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Author Topic: Spark plug conundrum  (Read 247 times)

June 18, 2020, 06:30:24 PM
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Brendanpd28

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Spark plug conundrum
« on: June 18, 2020, 06:30:24 PM »
Hi all,

      Been awhile but I’m back seeking expertise. The 170 is now living on a pond in Massachusetts where my wife and I recently bought a new home. Been a little different not being on the ocean. A lot more tubing and leisure rides instead of Striper fishing....I have lots of friends with boats for that LOL. I was tubing with some friends yesterday and was at WOT almost the entire time and making very hard turns all of a sudden the motor completely lost power. I managed to get it running again by manually operating the throttle valve while my friend turned the motor over. I immediately knew that one of my cylinders wasn’t firing because I could only get about half power. Remove the spark plugs first thing and found three of them to be perfect and one of them completely corroded or covered in grey stuff. I am concerned that this may be chunks from the piston. But after putting in a new spark plug the boat is running completely perfect as it was. Does this look like I may have scored a piston? I have done a lot of work to this motor over the years and it has overall been very good to me. Hoping I don’t have to retire her quite yet. I hope you are all doing well and I Appreciate all the advice as always!
Brendan P. D.

June 19, 2020, 07:33:48 AM
Reply #1

Capt. Bob

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Re: Spark plug conundrum
« Reply #1 on: June 19, 2020, 07:33:48 AM »
I'll let the pistonheads jump in on this but I'm guessing that had to come from somewhere and the piston seems the likely culprit.

Did you pull the new plug out and read it?  Did you try and see down into the cylinder (through the plug hole) with the piston at the top of its stroke?

Just thoughts.

Good luck. :thumright:
]
Capt. Bob
1991 210 Walkaround
2018 Yamaha 150 4 Stroke
"Reef or Madness IV"

June 19, 2020, 09:59:55 AM
Reply #2

Brendanpd28

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Re: Spark plug conundrum
« Reply #2 on: June 19, 2020, 09:59:55 AM »
Thanks Bob!  I ended up pulling off the cylinder head because I really wanted to get some eyes on the piston and cylinder walls to be safe.  You can see the piston in question does have damage but only to the face.  The cylinder walls are perfect (no scoring, etc..).  I can only assume that this cylinder overheated but I am really not sure how being the water jackets are all connected for each cylinder head.  Perhaps a lean fuel issue as well but again I would think that would have affected both pistons on that side. I rebuilt both double barrel carbs in the past couple years and also have all new ignition coils, leads, plugs etc...  The mystery continues with the 88 SPL hahaha. 
 
Brendan P. D.

June 29, 2020, 09:57:23 AM
Reply #3

Brendanpd28

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Re: Spark plug conundrum
« Reply #3 on: June 29, 2020, 09:57:23 AM »
Any pistonheads out there with any recommendations?  Really just trying to figure out if she can still run as is....170 is getting listed this week also.  Again....cylinder walls are still pristine....damage is only to the head of the piston.  Thanks!!
Brendan P. D.

June 29, 2020, 12:43:40 PM
Reply #4

Capt. Bob

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Re: Spark plug conundrum
« Reply #4 on: June 29, 2020, 12:43:40 PM »
Really just trying to figure out if she can still run as is....170 is getting listed this week also.

Conundrum indeed.
Well I think you answered your question on whether she'll run when you replaced the plug and since you are selling, it really doesn't make much sense to spend additional funds.

That stated, in light of full disclosure, do you disclose/show photo evidence of the piston? I certainly don't know how long it might run in that state. If it doesn't get hot again, maybe a long time. I would think since the metal (aluminum) has reach that level of temperature, it would be more likely to "hole" sooner than later.

How well do you sleep at night?

Good louck. :thumright:
]
Capt. Bob
1991 210 Walkaround
2018 Yamaha 150 4 Stroke
"Reef or Madness IV"

June 29, 2020, 01:10:48 PM
Reply #5

Brendanpd28

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Re: Spark plug conundrum
« Reply #5 on: June 29, 2020, 01:10:48 PM »
Thanks Bob.  I wouldn't sell the boat without disclosing that information.  But like you said....could run for a long time as long as that cylinder does not overheat again.  Finding the root cause is what I am working out right now.  I appreciate your feedback.

Cheers,

- Brendan
Brendan P. D.

June 29, 2020, 04:26:09 PM
Reply #6

GoneFission

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Re: Spark plug conundrum
« Reply #6 on: June 29, 2020, 04:26:09 PM »
Looks like water intrusion into the cylinder - probably a leak from the water jacket.  It does not take much.  Look carefully at the sealing face on the block between the cylinders - it looks like there might not have been a full gasket seal at the location right between the cylinders.  The head looks pretty OK, but I would put a good straight edge on it or take it to a machine shop and get it checked for flatness.  If it's flat - clean both sides very carefully, get a new gasket, new plugs, and put her back together.  Remember to use some anti-seize or compound on the head bolt threads and torque them in 3 series - snug, 15 ft-lbs, then 20 ft-lbs.  The sequence for each series is to start with the center bolts and work back and forth to the outside ones.   

I usually do a "hot" torque again after the engine has run and warmed up just as a little insurance.  You can start it on the muffs, set the idle, etc., and then do a final torque to 20 ft-lb when it's warm using the same sequence.  The bolts may move or not - but it makes me feel better.   :13:
Cap'n John
1980 22-2 CCP
Mercury 200 Optimax 
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June 29, 2020, 04:36:51 PM
Reply #7

Brendanpd28

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Re: Spark plug conundrum
« Reply #7 on: June 29, 2020, 04:36:51 PM »
Thanks for the tips!!  This cylinder head is actually a replacement that I pulled off a parts motor last year when I stripped out a plug....I don't trust helicoils.  I put on a fresh gasket on and torqued it down to spec....then re torqued after a few trial runs. I see where you are referencing as far as the potential leak goes.....the head might we warped as you mentioned.  I'll throw a straight edge on it.  Thanks!   
Brendan P. D.

June 29, 2020, 06:03:33 PM
Reply #8

Capt. Bob

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Re: Spark plug conundrum
« Reply #8 on: June 29, 2020, 06:03:33 PM »

Thanks CJ.  :salut:
]
Capt. Bob
1991 210 Walkaround
2018 Yamaha 150 4 Stroke
"Reef or Madness IV"

 

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