head gasket question

[jay dezman]

i've had it suggested that a head gasket can leak water into a cylinder despite holding good compression?<br /><br />anyone ever hear this?<br /><br /><br />ever heard of periodic head gasket replacement ?

 

[sschoener]

Re: head gasket question

what kind of engine?

 

[rodbolt]

Re: head gasket question

yes it can. a compression test is rather crude. if in doubt use a leak down test.<br /> good luck and keep posting

 

[jay dezman]

Re: head gasket question

sorry, suzuki 200hp v6 1987

 

[jay dezman]

Re: head gasket question

i don't understand how a gasket can seal high pressure gas but not low/no pressure water.<br /><br />also, i would think that in the combustion cycle a two stroke will be approach 0 pressure twice each revolution while the rest of the cycle is either pressurized by the cylinder filling or combustion process. can the cylinder scavenging be good enough to drop pressure below zero?<br /><br />any explations???

 

[31900]

Re: head gasket question

It happens, believe Rodbolt. When running or under test a slght leak in the gasket will not affect the compression too much other than blowing into the water jacket. Sitting idle if water is on the other side of that leak.....

 

[jay dezman]

Re: head gasket question

i could begin to understand that if i didn't know that the power head will drain when the motor is not running.<br /><br />still need an explanation of the physics though...<br /><br />i've seen the pee hole drain for minutes after shutting down and seen a delay (momentarily)on startup - this is while sitting in the water.<br /><br />when pulling the boat out on the trailer it likewise draining.<br /><br />guess i'll borrow a leak down tester and see how that goes - still hard to justify removing a head when the compression seems strong (at this point)

 

[rodbolt]

Re: head gasket question

cause I am stupid I guess. believe or dont. it happens.<br /> good luck and keep posting and forget I have almost 30 years of fixing them without physics

 

[jleus]

Re: head gasket question

Water coming in direct contact with the temperatures found in a combustion chamber creates steam in very short order. Slight leakage into the water jacket or from the water jacket can created a situation were some part of the engine will have to deal with steam. An outboard is not designed to deal with steam and its presures. Any head gasket leak is going to start small, its not an all paper gasket remember, that crush metal in there is pretty tough, has to be, its job is containing explosions. So you are always in tune with your outboards performance, STEAM in the combustion chamber will jack the piston into the wall, siezure maybe??.....steam in the water jacket is not a very good heat absorbing agent, hot spot, siezure maybe?? shut her down....take her home....check compression...maybe no problem there after a little cool down. But there is a bad gasket there. This is why many service instructions recomend retourqing the head over time.<br /><br />Rodbolt, your thirty years were nothing but keeping the physics of an internal combustion engine within the parameters required to make it perform.

 

[jay dezman]

Re: head gasket question

pulled the plugs yesterday. one was slightly less oily than the rest. not a steam cleaned pristine appearance i would have expected in the above scenario's.<br /><br />placed an inductive timing light sensor over all 6 leads individually. had one cylinder that had a "random" miss in the frequency of the pulses. guess i'll replace a coil and see what happens. <br /><br />as a separate issue, the idle switch on this motor has a different setting than the other engine. the "good" has the switch set at the lowest setting and it idles at about 820 rpm. the "weak" engine has the switch at the next to the top switch setting.<br /><br />i have (i believe) a spare cdi and selector switch. i'll try swapping out, weather permitting this weekend.<br /><br />the steam discussion above leaves me with more confused.<br /><br />the supposition above is that steam from the water jacket leaks INTO a running cylinder from a NON pressurized water jacket....if the water pump is working the water jacket will be full of circulating water, water that is not "contained" thus no pressure build up.<br /><br />i could see some liquid water migrating into the cylinder of a non running engine, but then is the quantity of water would hydraulic the cylinder and bend the connecting rod if the starter is strong enough or just lock it up.