Testing valve leak?

[DirtyDogs446]

I know you should use gasoline but if I use water with food coloring in it to see if the exhuast valve will leak would that be sufficient? So far it's been 20 mins with no leaks. It's a nee head and new ss valves for a predstor hemi. I lapped for about 8 mins total it has a nice line all the way threw it.

 

[mckutzy]

A black sharpie can be used to check the contact patch...

 

[Brianator]

A black sharpie can be used to check the contact patch...

When I tear my next head down I'll test a Sharpies accuracy against Prussian Blue for future reference.

DirtyDogs: I use a thin non evaporating oil (more specifically Marvel Mystery Oil) and put it over a paper towel overnight, 20 mins with no leaks is encouraging though and dont forget once it's been run the seal will improve even more. A clearly defined line that's even thickness all the way around is what you're after, if the two valves lines aren't the exact same thickness dont sweat it too much it should be fine.

 

[mckutzy]

Sharpie in a pinch... Im pretty sure the blue will be better.. But any coloured witness mark Is better than looking at a shiny patch of steel.....

 

[Brianator]

For sure! I've never tried a Sharpie as I have and use Prussian Blue and it won't take long to test side by side so why not right!? Curiosity is going to kill this cat if I don't! Lol. I may even try other things found around a shop/garage that the average fella might have and see what else works well.

 

[mckutzy]

Sharpie works great for layout on other thing needing a fine scratch mark on steel...In aluminum it might stain and permanently mark it in some case that might not be desired....

 

[JTSpeedDemon]

Honestly I keep water FAR FAR FAR FAR away from all my engine parts!
Why are you worried about the exhaust valve leaking? If it's held for 20 minutes, it should be plenty good.

 

[Brianator]

I worry about leaky exhaust valves, they can ruin your day in a hurry!

 

[anickode]

I know you should use gasoline but if I use water with food coloring in it to see if the exhuast valve will leak would that be sufficient? So far it's been 20 mins with no leaks. It's a nee head and new ss valves for a predstor hemi. I lapped for about 8 mins total it has a nice line all the way threw it.

Water can be funny. Surface tension can keep it from leaking through. A drop of dish soap can help that.

A very light oil works nicely. I like off road diesel fuel (with the red colorant) myself.

 

[Brianator]

That (colored diesel) would work even better than MMO (which is also red) as it's even thinner!

 

[jmaack]

kerosene

 

[DirtyDogs446]

When I tear my next head down I'll test a Sharpies accuracy against Prussian Blue for future reference.

DirtyDogs: I use a thin non evaporating oil (more specifically Marvel Mystery Oil) and put it over a paper towel overnight, 20 mins with no leaks is encouraging though and dont forget once it's been run the seal will improve even more. A clearly defined line that's even thickness all the way around is what you're after, if the two valves lines aren't the exact same thickness dont sweat it too much it should be fine.

There was a nice thin line that was even all the way around each area I just did not know if head and valves are both new if you got to do it alot longer or not. Thank you for all your advice. I used the red sharpie and it worked pretty well but I will invest in Persian blue sense that is the industry standard it seems. The reason I worried about it leaking is because I was lapping it for the first time and I don't want to assemble something for me to have to take apart and have to redo if I can prevent it that's all and it was my first time lapping

 

[anickode]

Just look for Prussian blue (not Persian) layout fluid.

Also when you're doing work on steel and need precise lines, you apply it then make your marks with a scratch awl. It's a life saver on clean smooth steel where a marker line is too fat and a scratch mark doesn't show up well by itself.

 

[Brianator]

Just look for Prussian blue (not Persian) layout fluid.

Also when you're doing work on steel and need precise lines, you apply it then make your marks with a scratch awl. It's a life saver on clean smooth steel where a marker line is too fat and a scratch mark doesn't show up well by itself.

Agreed, the stuff is awesome and tends to last quite a while! I got a tube when I rebuilt my cars cylinder head and there's no turning back now! Lol. I love you can use it to test for surface imperfections on almost anything that's supposed to be flat, if you want to run without a head gasket you can lap then blue to be sure you're good to go!

 

[anickode]

Agreed, the stuff is awesome and tends to last quite a while! I got a tube when I rebuilt my cars cylinder head and there's no turning back now! Lol. I love you can use it to test for surface imperfections on almost anything that's supposed to be flat, if you want to run without a head gasket you can lap then blue to be sure you're good to go!

I buy it in an aerosol spray can.

 

[Bansil]

I assume ya'll are talking about Dykem? Aerosol is good for big panels, the brush on for everything else, I prefer blue over red.
I would agree 20 min is gtg, we always used kerosene or diesel, funny how the oils can seep more than water based

 

[Wilson_Engine_Shop]

I might be a little late here but my machinist uses brake parts cleaner in the combustion chamber to check if the valves seal or not