rod oven. Don’t try to cut it apart. Gen3 rods are non-floating meaning they are press fit. Gen4 rods have pins that slide in place and are held in with circlips. Find a rod, throw it all back together with new headgaskets, and go drive that thing.
Crank Only Turing Half Way 
