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Miata Ignition Chamber


cbhaywood
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Prepare to unload upon me as the single least knowledgable engine mechanic in this series. I need someone to explain (small words will probably help) what I am looking at. I'm learning, but operate at a relative toddler level.

 

Miata with an NA 1.8 engine. Leaking some oil from an undisclosed place during Thompson. Engine compression is surprisingly good for a swapped engine of unknown mileage. And it had just finished its third race weekend for me, a 12 hour race, running as well at the end as it did at the beginning.

 

I put some UV die into the oil and ran it to try locate the leak(s) source. Specs of die starting showing up where coolant should be. Drained the system... sure enough there is some oil getting into my water. No milkshake on the oil side... it doesn't appear that water was in the oil system.

 

Great. My first head gasket job. Have to learn how to do it.

 

I pulled the head, cleaned off the deck. Definitely carbon buildup on the pistons. Cleaned off the Head. Found that one of these is not like the others. There is roughness/protrusions/pitting on cylinder 2. And the valves don't look as happy as the others either. I have attached a picture of the bad and the neighboring cylinder for comparison. While I don't believe this would affect the head gasket seating,  I'm sure it isn't good. What am I looking at and how/should I address it?

 

Thank you for taking a look.

IMG_6464.JPG

IMG_6465.JPG

Edited by cbhaywood
typos
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22 minutes ago, cbhaywood said:

Prepare to unload upon me as the single least knowledgable engine mechanic in this series. I need someone to explain (small words will probably help) what I am looking at. I'm learning, but operate at a relative toddler level.

 

Miata with an NA 1.8 engine. Leaking some oil from an undisclosed place during Thompson. Engine compression is surprisingly good for a swapped engine of unknown mileage. And it had just finished its third race weekend for me, a 12 hour race, running as well at the end as it did at the beginning.

 

I put some UV die into the oil and ran it to try locate the leak(s) source. Specs of die starting showing up where coolant should be. Drained the system... sure enough there is some oil getting into my water. No milkshake on the oil side... it doesn't appear that water was in the oil system.

 

Great. My first head gasket job. Have to learn how to do it.

 

I pulled the head, cleaned off the deck. Definitely carbon buildup on the pistons. Cleaned off the Head. Found that one of these is not like the others. There is roughness/protrusions/pitting on cylinder 2. And the valves don't look as happy as the others either. I have attached a picture of the bad and the neighboring cylinder for comparison. While I don't believe this would affect the head gasket seating,  I'm sure it isn't good. What am I looking at and how/should I address it?

 

Thank you for taking a look.

IMG_6464.JPG

IMG_6465.JPG

I’ve seen a few online mentions that localized damage like that is caused by a spark plug strap breaking off and then bouncing around in your cylinder. Other potential cause is a small rock or similar thing getting in. I raced a BMW engine looking like that on 3 of 6 cylinders for 6 events before it dropped a valve and ate itself due to unknown reasons. I never did anything to fix it. It looks like you could smooth it out with a TIG welder if you wanted to?

 

(Disclaimer: not an engine builder)

Edited by enginerd
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That cylinder swallowed something.  All the marks around the combustion chamber are from something harder than air getting btween the piston and the head.  Probably you have at least 1 bent valve so it isn't seating right, thus not burning right, thus the difference in color.  Piston needs to come out of the bore and look at rings and ring lands, plus look for scoring in the cylinder wall.

 

Check the spark plug for the ground, they can break off.  Look at the throttle body, see that there are still two screws holding the butterfly in place.  Check the air filter that it doesn't have a big hole in it that would allow rocks in.

 

All likely fixable - head gets shaved (compression bump), piston is inspected, valves replaced if bent, valves re-ground and seated regardless, might as well do rings while you're in that far.  If you have a  bent valve look hard at the valve guides.  If the bore isn't good it gets overbored and you replace the pistons with the next size up.  If you're in that far, might as well do new rings, oil pump and all gaskets. 

 

Are you signed up with Mazdamotorsports?

 

 

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I really do appreciate the quick responses from everyone, although I am still waiting for the "it's fine, run with it" response that I will jump to agree with.

 

Yes, I'm signed up with Mazdamotorsports (their head gasket arrives Friday). No holes in the air filter and the TB has all its parts... I wonder how long ago this happened, and suspect (kind of hope) it was in the motor's previous life.

 

Attached is a picture of the piston. Matching pit marks, but I suppose it could be much worse.

IMG_6467.JPG

Edited by cbhaywood
typo
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As already mentioned

There is no doubt that cyl ingested something foreign long time ago, by the photos, it would be suggested, at a minimum, have it shaved and those valves removed for inspection as it is definitely not burning the same as the others, slapping a head gasket is not enough.

 

Sometimes hearing the same more then a couple of times helps decisions.

 

 

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1 hour ago, cbhaywood said:

No. That's clear. My previous comment needed the green font.

 

Going to learn to remove valves. And lapping all of them while I am in here seems like something someone smarter than me would do.

I read something on the internet a few months back... the gist was:

lapping valves is fine for a lawnmower engine, but for anything beyond that you better send it to a machinist to properly recut the valves.

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1 hour ago, cbhaywood said:

No. That's clear. My previous comment needed the green font.

 

Going to learn to remove valves. And lapping all of them while I am in here seems like something someone smarter than me would do.

 

 

That head is not the one to learn how to assemble valves on.  The keepers are down in a hole that is near impossible to reach w/o special valve spring compressor ends.  Just pay someone to remove the valves, inspect, restore as needed, re-assemble.  Easy for most race shops.  The removal is easy, but keeping all the parts sorted out is a pain so just send it out intact. 

 

 

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Sounds like you have oil leaking past a high pressure passageway into the cooling system. I built a miata engine one, although it was 1.6 and almost 2 decades ago. I can't remember where the pressure oil feed to the head is in relation to the water jackets. This could be the source of your leak, at the head where this feed passed from block to head. On most engines this results in external seepage, as the feed ports are close to the outside edge of the head sealing surface, but you never know.....

 

If it was a return port, you generally would get coolant in the oil, as the handful of coolant PSI would beat out the psi (singular) or less of crankcase pressure. 

 

You will want to use a sanding pad, scotch brite, or "tootsie roll" to clean up the roughest part of the damage in the combustion chamber non sealing surfaces. You don't need to make them disappear, just knock the edges off to prevent hot spots. 

 

You can tig weld the damage as well, but this will add tons of processing to the head. I work with a guy that used to repair top fuel heads (for pretty good money), there are more steps than you would think even with OHV head. For you warping the cam bore would also be an issue to deal with\repair post welding.  

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EF IT!  Take a grinder to the head and block 80 Grit. Smear some jb weld in the pits and holes, re use the head gasket and ship it!

 

 

In all seriousness what did the spark plug look like?  You can turn the head upside down and pour a liquid around the valves.  Then check the intake ans exhaust runners for the liquid.  That is a very crude way to test if the valves are sealing.  But the safe way to do the job is have it all properly services.  May be cheaper to get another used motor?

 

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Thanks for all the input. I mean that. I’m reading everyone’s comments very closely.

 

Spark plug looks fine. Totally consistent with the others. Compression was 195ish before I removed the head, again surprisingly consistent with the other cylinders.

 

It might be cheaper to get another motor, but I’m going to continue further down this rabbit hole also as a learning process. 

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