elesjuan

iTrader: (11)

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 -------?

BogusSVO

iTrader: (1)

What fuel are you using?

If normal gas 87/89/93, white exhast valves means a decent tune and the depostis are trying to burn off

The oil consumption could be from bad valve stem seals, with the extra heat being made from being turbo, the seals may have gone hard if they are typical Black/grey/reddish ones.

You may need to step up to vition blues They can take up to 750*

The others range from about 300-500*

Another thing to check is for worn exhaust guides, extra heat causes extra wear on the ID of the guide from heat transfer.

With the cams out of the head, fluid test the head.
https://www.miataturbo.net/showthrea...361#post872361

A bead or drop or 2 of water after 5 seconds is ok

But a little river running past the valve needs to be looked at closer for sealing issues.

BTW the Honda head looks like it has been belt surfaced....

elesjuan

iTrader: (11)

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?

BogusSVO

iTrader: (1)

I would check both surfaces for flat first.

Use a new 3/8 or 1/2 extention, not the most accurate, but will get you in the ball park.

Also it will depend on what kind of gasket you use, as what spec you need to be under

If a single layer metal gasket, .002 or less
A perferated core gasket will take .003-.004

Do not sand either surface...

Get a good double cut flat file, and your favorite beverage, and a nice spot out under a tree and have at it.

If it is real bad then take it to a shop and have them surface it, a belt sufacer will do for this, as long as the machinist has a steady grip and truly understands how to work a belt surfacer.

elesjuan

iTrader: (11)

Between the turbo to manifold, manifold to wastegate, and wastegate to downpipe I'd prefer no gaskets at all. In the past we've just dropped them off at my local machine shop for surfacing.

Completely forgot about using a file on the flanges... I like that idea.

elesjuan

iTrader: (11)

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.

hornetball

iTrader: (4)

I'm confused. With that much leakage from the #4 exhaust valves, how is it that #4 is the only cylinder showing good leakdown in the pictures above? Or, are you showing two different engines?

rleete

iTrader: (21)

You're reading the gauge wrong. #1 is good, #2 is excellent, #3 is decent (a bit low) and #4 is crap.

Joe Perez

iTrader: (8)

Huh?

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.

BogusSVO

iTrader: (1)

What it tells you, is the head needs a valve job...

With the leakage in pic #3, and the vid showing it spitting oil....

It need to be taken apart, inspected, and see whats wrong with it and fixed.

Savington

iTrader: (31)

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.

rleete

iTrader: (21)

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.

Joe Perez

iTrader: (8)

Yeah, I'm completely with you there. It just doesn't make sense looking at the images of the leakdown gauge.

At any rate, I originally came in here just to say:

Q: Why are my exhaust valves white?

A: Because racist car.

hornetball

iTrader: (4)

I'm still confused by those pictures. The obvious conclusion is that the head needs to be reworked (the video wasn't confusing at all). But that may not be the only conclusion to draw here.

Also, my exhaust valves are Japanese. That might make them racist -- probably does if my time living in the Phillipines tells me anything.

elesjuan

iTrader: (11)

First off, Thanks for the feedback everyone. Always appreciated.


My first thought was just that, there is something wrong with my test. Might outline a couple things:

• Definitely believe I'm doing the test correct, as per Milton's instructions
• No timing belt installed
• Manually manipulated camshafts to proper locations
• Located TDC using the timing mark on crank pulley
• "Locked" crank in place with a pair of vice trips on pulley
• Cylinder #3 actually broke the crank pulley
• Head bolts were tight, but torque procedure was not followed
• Installed the original head gasket from this motor
• Shortblock has unknown mileage from salvage yard
• I did not clean the cylinder head or block deck surface of carbon/misc crud
• Discovered a LEAF under the #1 intake valve ????
• Cylinder head has been in my garage since it was pulled from the car
• Head was on a perfectly running engine until it threw a rod, car made plenty of power

I have another miata head laying around in unknown condition, along with a completely bare stripped EscortGT cylinder head which I tore apart to lap the valves.

Here is the shortblock:





It's dirty, but the walls don't look trashed.. I realize that doesn't mean the rings are any good though. Does any of this help?

Miater

So you've been Frankensteining motors together with dirty reused parts of questionable condition and you can't figure out whats gone wrong?


Those walls don't look all that good either.

elesjuan

iTrader: (11)

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!

BogusSVO

iTrader: (1)

I can see the oil scraper imprint in the bore... Block needs honed.

Read thu these then try your tests again

https://www.miataturbo.net/engine-performance-56/head-gasket-repair-how-clean-block-surface-w-pistons-installed-65074/

https://www.miataturbo.net/showthrea...665#post862665

elesjuan

iTrader: (11)

Today was busy and I'm tired so I'll do that tomorrow afternoon then slap the head back on. Will post results.

Recorded this last night and forgot to post. Cylinder 4 valve #2 leaks a lot and #1 leaks only slightly:



Number One and two were very similar to cylinder three. I'm going to slap this on whatever motor I end up putting in and calling it good.

(Don't ask about the video title.. swype didnt put what I wanted in and felt too lazy to correct it with my filthy fingers.

BogusSVO

iTrader: (1)

You slam that head on any short block, you should be slapped.

#4 will be low on compression, if not a flat out miss.

At a min, pull those 2 valves, go to a machine shop ask them to clean them and face them, then lap them back in.

Bet the valve stem seals are trash and should be replaced to boot.