LS7 engine problem

[samantha]

Hi, Can any one suggest why i have a piece of my piston missing, with no damage to the head or piston? i would have thought if a piece this big has broken away in would crash into the valves & piston. I had to remove the head to check for a suspected gasket fault. which there was accross this piston & a water port.

Could this piston have been like this from new? it is a stock motor.

Any advice would be usefull in trying to pinpoint the cause.

Engine was running fine until i noticed the water in the oil & steam comming out of the exaust on cold start

Pics attached

[Will Campbell]

It could be just a defective piston, but it is much more likely to be from unexpected operating conditions.

Broken at the land- looks like detonation damage.

Assuming natural aspiration, it is probably a result of too much timing, or too lean a mixture under load. If forced induction, well, that should be obvious.

Is it a stock tune? If so, perhaps there is an air leak after the sensor, perhaps at the manifold.

New LS7s come with a 2 year 50,000 mile warranty.

[Jac Mac]

Detonation! Now as to its reason for occuring it could be one of several causes. Its a little odd in that is adjacent to the inlet valve pocket which would be a cooler part of the chamber. My guess at this point would be stale fuel or possibly a dud injector on that cyl, detonation or even pre-ignition might have caused the head to lift slightly and then coolant pressure has pushed the fire ring of the gasket into the chamber. Is this the motor you have been using for hi-speed runs etc? a lean out at hi RPM would cause this. Also when you pull the piston check the ends of the top ring for signs of 'butting' contact to make sure you have enough ring gap, these motors run the top ring quite close to the top of the piston and in your particular case/usage it may require more initial gap to prevent this and the localised overheating that can occur.

[Big-Foot]

I agree to the detonation... Also - Check the inside of your intake manifold for the chunk of piston.. Wouldn't be the first time that a new engine ingested a piece of the old engine.. Judging by the oily carbon deposits on the other pistons - she was pumping just a bit of oil. That will help promote detonation as well.. The clean piston is odd unless it got a good steam cleaning from the leaking headgasket..

[samantha]

the motor has run for 2500miles mainly road use & 4x trackdays about 2 hours of hard running. the motor has been set up on a dyno. & produced 527hp @ 5639rpm torque 534lb @ 4698rpm these figures are at the rear wheels, The induction system is kinsler & uses 2.5" throttle bodies. So more fuel will be used than normal induction.

I will check on the dyno map the ammount of timming used.

I will also have a look in the kinsler for the piston part, no damage can be seen anywhere on the piston or head. I would have expected a few dints at best.

Regards

[Howard Jones]

You might also look in the muffler. And for more than one piece. I drought that a piece that big came off the piston in one piece and was pumped out of the cylinder in one piece without any other damage. A couple of pieces maybe.

[samantha]

Checked the kinsler & Muffler, I have the Hushpower R mufflers after the header which have a stainless cone ending at a point, this should catch the bits. I can only think that the bits have vaporised in the heat. My headers are wrapped & I know the glass wadding melts in the mufflers, so I guess around 1500 centigrade will occur inside the system. the car was dynod & a detonation detector was used when dynoing the engine.

would a dodgy batch of fuel cause this? as after a fuel fill pinking was noticed when i exelerated in 6th. a few weeks ago.

[Jac Mac]

would a dodgy batch of fuel cause this? as after a fuel fill pinking was noticed when i exelerated in 6th. a few weeks ago.

Yes, & re your EGT--1500° C ??

Heaps of other possibilities that I will elaborate on later-

[Straight 8 Racing]

From the non Technical Department,

We had detonation issues on our engine at the top end of the rev range on the dyno, we changed to very high octane fuel (109) which appeared to solve the problem, however it transpires that we were only masking a problem with the water pump and its ability to disperse the heat at the top end of the performance range. This issue has now been solved with the addition of a "De-Aeration tank" that helps to strip out air from the system caused during high rpm, if you are interested I will dig out the single line diogram and post it along with some pictures of the installation,

Regards

Iain

[Jac Mac]

While it could be just a bad batch of fuel, the possibility remains that part of the damage had already occurred on the previous run and the 'pinking' was as a result of the damaged piston causing preignition from the broken area/exposed ring/ & oil in the fuel mix.

Pay close attention during teardown to the following- Look for detonation signs on plug porcelain , wrist ( gudgeon ) pin for partial seizure in piston pin bores [ this causes piston to 'tip' in the cylinder and unseat the rings which allows oil to get in the fuel mix where it lowers the effective octane rating ], condition of top bearing shell in conrod [wear and has it still got 'crush' & and a 'snap' fit in rod], any sign of 'fretting' or movement of main bearing caps or main brg shells.

Also during the fuel stop an airlock might have developed in the cooling system from 'afterboil' or heat soak which might have created a hot spot in the water jacket during the next run.

You may have a 'dynamic airflow' issue at speed which favours one ram tube more than others creating a lean out, or in some cases where one cyl fires immediately before its mate and robs airflow. Airflow around the drivers helmet can also play havoc.

Was the motor built specificly for its purpose? or have you simply used a 'crate' motor without any attempt to blueprint or check vital clearances etc.

With detonation a lot of the above fall into the 'what came first-the chicken or the egg?' category-- thats why you have to look hard at what happened in the runs prior and also examine the engine parts on teardown very carefully. The fact that you did not experience any problems on the dyno means little once you start to factor in stuff like airflow at speed and cooling etc. If you find definite indications of most or all of the above signs, consider the motor a throwaway, it will be nothing but trouble from here on if its really had an extended run in this state.

[Howard Jones]

Str 8, I'd like to hear more about cooling at high revs. My car seams to cool well when driven at low to med power levels even in hot weather (95F). But when reved to 6K and at near full power for several laps (20-30 mins) it will climb to aprox. 220-240F in 90-100F air temps. Car cools right down on cool down lap to aprox 180ish F. Is this a problem?

Could this be I'm turning the water pump to fast? Slow? I am sure it is not air in system because I have blead lines from the rear of the intake (both sides) as well as both tanks of the radiator (top) back to the expansion tank. What would you recomend for a reduction ratio between the waterpump pully and the crank pulley?

Could I be making air in the system with pump cavitation and then pulling it back out when revs go down?

I have a eldenbrock victor junior alum pump and alum heads and aprox 300hp at the wheels. The engine oil is cooled and holds 8 quarts. Oil temp never goes over water temp at top of heat range and is usually about 200F.

Any other ideas?

[samantha]

Iain, interested in the cooling system , this could be a factor,

Prior to any problems with the car. I used the car for nearly 2 hours giving the car full use on the race track, driving it at its maxumin power. coming in only to change passangers, however i did slow the car down for a lap prior to comming in to the pits. turned the engine off changed passanger & off again. this is the hardest i had driven the car. When I had finished I put the car on the trailer & drove home.

Only on start up after leaving the car over the weekend I noticed the problem of the steaming exaust. It seemed to go away & did not steam again untill i took it out on track again. used it for around 20min steamed at first then went away although I thought something was wrong Oil & temp read okay with 90degrees on the water & 100lb on the oil. ocaisionaly temp creeps up after full power on the track to just over 90.

Another point when I drained the radiator down water did not flow out only trickeled out & did not drain the engine? so air lock? or hot spot?.

I hope this helps in the thinking.

Thanks

[samantha]

PS Engine was a new crate motor, Kinsler was added,

[J. Salmon]

Originally Posted by samantha620

PS Engine was a new crate motor, Kinsler was added,

Did you use the maps supplied by Kinsler, or did you develop new maps on the dyno? I am using a crate LS7 with Kinsler EFI and intend to start with the programming baseline from Kinsler.

[Jac Mac]

Here is a better pic of the car in question

[Steve]

steve

this engine was supplied and fitted and dyno'd in the car you bought, right?

What do those chaps think has gone wrong?

[Steve]

when you drained water, was the water tank cap on? if so it'll only dribble slowly

[Paul Osborn]

Hey:

Looking at your piston, it looks like an awful lot of material broke off. If it came off in one piece, I also don't see how you avoided any head damage. So, is it possible that that piston material broke off in a series of little pieces?

[samantha]

Decided the best solution is to order a new engine from katech.