Lost Water / Head gasket ?

Ordered an OEM head gasket from thumper talk store. Hopefully they have it in stock and can get it out quick.

My only complaint was the shipping costs.. $25 for second day shipping on two gaskets was a little high in my opinion (ordered a cam tensioner gasket too)

I don't believe that's correct.

A warped head or failing head gasket can cause the exhaust to blow into the water jacket of the cylinder. That in turn pressurizes the cooling system to the point where it will escape the radiator cap to the overflow.

If the bike has the coolant topped up, and immediately dumps coolant out of the overflow from a cold start, it is almost certainly a warped head or bad head gasket. I had a warped head on a 2000 YZ426 that behaved this way. I took the head to a machinist who put it right for me.

You probably have some amount of coolant in the crankcase now too. Drop the oil. If it is milky, then that's another sign of a head sealing failure. Don't ignore it - get it fixed. Coolant in the oil will play havoc with your bearings.

This is off topic, but is this the case with truck engines as well? say your buying a used truck and you want to check the head gasket. When it's cold, pop off the rad cap and crank it over and coolant should not spurt out?


More or less.. Probably.

One thing I've seen happen was the radiator hoses being pressurized as soon as you started the car. Like, you could squeeze the hose and it was squishy until you started the car then they'd tighten up like a balloon and water would start coming out of the overflow tube.

The cooling system should not pressurize that fast..

It is off topic, but the fact that there's a thermostat complicates the matter considerably. Because the cooling system is in by pass, with circulation through the radiator cut off until the thermo opens up and stays that way, various different surge conditions can and usually do occur that push water out of an open radiator cap as the engine warms.

If, on the other hand, you wait until the coolant temperature has leveled off and circulation is established, you can CAREFULLY release the pressure from the system and remove the cap. Water should not be blown out as the engine revs. It might surge as push some out as it coasts back to idle though. Something a professional should look at, really.

Normally a car or truck engine with a blown gasket will also misfire noticeably at idle.

You could always pull the thermostat out... :ride:

You could always pull the thermostat out... :ride:

That's not always as simple as you make it sound, and I don't think you'll find many prospective sellers willing to let you do that much monkeying around with their truck.

Details, details..

This is about as clean as I can get this head using the "thick ass piece of glass and sandpaper" method. Went over it with the edge of the glass at different angles all over it and can't get the smallest feeler gauge I have under the glass (Don't recall the size, but it's smaller than the max allowable per the manual). Wish I had a good machinist straight edge but for now this will have to do.

The marks going around where the cylinder would be towards the bottom right I can't seem to get out.. I can't feel them at all with my fingernail so here's to hoping they aren't an issue later on.

Also, checked valve clearances while I was bored and everything is in spec. Exhaust valves are at the limit on the tight side, but within spec so I'm leaving them alone.



i think yamaha keep them at the limit from the factory from earlier threads so i dont think they will go out of spec

An update for anyone interested: got gaskets in today and put it back together. So far so good on the head gasket.. All symptoms are gone. Only took 4-5 kicks to start it afterwards too.. Finally started when I turned the choke off, lol

The o ring on the coolant pipe coming out of the head needs replacing as I'm getting a small leak there and I might end up having to replace the valve cover gasket.. But at least the big stuff is fixed, knock on wood.

Next up is a new cam chain. Should have done it while I had it apart but wanted to get this fixed first.

An update for anyone interested: got gaskets in today and put it back together. So far so good on the head gasket.. All symptoms are gone. Only took 4-5 kicks to start it afterwards too.. Finally started when I turned the choke off, lol

Dude, that's great. Good work.

And one last update. Replaced o ring on the coolant tube that bolts on to the head which fixed the small coolant leak. Rode for an hour or so total and it's not leaking a drop now. Hopefully it stays that way.

Also replaced plastics, graphics, grips and am ordering cam chain and flywheel puller tool this week to finish off the maintenance that it needs most. After that I'll take it for some real riding further from home. Has a little bog that I'm not too happy with but my understanding is that it's pretty common so I'll work on that at some point.

Edited by Schpenxel

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