Blown spark plug hole- is it fixable or junk?

jopaped

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Mar 10, 2012
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The spark hole blew out about 1-2 millimeters past the threads on the left hand side of the hole. Is this fixable or junk now?

Thanks!

spark plug 005.JPG
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Re: Blown spark plug hole- is it fixable or junk?

can be fixed, however will require the head coming off, and taking it to a machine shop. however may be cheaper to buy a head off of ebay.
 

JB

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Re: Blown spark plug hole- is it fixable or junk?

That might be fixable with a Time-Sert kit, jopaped. Is your engine one with a removable head or is the head cast into the block, like many (most?) Mercs.

I would give it a try, either way. It would be very risky in the integral head/block, but what do you have to lose? If you can exclude shavings from inside the cylinder, you win.

Good luck. :)
 

jopaped

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Re: Blown spark plug hole- is it fixable or junk?

Hi JB,

The head is part of the block. I have been reading about the time-sert kits the last couple of days. I just dont know if if they would have the size insert I need since this would be an oversized hole.

I'm open to all suggestions.

Thanks,
John
 

Chris1956

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Re: Blown spark plug hole- is it fixable or junk?

There are solid inserts that will repair that hole. They are avail lots of places. The original hole would need to be drilled and tapped, and the insert screwed it. Normally epoxy would be used on the threads to hold the insert in. If the head is ono removeable, the block should be stripped down to do the repair right. Otherwise, metal chips can get into the crankcase, which can ruin the engine.
 

AviatorJim

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Re: Blown spark plug hole- is it fixable or junk?

Easy to fix. Don't have to take anything apart or drill it out. If you don't want to try it yourself, the guy at your airport who works on private planes will fix it for you. You need to get the 14mm helicoil kit (for sparkplugs). Slather the tap with grease (it will catch and hold your shavings). Just tap the hole for the helicoil. The aluminum is soft and will just cut away, no need to drill like you would if it were a steel cylinder head. The put the heli coil in with some locktite red. And break the tang with needle nose pliers so you can pull it out.

Any shavings or the tang will depart the engine via the exhaust ports when you crank it up if you missed any. Chips can't get into your crankcase unless there is already a hole in your piston, and if there is, a metal chip isn't something you need to worry about.

We do this job on small airplane engines all the time. $2000 cylinder replacement into a 1 hour job. Airplane engines come new with a helicoil in the sparkplug hole (18mm).

--Good luck.
----Jim
 

oldman570

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Re: Blown spark plug hole- is it fixable or junk?

I have done a few as Jim stated and have had good success as long as the heil coil is solid and fills the gap that is there. Make sure that the heil coil is the solid one and not the coiled one, and use the red locktight.
Oldman570
 

JB

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Re: Blown spark plug hole- is it fixable or junk?

Jim has good advice, coming from real world experience. I do prefer the Time-Sert, however, to the Helicoil. The Time-Sert is aluminum alloy, which has the same heat transfer characteristics as the alloy head/block which will allow the spark plug to perform as the original, whereas the Helicoil is steel.

I have used Time-Serts in alloy heads for both 2 and 4 stroke engines (Chevy Corvair alloy heads) with success. I cannot argue with the success of Helicoils, I just prefer Time-Serts.
 

Faztbullet

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Re: Blown spark plug hole- is it fixable or junk?

I use Keenserts that come with Merc thread repair kit.
 

wired247

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Re: Blown spark plug hole- is it fixable or junk?

I think his repair is beyond the level of the usual thread repair kits. Theres a LOT of metal missing there. I could do it on government time at work and any machine shop worth its salt could repair it but it would involve boring the hole out larger and making a custom machined insert for it that is threaded or even welded in place. It is repairable but you'd pretty much have to know the guy doing it and have him be one of your buds to make it economical.
 

PS94

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Re: Blown spark plug hole- is it fixable or junk?

No one has suggested getting it professionally welded, then re-drilled and tapped...that would be the best fix i would think...
 

AviatorJim

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Re: Blown spark plug hole- is it fixable or junk?

There are two issues with a welded repair. The fill metal (welding rod) used won't be the same alloy as the base metal (engine) and it may result in an area weaker or stronger than the area around it. It may also expand and contract at a different rate. Also the welded area would need to be baked (heat treated) for stress relief. That means taking it off and disassembling it. It may also warp in the oven and need to be remachined to mate to the rest of the case. If you are doing all that work, might be better to just replace it.

In aviation field repairs are always done mechanically with rivits, adhesive, patches, doublers, and inserts just because it is impractical to get bigger pieces off the plane and into a welding shop.

There is a type of helicoil called a twinsert, which is a coil inside a coil, for fixing bigger damage. There is a also an oversize Time-sert called a Big-sert. Time-serts and Keenserts are just as good. It does boil down to personal preference which to use. I also recall an insert they used to sell at the autopart store that cut it's own hole, and just stayed in place as the repair. It does increase the height of the sparkplug, and that is usually an issue on an inline outboard. But cheaper, and doesn't need special tools.

--Jim
 

wired247

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Re: Blown spark plug hole- is it fixable or junk?

I don't think he has enough metal reamaining on the left side for an insert repair. Theres a lot missing. Welding might do it but not without total disassembly and a possible rebore of the cylinder.
 
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