How can this happen
 

- So another bit of bad luck unfortunately here are the details maybe the OSO community can chime in so I can better understand what went wrong, here are the details

New HP500 carb stock rebuild, New gen6 block, pistons, rods, bearings, new oem cam from mercury, new intake, oil cooler, new EMI thunder dry exahaust etc.

Rebuilt stock heads , new springs valves retainers rocker arms push rods, lifters etc, castings were freshy magnafluxed decked etc



Had Motor put back in the boat took boat to ramp idled out of 5mph zone 5 minutes ran the boat up to speed 3-5k rpm for 20 minutes boat ran perfect returned home put the boat up on the lift, no alarms no overheat or oil pressure problems, like I said boat ran great


2 weeks later after lots of rain in NY decided to take the boat out after work, idled down my canal 10 minutes..... jumped on plane only brought up to max3000 rpm;s almost completely on plain and motor started stumbling and missing bad, limped to the nearest boat ramp pulled boat out. Less than 45 min on the new motor probably less than15 min above 1,200 rpm, My boat shop calls me with news that I have 0 compression on # 5 and # 7 cylinders, pulled heads and below are pictures of what he found, two bent exst valves that kissed each piston... what do you guys think

https://www.dropbox.com/sh/tlt8p1gf6...PE67ZEx_a?dl=0

Drop box isn't opening for me anyway. Does it look like anything went out the exhaust? Without seeing hard to say but remember foreign objects can transfer from port to port and then blown out. Hydraulic roller cam correct? Check number 5 and 7 exhaust manifold. Wish I could open pic. Will try a shut down and reboot.

Was able to open up and see pics. Wtf. Got me... you check spring pressure on seat and open? Only thing I can think of. How many hours are on valves? Degreed cam? I feel bad for you!

Here you go.....




[ATTACH=CONFIG]567650[/ATTACH]

[ATTACH=CONFIG]567651[/ATTACH]

[ATTACH=CONFIG]567652[/ATTACH]

[ATTACH=CONFIG]567653[/ATTACH]

Any thoughts here guys. Nothing obviously went in through the intake ports. At least no evidence anyway. Fatigued exh valves? I have no idea.

Valve guides need to be checked,,,possibly to tight of a clearence

/Who rebuilt the motor?

Were the lifters replaced ?...........seems odd...5 & 7 fire back to back............seems like a timing event

Exhaust valve looks rusty to me

I have the heads at a new machine shop getting rebuilt , so I hope it is a valve guide issue that will be fixed once and done, With that being said it will be a nightmare if I put it back together and it happens again it will be a season ending disaster, what should I do to rule out a timing related issue before I run this motor again, this is my second motor in 12 months first one was wrecked by reversion I have to get this right

When you were getting on plane, was it coming up easy or did you work at it or let off for any reason?

Valve guides were too tight. Both exhaust valves stuck open and the pistons hit them.
Have the heads rebuilt again the right way and replace any valves that have scuffed stems as well as the two that are bent.
The fact that the exhaust valves stuck tells me that they were too tight. Those stems get hot.
Did anyone do a plug check to see if it is running lean on those cylinders.

Yes checked plugs no sign of running lean

Any chance piston to valve clearance is too tight. A lot of aftermarket piston makers raise piston deck to reduce the 016 to 020 in the hole pistons leave the factory at. But whatever it is, count your blessings. The valve heads are still attached to the stems, instead of stuck through the cyl walls.

can we see the plugs,,we may see something different.

Sorry about your bad luck but in some ways it looks like you got off easy - having parts touch with no catastrophic results is good luck in some ways (if that offers any solace)

Clearance on the exhaust side usually isnt an issue, i agree looks like he stuck a couple valves, any idea what the clearance was on them? Maybe they didnt put assmbly lube and they were dry when you brought it up to 5k?

If the 5&7 wires are touching it can cause detonation, but not this extreme.

Clearance was my thought as well. May be so close that they just barely teenage kiss or peck on the cheek. Clearance or guides too tight. I'd think anything else would've caused much more damage. What's the exhaust lift? What spring pressures?

If it had been V/P clearance it would have shown on more than just those two. And it takes a LOT more than a kiss to bend a valve like that. Those valves were open when the piston came up.
Made a V/P clearance mistake YEARS ago and had the valves just touching the pistons. Every piston showed slight contact. At 7000 RPM one of them let loose. SBF 302.
12.5:1 compression and solid roller cam. engine made over 500 HP NA. Engine had 5 hours of unbelievable performance before it let loose.
When that engine was idling it would make your voice sound like you were driving down a bad washboard road.
That was the engine I had in my Glastron CVX 18 that did 95 MPH.
Everybody that saw me drive it thought that I was nuts.
It was a white knuckle drive. At 95 that boat was past the edge.

i would check piston to valve clearance just to be safe.never assume anything is what it should be when installing new pistons and or camshaft.i have seen parts with incorrect part numbers on the package,had custom pistons made incorrectly,etc.

As said before, ck piston to valve clearance, think it is ok, but make sure, will go along with valves seized in head and hit, now if the cam timing was off, either changed or screwy timing chain could cause this as well. Also if the timing was real late and exhaust valves overheated in a new build with tight clearances also could have been the cause, make sure balancer has not slipped in rubber throwing timing marks off, found that a few times recently...one killed a complete engine.

Tinkerer got it. Never had that happen but you'd think heads refreshed back to specs that wouldn't be the case but wonder what pushrods and lifters look like. As mentioned for exhaust to have a clearance issue is not a result of this. Pistons/deck height wouldn't be an issue or would have been caught during assm and also would have happen first trip out. If valveguides were clearanced properly I would have to think it would be a lubrication issue or lack of.

Regardless it sucks but also as mentioned this could have been a complete disaster. Now it's getting to the real cause and move forward.

Thank you to everyone who chimed in to help me figure this out, after all the feedback it seems that the most likely culprit is the two valve stems... thanks again everyone

16 valve stems.

You learned a lesson and it didn't cost you that much.
NEVER use an automotive engine shop to rebuild a marine engine.
Cars don't go through the load that a boat does. Heck most cars run at 1500 to 2000 Rpm at highway speeds. With a boat your not even on plane yet at that RPM.
Take your family car and run it up to 5000 RPM for 10 to 20 minutes like some of us do ( that is my fast cruise RPM ) and see how long it lasts.
When building a marine engine you have to be very precise if you want it to stay together. The more HP you want to build the more anal you have to be.
I had my schooling of hard knocks years ago. I have about $20,000 in parts and machining in my 598 - I don't even want to know what it would have cost to have one of the high performance engine builders put it together.
With that much $ invested I don't want to get schooled.
Steve

Those valves hit hard. I'm with tinkerer, guides too tight or lifters. Doubt it's the lifters though. Cam timing or piston to valve clearance causing it to hit that hard would at least have witness marks on the other 6.

Clearance and likely cool oil temps. Not a good combo.

Did the engine builder give you a build sheet? If so would love to see it. Need to know, are the valves seized in the head or were they difficult to remove in disassembly? Based on pic #1 the valve is bent but looks to be closed. I realize this is my first post but I have a background in building and maintaining performance engines. You need to find the cause or causes of why this happened. Don't just fix whats broke without knowing why or you will be doing this again. Glad to help if I can.

Update.....
 

ok so here is an update on the head issue on my newly built motor, it seems the issue was a combination of valve guides being too tight and replacing my exhaust valves with non Inconel valves, the Machine shop ignored my request of keeping everything to standard OEM hp500 specs

i had had the bent exhaust valves tested and they came back 50% chrome , 50% steel ferrous basically a magnetic cheaper grade stainless certainly not Inconel

i decided to order the Ch454a EQ heads and having them gone through at a new machine shop, hopefully my luck will be better this time around