Could a tight exhaust valve be related to a super-heated coil? 225.

I finished adjusting the valves today on the twin 225's. Both motors were consistent except for one exhaust valve on #6. All 24 intake valves were slightly loose @ approx 0.26mm, and all but 1 exhaust valves were dead on @ approx 0.30mm. I adjusted the intakes to 0.21.

The one exhaust valve on #6 was dramatically tight @ 0.22mm, as if someone in the past had mistakenly adjusted it like an intake.

Well, this cylinder is also the one that produced a coil so hot that it nearly fused to the surrounding tube, and was hell to get out. I found crazy ohm and voltage readings coming from the old ecm and assumed that was the reason. Now I'm not so sure.

Could that tight exhaust valve have caused the super-heating of the coil?

It's only MY opinion but I would say yes, absolutely. Here's why...

Pretty much every modern engine valve train has a certain amount of valve "overlap" designed in to help "scavenge" exhaust gas out of the cylinder while, at the same time, ensuring a fresh load of intake air has a chance to "pack" the cylinder. With that in mind, let's look at something referred to as the 1/3 rule in engine cooling.

The cooling system of an engine can't remove all of the unwanted heat of combustion. It is said that the heat exits the engine via 1/3 the cooling system, 1/3 out the exhaust and 1/3 "other ways" IE:fuel vaporization+ oil system + radiation to atmosphere.

As you can see, anything that disrupts the "designed in" flow of exhaust gasses from the cylinder COULD adversely effect the way the cylinder gets cooled.

Also, the tight valve adjustment has the valve opening too early and closing too late. This is going to upset the "packing" of the cylinder with fresh air and that will effect fuel burn. On a csrbureted engine this might be expected to lead to a rich condition. But. in a computer controlled engine that relies on the reporting of an O2 sensor, it COULD lead to a lean burn condition depending on how the computer interprets O2 and adjusts the pulse of the injector. A lean condition would also lead to localized heating of the cylinder.

That's my best guess and I realize a sophisticated Honda engine designer could come along and shoot down all my theories but, until then.....
THAT'S MY STORY and I'm stickin' to it!

And that's why one of the first things that ought to be checked when an engine is running poorly is compression and valve clearances. Unfortunately, Honda makes it a PITA to check and adjust the valves, at least on their bigger outboards.

Thanks Jimmy - that makes sense.

Adjusting valves on ANY engine has never been a favorite exercise of mine. And I might be one of the slowest professional mechanics that ever put food on the table turning wrenches. At age 18 I gave being a "flag" or flat rate mechanic a try at my local Ford dealer. I almost starved! And I would have for sure if I hadn't eventually landed at a fleet repair shop paying hourly wages. WHEW!

The great thing about Honda iron is that when they decide to make something out of metal and want it hard......they make it HARD! That's why, i believe, that when I check valve clearance on Hondas, they typically don't need adjustment.

I just hope btravlin2's assessment as to why the #6 exhaust valve was tight was due to someone making a mistake. Because if not that then the alternate explanation is that the valve has sunken into the head for some reason.

jgmo said:

I just hope btravlin2's assessment as to why the #6 exhaust valve was tight was due to someone making a mistake. Because if not that then the alternate explanation is that the valve has sunken into the head for some reason.

Click to expand...

I'm hoping for "mistake" as well. What could cause the latter? And how would I know? And if it has sunk, how will that manifest itself down the road? I imagine the adjustment alone won't make up for a sunken valve.

As far as getting to the valves, the first time through on the port motor I was grumbling about all the "stuff" I had to remove. But on the stb motor I blew through it in half the time. It's really not a big deal.

Would getting a scope in that cylinder show me anything about that valve?

Have a look it can't hurt.You guy's are talking about a sunken valve,meaning valve has sunk into seat? Wouldn't that throw the geometry of valve train off,my thinking valve clearance between cam &valve ,if this is an overhead cam engine. Thus a tighter clearance as posted.