I was wondering what others do to bench test valves for leakage when checking used heads or when they are off for gasket replacement etc? I know that you can spray brake cleaner down the intake and exhaust valve ports and look at the faces for leaks. Some folks pour water in the combustion chambers and use a blow gun to push air in to the ports against the back side of the valves and look for bubbles, is this a better way?

 

It seems like almost every valve I check with brake cleaner seeps a little bit, yet they were running fine? Is lapping in this situation recommended or will that just accelerate wear and make it worse?

Edited October 15, 20169 yr by Crazyeights

I never tested them. I've lapped some, some just looked at and or wire wheeled the crud off. If the contact surfaces look good, I've left them alone. Not had a problem I'm aware of. I'll note, that I had no reason to be suspicious that the valves had a problem on the engines I've had apart.

Dump alcohol in the port sides, if it leaks through the valve is not sealing. In fair condition the valves hold wd40 without leaking though

is there a reason to test them? broken belt or some other compromising situation?

 

i don't routinely test heads during a head gasket job, there's no reason too.

 

i've tested a couple for various reasons - i think it's said not to use water as it promotes rust. pretty sure minimal seapage, weeping, isn't rare on nominally running engines. at thousands of RPM's and thousandths of a second internal combustion temps/pressures, the losses are probably immeasurable. but that is just guess - it may come down to more nuanced questions and answers.

Edited October 16, 20169 yr by grossgary

It sounds like I am being way too fussy. It looks like the general consensus is to just run them unless they have been creamed by a piston or show obvious signs of being burnt. That's exactly what I wanted to know. Thank you for all of your opinions 

 

As far as the customers cars I work on the machine shop makes the call, so this info is just for my own projects.

Edited October 17, 20169 yr by Crazyeights

or if there were timing belt issues - broken belt, tensioner, etc.  then you're wondering which valves are bent or not.  but yeah on an uncompromised, normal looking engine, i've never even thought about it. 

Ok Thanks

And broken timing belts aren't an issue on the EA82 anyway.

And broken timing belts aren't an issue on the EA82 anyway.

??  Want to bet.

?? Want to bet.

Well, they break but don't cause catastrophic failure like valves into pistons. Unless you have shaved heads and high compression pistons then maybe.

If I break one on the new engine, we will find that out.

I don't bother to check them unless I have a runability issue and it fails a leakdown test. Then, as Downwash said, use rubbing alcohol (or brake clean) or WD40. The reason you don't use water has nothing to do with rust. Water has a very high surface tension compared to alcohol and WD40  and will just sit there unless the leak is drastic.