Pressure leak on spark plug

[Sawyer94]

As title states, rebuilt saw, new bearings, new seals, new gaskets, new everything practically and new spark plug. It passed vacuum test everywhere, failed pressure test. Found it leaking at the newly installed spark plug.

I don’t have another new plug on hand to check but wondering I’ve had this before on old plugs but usually fixes itself with new plug but this was right out of the box. Also should add threads of the spark plug appear clean. Spark plug threads on easily. I don’t want to have to jb weld this plug in but I will if I have to. Haha I will be making a trip to the hardware store and pick another one up and see. Just wondering what you people think.

 

[Maintenance Chief]

Has the cylinder head had the threads repaired?
What saw?

 

[Sawyer94]

Has the cylinder head had the threads repaired?
What saw?

I mean it’s a possibility it’s a used oem mahle cylinder from a 200 I’ve rebuilt. I can’t tell if there has been any repair or not.

 

[Maintenance Chief]

I mean it’s a possibility it’s a used oem mahle cylinder from a 200 I’ve rebuilt. I can’t tell if there has been any repair or not.

Well just a thought , I've seen lots of Heli-coils leak , they're pretty obvious to spot though.

 

[Sawyer94]

Well just a thought , I've seen lots of Heli-coils leak , they're pretty obvious to spot though.

Oh I see yeah nothing like that from the looks of it, I have another cylinder and it’s the same looking. I just know sometimes the washer goes bad on the plugs after repeatedly taking it off and on. I suppose worst case scenario I just put some loctite but that doesn’t sound appealing to me.

 

[thompsoncustom]

why not just use some plumbers Teflon tape?

 

[Wonkydonkey]

You have to ask yourself why is it leaking, are the threads damaged in the cylinder? And is the top of the hole smooth/clean/no gouges
Unless it was pissing out, I wouldn’t worry to much about a slow leak from the spark plug. It maybe a little loss of power but at 12k it’s not going to be noticed.


After all the p & v test is really for the fuel/air mix so it runs and don’t seize.

If you have another saw with the same spark plug you could swap them and check etc.

 

[bertfixessome]

Well just a thought , I've seen lots of Heli-coils leak , they're pretty obvious to spot though.

I never use heli coils ( or similar wire inserts ) on anything that has to be pressure / oil tight
Had way too much trouble with them over the years
Lots of solid inserts which do a much better job on spark plugs .
Down side is most are stainless or high nickel so you have to use some anti sieze on the plug to avoid stiction.

 

[drf256]

I’d just run it. Unless it’s a major air leak it will do nothing to the saw. It’s above the piston at TDC.

 

[Sawyer94]

I’d just run it. Unless it’s a major air leak it will do nothing to the saw. It’s above the piston at TDC.

Not major very small few psi a minute or so. I will pop a new plug in and see this afternoon.


Thank you everybody who chimes in.

 

[Sawyer94]

I just like to be cautious after spending a few $100 to rebuild I don’t want to make the mistake I have in the past. Too expensive and too much time waiting on parts.

 

[jbolts]

I'd clean up where the plug sits best I can and make sure it's smooth... I don't think the threads would cause a leak.... I always just assumed it was the washer that makes the seal?
Torque it down a bit tighter and see if that changes anything but that might be what caused the washer to crush in t he first place.
John's custom saws on youtube always tosses the plug he takes off and puts on a new one even if it's brand new... I wouldn't do that personally, just throwing that out there.

 

[Duce]

Not major very small few psi a minute or so. I will pop a new plug in and see this afternoon.


Thank you everybody who chimes in.

Not a problem with that slow leak as @drf256 stated. Run it.

 

[Sawyer94]

So I finished putting the saw fully back together and she seems to run fine. Only time will tell but thanks everyone.

 

[SE#1]

As title states, rebuilt saw, new bearings, new seals, new gaskets, new everything practically and new spark plug. It passed vacuum test everywhere, failed pressure test. Found it leaking at the newly installed spark plug.

I don’t have another new plug on hand to check but wondering I’ve had this before on old plugs but usually fixes itself with new plug but this was right out of the box. Also should add threads of the spark plug appear clean. Spark plug threads on easily. I don’t want to have to jb weld this plug in but I will if I have to. Haha I will be making a trip to the hardware store and pick another one up and see. Just wondering what you people think.

Try chasing the threads, see if thread chaser is loose as well