Spark plug electrodes going to 0 gap!

[MuskyTime]

So here’s one that I cannot seem to get a good answer on. I have a 2007 175 that for 7 years never had any problems with. Last year on the last day of a 2 week trip (where I was putting on 50 miles a day) I was losing power at top end and the motor was really missing badly at idle. I found that the #3 plug electrode was at 0 gap and actually the ground electrode was contacting the center electrode. I replace my plugs each spring so I thought maybe I forgot to gap that plug or I dropped it during install. I bore scoped the cylinder and did not see any evidence of the plug making contact with the cylinder head. So I replaced all the plugs and the motor ran great the rest of last year and this summer up until Last week. Running across the lake the motor developed the same symptoms of slight loss of power and missing at idle. I removed all the plugs and found that the #3 plug electrode was again at 0 gap and also the #2 plug was at 0 gap. I replaced the plugs and the motor ran great the rest of the week.
What would cause the plugs to go to 0 gap? I did gap all the plugs during install so I know they were set correctly. There is no evidence of contact on the electrode or cylinder head, never had this issue for 7 years!
Could it be that I am running lean and hot causing the electrodes to super heat and bend from compression pressure?
Haven’t been able to find a mechanic that can explain it?
Motor runs and sounds great, could I be causing damage to the motor running like this?

[MuskyTime]

I have been told that it might be a bad rod or piston bearing. If I run the engine for a while and the gap remains good, could I assume the bearings are good? Or could it be an intermittent problem that only shows at high RPM or over duration?

[Ocean Obsession]

Need to check your throttle body(s) on the intake. They're known to come loose/crack apart when aged and enter the cylinder, bounce around a bit in there mashing the plug and then usually ejected.

There us a post on the hull truth where another df175 owner had the exact problem you did. I guarantee you it's not a bearing.

[MuskyTime]

Thanks for the info on the post at "The Hull Truth" good info there on this topic. Please don't take this the wrong way Ocean Obsession but what makes you so sure it's not a bad bearing? I sure don't want it to be a bad bearing. Thanks! Ed

[Moonlighter]

Because you would, I suspect, be hearing a lot more noise, clanking, and vibrations and other bad things if a bearing had failed to the extent that a piston was bashing into the spark plug!

Not only that, but you would have seen evidence when you scoped the bore.

Check the butterflies on the throttle body as already suggested.

[redlowrey]

Thanks for the info on the post at "The Hull Truth" good info there on this topic. Please don't take this the wrong way Ocean Obsession but what makes you so sure it's not a bad bearing? I sure don't want it to be a bad bearing. Thanks! Ed

'''''' Mate you would know all about it if you if you had a con rod bearing gone, if the piston broke a ring land pieces could hit the plug and close the gap, but the engine would be missing and fouling the plug. I think when you pull the inlet manifold off you will find your problem.

[MuskyTime]

Thank you all for the input! I will check out the butterfly valves as suggested. Thanks! Ed

[Harper]

Just to clarifiy, Musky.... those butterflies are not in the throttle body, they are in the intake manifold itself. And if you choose to replace them, you have to replace the entire intake manifold. I am not sure that it's worth the money to replace. It should run fine with some of the butterflies missing. Maybe not quite to specs, but nothing that you could notice in the seat of your pants.

[Harper]

The manifold costs about $400. Here's a picture of the intake manifold showing the butterfly valves that control the path of the intake air according to RPM. There are four valves total, one in each intake runner. They are plastic, just like the manifold, and have been prone to breakage.

[MuskyTime]

Thanks Harper!

Any thoughts on where to find torque values for the intake manifold bolts?

[Harper]

throttle body to manifold ...16.5 Ft lbs
manifold to cyl head .. 16.5 Ft lbs.

[MuskyTime]

Awesome! Thanks Mike!

[Stamas31]

In the same boat

Awesome! Thanks Mike!

Hey MuskyTime, I have the exact same senario. Has I have been studying the manual I am unsure of where the plastic "part" may have come from. Is it actually in the manifold or the collector. Looking at pictures I can not make out any plastic piece on the manifold.
The first guy said it was from the throttle body. I am looking for some clarity on what part may have lost this plastic piece?

[Harper]

Hey MuskyTime, I have the exact same senario. Has I have been studying the manual I am unsure of where the plastic "part" may have come from. Is it actually in the manifold or the collector. Looking at pictures I can not make out any plastic piece on the manifold.
The first guy said it was from the throttle body. I am looking for some clarity on what part may have lost this plastic piece?

Stamas, have a look at post #9 in this thread.....those four plastic butterflies are in the manifold, in the runners. The throttle plate (in the throttle body) is metal. And the only way to fix it, if that is your intent, is to replace the entire manifold.