thoughts

[850cc racer]

Hey guys just wondering what everyone thinks about this: its my 920cc that went booooom yesterday, its fingerported, ill give more info on it but first i'd like to hear why people think why its gone boom :eek::o

[850cc racer]

and heres this pics

[Detroit Whitey]

LEAN!!!!!!!!!!!#1 is this motor a 50or60 hp block ? the idle releaf`s kinda give it away. Do you race this in some kinda class or play motor?

[850cc racer]

Hey DW thanks for the reply.. its on a sst60 boat we call them F3's over here. i dont know hp? i would imagine 60 standard or 70. it was the first time i took it out too!! everything seemed fine after the first go then this happened!!!

[looseunit225]

that looks like a really bad high speed lean out!

or a combination of a lean out and a detenation!

[kraazyboat]

Like some water was in gas or water in exhaust. Dave

[850cc racer]

Thanks for the reply guys, ill have it pulled down soon, and work out exactly whats happened. im getting a new sleeve for it aswell as piston, im not sure but this cylinder's sleeve is a tad lower then the rest so maybe this has happened before:eek:

thanks guys will post more pics once pulled down!

[john miffco]

water got in cyl from blown head gasket
piston top away from ex is grey smoother melted,,,had water on it
from lack of water is a cleaner (more rough or jagged )melt
if look at top of cyl where the sealing gasket is
#1 can see side of allunimum corroded away on left side in pic,,,,,,,
#2 can see steel sleeve is dropped below allunimum
#3 and also seperated,,,,,,,,,,,,,steel to allunimum

there is no way the cylinder had good compression to start with
the corroded area,,,,
1 a guess deduction is that motor was never properly flushed through the yrs of use
2 the corrosion erroded away metal sealing area and allowed head gasket to blow
then ran till fried
3 the sleeve sunk during the excess heat
since corrosion already made loose and sepaerated
4 that sleeve looks as it has been replaced in the past,,
can see 2 steel rings on the bad cyl,,,,,
the other 2 look original
machinest may have
machined bottom of cyl too low or cut bottom of sleeve too much when installed,,,,,
causing sleeve not to be cradled on bottom,,in hense allowing to sink
suggest when replace sleeve (which is a must) go to
an oversize outside diameter,,,,to get rid of the remainder of the factory oem sleeve
and make sure sleeve is installed to hit bottom

had to reword reply
also that looks like a handfull of fun to drive
john

[WESTBros.]

At top speed, unit raised to high out of water. No water no good.

[850cc racer]

Hey John, it had been rebuilt and only ran twice since he built it, when i got it first thing i did was replace headgasket as it had blown, so the headgasket that was on the motor was brand new. the sleeve was already a little lower before i took it out.. however alot of what you have said appears to be correct... could it be the headgasket couldnt/didnt seal correctly due to sleeve and has then allowed water into cylinder after it warmed up? as i took it out for about 15 minutes brought it back refueled then went out again for about 20mins which is when it blew up!

WestBros:
I think i need a low water pick up too.. just so happens Mr Hill wants something i have and he has low water pick up nose cones!! :eek::D

[john miffco]

makes more sense with more info
and not guessing,,,,,,,,
could tell cyl was replaced but not how long ago

when rebuilt the sleeve was improper installed
thats why it blew the 1st gasket
then blew the 2nd gasket
the sleeve was installed to low or sunk the 1st time motor was ran
so why it was low when you replaced gasket

gasket surface must be flat across all cyls,,,,,,,,,,,
learning experience not to run motor again if find a blown gasket and see mating surface not flat or sunk

to have properly installed the sleeve in the block
1 would have welded the top of cyl to get rid of the lower corroded area
of allunimum
2 then after installing sleeve milled the top deck flat across all cyls
to have a true plane
and make sure gasket would seal

gotta replace sleeve again or find another block with less corrosion
for a better starting point
for longevity
john

[850cc racer]

okay thansk john, was going to have sleeve removed and check block then replace sleeve & piston and have decked so it is a flat area again.

once i have it pulled down ill post some more pics!

thanks

[Sam La Banco]

I think John is right about the water.

The SST 60 motor will burn a head gasket in a heart beat if things are not 100%, we change them after a few races all the time.

[Tim Kurcz]

The attached image shows #1 damage caused by simple fuel starvation. Sad to say I've seen this many times. Though you may have a cooling issue, be sure to thoroughly check your fuel delivery system. The top carb is the last to get fuel. It will get you every time. Good luck!

Tim

[john miffco]

that pic of a piston you show is NOT the same melt
as the piston this thread is about
look at the 2,,,,,,,,,,compare,,,,,,,,,,,

what i described in detail earlier in this thread

a piston melt from a blown gasket,,,
looks like the 1 in this thread,,,,,dark grey/black burned with smooth edges
from exhaust blowing in the water cavity creating a steam pocket around the cyl,,,which causes the heat to start the burn
the reason for blackened and smoothing on the burn is from the water sucking in on intake stroke,,,,,,,,

same as throwing water on a hot frying pan,,,it sizzles and burns leaving residue,,,,,,,,,,

the piston you show was burned from lack of fuel
from everything DRY,,,,,,,,,clean melted areas,,,,,,,more jaggy
no residue/goo burned into piston,,,,,,,,,,,,,,,,

if it was from lack of water or way too much timing
there would still have oil residue on the rod,bearings,inside cyl under piston

the 3 ways to burn a piston,,,,,,,

[Tim Kurcz]

If it were my engine, it wouldn't get reassembled until every system was checked including clocking of the ignition system.

[850cc racer]

Hi Tim, the whole thing will certainly be checked!

Hey John: When i got the boat on the trailer and took spark plugs out there was no water/residue on number 1 spark plug?

maybe Fast Fred might see this hopefully: something ive found over here x3 :eek: looks like this one has had a boom at sometime!