Spark plug adapter for Pressure/Vacuum testing

Easy on me fellas…

I made this adapter and was trying it out on a Stihl FS80 string trimmer (no impulse hose) that I just got back to working on FS80 troubleshoot. Something is not right. With the exhaust and intake blocked on the FS80, it wouldn’t hold vacuum or pressure at all.

I thought I’d try it on the 260 (exhaust, intake, impulse blocked off), and it would hold some vacuum (didn’t try pressure). I then tried putting the spark plug back in and applying air through the impulse hose (like I usually do) and it held vacuum like it should.

The spark plug used to make the adapter is a Champion lawnmower plug. I used JB Weld to hold the hose barb fitting in place. I held my thumb over the opening and applied vacuum to the adapter and it held the vacuum. The adapter threads into the cylinder(s) fine, and I tighten it down securely.

Now I realize that the problem I’m having with this FS80 could be blown crank seals (as Fish and THALL have mentioned in the linked thread), but the fact that it’s not working on my saw (as I have described) doesn’t seem right. So here comes the ‘dumb’ question…does the piston have to be at a certain place in the cylinder to use the spark plug hole to apply the air vacuum or pressure? Or is there something else I’ve missed using this method?

Kevin

Doesn't matter if the piston is at TDC or BDC or anyplace in between. If the adaptor holds vac/pressure with your thumb over it, the issue is someplace else.

Make sure you have it firmly seated in the saws (is the ring still on the bottom of your adaptor?), check with soap and water around the muffler and carb, if you have a compression relief, check that it is in the up position and then give it a spray. Don't forget to spray around the base of your adaptor once screwed in.

Last option, reduce the pressure from your hose (1 or 2 psi) and run constant pressure in, dunk it in a tank of water...you'll find the leak quickly

Paul001 said:

Doesn't matter if the piston is at TDC or BDC or anyplace in between. If the adaptor holds vac/pressure with your thumb over it, the issue is someplace else.

Make sure you have it firmly seated in the saws (is the ring still on the bottom of your adaptor?), check with soap and water around the muffler and carb, if you have a compression relief, check that it is in the up position and then give it a spray. Don't forget to spray around the base of your adaptor once screwed in.

Last option, reduce the pressure from your hose (1 or 2 psi) and run constant pressure in, dunk it in a tank of water...you'll find the leak quickly

Click to expand...

Thanks for that. The ring is still there.

Kevin

the rings will cover the ports and isolate crankcase from cylinder, just like when its running. There would be ring leakage and maybe piston motion slightly if the piston is too high. but I'd do it at somewhere below where the transfer port opens

I took the easy way out and bought the adapter from NAPA. SER 901

The sparkplug adapter you are using are like the ones I make and use, they will leak around the threads unless the compression ring is still on the plug, seat it tightly with a compression ring on it and it will seal properly.
Pioneerguy600

pioneerguy600 said:

The sparkplug adapter you are using are like the ones I make and use, they will leak around the threads unless the compression ring is still on the plug, seat it tightly with a compression ring on it and it will seal properly.
Pioneerguy600

Click to expand...

KMB said:

The ring is still there.

Kevin

Click to expand...

Thanks. I might have to tighten it down a little tighter.

Kevin

deezlfan said:

I took the easy way out and bought the adapter from NAPA. SER 901

Click to expand...

Do they come with some type of rubber O-ring that seals off the hole?

Kevin

Cool. I've never thought about vacuum testing something that doesn't have an impulse line. At first I thought you were doing it to save the hassle of disconnecting the impulse line and were just pinching the impulse line closed. Good idea.

KMB, I like the adapter you made up. I use the quick-connect from my snap-on compression tester. I removed the schrader valve and hook the air compressor to it with about 5-6 pounds pressure. I spray Windex on all the seals/gaskets.

Teflon tape.

I did basically the same thing except I went to Autozone and bought an "antifouler", screwed a hose barb into it (with JB), and bought an o-ring the correct size. I put it in finger tight and it seals very nicely.

Arrowhead said:

KMB, I like the adapter you made up. I use the quick-connect from my snap-on compression tester. I removed the schrader valve and hook the air compressor to it with about 5-6 pounds pressure. I spray Windex on all the seals/gaskets.

Click to expand...

Thanks. I use a bicycle pump with a shut-off valve for pressure testing.

Kevin

barneyrb said:

I did basically the same thing except I went to Autozone and bought an "antifouler", screwed a hose barb into it (with JB), and bought an o-ring the correct size. I put it in finger tight and it seals very nicely.

Click to expand...

If mine is leaking at the plug hole, then I'll try using a rubber O-ring.

Kevin

KMB said:

Easy on me fellas…

I made this adapter and was trying it out on a Stihl FS80 string trimmer (no impulse hose) that I just got back to working on FS80 troubleshoot. Something is not right. With the exhaust and intake blocked on the FS80, it wouldn’t hold vacuum or pressure at all.

I thought I’d try it on the 260 (exhaust, intake, impulse blocked off), and it would hold some vacuum (didn’t try pressure). I then tried putting the spark plug back in and applying air through the impulse hose (like I usually do) and it held vacuum like it should.

The spark plug used to make the adapter is a Champion lawnmower plug. I used JB Weld to hold the hose barb fitting in place. I held my thumb over the opening and applied vacuum to the adapter and it held the vacuum. The adapter threads into the cylinder(s) fine, and I tighten it down securely.

Now I realize that the problem I’m having with this FS80 could be blown crank seals (as Fish and THALL have mentioned in the linked thread), but the fact that it’s not working on my saw (as I have described) doesn’t seem right. So here comes the ‘dumb’ question…does the piston have to be at a certain place in the cylinder to use the spark plug hole to apply the air vacuum or pressure? Or is there something else I’ve missed using this method?

Kevin

Click to expand...

Kevin, if testing through plug hole cylinder needs to be at BTC.
Bob

KMB said:

If mine is leaking at the plug hole, then I'll try using a rubber O-ring.

Click to expand...

That is the ticket right there. I use the hose/adapter from my leakdown tester to do exactly what you are doing. It has an o-ring instead of the metal gasket.

The metal gasket on a spark plug can fail over time, maybe check the sealing surface on the jug too, maybe that's where your leak is.

redunshee said:

Kevin, if testing through plug hole cylinder needs to be at BTC.
Bob

Click to expand...

Sorry for my ignorance...BTC?

Kevin

Streblerm said:

That is the ticket right there. I use the hose/adapter from my leakdown tester to do exactly what you are doing. It has an o-ring instead of the metal gasket.

The metal gasket on a spark plug can fail over time, maybe check the sealing surface on the jug too, maybe that's where your leak is.

Click to expand...

Good one, thanks. I have an adapter for my compression tester that has a rubber O-ring...I'll give that a try.

Kevin

Update

The compression tester adapter that I mentioned did not work (for the FS80) because it would not thread down deep enough into the cylinder. I guess Teflon tape on the threads would have worked, but then I could have used Teflon tape on my homemade adapter.

I tried my homemade adapter with a rubber O-ring, and still didn’t hold vacuum or pressure. So I removed the coil, dunked the engine in water, applied air pressure, and found the big air leak on the flywheel side. Also I didn't notice any air bubbles at the spark plug hole, so I guess my homemade adapter by itself (without the rubber O-ring) was working. I know there was air leakage at the flywheel seal, but I'm sure there would have been air bubbles at the adapter if it wasn't sealing properly.

I was looking through my service manual for my 044 an noticed that when going through the intake (using the Stihl adapter) for the air supply for doing the vacuum and pressure tests, they say that the piston should be at TDC. So for me, I’ll have the piston at BDC initially (when going through the spark plug hole). Then when I can confirm that it is holding pressure and vacuum, I’ll rotate the crank a few times as mentioned in the end of the first post and post #12 of this thread: http://www.arboristsite.com/showthread.php?t=42768&highlight=poor.

I’ll retry my homemade adapter with the rubber O-ring in my 260 later.

Kevin

KMB said:

Sorry for my ignorance...BTC?

Kevin

Click to expand...

Good catch Kevin!
Pioneerguy600