exploding spark plugs!??

[trog100]

Re: exploding spark plugs!??

"-the #3 exhust valve was melted"<br /><br />i dont think that one is a "cause" more a symptom.. whatever the cause is its a pretty severe cause if it did that during its breakin voyage..<br /><br />trog100

 

[rodbolt]

Re: exploding spark plugs!??

I tend to agree with Trog.<br /> the melted vavle is a symptom most likly not a cause. have the manifold pressure tested and if it passes replace the riser. risers dont live forever.then its on to the fuel system. to cause a cyl to lean out enough to have the detonation problems yours shows would be a big leak. most likly would affect idle adversly. if the timing is not advancing it will cause exhaust valves to overheat and the engine will not make power. does the motor still have the point type distributor?

 

[Buttanic]

Re: exploding spark plugs!??

Don S, I have to disagree with you on a non working centrifical advance causing detonation. Most I have found frozen were frozen in the retarted position which results in poor preformance, increased fuel consumption and higher exhaust temperatures. I ran race engines with the advance locked at 36 degrees, They are hard to start with that much advance but it won't cause detonation if the advance is not set above the engine's tolarance limit for detonation based on combustion chamber design design, plug heat range and fuel octane. I don't think water injestion would contribute to a melted exhaust valve. Water would tend to cool the cylinder.

 

[trog100]

Re: exploding spark plugs!??

WAP or war emergency power.. something WW11 piston engine planes used to have actually involved spraying water directly into the carb intake.. the idea was to cool the charge therefore making the mixture more dense which is another way of saying getting more in there so as to get more power out of the engine.. this was done at high altitudes mostly cos that where planes operate.. he he.. but the same principle would apply at sea level which is more where boats tend to be..<br /><br />it would cool things down not make thing hotter.. makes a good job of cleaning piston tops too.. so a nice clean piston top is a good way of telling if water has been getting into a cylinder for any lengh of time..<br /><br /><br />sounds like the engine in question could do with a nice water injection system fitted.. it might live a little longer.. he he.. only joking.. whoops..<br /><br />trog100

 

[Capt Ken]

Re: exploding spark plugs!??

With the #3 cylinder having a melted valve, the problem is for sure a lean fuel burn in that cylinder. May have a vaccuum leak between the manifold and head. Those nuts are a bugger to get to and tighten on the manifold. Doubt if the problem is with the carb or timing or all the exhaust valves would show the same signs.

 

[rodbolt]

Re: exploding spark plugs!??

while water itself may have a cooling effect it can also lead to a valve sticking open slightly. as the hot combustion gasses whoosh past it it tends to take out the valve head. as far as the advance timing I have seen it many times. the old hei ign was notorieous for rusting the advance mechanism. it will cause pre-ignition if held retarded. my old suburban was a prime example. a friend of mine actually made his manifolds glow red when he ran his 350 chebby with a loose distributor,not headers, cast iron manifolds, he pulled up in my yard and I think it dieseled for 10min .<br /> trog<br /> chysler tried the water injection trick as well. worked ok but was troublesome. water expands slightly slower than gasoline when heated but expands with several times the volume. if injected properly it will not only cool the combustion temps some but will also increase power by expanding, the piston really does not care what is expanding just that a rapid expansion in a sealed cylinder takes place. the major drawback is that it has a tendany to steam clean all the lubrication from shiney parts. hot water is about the most corrosive substance known. not much it wont affect.just might take a while.<br /> we wont get into all the myths about NO2. other than the german bombers used it in WWII and it worked well.

 

[Richard Petersen]

Re: exploding spark plugs!??

You said that you lost a valve in one cylinder last year. Had everything rebuilt and lost another valve in a cylinder. Only thing I come up with is a valve being held open at higher revs. Valve springs have had it. Check their tension or better yet replace them. Rocker arms. Bent pushrod-s, clean and roll on glass to check, also their length - correct?. Valve gap set to tight. Hell, it is probably a used old engine made of pieces to get it running. Buy new or go crazy paying for rebuilds. Does the engine have a REV LIMITER? If no, all bets are off. I hate beating up, but CRIPES, where does it end? Good luck with it.

 

[Richard Petersen]

Re: exploding spark plugs!??

When the heads are milled down. Who is responsible for a DRY FIT of the intake manifold to make sure the surfaces are still meeting flush by installing a gasket, tighten, remove gasket and measure the difference between top and bottom crush areas ? Old stuff, need to be a damm good mechanic, not average. Thereis no way you will know. You probably need a better engine rebuilding shop.

 

[skierrrr]

Re: exploding spark plugs!??

All:<br /><br />Thank you so much for all of the input. What a great wealth of knowledge you are. It's very generous of you all to take time out of your days to offer your experience. I think there is still hope for humanity! <br /><br />The head is in the shop, the manifold is being checked and I've ordered an electronic distributor conversion a along with new coil. As soon as it's all assembled and running I'll post the results if you care to know. Until then Keep spreading the love!<br /><br />thanks, <br />Marc

 

[Don S]

Re: exploding spark plugs!??

Hey RP, read his post..... he only has an inline 4 cylinder engine, not a V8 or V6. No need for all the doom about the intake.

 

[deputydawg]

Re: exploding spark plugs!??

One thing about watewr intrusion. I have worked with it on 4x4 racers. It does cool the mixture a little, but it also workes like nitrous oxide. It won't burn and takes up space, giving a short increase in compression. The problem that has come up, if the water is not completely expelled from the cylinder, it could "hold" heat in an area around where the water has clung. <br />Am I right in reading that after the head was reworked, there was a broken exhaust valve? Possibly an air leak into that cylinder or exhaust port somewhere. When the hot engine is shut down, or throttled down a cool rush of air or even water entered breaking the valve. This could also happen to the plug if it was too hot then cooled. <br />It would also depend on his description of "exploded". If a plug became brittle from overheating it could shatter giving the appearance of exploding.

 

[seadog2be]

Re: exploding spark plugs!??

so many post.. not enough to read all. <br />I would look at your cam. sounds like a stuck valve. if a lob is worn, probley ex. then eng com. could blow a plug out. comone problem on older chevys is soft cams.