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View Full Version : Piston Destoryed Why???



lostlake
09-03-2001, 07:47 PM
O.K.Brand new boat. Motor Heads.. 502,edelbrock heads,intake,290x570 cam,750 holey (Gary Williams)Lighting. O.K... Ran Great !!!! 5200 Rpm @ 70 ( 21 Jet Deck boat Pickle) 5 1/2 hr 3rd day, Crusing at 4300, ran up to 5200 for 1/2 mile, down to 4500 for 2 miles and clouds of white somke from the equast, Pulled plugs on other side, water in block, can hear rod knocking when cranking, Taking it in the moring to shop but still at the river and trying to get some answers as to what the brains out there have some therory, Water temp was 130 altough the enclosed motor seemed hot.

Racing Ray
09-03-2001, 08:51 PM
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[This message has been edited by Racing Ray (edited March 12, 2002).]

spectras only
09-03-2001, 08:52 PM
Lost lake,sorry to hear about your troubles.First comes to mind is a blown head gasket [improper torquing the heads,wrong headgaskets?],water in the cylinders will give you a heavy knocking noise like a very high compression engine.BTW you should run at least an 800 holley for a 502cu engine.Lets hope it 's an easy fix with new headgaskets and new headbolts.You said brand new boat,who did the engine? Checked your plugs for white deposits [piston failure ,by detonation]?
[This message has been edited by spectras only (edited September 03, 2001).]

bajaruner
09-03-2001, 09:43 PM
In an earlier post you asked about valves hanging open on the 502's from INDAMAR. Have you looked through any ports?

lostlake
09-04-2001, 03:26 AM
have not looked at anything yet, the plugs looked white but no deposits on them, I upgraded the heads because of the valve problem in my eairler post, hopefully to elimante that, the knocking noise i hear is a rod clanking with no piston on it, if i run my finger in the equast its full of oil.

ponponracing
09-04-2001, 06:20 AM
Wrong assembly procedure,water in fuel, lean carburator, wrong fuel lines, wrong timing, wrong ignition connections, wrong spark plugs, wrong water pressure, wrong fuel, wrong fuel pressure, wrong head bolts sealer, wrong compression ratio, wrong head gaskets, bend deck or heads, leaking head, broken valve. Pick one.

ponponracing
09-04-2001, 06:23 AM
Please add: wrong fuel level in carb, wrong needle&seat.

lostlake
09-04-2001, 03:47 PM
Took it to the shop today. and they pulled all the plugs and valve covers, springs, rockers look good, #8 plug destored,Looks like someone took a grinder to it. Going to pull the motor tommorow..

spectras only
09-04-2001, 04:05 PM
Sounds like detonation to me,you'll find your piston bit the dust. http://free.***boat.net/ubb/eek.gif

bajaruner
09-04-2001, 07:33 PM
Sounds like a piece of valve or a screw got into the cylinder. Have you fliped the carb over to see if your missing a throttle plate screw? this happens alot on open plenum manifolds where the center throttle plate screws are not removed during assembly due to inexperience. Hopefully neither screw is there, if one is and the other isn't then your mystery is solved.

lostlake
09-06-2001, 05:18 AM
NO screws in Carb... #8 intake valve destroyed ( broke at stem). Why would a valve hang in the guide.? To Tight Clearnce? Motor running lean? Other pistons look good, the other edge of pistons are clean(inside of pistons are black) Does that tell anything?/// Thanks LL

schiada96
09-06-2001, 06:33 AM
It dosent sound like it with the cam your running but check valve to piston clearance at overlap. Valve float weak spring?

boatnam2
09-06-2001, 06:57 AM
if you lean out a cylinder bad the guide will expand to much and grab the valve.

bajaruner
09-06-2001, 07:04 AM
Does not sound like valve to piston clearence (one cylinder only). I would like to know what kind of valves you are running, and yes it is possible for a valve to hang in the guide if the guide was machined to tight, i've seen it before just not in a boat application. Also Edelbrock heads right? Marine or Street?
[This message has been edited by bajaruner (edited September 06, 2001).]

lostlake
09-06-2001, 07:46 AM
Valve clearance good... Inconel equast,SS intake, Marine heads Hard anodized, Dual springs, Head guy is checking clearance in guide today, . I still think it was running lean. but don't know how lean it would have to be in order to tighten up the guide enough to hang a valve. Did not overrev at all, water temp 130, but motor felt hot when it blew. (The plugs showed signs of blueing at the base of the threads ????)

spectras only
09-06-2001, 07:54 AM
Do you have bronze guides?

lostlake
09-06-2001, 08:10 AM
yes, bronze guides

spectras only
09-06-2001, 09:41 AM
Bingo, I've met a few guys years ago having the same problem with the tight tolerances with bronze guides.I rather stick with cast iron that's porous and retains lubricant.The bronze guides should be honed smooth .
[This message has been edited by spectras only (edited September 06, 2001).]

Racing Ray
09-06-2001, 11:22 AM
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[This message has been edited by Racing Ray (edited March 12, 2002).]

bajaruner
09-06-2001, 02:24 PM
Damn man! BLUE PLUGS. The knocking going on in that engine had to be horendous. Well anyway sorry to hear the bad news, next time out make sure you monitor ignition timing, jetting, and fuel presure very closly, also make sure you check the distributor advance curve it may be way to soon and way to much.
HOPE THIS HELPS.