After my motor blew up I pulled the head off to inspect the carnage and ensure the head wasn't damaged. Immediately noticed that all 8 of the exhaust valves were VERY white. Traditional knowledge suggested to me this means the exhaust valves are "burnt?" Slapped the head on another short block and ran leakdown test but don't recall exact numbers, all I can remember is that the results were very unsatisfactory. Listening to the leak it appeared strongly coming from the closed exhaust valves more than the intake valves, and more than the crankcase. This could be related to lack of any exhaust manifold, but an intake manifold in place.
This is a pure estimate because I never wrote down mileage, but this freshly built head only ran about 10k miles on the factory ECU and approximately 7000 miles with megasquirt, 2 of which were supercharged. Can get a photograph of my exact head tonight and plan to run another leakage test, but should I be concerned?
The valves kinda look like this honda head:
The last motor was from a junk yard escort and had about 186k miles but the head was trashed. Disassembled the motor completely to clean, the cylinders even had crosshatch still evident. Slapped it back together and ran a leakdown with my freshly built miata head and this was the result, dry leakdown right after assembly:
Eventually it started to consume some oil which may or may not have lead to it's demise. Eventually I'd like to get a 99 head, but this has to do for now. Six speed is higher on the list...
tl;dr - I'm a paranoid ------- with white exhaust valves on my 20k mile cylinder head and they seem to leak. Should I worry or quit being a paranoid -------?
Fuel used was always 91 octane from a local chain station and never added my own fuel additives. Honestly I was worried the white valves were from a bad tune or lean condition too many times while learning megasquirt, but that might be good news.
I'm pretty confident the oil consumption was the fault of shortblock and not really the head, which hasn't seen turbo yet.
Will pull head tonight and run water test you recommend then report back. Really hope I'm just being paranoid, this thing cost me about $450 to rebuild...
On a side note, speaking of belt surfacing.. I planned on having my trubo and manifold surfaced before assembly, can I do that myself with a ~400 grit belt or better to let machine shop?
This pretty much tells the story. Now I remember why this motor never ended up in my miata 2 years ago after buying it from the junk yard.
Ruined my mood.
This tells the story of my valves: (Make sure to select 1080p for the ultimate quality of my trashed head.)
I put a little bit of 30 weight motor oil in the cylinders via funnel and spark plug hole, spun motor around a few times with the number 4 intake and exhaust valves shut. Not only can you hear a TON of air leaking out of both sets of valves, check out the oil... Looks like I can add a 99-00 cylinder head to my build sheet. Mother Fu*ker.
You're reading the gauge wrong. #1 is good, #2 is excellent, #3 is decent (a bit low) and #4 is crap.
I interpreted this the same way as Hornetball, wherein cylinders 1 and 2 are both indicating leakdown values of "high" (in the red) which indicates a large amount of leakage.
Unless I'm completely off-base, that gauge is simply displaying the pressure between a restrictive orifice and the cylinder, such that leakage of air through the cylinder causes a pressure drop across the restriction, and a decreased reading on the gauge.
As I see it, #4 is the one producing the highest reading on the gauge, meaning that it has the least leakage.
Doesn't jive with the valve observation, I know, but I don't see any other way to interpret the leakdown gauge.
95% leakdown is unrealistically high. If you accidentally set it at the wrong TDC (TDC exhaust, with intake/exhaust valves open), you'll get ~40% leak. The worst I've ever seen was ~75%, and that car idled on 3 cylinders and pulled ~50kpa at idle. 95% leak would indicate that you have a valve missing or something.
Joe, I agree that my interpretation is *** backwards, but it's either that, or the head is completely shot, with #1 & #2 leaking as if they had screen doors, and #3 nearly as bad. No engine would run very well with leakage at 80% or more on half the cylinders.
In my defense, the head which came on that escort motor was complete crap. With valves closed you could pour liquid in the ports and it would flow out of the valves, plus the head in photographs came directly off an otherwise fine running motor if you don't count the extra block ventilation.
I completely understand my negligence to clean the mating surfaces is likely a large contributor to the problem. This will be addressed before further tests are performed on cylinder pressure. Do have a question about head gasket... In theory, if it was really only for a short period, could the stock type metal head gasket be reused reliably if it and both mating surfaces were clean and true? Have a motor build in the works but *NEED* to get my car moving asap, that's partially why I'm dicking with this crap.
Again, Thanks all for the input. Appreciate any dialogue, even criticism!