Pictures of piston, valves & spark plus: what does this tell you?

One Cylinder is running leaner that the others (#4?) (Typical for a Miata.) How long were the plugs in the engine? Do you know what the compression was before you opened things up? This is usually a good indication as to what to do further. What caused you to pop the head for a look? This might also help in making a decision. The pictures may be misleading, but it looked like there might be some pistion damage on one piston at the edge. There are ways to keep the crud from cleaning out of the piston cylinder wall gap, if you really want to de carbon. One method was to move a given pistion down from the top of the cylinder, lay a small bead of RTV between the pistion and the cylinder. Move the pistion up slightly while the RTV is still wet, so it seals the gap. Removal -- move the piston down, Remove the RTV. If you are not going to use a solvent in the cleaning process, a bead of grease will also work well. You can even use grease, remove the excess with a rag wet with solvent, let the solvent dry, and then put the bead of RTV down. This helps to keep the RTV from going too far down between the piston and cylinder wall. Before RTV we used to use just heavy grease. Ideally, the engine has enough milage and age to justify an overhaul, or possible replacement with a low milage used engine or short block.

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Chuck,

The pictures are a bit misleading. They make the piston top look like moutains and canyons while in reality it's very flat. The damage is not there (went out to check the car), want you probably see are valve cut-outs (is that english?).

I had a leaking waterpump I'm about to replace. So that's why I had to do the timing belt stuff.

Then why did I pop the head? Two reasons: some months after I got the car (about 7 years ago) I noticed the coolant was very dirty and had an "oily" look to it. I replaced the coolant but it stayed more or less clean. Still, I was unsure what to think about the head gasket. Second reason is the engine block is always very greasy below gasket level. Not the front, but the back (also both sides second half).

So I didn't plan to pop the head, but after doing the timing belt it seemed to be a small amount of extra work to (finally!) get a chance to check the head gasket.

So, stupid me, I don't have compression figures (really should have done that!).

I'm not planning on replacing the engine yet.

Would you de-carbon the pistons? Like the RTV story, but it scares me! Grease might be a better solution for me if I decide to clean the pistons.

Steven

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Nothing looks alarming to me there. There may be a little oil getting onto some of the inlet valves, could be stem seals. I would replace them anyway, if you already have the head off. Carbon buildup in minimal, I think I would just put a can of cleaner through it one I had everything together.

Steven, If you ever get the engine back together, I would change the brand of gas that you use. It looks like the valve guide seals on the intakes (rear on #1, Front and rear of #2 and the front of #3 ) are bad, (leaking oil) . That will cause carbon build up, but even #4 shows crap on the cyl. top and that is usually a sign of (bad chemical mixture) of the gas. One of the Cyl's shows a "hot spot" on the side. That can be a "burn" or a cooling leak. ( A look at the cyl. wall should tell you more. )

It is just so hard to tell from "just pictures". As someone has asked, why did you pull it apart ? Did you have some other bad indications of the power, smoke, liquid loss, oil use ??

I think, for my personal use, I will run some good carbon and cyl. cleaners thru the engine before pulling it apart. First of all, some times it cures the problem and next, it lets you have a clean area to work in.

For what it's worth, (& that might not be much for you :-) ) I switched to NGK double platinum spark plugs $11.95 each online from Sparkplugs.com , ($29.95 each over the counter) But! they are worth it! I run Chevron gas and you can run your fingers around the inside of the tailpipe and not get any soot on them ! It runs that clean!! I have

Just my shot at your problem.

Bruce Bing '03 LS

I think Bruce has nailed this one. At the same time, giving some leeway for pictures coming off as more gross than real life, this may just look to me like an everyday 110k+ mileage car. If no one is able to get a really good answer of something bad (and it doesn't sound like you were having all that many problems) I'd replace all the gaskets you can, brush everything down (cleaning is never a bad idea!), replace those spark plugs, and actually replace your spark cables too, and put it back together. These are all normal high- mileage maintenance items anyways, and would give you some peace of mind.

Wait a week, then pull the cables and plugs...check if the plugs are fouled up, then go to your mechanic or miata club and borrow a leak- down tester and try it out.

Best of luck!

-r0ll

Plugs are fine. May be a stem seal leak on nos 2 and 3 (I assume you'll replace the stem seals at this sort of mileage anyway), but the outside cylinders may also be running hotter due to the cooling system layout. Most of the mess is good honest carbon.

You should put the piston to be cleaned at TDC and fill the gap between it and the bore with grease. Then decoke it and polish it, finally dropping it back down a bit and carefully wiping all the gritty grease out. The valves can also be decoked, but don't touch the lapped surface. You can relap them in the traditional way if you like, but go very gently - I think the seats are triple-cut.

Hi,

Because the newsserver of my provider wasn't working, I used google...

The damn site used my email to publish messages!!! :-(

Anyway, thanks all for responding!

Steven

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Wasn't planning to...

I checked the manual, seems like there's a lot of work involved (remove cams, spring, lifters, ...). If I'm only burning a little bit of oil, so I'm not sure it's worth the time.

It might be better to clean the valves a bit, and drive the car for a few more years until it needs a serious overhaul. At that point I might swap the complete head or do a full valve lapping job.

Disassemble the head to replace some valve seals seems like a lot of work with minimal gain. Does that make sense?

Since I'm still waiting for parts to arrive, I cleaned the pistons. In the picture I was halfway, by now I'm finished. Let's hope you can see the difference with the naked eye :-)

Steven

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LOL, very pretty. Probably make bugger all differance. I would be changing stem seals, if they are a little iffy now, in a few years they could be gushing.

Yes.

Wasn't planning to...

I checked the manual, seems like there's a lot of work involved (remove cams, spring, lifters, ...). If I'm only burning a little bit of oil, so I'm not sure it's worth the time.

It might be better to clean the valves a bit, and drive the car for a few more years until it needs a serious overhaul. At that point I might swap the complete head or do a full valve lapping job.

Disassemble the head to replace some valve seals seems like a lot of work with minimal gain. Does that make sense?

Since I'm still waiting for parts to arrive, I cleaned the pistons. In the picture I was halfway, by now I'm finished. Let's hope you can see the difference with the naked eye :-)

Steven

- - - The motor is still very young w/115k , you could leave it along or you could have it all done by a proffessional ( the head ). Which in that isn't all that much money. The Miata is a very solid, well built car . Maybe if you were to keep it, you would enjoy it more to find out what it's like to own a new one. If you were to do the machining to it , it will be the boss ! I bought a '90 new, Didn't know to much about it at the time . I was amazed by it , and still am. What ever you decide to do. Enjoy , It will last a long time.

My 1997 NA also runs very clean at the tailpipe - generally Esso petrol and NGK iridium plugs, 14 deg advance, 67,000 miles on the clock.

Wire brush? Won't they scratch the surface?

Leon

Shouldn't, some wire brushes can be pretty stiff but the softer ones work OK on alloys.

Hakuna Miata had her valves cleaned like this:

Steven

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