Why such a dry spark plug?

[rodbolt17]

folks this aint difficult.
first guage is a simple set point,typically 100 PSI.
this is a KNOWN quantity of air pressure being injected into a theoretically sealed cylinder.
the second guage simply measures the amount of air it takes to maintain the 100 PSI set point in that cyl.
will work on a two liter coke bottle.

now we know that the cyl really cannot seal perfectly due to ring gaps and such.

what we can do is as air is leaking we can FIND OUT WHERE.

this is where plastic bags tape and soapy water come in handy.
we do KNOW this sealed cyl will or should be sealed perfectly from the cooling system.

[bondobill]

Thanks for your info guys...much appreciated
As rod bolt stated water can get into the cylinder either through the head gasket or the exhaust. I replaced the head gasket and that cylinder has good compression...120.
This morn before heading to work I took a look at the exhaust cover plate.
Photo shows the top two bolts right next to # 1 cylinder. There was a lot of build up of salt crystals between the top and bottom bolt. Sorry guys I rubbed it off with my finger before taking a photo.



All the other bolts on the plate show no signs of corrosion or salt build up.
What's ya think...could this be s sign of leakage.

[zenoahphobic]

I just lost my extensive reply, so briefly I'll try again (damn computer!).

The corrosion and bubbling of paint is external, perhaps from water from the inside pushing out through the bolt hole, or by damaged from the turning of the bolt.
This doesn't, and the condition of the two gaskets below don't indicate whether there is a leak on the inside.
From the limited view these gaskets look fine but appear older than your repair, suggesting the plates were not removed or inspected then.
As you probably cant avoid some disassembly, it would be a good idea to unbolt and inspect the inner plate for holes and replace etc. Be careful not to break bolts!
More pictures would enable better opinion. Those given may only show the general state of corrosion of the engine.

[bondobill]

I just lost my extensive reply, so briefly I'll try again (damn computer!).


More pictures would enable better opinion. Those given may only show the general state of corrosion of the engine.

Thanks Zeno
Here's a shot of the exhaust cover plate








The rest of the engine is pretty clean


It doesn't appear to have any or very little corrosion around the rest of the bolts on the cover. I guess it could be just a coincidence that the top bolts next to #1 show corrosion.
I really dread taking off this plate...as in "Busted bolts " But at this point doesn't seem like I have any other options....

[zenoahphobic]

Just a thought try loosening that corroded bolt, it may be loose or broken (like an attempt was made to remove and the bolt snapped, abandoning attacking all those other bolts.)
The pictures don't show the edges of the gaskets around this bolt, so have a good look.
As previously responded, try to do the leak down test again (reassemble your guage) and get the PSI guage to 100. This may show a leak between the head and coolant chambers.
Also there is a possibility if the water jackets were also not removed that corrosion has eaten a leak in thru the head. This not very likely as you would experience something greater.

[bondobill]

Thanks Zeno
I inspected the gaskets on outside of the exhaust plate . No signs of leakage to the outside anyway.
This gauge I got ,you turn the regulator on the gauge till the leak gauge reads zero. At that point pressure gauge reads around 12 psi. If I turn the pressure gauge up to 100 psi the leakage gauge is pegged out on the backside of the pin


That's why I moved the psi gauge over to the leak gauge hole. At least that way I could get 100 psi in the cylinder. I listened for air leaks and couldn't detect any.
Im going to rig up a shut off valve forward of the where air comes into the unit so I can turn the air off after I reach 100 psi in the cylinder and see what happens then
Besides listening for air leaks ... any other tricks I can use


I'll try it again today

Thanks again

[99yam40]

kind of sounds like what you bought is not what should be used and believed to be working properly

[rodbolt17]

on that rig you turn the regulator with the system disconnected from the cyl to bring the second gausge to the 0 set point.
connect and disconnect a few times to insure the second gauge returns to the set point.
\ now you can hook it up and correctly measure how much make up air(% of leakage) this sealed cyl displays.

[bondobill]

I gave up on the leak down test with this pos harbour freight gauge
I had the gaskets for the exhaust plate so I decided to go ahead and change them out.
I had 3 bolts out of 29 that where somewhat difficult. A little heat applied to the bolt heads,some penetrating oil and a couple of ****tails later they came out.
I wasn't all that convinced that I had found the problem after removing the exhaust plate......

Photo of exhaust plate at #1 cylinder




A shot of the block exhaust chamber at # 1



Any how's, after installing new gaskets....I cleaned and inspected the divider plate and it looked good ..... I put the muffs on the engine and ran her for around 15 minutes at various rpms. After letting her warm up I pulled #1 plug


The plug has a sheen...YEEEEHAAAAA !!!!!

Thanks guys

[zenoahphobic]

Bondobill I'm glad you did this as you can see the gasket was a bit iffy.
Looking at the side of your piston thru the exhaust port, it does look slightly baked on greaseish.
Not too bad but you don't want your rings sticking. A forum member Townsend would recommend you use Yamaha Ring Free in your fuel. Surprised he hasn't commented.

[ausnoelm]

The water passages are also nearly blocked at one point, possibly causing lack of cooling on that cylinder? did you clean it all out?

[bondobill]

Thanks guys
I cleaned up the water passages before putting it back together.
I add a can of seafoam ever time I put gas in it. Also the last few fill ups I have been adding Yamaha ring free.
I have a small remote gas tank that I use on the engine a couple of times a year. I put a can of Seafoam and a gallon or two of gas in the small tank and run the motor off of that on the muffs.

Two fishing trips ago when I noticed the dry plug...was thinking it was running lean...I added a gallon of oil to the fuel tank while out fishing just to be safe. It's a 90 gallon tank. Still working on that tank of fuel so she's getting more oil then it needs.

Bill