Now what?!
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Now what?!
So I'm buttoning up the motor after a complete top end re-build. Got new James Viton O-ring seals, Cobra intake clamps (just for testing, got stock style clamps I'll use once I figure out *how* the damn things work), and I'm pressure testing the intake @ 10 psi. Got it just about perfect when I hear a slight hissng coming from somewhere else. The spark plugs! Both plugs are leaking, even after tighting them to spec. Even a set of new plugs leaked. The threads look great, tighten right up, but it IS leaking at only 10 psi. Now what?! Any ideas?
-Kuda
'49 panchop
-Kuda
'49 panchop
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Kuda!
I have been cutting indexing washers from PEEK scraps. They can be as wide (or as thick) as you like.
But anyway you look at it, they would only be a band-aid.
Normal crushwashers should give a seal. A fresh counterbore may be in order.
Meanwhile,
I'm surprised you didn't have the intake valves closed during the manifold test.
Might as well check your headgaskets while you are at it.
....Cotten
I have been cutting indexing washers from PEEK scraps. They can be as wide (or as thick) as you like.
But anyway you look at it, they would only be a band-aid.
Normal crushwashers should give a seal. A fresh counterbore may be in order.
Meanwhile,
I'm surprised you didn't have the intake valves closed during the manifold test.
Might as well check your headgaskets while you are at it.
....Cotten
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Plug thread inserts will "pull" over time just like head bolt inserts. It is good practice during a complete head overhaul to have the plug thread insert spot faced so that the insert and the surrounding head surface are perfectly flush.
I have done this to every aluminum flathead head when doing a top-end rebuild for the exact same reason. I have some pictures somewhere of bubbles around the plug threads, spot facing the insert and the surrounding head surface fixed it. I even spot face the outer headbolt surfaces on the flathead heads even though they don't have inserts to make them perfectly parallel to the head gasket surface, I've never blown a gasket!
just an observation.....
mike
I have done this to every aluminum flathead head when doing a top-end rebuild for the exact same reason. I have some pictures somewhere of bubbles around the plug threads, spot facing the insert and the surrounding head surface fixed it. I even spot face the outer headbolt surfaces on the flathead heads even though they don't have inserts to make them perfectly parallel to the head gasket surface, I've never blown a gasket!
just an observation.....
mike
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I always use copper (high temp) anti-sieze when installing plugs, didn't make any diff. I did try using teflon tape just to see what happens (I wouldn't run it like that, just for testing) and it did seal 'em up...john HD wrote:kuda
try painting the threads up with a liberal amount of anti seize compound.
perhaps it will stop the leak and make the next exchange easier.
-Kuda
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Counterbore? Could you explain that one to me? I'm not sure what you're referring to in terms of a spark plug hole...Cotten wrote:Kuda!
I have been cutting indexing washers from PEEK scraps. They can be as wide (or as thick) as you like.
But anyway you look at it, they would only be a band-aid.
Normal crushwashers should give a seal. A fresh counterbore may be in order.
Meanwhile,
I'm surprised you didn't have the intake valves closed during the manifold test.
Might as well check your headgaskets while you are at it.
....Cotten
As for the intake valves, that's even more worrysome. I hadn't even installed the pushrods yet, so the valves were closed. And both heads just got fresh valve jobs, too. Guess I'm gonna have to pull the heads and take 'em back to the machine shop. Oh, and the head gaskets are also new, but I bubble checked 'em just in case. No leaks there, at least with only 10 psi on 'em...
-Kuda
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Funny you should say that, 'cause I DID have the head bolt inserts spot faced when they were in the shop. The plug inserts *look* flush, but that's something else I can try...FlatHeadSix wrote:Plug thread inserts will "pull" over time just like head bolt inserts. It is good practice during a complete head overhaul to have the plug thread insert spot faced so that the insert and the surrounding head surface are perfectly flush.
I have done this to every aluminum flathead head when doing a top-end rebuild for the exact same reason. I have some pictures somewhere of bubbles around the plug threads, spot facing the insert and the surrounding head surface fixed it. I even spot face the outer headbolt surfaces on the flathead heads even though they don't have inserts to make them perfectly parallel to the head gasket surface, I've never blown a gasket!
just an observation.....
mike
-Kuda
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Folks, sorry for the dumb-a** question, but I've always wondered about the manifold leak test using pressurized air.
Is it possible that even 10 PSI can force the intake valves open? I realize it's not much pressure but the valves are built to seal from pressure *inside* the cylinder; pressure on the other side of the valve will force the valve open - it's only a question of how much pressure....
Thoughts?
steve
Is it possible that even 10 PSI can force the intake valves open? I realize it's not much pressure but the valves are built to seal from pressure *inside* the cylinder; pressure on the other side of the valve will force the valve open - it's only a question of how much pressure....
Thoughts?
steve
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Use Teflon tape as was said , Just wrap it around a couple of times every time you change plugs ( ya have to wrap it around there correctly , nice and tight ). I have seen where the inserts were replaced with a special (supposedly leak proof ) insert and they still leaked around the threads . I also had a slight leak around my older motor and that Teflon tape works fine and I am running with it on there now , it may be a band aid ,but it works for me and I don't change plugs very much since I put my CV carb and electronic ign. in .Once a year and they still look new ( it is a cheap tune up . Just my two.
I think you will need more than 10 psi to lift the valves .
I think you will need more than 10 psi to lift the valves .
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Kuda !
By "counterbore", I meant the same as Mike Flatheadsix: recutting the surface that the washer seals upon to assure that it is un-blemished and square to the threads.
If yours still leak after this operation, the accuracy of the set-up must be questioned. I use a counterbore/spot-facer that is piloted off of the threads, however it is prone to "chatter" if the application isn't careful. If your surface has radiating lines, then it becomes very hard to seal.
Teflon tape wouldn't any more of a sin than any other band-aid, but it will insulate slightly, making the plug burn hotter.
Steve!
If 10 psi starts to open an intake valve, then the springs must be very weak.
Generally, there is about 90 lbs (or more) of pressure on the valve when closed. If we round off the area of the valve to nearly 3 square inches, then it takes nearly 30 psi to start to open the valve.
It is always a good idea to kick the motor through to open each valve and check for possible leakage everywhere else.
(As I have mentioned before, I have found casting porosities, cracks, and even leaking pan cover screws over the port by bubbletesting. When addressing the combustion chamber, you can put the air in at the sparkplug, and boost the pressure quite high.)
....Cotten
By "counterbore", I meant the same as Mike Flatheadsix: recutting the surface that the washer seals upon to assure that it is un-blemished and square to the threads.
If yours still leak after this operation, the accuracy of the set-up must be questioned. I use a counterbore/spot-facer that is piloted off of the threads, however it is prone to "chatter" if the application isn't careful. If your surface has radiating lines, then it becomes very hard to seal.
Teflon tape wouldn't any more of a sin than any other band-aid, but it will insulate slightly, making the plug burn hotter.
Steve!
If 10 psi starts to open an intake valve, then the springs must be very weak.
Generally, there is about 90 lbs (or more) of pressure on the valve when closed. If we round off the area of the valve to nearly 3 square inches, then it takes nearly 30 psi to start to open the valve.
It is always a good idea to kick the motor through to open each valve and check for possible leakage everywhere else.
(As I have mentioned before, I have found casting porosities, cracks, and even leaking pan cover screws over the port by bubbletesting. When addressing the combustion chamber, you can put the air in at the sparkplug, and boost the pressure quite high.)
....Cotten
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Thanks to everyone for the suggestions. As much as it pains me, I'm gonna pull it down yet again this weekend. I plan to have the hole spot faced (counterbored?) and see if that seals them up. If not, as much as it pains me I guess I'll have to have them heli-coiled, or welded up and re-threaded. For a the most proper (read accurate and long lasting), what's the better fix: weld, drill, and tap, or heli-coil? I know I could just use tape, and I'm certainly not above using a bandaid in the field or on a trip, but I don't want to head out on another cross country trip knowing I haven't done my best to get all the problems corrected to the best of my ability...
-Kuda
-Kuda