Hoping I don't need to pull my head here.

How reliable would a leak-down test be immediately following a walnut blast? I am getting some incredibly poor results and hearing a lot of air escaping the intake ports (manifold removed). Debating if I put the car back together or tear it further apart to inspect the valves. A local machine shop told me that the test could be unreliable post-walnut blast, but then he admitted to not really understanding walnut blasting.

Thanks in advance.

 

Wow! Well, his remarks say it all; I don't understand something, so I'll say it's unreliable.

Who performed the walnut blasting? If performed properly, the intake valves are closed when blasting the back of the valves; since the valves are closed, the contact surface between the valve and the valve seat are not subject to the blast media. Now if you blasted the valves and they were partially open, not only did you fill the cylinder with blast media, but there is probably some stuck between the valve and the valve seat. Another possibility is that you already had a dropped valve seat and when you blasted it, the medial got in between the seat and the cylinder head boss.

Next is assuming the lead-down procedure was performed correctly.with the tested cylinder's piston at TDC on the compression stroke.

Pull the suspect cylinder's spark plug, and use an articulating fiber scope (available online) to see if there is blast media in the cylinder. Then, with the piston at the bottom of it's stroke, articulate the scope and look at the valves and valve seats. MINI engines (N12, N14, N16, and N18 are notorious for dropping valve seats.

If you have the intake off, you can also scope the valve seats from the intake manifold port. What you don't want to see is this.


or this.

 

Hi thank you for your input here. The pictures are very helpful!

I did the walnut blast using one of the DIY guides on the forum and the associated harbor freight parts. Using a long metal tube loosely inserted into the spark plug hole, I turned the crank until the tube was at its highest point. I couldn't visually confirm with 100% certainty that the valves were closed as the hole intake port was covered in carbon. I can see that some trace amounts of wanut media did end up in the cylinder head. How worried should I be about this amount? Hopefully this amount can be burned off and not score the piston.


Cylinder 1

Cylinder 4

Also, this is the valve in the "closed" position. I am unable to turn my bore scope around 180 degrees to see the valves from inside the cylinder (that would make this much easier). Does this look too low?


Valve at TDC

you can see from the image that there is clearly carbon buildup between the valve seat and the valve itself. not sure what I can do here besides take the head off. I just don't understand how I could go from a car that was driving like a dream with no sputters etc, to this. Could the carbon buildup have been a beneficial "sealant"?

 

Really, you can't see any carbon between the valve and the seat in this picture because the valve is closed.

Carbon is not a sealant, and it's not beneficial. Otherwise they would sell tubes of it to put in your engine instead of tools to remove it.

I think that DIY guide you found needs some work. The proper way to walnut blast is to bring the piston up to the top of the compression stroke (intake valves closed) and insert the special tool into the intake port on the cylinder head. Then you connect the shop vac to the tool to suck up the carbon and media. The wand from the media blaster goes into the round port on the tool NOT INTO THE SPARK PLUG BOSS! Then you start spraying the media around to clean the back side of the intake valves. This process was never intended to clean the tops of the pistons. If performed correctly, media will not enter the combustion chamber.

Here's a picture of the BMW N54 tool for media blasting the intake valves; I've performed this twice on my BMW with no issues.




You need to try to get all that media out of the cylinder.

 

sorry for my lack of clarity.

i use the media blaster in the intake port only. The scrap piece of tubing I used in the spark plug hole was solely to get a visual of when the cylinder head was at its highest point. Any media that fell through was either due to the valve drop or was between valve and seat out of sight and then fell when opening the valve while working on the next.

re camera, I have a fiber camera but it’s not able to look back 180 degrees to the top of the chamber nor can I bend it enough to fit through the small hole without breaking. Do you have one you can link or post a picture of?

thanks for your help.

 

This is the one I have. Since most modern cell phones have 4K resolution, this scope makes good used of your phone.

 

I am sure this is useful on several fronts !

 

so quick update. I ran the car for about 15-20 min and she started up fine. Smooth idle. Still getting smoke out the exhaust even with a new valve cover so I’m starting to lean in on the valve seals.

after I shut her down, I ran another leak down test. This time utilizing a TDC whistle and hand on the breaker bar the resist any air pressure on the piston. Maybe 2% leakage on cylinders 1,2, and 4. Keep in mind this is with the intake manifold back on and only the oil fill cap and coolant caps open. Cylinder 3 showed about 10-15% leakage.

i think I’m ok with this unless someone thinks otherwise. My plan is to leave the head on and just proceed with the valve seal and timing chain job. Timing chain looks fine but might as well put a new one in while I’m in there.

 

definitely a cool camera. I have a similar one but I question if the articulation bend is thin enough still fit down the spark plug bore.