Improved spark plug boot?

[growingupninja]

Is there such a thing?

Armed with a garden hose, rinse tub, spray bottle, and buckets of saltwater I finally faced down the demons in my outboard and discovered that the problem--very likely what it's been all along--is seawater around my spark plug boot. The kaboat sits so low that the engine is practically in the water, then you add a little midchannel swell and chop, plus the design of the engine itself (the cowling is not designed to seal the engine watertight but rather drain instantly).

Just a little touch of saltwater on the boot was causing it to sputter and die. When I investigaged it has never had dielectric grease on ANY of the electrical as far as I can tell, and it was bought new just over a year ago. Go figure. I put some silicone grease on the plug boot which improved things in my testing, but it still isn't 100% and I am sick of the thing getting fussy when I need it most. There is no reason in my mind why it it shouldn't run when submerged up to the intake, at least for brief periods.

I googled but didn't see anything, but is there a more heavy duty spark plug boot, or secondary cover that would seal it 100%? I am thinking I am going to cast one from silicone if not....

thanks.

[Dannowar]

What outboard do you have? Seems pretty strange that the spark plugs could be that exposed

[growingupninja]

Originally Posted by Dannowar

What outboard do you have? Seems pretty strange that the spark plugs could be that exposed

Tohatsu 6hp four stroke. I bought it December 2014. It isn't totally exposed, I think it's just that most people are using those as harbor tenders or a long shaft models on a sailboat so they don't get as much water inside, and because it's a single cylinder if it misfires it doesn't have any other cylinders to keep it going.

Anyway, I printed a mold box just now and will cast a silicone sleeve while there is still light to see in the driveway. I think that should fix it for a good long while.

I'll try and post photos for any other small engine guys. It's been really, really, really frustrating--I've cleaned a rebuilt the carb four times in the last year trying to figure it out. A little miffed too because the first time it gave me trouble I took it into the shop and they put in a new plug but from the current state of the boot I don't think they used any silicone grease, which is the kinda dumb mistake I can make on my own and save $90.

Shoulda tried the saltwater sooner.

[Johnoly]

Originally Posted by growingupninja

....Just a little touch of saltwater on the boot was causing it to sputter and die....

Remember that electricity will always try to seek the easiest ground. Your spark plug terminal actually shouldn't even need a boot and the boot is mainly for corrosion protection, not to contain the electricity. Somewhere in the wire or even the spark plug you have too much resistance. I'd start by replacing the ceramic spark plug with the original equipment equivalent plug.(look it up in the OE manual, don't just replace what's in the engine cause it could have been swapped) If the condition continues then you have a bad spark plug wire and it's best to replace the whole wire.

[growingupninja]

Originally Posted by Johnoly

Remember that electricity will always try to seek the easiest ground. Your spark plug terminal actually shouldn't even need a boot and the boot is mainly for corrosion protection, not to contain the electricity. Somewhere in the wire or even the spark plug you have too much resistance. I'd start by replacing the ceramic spark plug with the original equipment equivalent plug.(look it up in the OE manual, don't just replace what's in the engine cause it could have been swapped) If the condition continues then you have a bad spark plug wire and it's best to replace the whole wire.

Pretty sure the boot is neccesary in a marine engine because saltwater conducts. Without the boot, salt water would complete the circuit between the center pin/plug wire and engine body OUTSIDE the combustion chamber, causing a misfire, which is what appears to be happening.... Besides that, in an effort to chase down the problem, the plugs have been correctly replaced 3 times since I got the engine a year ago! If better waterproofing doesn't fix it I will look at the wire... Pretty sure it is the boot though since that was the only point on the engine where when I hit it with a squirt of brine from the spray bottle I could get it to die.

[rojodiablo]

Originally Posted by growingupninja

Is there such a thing?

Armed with a garden hose, rinse tub, spray bottle, and buckets of saltwater I finally faced down the demons in my outboard and discovered that the problem--very likely what it's been all along--is seawater around my spark plug boot. The kaboat sits so low that the engine is practically in the water, then you add a little midchannel swell and chop, plus the design of the engine itself (the cowling is not designed to seal the engine watertight but rather drain instantly).

Just a little touch of saltwater on the boot was causing it to sputter and die. When I investigaged it has never had dielectric grease on ANY of the electrical as far as I can tell, and it was bought new just over a year ago. Go figure. I put some silicone grease on the plug boot which improved things in my testing, but it still isn't 100% and I am sick of the thing getting fussy when I need it most. There is no reason in my mind why it it shouldn't run when submerged up to the intake, at least for brief periods.

I googled but didn't see anything, but is there a more heavy duty spark plug boot, or secondary cover that would seal it 100%? I am thinking I am going to cast one from silicone if not....

thanks.

Really common issue with O/B motors. My engine would inhale unusually large amounts of wet air, and the motor was always caked with salt after running a few days, and especially in lumpy seas. (And that was a 225, up and out of the water)
I have long been the worlds' biggest fan of NoAlox dialectic grease. It's heavier once applied than silicone grease, and kinda dries to a half clay texture which fights water well, does not wash off easily.
I also swear by WD40. The entire motor gets coated lightly with it, and I keep it in my gear, regardless of whose boat I go on.

For a boot which does not seal really well, best bet will be a silicone plug. Use a light, light coating of silicone grease into the cylinder hole and on the spark plug shaft itself, but with the plug wire off. Then, clean plug wire itself with acetone so it will be really dry and clean of all grease. Install plug wire, and use regular silicone caulk to fill the plug hole and make te plug cover. Once dry for a couple days, pull out the plug wire, add a bit more silicone grease, reinstall and you should be long term much better off.

[growingupninja]

Originally Posted by rojodiablo

Really common issue with O/B motors. My engine would inhale unusually large amounts of wet air, and the motor was always caked with salt after running a few days, and especially in lumpy seas. (And that was a 225, up and out of the water)
I have long been the worlds' biggest fan of NoAlox dialectic grease. It's heavier once applied than silicone grease, and kinda dries to a half clay texture which fights water well, does not wash off easily.
I also swear by WD40. The entire motor gets coated lightly with it, and I keep it in my gear, regardless of whose boat I go on.

For a boot which does not seal really well, best bet will be a silicone plug. Use a light, light coating of silicone grease into the cylinder hole and on the spark plug shaft itself, but with the plug wire off. Then, clean plug wire itself with acetone so it will be really dry and clean of all grease. Install plug wire, and use regular silicone caulk to fill the plug hole and make te plug cover. Once dry for a couple days, pull out the plug wire, add a bit more silicone grease, reinstall and you should be long term much better off.

What you describe looks like a good hardware store fix, especially for a bigger engine with multiple cylinders that are farther from the water. I went full nerd on mine though yesterday, having already lost days on it what with all the fuel system rebuilds and frustration of putting along at 25% throttle. I want to be confident it will run flawlessly even if the spark plug is entirely underwater, and I had the stuff around for what I hope will be a permanent or at least 5 year fix...

For posterity and anyone else who is damn-fool enough to make channel runs in a single cylinder 4 stroke, here's my improved spark plug boot (it's really a secondary jacket):

I 3D printed a very small nylon mold box since it's tight in there and I needed to have enough clearance to get a clamp around the new jacket, and went with a tough platinum cure silicone for the actual jacket.


That's the mold box over plug, and before pouring the silicone I'll connect the boot. Sulfur free clay is holding it together and sealing the bottom of the mold, and I put some mold release on the rubber part of the boot.


Vacuum system for degassing the silicone courtesy Harbor Freight, Home Depot, and Target. Looks ghetto but actually works well and pulls a very solid vacuum past 29 inches.


Pouring the silicone into the mold, using a little industrial syringe since there is not much clearance in there.


Clamped level to the side of the engine, letting it cure overnight.


Removed the boot from cured slilcone. Looks good, no air bubbles in the part. Now to fully demold the jacket.


Demolded the part, takes an x-acto knife and pliers to rip the nylon mold box apart.


I cleaned off and reinstalled the spark plug. Here's a detail of the actual jacket in relation to the plug. Used silicone grease everywhere it should be, and of course not so much that it would glob up the electrical contacts.


Jacket over the plug, just needs the boot re-attached.


Finished part. Milspec zipties are clamping it very tightly for a fully watertight seal. I was a little worried about the zip-tie closest to the engine block getting hot and melting but the silicone provides some insulation and I did tests on those zipties with a lighter... they can take a lot of heat so I think it will be a non-issue. I started using some stainless steel wire but what I had was too thick and hard to work with.

Tests were successful, I started it up and poured a few gallons of warm saltwater over new jacket. Engine never once hiccuped...

[Benny]

Originally Posted by growingupninja

What you describe looks like a good hardware store fix, especially for a bigger engine with multiple cylinders that are farther from the water. I went full nerd on mine though yesterday, having already lost days on it what with all the fuel system rebuilds and frustration of putting along at 25% throttle. I want to be confident it will run flawlessly even if the spark plug is entirely underwater, and I had the stuff around for what I hope will be a permanent or at least 5 year fix...

For posterity and anyone else who is damn-fool enough to make channel runs in a single cylinder 4 stroke, here's my improved spark plug boot (it's really a secondary jacket):

I 3D printed a very small nylon mold box since it's tight in there and I needed to have enough clearance to get a clamp around the new jacket, and went with a tough platinum cure silicone for the actual jacket.

Attachment 224109
That's the mold box over plug, and before pouring the silicone I'll connect the boot. Sulfur free clay is holding it together and sealing the bottom of the mold, and I put some mold release on the rubber part of the boot.

Attachment 224110
Vacuum system for degassing the silicone courtesy Harbor Freight, Home Depot, and Target. Looks ghetto but actually works well and pulls a very solid vacuum past 29 inches.

Attachment 224111
Pouring the silicone into the mold, using a little industrial syringe since there is not much clearance in there.

Attachment 224112
Clamped level to the side of the engine, letting it cure overnight.

Attachment 224113
Removed the boot from cured slilcone. Looks good, no air bubbles in the part. Now to fully demold the jacket.

Attachment 224114
Demolded the part, takes an x-acto knife and pliers to rip the nylon mold box apart.

Attachment 224115
I cleaned off and reinstalled the spark plug. Here's a detail of the actual jacket in relation to the plug. Used silicone grease everywhere it should be, and of course not so much that it would glob up the electrical contacts.

Attachment 224116
Jacket over the plug, just needs the boot re-attached.

Attachment 224117
Finished part. Milspec zipties are clamping it very tightly for a fully watertight seal. I was a little worried about the zip-tie closest to the engine block getting hot and melting but the silicone provides some insulation and I did tests on those zipties with a lighter... they can take a lot of heat so I think it will be a non-issue. I started using some stainless steel wire but what I had was too thick and hard to work with.

Tests were successful, I started it up and poured a few gallons of warm saltwater over new jacket. Engine never once hiccuped...

Holy shit Lance. Solid work!

[tommy7]

Yup, That should about do it .... Great work. Why didn't they have 3D printers when I was growing up!??

[rojodiablo]

Nice!!!!

[growingupninja]

Yeah, the 3d printer is nifty but a rabbit hole, the next step would be to print a snorkel intake. I don't think water has been getting into the intake though, I tried spraying up through the vent holes with the garden hose and it stayed protected, pretty sure the issue has been the plug boot all along.

[Monger]

Originally Posted by Johnoly

Remember that electricity will always try to seek the easiest ground. Your spark plug terminal actually shouldn't even need a boot and the boot is mainly for corrosion protection, not to contain the electricity. Somewhere in the wire or even the spark plug you have too much resistance. I'd start by replacing the ceramic spark plug with the original equipment equivalent plug.(look it up in the OE manual, don't just replace what's in the engine cause it could have been swapped) If the condition continues then you have a bad spark plug wire and it's best to replace the whole wire.

This is good to keep in mind. If you increase the air gap on the plug electrode you are also increasing the resistance to current flow. Which makes it more prone to jump elsewhere (i.e. Through the boot or wire). Also it could be jumping through the porcelain if the terminal end is over tightened causing a small hairline crack. I have also had problems with plug wires just not being good enough for some hei ignition system. Best way to troubleshoot is with a long screwdriver with a copper wire wrapped around it and grounded well then use the tip to pinpoint exact location.
Your secondary boots appear to look and work great but I would still be looking for the real problem. Just my 2 pennies

[Scottywotty]

Nice work!!

I am impressed!

Scotty

[growingupninja]

Originally Posted by Monger

This is good to keep in mind. If you increase the air gap on the plug electrode you are also increasing the resistance to current flow. Which makes it more prone to jump elsewhere (i.e. Through the boot or wire). Also it could be jumping through the porcelain if the terminal end is over tightened causing a small hairline crack. I have also had problems with plug wires just not being good enough for some hei ignition system. Best way to troubleshoot is with a long screwdriver with a copper wire wrapped around it and grounded well then use the tip to pinpoint exact location.
Your secondary boots appear to look and work great but I would still be looking for the real problem. Just my 2 pennies

Thanks. I will keep this in mind. The plug wire has a rubber disc which keeps it away from the engine block. I assumed this was for thermal reasons but if the insulation on the wire is inadequate and the wire and engine is damp with seawater I could imagine it creating problems. Before I take it out again I will take off the flywheel and check out the electrical in there. That part of the engine stays fairly dry but I suspect they did the bare minimum in the factory and on long runs enough vapor and moisture could accumulate to cause some issues. Worst problem was definitely the boot, unlike bigger outboards I've seen the design of my engine puts the spark plug relatively near the bottom of the housing so when the sea is up and the boat is heavy it always gets wet.