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M14P intake leak test procedure.

 
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waterpro



Joined: 31 Dec 2011
Posts: 9
Location: Ontario Canada

PostPosted: Thu Jan 12, 2012 10:58 am    Post subject: M14P intake leak test procedure. Reply with quote

Thought I would post this to give back to the community and to help others keep their M14`s in top shape.

One thing we have noticed with an engine that has been sitting for awhile, or may be up in time, is that the intake manifold pipes can leak at the seals from either end and cause a lean condition, or rough running on the associated cylinder
The intake manifold pipes on the M14 have a solid gasket at the cylinder head end and a rubber `Quad`gasket at the supercharger end. Both are held in place and sealed by compression from tightening a threaded ring to either the cylinder jug or the rear engine casting.
The rubber quad rings will shrink over time and necessitate tightening of the rings to keep air from leaking in at the joint.
Eventually you can not tighten the rings any more and an air leak will develop meaning that replacement of the rings is the only option.
This is not an easy task and will probably set you back 2-3 hours at best if you have easy access to the entire engine and have the M14 tool kit with the special wrenches. (Wrench 14-24-571 and Wrench 10-32-12)

The big question is "How do I know if I have a leak ?"

If you have a 9 cylinder Display for EGT you may see a slightly higher temperature on one or 2 cylinders. This may or may not mean a leak but it can be an indication especially if the temperatures have been rising over time or appears suddenly.

For the rest of us poor folk without fancy digital engine gauges, here is an easy way to check for leaks.

You will need only 4 general shop items and one not so easy to get item.

(1) A decent Shop Vac that can have the hose attached for a blower.
(2) A roll of "Tuck Tape" (Sealing tape for home vapor barriers)
(3) A spray bottle full of clean water.
(4) A few drops of dish soap.
And the hard to get item is an old pair (or new) of panty hose.

Process:
Hook up the Shop Vac so the hose is on the "Outlet" side of the vacuum.
Place one leg of the panty hose over the end of the hose. (this is to keep from blowing dust or other material in to your engine)
Wrap the panty hose on the the vacuum hose with tape to keep it from blowing off.
Now place the hose against your carb air intake wherever it is convenient and tape it on so that there is no leaks between the hose and the attachment point. (The carb heat hose fitting is a great place to do this)
Use more tape to block off any other points of your air box or intake so that when the vacuum starts blowing air in to the engine it will not come out anywhere.
Turn on the vacuum. (Blower)
Make sure that there are no leaks around the hose or intake. Block with tape if required.
You should hear air coming out of the exhaust as the vacuum blows air through he engine.
Take your spray bottle full of water and add a few drops of dish soap to it. (Don't forget to return the dish soap to the kitchen or your wife will be quite upset. Also wipe the oily fingerprints off of it so she does not know you used it.)
Here is the fun part.....
Start spraying the soapy water around the joints in the intake manifold pipes at the engine casting and the cylinder heads.
Do one at a time and watch for small bubble to appear anywhere around the joint. If you see bubbles, you've got a manifold intake air leak!
Tighten any joints you see bubbles coming from using the special wrenches from the tool kit, and spray again to see if it has sealed the leak.
If bubbles are still present after tightening, you need to replace that seal.*
When you are sure that there are no leaks, shut the vacuum off and remove any tape.

That's it. Your done. You now know that there are no intake air leaks in your engine.

Peter.

*Thank you to George Coy who was very helpful in supplying new seals for us and for his exceptionally fast service.
He has spent hours on the phone with us diagnosing problems and pointing us in the right direction. We probably have not spent the money that others have with him, but he has treated us as if we did.


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GeorgeCoy



Joined: 02 Dec 2010
Posts: 253

PostPosted: Thu Jan 12, 2012 12:13 pm    Post subject: M14P intake leak test procedure. Reply with quote

Hmmmmm maybe you should be careful when pressurizing a pressure carburetor.

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GeorgeCoy



Joined: 02 Dec 2010
Posts: 253

PostPosted: Thu Jan 12, 2012 12:21 pm    Post subject: M14P intake leak test procedure. Reply with quote

AND It might be wise to disconnect the manifold pressure gage as well

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MONTY(at)bpaengines.com
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PostPosted: Thu Jan 12, 2012 12:33 pm    Post subject: M14P intake leak test procedure. Reply with quote

I don't think you will see a higher EGT at wide open throttle. You may
see a slight drop in maximum attainable manifold pressure. This applies
to only the case end of the pipe leaking. IF it leaks at the cylinder
flange that one cylinder will likely run lean.

However, when the engine is operating at less than ambient pressure you
will see some increase in ALL EGT's because a leaking pipe joint is
common to the whole induction system, meaning that it is in a big
plenum. Also idle will become more rough and there will be a slight
increase in idle RPM compared to the previously set value.

The text book answer is to check these for security at each condition
inspection. End of problem.

Monty Barrett
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waterpro



Joined: 31 Dec 2011
Posts: 9
Location: Ontario Canada

PostPosted: Thu Jan 12, 2012 3:44 pm    Post subject: Re: M14P intake leak test procedure. Reply with quote

All good points.

Quote:
Hmmmmm maybe you should be careful when pressurizing a pressure carburetor.


I had thought about that but was not worried about it too much as there is not much likelihood of the air not being able to escape from the engine with at least one intake and one exhaust valve open to some degree at any point of the prop rotation.

Would the pressure on the carb with the engine stopped even be an issue to the barometer in the carb?
I am guessing that it would not be any worse than ram air entering the carb when the engine is stopped or at low idle.

Not knowing the carb like you do, I have to go by what you suggest.
Quote:
AND It might be wise to disconnect the manifold pressure gage as well


I agree 100%

Peter


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stephen092



Joined: 06 Mar 2018
Posts: 6

PostPosted: Mon Apr 16, 2018 6:23 pm    Post subject: Re: M14P intake leak test procedure. Reply with quote

You describe it well by applying different electronics industry. It's good time for me that I join thepensters reviews to manage my task. I really loved and enjoyed to read this article. Really great content created in this article.

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