Bent spark plug electrode twice in 12 months?

[DMAN1968]

I have a 1974 Johnson 115 on a 24 foot party barge. After replaceing coils, fuel pump, flywheel shear key, plugs, water pump...well pretty much everything, I finally got it running good. That was over a year ago and it has been doing well pushing the barge since, except for 2 times. It starting running as if only on three cylinders, pulled the top plug on the starboard cylinder and found the electrode bent enough to close the gap completely. If I bend it back out starts running great again. It just did it again for the second time.

I understand that I probabley have some connecting rod bearing issue or something of that nature but it seems strange that it would only do it sometimes and not regularly.

When i purchased the motor a compression check showed 100-105 across all 4 cylinders, not the best but has been acceptable. I really don't think the motor has the value to justify a major rebuild.

Long question made short...If I change from the 77jc4 plugs back to the ul77v gapless plugs can I continue to run it? If so, for how long?

 

[tx1961whaler]

Re: Bent spark plug electrode twice in 12 months?

Long question made short...If I change from the 77jc4 plugs back to the ul77v gapless plugs can I continue to run it? If so, for how long?

It will run until the connecting rod goes through the engine block, which could be the next time you start it. If it's in good shape outside of the slappy piston, I think it is worth putting a few hundred in it to get that cylinder fixed, especially when you look at the price of a new motor.

 

[Joe Reeves]

Re: Bent spark plug electrode twice in 12 months?

Remove the cylinder head to inspect that piston, clyinder walls, etc.

As Whaler states..... It'll run and run poorly until a connecting rod comes flying thru the side of that crankcase.

 

[DMAN1968]

Re: Bent spark plug electrode twice in 12 months?

I did test for play in the piston after the first time. As instructed on this forum I brought the cylinder to just past TDC and pushing it with a screwdriver. I found no play at that time. I visually inspected inside the top of the piston as best I could and couldn't even find a sign of contact with the electrode.

I'm probably just reaching here but is there any other possibility for the contact. I'm comfortable working on anything on the outside of the engine...but the internals...that's a bit more intemidating.

Thanks for your time.

 

[F_R]

Re: Bent spark plug electrode twice in 12 months?

I did test for play in the piston after the first time. As instructed on this forum I brought the cylinder to just past TDC and pushing it with a screwdriver. I found no play at that time. I visually inspected inside the top of the piston as best I could and couldn't even find a sign of contact with the electrode.

I'm probably just reaching here but is there any other possibility for the contact. I'm comfortable working on anything on the outside of the engine...but the internals...that's a bit more intemidating.

Thanks for your time.

Could be most anything else that the engine has swallowed. If it isn't a bearing or piston rings or something related, it could be a screw or something. Whatever it is, it isn't good and can cause catastrophic damage.