tune is important !!!! - Pontiac G8 Forum: G8 Forums - G8Board.com
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post #1 of 21 (permalink) Old 11-14-2017, 03:13 AM Thread Starter
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Unhappy tune is important !!!!

so i changed the cam and was waiting for the tuner to come back from his vacation so i took it for spin and that what happened

the question is would you guys recommend to re-build the engine or get a new one? the dameged parts are piston obv, exhausts valve and crankshaft. so what i mean is it ok to use the engine block or nah
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post #2 of 21 (permalink) Old 11-14-2017, 07:26 AM
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You need to get the piston out and take a look at the bore. If it is scratched you can have the block re-bored unless the gouges are really deep beyond the capability of resurfacing.

I'd take the block into a machine shop to have them take a look at the bore. If they can bore it, have it x-rayed and otherwise examined for integrity. Then you can choose some pistons to their recommended size and have them bore it to that size.

They'll polish the bearing journals and make sure they're aligned, and they'll top it off with a cam bearing installation. It'll be like a new block.

I'm curious, though.... Driving before a tune shouldn't damage the engine. Did you go full tilt with that pedal? Still, it is a mechanical system and those are some pretty rough strikes. What did you install for rockers and springs?

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post #3 of 21 (permalink) Old 11-14-2017, 08:34 AM
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Without a tune, the engine would have been running extremely lean, especially if he went WOT, which is what I'm guessing happened.

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post #4 of 21 (permalink) Old 11-14-2017, 08:57 AM
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Looks like a valve dropped to me. I suspect that the valvetrain was installed incorrectly.
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post #5 of 21 (permalink) Old 11-14-2017, 09:57 AM
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So it dropped the exhaust valve? Bring the piston down to Bottom Dead Center and inspect the cylinder wall. Dont worry about damage above where the top ring stops. Any damage below that is a problem, general rule of thumb is if you can feel the scratch or ding with your fingernail running across the wall its no good. If you have cylinder wall damage you have 3 options. 1) take it to a machine shop and have them machine it. 2) get a new/replacement engine. 3) if it is light damage, live life on the wild side. take some fine sand paper and gently work it until your nail no longer catchs on it.(not advised to do this, but at this point what do you have to loose) And most important you need to check your valvetrain and figure out why this happened. Stock valves couldnt hack it, bad piston to valve clearance, valve float due to the springs not being up to the task, timing being off, or valve/spring not being installed correctly. But best case right now is you are going to need a new piston/ connecting rod/ bearing/ rings, cylinder head and valve, and any other parts that were damaged. Look all the valves and pistons over good and check for additional damage.

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post #6 of 21 (permalink) Old 11-14-2017, 10:23 AM
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Quote:
Originally Posted by davidfoster View Post
Without a tune, the engine would have been running extremely lean, especially if he went WOT, which is what I'm guessing happened.
That is true, but I can't see it causing a major piston strike due to a busted valve. If the motor ran without strikes at idle, then it suggests the springs either got into float, or were still open due to the lifter pumping up.

OP. Do tell us the specs of your Valve train build. Also, what size pushrods did you use, and what level of preload did you achieve on the lifters?

Many times, incorrect preload (too much) causes the valvetrain to be too stiff. The lifters pump up with oil and the valves fail to seat or even bounce thus causing a piston strike (in this case multiple).

Since it was one valve, it appears to be a tolerance issue with that cylinder but surely all of the other ones are now suspect.

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post #7 of 21 (permalink) Old 11-14-2017, 11:28 AM
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I really feel bad for you man, good luck with everything. I thought you could not even start an engine with a new cam and no tune, guess I was wrong.

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post #8 of 21 (permalink) Old 11-14-2017, 11:47 AM
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Quote:
Originally Posted by Jova007200 View Post
That is true, but I can't see it causing a major piston strike due to a busted valve. If the motor ran without strikes at idle, then it suggests the springs either got into float, or were still open due to the lifter pumping up.

OP. Do tell us the specs of your Valve train build. Also, what size pushrods did you use, and what level of preload did you achieve on the lifters?

Many times, incorrect preload (too much) causes the valvetrain to be too stiff. The lifters pump up with oil and the valves fail to seat or even bounce thus causing a piston strike (in this case multiple).

Since it was one valve, it appears to be a tolerance issue with that cylinder but surely all of the other ones are now suspect.
I thought those were burn marks, looked at it on my phone the first time. Is that the actual valve sitting there?

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post #9 of 21 (permalink) Old 11-14-2017, 11:51 AM
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Are those pistons stock? Thought we all had flattop pistons, or were those valve reliefs flycut? It it were me, if the bores were in any way questionable, I'd put my money towards a new LS3 block. $1700. I have to admit having 0.2L of envy.

I also agree that was not the tune.

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post #10 of 21 (permalink) Old 11-14-2017, 11:56 AM Thread Starter
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Quote:
Originally Posted by Jova007200 View Post
You need to get the piston out and take a look at the bore. If it is scratched you can have the block re-bored unless the gouges are really deep beyond the capability of resurfacing.

I'd take the block into a machine shop to have them take a look at the bore. If they can bore it, have it x-rayed and otherwise examined for integrity. Then you can choose some pistons to their recommended size and have them bore it to that size.

They'll polish the bearing journals and make sure they're aligned, and they'll top it off with a cam bearing installation. It'll be like a new block.

I'm curious, though.... Driving before a tune shouldn't damage the engine. Did you go full tilt with that pedal? Still, it is a mechanical system and those are some pretty rough strikes. What did you install for rockers and springs?
if i am guessing the reason i would say because of the cam shaft being too large that it was hitting the piston or because of the valve open- close timing it was hitting the piston, not sure yet
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post #11 of 21 (permalink) Old 11-14-2017, 11:57 AM Thread Starter
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Originally Posted by hooker9110 View Post
So it dropped the exhaust valve? Bring the piston down to Bottom Dead Center and inspect the cylinder wall. Dont worry about damage above where the top ring stops. Any damage below that is a problem, general rule of thumb is if you can feel the scratch or ding with your fingernail running across the wall its no good. If you have cylinder wall damage you have 3 options. 1) take it to a machine shop and have them machine it. 2) get a new/replacement engine. 3) if it is light damage, live life on the wild side. take some fine sand paper and gently work it until your nail no longer catchs on it.(not advised to do this, but at this point what do you have to loose) And most important you need to check your valvetrain and figure out why this happened. Stock valves couldnt hack it, bad piston to valve clearance, valve float due to the springs not being up to the task, timing being off, or valve/spring not being installed correctly. But best case right now is you are going to need a new piston/ connecting rod/ bearing/ rings, cylinder head and valve, and any other parts that were damaged. Look all the valves and pistons over good and check for additional damage.

yup the exhaust valve was in the piston chamber
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post #12 of 21 (permalink) Old 11-14-2017, 11:58 AM Thread Starter
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I thought those were burn marks, looked at it on my phone the first time. Is that the actual valve sitting there?
yeah lol
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post #13 of 21 (permalink) Old 11-14-2017, 12:00 PM Thread Starter
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Originally Posted by jgeorger View Post
Are those pistons stock? Thought we all had flattop pistons, or were those valve reliefs flycut? It it were me, if the bores were in any way questionable, I'd put my money towards a new LS3 block. $1700. I have to admit having 0.2L of envy.

I also agree that was not the tune.
its actually ls7 engine, yup ls7 swap it was running fine daily driven but i needed more power
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post #14 of 21 (permalink) Old 11-14-2017, 12:01 PM
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yeah lol
WOW I bet that made one hell of a racket!

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post #15 of 21 (permalink) Old 11-14-2017, 12:54 PM
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Unfortunately nothing in the tune would have prevented that. What year LS7? Some of them were prone to drop exhaust valves.

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post #16 of 21 (permalink) Old 11-14-2017, 01:26 PM Thread Starter
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unfortunately nothing in the tune would have prevented that. What year ls7? Some of them were prone to drop exhaust valves.
2008
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post #17 of 21 (permalink) Old 11-14-2017, 01:45 PM
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LS7 is a very important piece of the puzzle here. LS7s have alot of problems with valve guides and dropping valves. This is a very common issue, and gm has a service bulletin out on it. Due some research and you will find alot of info, and get a better idea of the direction you need to be heading. But your cylinder wall inspection and how you are going to fix that still applies.

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post #18 of 21 (permalink) Old 11-15-2017, 07:59 AM
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Oops.

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post #19 of 21 (permalink) Old 11-15-2017, 01:07 PM
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Quote:
Originally Posted by kabbas1 View Post
2008
That year would be in the range, have the guides checked in the heads, it's believed the sodium filled guides are part of the problem.

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post #20 of 21 (permalink) Old 11-17-2017, 06:06 PM Thread Starter
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after research i found out that yeah the reason wasn't the tuning it is a manufacture default the exhaust valve is weak on the ls7
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