Need root cause of engine failure!
Need root cause of engine failure! Help an idiot out here,
I have a HCI LQ4 with a small cam. TSP 224R. Can't brag and say the engine cranks out a lot of HP.
Was cruising down the highway barely even using the gas and heard what sounded like a bag of hammers being dropped down a metal staircase. The engine stalled the second it went into reduced engine power. I tried to crank the engine in an attempt to get to a more safe location and could tell the engine was locked up.
On tear down I noticed that cylinder 6 has rotated 120 degrees and it has marring all along the edge of the dish in the piston. Valve contact. It has a huge crack along the dish as well. I also can see a crack running from the top right to the bottom left of the piston but it didn't show well in the picture. One valve (darkest one of them all) was stuck open and appears bent in the cylinder. I am an engine noob but exhaust valves look too white and that means lean right?
I believe the engine broke due to a tuning issue or it ran lean. I installed aftermarket fuel rails days before the engine broke. I also installed a 90mm TB. The WB looked to have good AFR at WOT. Which I wasn't even WOT and was below 2K when she went.
What do you guys think? Tuning issue or broke because It was making too much HP for stock rods? Broke cause it has 205K miles on the motor?
Also can these heads be rebuilt or junk them?
I have a HCI LQ4 with a small cam. TSP 224R. Can't brag and say the engine cranks out a lot of HP.
Was cruising down the highway barely even using the gas and heard what sounded like a bag of hammers being dropped down a metal staircase. The engine stalled the second it went into reduced engine power. I tried to crank the engine in an attempt to get to a more safe location and could tell the engine was locked up.
On tear down I noticed that cylinder 6 has rotated 120 degrees and it has marring all along the edge of the dish in the piston. Valve contact. It has a huge crack along the dish as well. I also can see a crack running from the top right to the bottom left of the piston but it didn't show well in the picture. One valve (darkest one of them all) was stuck open and appears bent in the cylinder. I am an engine noob but exhaust valves look too white and that means lean right?
I believe the engine broke due to a tuning issue or it ran lean. I installed aftermarket fuel rails days before the engine broke. I also installed a 90mm TB. The WB looked to have good AFR at WOT. Which I wasn't even WOT and was below 2K when she went.
What do you guys think? Tuning issue or broke because It was making too much HP for stock rods? Broke cause it has 205K miles on the motor?
Also can these heads be rebuilt or junk them?
The heads have a dual valve spring combination and I found no broken springs. It is looking more like it started in the bottom end. The valve stem is pretty bend but there are no cracks in the head itself or pitting.
TECH Enthusiast
Joined: Jan 2012
Posts: 557
Likes: 9
From: Bowling Green KY
Guys are pushing 1000hp on SBE LQ4s. Just not for extended periods. Even stock vehicles have engine failures. Adding power is a factor, but engine failures do happen regardless of modifications. You said it had 205K on the motor. You don't know the history of it? It could have been a hard life on that motor. I have a friend that is a contractor, he buys work trucks, replaces them every year. He does zero maintenance unless something breaks. They get traded in with the same oil in them they had when new. They drive them about 30K miles a year, pulling trailers, a lot of short trips, and are worked hard. I'd hate to buy one of those motors from a JY even if it was low mileage. He is a little extreme, but not unique. I work with people that are just plain stupid and only change their oil about every other year or when the low oil light comes on. I'd just try to find another JY motor, swap you cam over, if it looks ok, and run with it. If you had those heads ported, you may want to have them looked at by a machine shop, and see if you can use those as well. From the pictures, you can't tell if the head is ok, you would need to pull the valve out and check the guide area for damage. It is probably ok, those powdered metal guides are tougher than the valve I think. It will need a new intake valve and seal at the least.
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I am just wondering if the motor was built up too much for the stock bottom end, fatigue, manufacturing flaw, over revving? When the motor let go I was barely on the throttle and had not be running out all that much.
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GM doesn't give much clearance there in the pin bores. They're usually about .0005" and most performance engines will have twice that. When you get the other rods and pistons out, see how freely the rod moves in the piston.
but I agree, sounds like it was just one of them firecrackers that seem to fizzle out and then BANG
Did you ever get this figured out? Last week I had almost the exact same failure mode. My pictures look very much like yours.
2,000 rpm in a neighborhood, engine seized. Pulled to find #6 piston cracked and broken, wrist pin in the oil pan, piston looked to have contacted cylinder head while still in one piece. Maybe lean condition because my heads look identical to yours. My guess is wrist-pin area failed, rod separated, pushed the piston into head which cracked it in half, and the rod shattered as it got thrown around by the crank a bit.
2,000 rpm in a neighborhood, engine seized. Pulled to find #6 piston cracked and broken, wrist pin in the oil pan, piston looked to have contacted cylinder head while still in one piece. Maybe lean condition because my heads look identical to yours. My guess is wrist-pin area failed, rod separated, pushed the piston into head which cracked it in half, and the rod shattered as it got thrown around by the crank a bit.
Did you ever get this figured out? Last week I had almost the exact same failure mode. My pictures look very much like yours.
2,000 rpm in a neighborhood, engine seized. Pulled to find #6 piston cracked and broken, wrist pin in the oil pan, piston looked to have contacted cylinder head while still in one piece. Maybe lean condition because my heads look identical to yours. My guess is wrist-pin area failed, rod separated, pushed the piston into head which cracked it in half, and the rod shattered as it got thrown around by the crank a bit.
2,000 rpm in a neighborhood, engine seized. Pulled to find #6 piston cracked and broken, wrist pin in the oil pan, piston looked to have contacted cylinder head while still in one piece. Maybe lean condition because my heads look identical to yours. My guess is wrist-pin area failed, rod separated, pushed the piston into head which cracked it in half, and the rod shattered as it got thrown around by the crank a bit.
I am seeing this as fatigue and a normal mode of failure given the age of the motor. i ended up scrapping everything but the iron block. i had a local builder quote me like 1400 for a stock rebuild. i went ahead and did a "performance" rebuild and the block is back on the road. but like i said i replaced everything down to the sensors.