Leak Down Test failure. =~ (

Check my logic:   Introduce 80 psi through the spark plug hole.  Rotate the engine until the valves are closed, the chamber should hold 70 - 80 psi.  If it doesn't and you hear hissing through the dipstick, it's Rings.  Hissing out the exhaust pipe = leak at the exhaust valve  and a hiss from the carb or manifold means a bad intake valve.

I have hissing through the carb.  Pulled the valve  cover and found the intake valve adjustment on the rocker has no backlash, the valve isn't fully closing.  OK.  I loosened the lock nut, backed off the adjustor and lightly tapped the valve stem to shake off any deposits or maybe get a better seat.

NFG.  The engine was stone cold.  I'm going to run it until warm and recheck the leak down and valve adjustment.

Thoughts, suggestions?

The valve could have some crud on the seat area, or be burnt from the improper lash.  Throw a bottle of sea foam in a half tank of gas, hope for the best.

I should Edit this in; I really don't want to pull the head.  Seafoam it is.

I've been running 91 Octane Ethanol Free.

If adding Seafoam to the fuel doesn't help, there's always the dump-it-directly-through-the-intake technique. Seafoam even makes a can with a bent sprayer tube for this purpose. Personally, I've always just done with water, sometimes with a little Windex or rubbing alcohol mixed in. Either way, it makes a nice big cloud of dirty steam. Nothing beats steam-cleaning for getting crap out of the combustion chambers; I'd think it would tend to do a decent job on intake valves as well.

What sort of engine?  Hydraulic lifters, or solids?  Why are you checking it?  Was it misfiring, or are you curious before you install?

Hydraulic lifers won't have any clearance.  Leakdown on a cold engine that hasn't run for a while won't give you dependable results.

Not hydraulic lifters and it wasn’t misfiring.  It’s part of an annual inspection;  the engine is a 2.0 liter boxer VW bus with two Stormbergs.

It’s  been run for a bit and feels- sounds strong.  I got it after sitting for a few years.

Dan

If it's been sitting for a few years, drive it for a while and then test it again.  You never know, it may cure the leakdown issue.

I bought an engine off craigslist last year, did a leak down test and one cylinder failed with air blowing out the intake. I pulled the intake and looked down into the port of that cylinder. Turns out there was a mouse turd holding the valve open. Rolled the engine over to open the valve and gave it a quick blast with carb cleaner, and all was good after that. 

Pretty dense mouse turd!

I have seen engines fail leakdown after sitting and then run fine pretty shortly after startup. I tend to think it has to do with corrosion on valve faces and seats that is broken loose or beaten flat after a few thousand impacts. 

Until i witnessed it i would assume that anything that failed leakdown had a problem. Now i am reluctantly in the 'wait and see' camp based on what i've seen.  Sucks because it makes it even harder to assess a used motor without actually installing and running it. 

What Vigo said.  We regularly get cars in at Eclectic that have been sitting for 10-30 years and the owners have us wake them from their slumbers.  It's common to see one or two cylinders be around 20-40 on an initial compression check when the others are 125-150.  Once we've got 25 miles on the car, the compression comes right up on the low cylinders.  The low cylinders are always the ones that were sitting with valves open.

I also think people worry too much about leakdown numbers.  If the engine has fairly even compression (each cylinder within 10-15% of the others), it's okay.  The leakdown will tell you where it's worn, but lots of times it will keep running well for a long time if the compression is good.

In reply to 02Pilot :

That is really old school procedure. LOL We used to do that alot.

outasite said:

In reply to 02Pilot :

That is really old school procedure. LOL We used to do that alot.

Yup, it's old school. Still works though.

BTW, there are a couple of aftermarket pushrods for these engines that basically call for the valve clearance set to zero when cold. You basically adjust the valve clearance until there is no clearance but the pushrod still turns freely.  

Yup, it's old school. Still works though.

I haven't taught a class where this was relevant in a while, but i remember that several times i would feed a running engine a cup of water in front of students. A lot of them know what hydrolocking is but I haven't yet run into anyone that wasn't scared to pour water down an intake. I try to explain to them that the volume being pumped through the engine vs what we're pouring in (and how slowly) is such a tiny ratio that you could never actually fill a cylinder with water this way. 

I haven't done it in a long time but when i did it to my own cars i also used to disable the coolant fan and let it get pretty hot before the water treatment. Another thing that would raise eyebrows of the uninitiated.  

In reply to BoxheadTim :

That sounds more like hydraulic lifter adjustment..

How can a different push rod make a difference in adjustment.

sounds fishy to me.

Knowing what the OP is using this engine for I doubt that it has such a questionable aftermarket pushrod as Boxhead mentions. The pushrod can make a difference based on metallurgy and expansion rates, but zero lash on a mechanical type 4 Volkswagen sounds like a recipe for burned valves.

BIn reply to 914Driver : remembering the initial problem, you’re done.  Time to pull the head and have it rebuilt.  

Air cooled VW’s are as simple as it gets, but if you don’t want to hire a mechanic. Just be sure to tell him it’s on something that flies.  

I've done VW heads before, valves,  seats, port & polish, all that.  I just don't want to.

Tomorrow it won't be raining here, going to fire it up, adjust the valves and recheck it.  Thanks for the help guys.

iceracer said:

In reply to BoxheadTim :

That sounds more like hydraulic lifter adjustment..

How can a different push rod make a difference in adjustment.

sounds fishy to me.

Nope, they're aftermarket VW engine pushrods. Basically they're making use of the different thermal expansion rates between the materials used for the block/cylinders and the steel pushrods: https://www.jbugs.com/product/4033.html

Not saying that's what's in the engine that 914Driver is referring to, but they do exist for a/c VWs.

If it ran good, I wouldn't worry about it.

You know how metal expands as it gets hot... well, metal in an engine gets hot at different rates throughout the engine.  Some engines have horrible valve seal when hot because of this.  So, smart engine builders with access to the right equipment will only cut the seats on hot cylinder heads... and then the valves seal horrible when cold.  But you don't drive cold engines, you drive hot ones.

It's not as good as cutting the seats on a running engine, but given that is pretty much impossible, machinists gotta make do with good enough

Update:

Sorry.  Pulled the head, did a nice 3 angle valve job, also on the valve seats.  Reassembled, retest.  STILL leaks at the intake.  WTH?

Going to pull it again and Zyglo or do Liquid Penetrant looking for cracks.  None are readily visible to the naked eye.  Once off I want to cover the chamber with plexiglass, introduce air and oil in through the spark plug hole and see where it blows out.  (valves in).   Make sense?  No?  Open to ideas.

Someone here emailed me offering ideas and/or parts but I can't find his email.  Please reach out to me.  I have all winter now and a heated garage to UnBerkely this thing.

Thanks, Dan