first launch in a while, mystery klunk thud

[berk]

got the boat wet for the first time this year (since feb) and i have mystery noises already. motor is on its second season, mild 383, real reliable so far. i launched and warmed it up a bit, but i actually had a pop rivet chunk sticking up the gas pedal, so when i pumped the carb up it stuck at about 2200 rpm for a few minutes while i figured out the problem. then i got er on plane and it started knocking real loud. limped it back to the ramp, thuds heard at any rev abouve 1100. could the warm up have killed something? to loud and thud-like to be a lifter i think. any guesses?
:confused: also oil looked good before launch.

[RCB19]

Sounds like a rod bearing to me. Bummer!! Good luck man.

[SmokinLowriderSS]

The high idle shouldn't have hurt anything by itself. My 454 ran a solid 2,000 to 2,500 for 20 minuites this spring breaking in the new cam. Only a shortage of oil or a rod bolt loosening up should cause a rod bearing failure. Yea, sounds like a spun rod bearing to me too.

[Cas]

you positive it's coming from the engine? did you check the drive line? How about something that got sucked up into the pump?
Just trying to think of simple fixes before going to the bad stuff :)

[berk]

you positive it's coming from the engine? did you check the drive line? How about something that got sucked up into the pump?
Just trying to think of simple fixes before going to the bad stuff :)
yeah my first thought was driveline but it felt solid to the hand. sound not coming from pump, but it is difficult to hear due to the aluminum hull and solid mounts, kinda like a big soundboard! DANG i was afraid it might be rod.
unfortunately it was upstream/upwind to get back so i had to limp for o long way. hope shes not toast!

[Wicked Performance Boats]

Sound transfers thru everything. From past experience, I would disconnect driveline and run motor to isolate problem. Then you know that it's in the engine 100%. Then I'd wouldn't screw around, I'd pull the engine and drop the pan. Budlight

[berk]

isolated the funky jug, saw evidence of loose junk itting spark plug so i ran it with the plug out for a sec and a chunk of ring flew out into the bilge. LAME! is this what i can expect from forged pistons that havent seen more than 5000 rpm? :frown:
can you guys line me out on the next step to get this thing wet again?
pull head, pull motor, pull pan, pull piston, then what?

[SmokinLowriderSS]

I'm with Wicked. Disconnect drive and see if the ENGINE makes the noise for certain. If you still have it, yep, haul it out, flip it over , and open her up. If no noise disconnected, open the drive up and you will find SOMETHING loose somewhere. Good luck.

[Wicked Performance Boats]

Put it on the motor stand , strip the top off, turn it over and remove said piston. Go over everything, have knowledgeable friends or expert diagnose problem. Figure out what to do to correct problem and reassemble motor. Budlight

[berk]

the pistons are claimed to be Probe and the rings are hastings. dont know which models though. :boxed:
can you buy one piston?

[Wicked Performance Boats]

Yes you can buy 1 piston. It's harder to find someone to sell you only 1 set of rings. BUT what happened to your motor and why? Budlight

[berk]

i dont know! been a real solid motor, could improper warmup cause this? or is it just crappy pistons?i wouldve thought any forged would hold up better than the best cast pieces. makes me scared to get nitrous like i was planning :(
i just hope my head is ok. :cry:
by the way this motor was built from a longblock off ebay. came assembled. then a speed shop finished it so no warranty.

[berk]

well heres the deal. cylinder wall looks decent, i think the head looks ok too, you guys would be better judge of that. numbers on the piston say P3831-30
http://www.hotboatpics.com/pics/data/500/10373DSC08597-med.JPG
http://www.hotboatpics.com/pics/data/500/10373DSC08600-med.JPG
http://www.hotboatpics.com/pics/data/500/10373DSC08598-med.JPG

[CrdStang]

Could an extreme case of not-enough-ring-gap cause that?
Maybe another piece of junk in the cylinder got between the outside edge of the piston and the head, then broke that chunk out of the piston when it got back up to TDC?

[berk]

Could an extreme case of not-enough-ring-gap cause that?
Maybe another piece of junk in the cylinder got between the outside edge of the piston and the head, then broke that chunk out of the piston when it got back up to TDC?
seems strange a piece of stuff would appear in there whithout having done any work to the motor. although the next jug over has a small ding in the piston. maybe my carb is bio-degrading. found a seller of single pistons, these are a flat top forged lower end piston from probe. does anyone have a line on single sets of hastings rings?

[ARS Marine inc.east]

Jist Buy the one piston and replace it , making sure you use the marine clearance on the ring.
That looks like it could have had the wrong end gap clearance on the ring.
Make sure you check your timing. On high H.P. motors I've had the top ring Crack because of detonation.
Anyways you should be able to find a local dealer to sell you one set of rings.
Alot of people out there just replace what needs replacing.
Sorry to see you had problems on your first time out, But its still just the begining of the season. Youll get it back togther

[ARS Marine inc.east]

I'm a slow typer
Just saw you found a single piston thats cool ;)

[1HOTGMCJET]

I notice a slight amount of corrosion at the top of that bore, perhaps the ring was stuck to the cylinder wall (after having been sitting for awhile), and broke when you started the motor (possibly causing the piston damage seen), and bounced around a little giving your noise? Just a guess, like I said.....good luck!

[Wicked Performance Boats]

Looks to me , you had a head gasket starting to go away. It's black between 2 cylinders and some leakage too. Budlight

[CrdStang]

Jist Buy the one piston and replace it , making sure you use the marine clearance on the ring.
So, uh, just what should marine marine ring clearances be? I..uh..just slapped my rings in...
:(