Stripped Spark Plug

[fishnfire]

Found a cross threaded #2 spark plug in my 2002 50 HP four stroke EFI Merc OB with only 50 hours on it. My question is: Heli-Coil; pull the head and Heli-Coil; or pull the head and replace head? I don't want to get stuck out in the middle of the lake with my kids and a failed Heli-Coil. I'm also concerned a couple of fillings might have fallen into the cylinder. Some say no big deal, others say got to clean em out.

 

[WillyBWright]

Re: Stripped Spark Plug

Welcome to iboats. <br /><br />Line-up TDC on the flywheel and pull the head. That will take care of two birds ... you'll be able to see if there's any damage in there, and you'll be able to do the helicoil without getting any metal in there. Those are long reach plugs. Those helicoils would be pretty hard to damage.

 

[timmathis]

Re: Stripped Spark Plug

Yep Pull it and fix...

 

[gss036]

Re: Stripped Spark Plug

http://www.timesert.com/ <br />This another method I have heard of people using. If you could find someone with the kit. They look to more of a permanent way than helicoils. I think helicoils will also work, I have a couple installed on my old Stihl chainsaw and they seem to hold ok, lot more vibration than an outboard engine.

 

[Texasmark]

Re: Stripped Spark Plug

On helical coils.<br /><br />Where I used to work we used lots of aluminum. Any screw that was designed to be removed for normal servicing had to be screwed into a helical coil; not bare aluminum. In 36 years, I never saw aluminum stripped. Saw some damaged coils that had to be replaced and the replacements worked just fine, but never where the coil ripped the aluminum out.<br /><br />The problem with SS screws screwing on aluminum is that the twisting forces help to cause the aluminum to desintegrate and thus strip out.<br /><br />With a helical coil, you are twisting steel against steel. The aluminum only sees a pulling force, not a twisting and pulling force (normally). Works.<br /><br />Also, if you can do as said, and position the engine upside down so that the filings can fall out via gravity it will help to keep the crud outta da cylinder. A little wiping with a Q-tip broken (bent at a 90 degree angle) helps too as does a fogging with automotive brake cleaner liberally sprayed into the sparkplug hole.<br /><br />Then rotate the engine up so that the plug hole is up and liberally apply TCW 3 gas mix oil to the cylinder and pull her thru a few times before you put the plug back in.<br /><br />Mark

 

[Texasmark]

Re: Stripped Spark Plug

Forgot something. Spark plugs into aluminum only require about 25 inch pounds to seat. That translates to good and snug with the wratchet wrench in the palm of you hand, not with your hand out on the end of a 12" breaker bar. If it (the plug) has an aluminum seal, you can feel when the seal contacts the head and feel when it stops squishing. Don't over do it. Soon as the friction increases, stop turning. Never had a plug loosen up.<br /><br />Mark

 

[fishnfire]

Re: Stripped Spark Plug

Thanks folks! There are many schools of thought on this as I've been asking around. Such as Time-Serts vs. HeliCoils vs. machine shop tapping; Do it with the head on vs. head off; Repair vs. replacing entire cylinder head; a couple of aluminum shavings in the cylinder no big deal vs. big deal.<br />A new cylinder head alone for this motor is 1500 bones. Pulling the head looks like an ordeal for the average guy with the holly-hobby tool kit and his allotted (by wife & kids) 1 extracurricular hour a week.<br />So, I think I'll be Helicoiling it with the head on.

 

[Texasmark]

Re: Stripped Spark Plug

I did it before I learned not to do it and it's not that difficult. You could probably pull into a marine dealer and get a mechanic to tap it for you for $20 then you go home and clean her up.....Like drive in and get him to do it...some will (stop what they are doing) and it will only take a second of his time, and he has the tap....you'd have to buy it.<br /><br />Mark