Well I went and broke my Miata

JamesMilko · **Posted:** Sun Feb 27, 2011 8:21 pm

Somehow I broke the Miata this weekend at VIR. Not exactly sure what is wrong yet but I'm open to suggestions. Once Andrew gets his car out of my garage I'll be taking the head off to see how bad it looks in there. I'm thinking rings, my father is thinking bent valve. I'm hoping rings since I have a spare bottom end.

In the middle of one of the sessions the car suddenly lost a lot of power and started missing horribly. Wouldn't idle and couldn't restart it. After letting it cool a bit it would try to fire but never actually stay running without the starter going. Ended up narrowing it down to the 1&4 coilpack seemingly being bad. Pulled the coilpack and plugs to see what was going on there and found:

Pushed up to 0.00 gap, no sign of any impact damage on the plug or piston, heavily oil fouled. Regapped the plugs and it started up and ran at seemingly full power. Ran parade laps and another session after regapping them.

However now I leave a smoke screen when I transition from high vacuum to high load and have an exhaust that would be healthy for a 2 stroke at idle.

Steven Carter · **Posted:** Sun Feb 27, 2011 9:11 pm

Sorry to hear it, James. I hope it's a relatively painfree and inexpensive fix.

noahfleming · **Posted:** Sun Feb 27, 2011 9:12 pm

Damn, I'm sorry James!

Do you think it could be the valve cover gasket or PCV valve since there seems to be oil on only 2 of the 4 plugs? The gap issue is puzzling to me, but what do you think about increased cylinder pressure due to the presence of oil in the cylinder? Was there any oil in the cylinders that you could see or just the mess on the plugs?

Very curious to hear what you find when you are able to open it up!

JamesShort · **Posted:** Sun Feb 27, 2011 9:30 pm

I thought BP engines were non-interference?

Andrew Jonell · **Joined:** Mon Mar 23, 2009 6:43 pm **Posts:** 1350

JamesShort wrote:

I thought BP engines were non-interference?

They are.

Ryan Holton · **Posted:** Sun Feb 27, 2011 10:01 pm

Ahhh the memories. I did that to my Miata at VIR, twice. Never figured out what the hell was going on. I will go back thru some of my old notes and see if I can find anything. I didn't notice a reduction in performance or smoke of any kind.

I swear someone else in the track program (Ashraf) had the same problem.

JohnByers · **Posted:** Sun Feb 27, 2011 10:39 pm

This def sucks... but bent valve doesn't sound right to me in this situation. I suppose rings could be a possibility but check the simple things first. Would hate for you to tear into this because of something simple.

KendtEklund · **Joined:** Tue Mar 27, 2007 7:29 pm **Posts:** 1204

I did a quick googles - and of course because it was on the internet it must be true :lol:

- Detonation can close the plug gap
- Someone suggested carbon build-up on the top of the piston

Hope it turns out to be nothing major!

JamesMilko · **Posted:** Sun Feb 27, 2011 11:48 pm

PCV, looks good. I didn't suck on it to make sure the check valve was still good since it was filthy but I pulled it in the paddock and it was venting (significant amounts) to the atmosphere. Same with the crank breather line.

2&3 were both oil fouled, not anywhere near as bad as 1&4, I'm thinking the fouling on 2&3 is from oil getting sucked in through the intake.

Kendt,

I thought about detonation as well but the electrodes look fine. If there was enough det to change the gap I would have thought there would be other noticeable detonation damage to the plugs. Also the car has a WBO2 and MS3. I looked at the logs from the session where things really started to go downhill and the AFRs were spot on, my spark table isn't aggressive at all and the car is running 93 octane to be completely safe.

Noah,

Carbon buildup was my top idea for the re-gaping of the plugs. Doesn't explain the oil consumption though unless it built up enough to bend a valve as well. I don't think the tolerances are that tight in a late 80s econobox motor. Tops of all 4 pistons were wet after some parade laps, 1&4 were significantly more fouled than 2&3.

I'm finding a lot of people on the Internet blaming detonation on closing spark gaps. I'll have to bust out the bright light and magnifying glass to get a better look at them.

Ryan Holton · **Posted:** Mon Feb 28, 2011 8:32 am

Hmmmm, this is weird. I went back and looked thru my Miata notes and in February of 2007 I did the same thing at VIR. Plugs 1 and 4 had zero gap, 3 had about 1/2 the specified gap. It happend to me on a Saturday. I regapped my plugs and went out and set my fastest time of the day in the time trial, ran all Sunday and picked up a .1 in Sundays TT.

I was also running MegaSquirt v3.0 and had been for about 4 months.

The only answer I could come up with was detonation. I ran the car for another 6 months a blew the motor up at CMP when the TB shaft snapped and the motor ate some parts of it.

JamesMilko · **Posted:** Mon Feb 28, 2011 9:11 am

Oddly enough my MS install was almost 4 months old to the day on saturday. I got everything together for the Oct 26th Autocross but wasn't totally ready for the 15th at CMP.

I'm pretty confident it was detonation now. No idea why I got detonation though, I'm leaning towards that I was running the colder of the two OEM plugs.

I'm pretty sure this is the incident that regapped the plugs. This is the first spot where the car started having issues. My AFRs for the rest of the session look like the first second of the graph rock solid right on target.

JamesShort · **Posted:** Mon Feb 28, 2011 9:16 am

Quote:

...I'm leaning towards that I was running...

No pun intended

.

Well looks like two James' blew engines due to detonation/AFRs in 1 week. Do we get to share the burnt piston award this year?

Ryan Holton · **Posted:** Mon Feb 28, 2011 9:31 am

JamesMilko wrote:

Oddly enough my MS install was almost 4 months old to the day on saturday. I got everything together for the Oct 26th Autocross but wasn't totally ready for the 15th at CMP.

I'm pretty confident it was detonation now. No idea why I got detonation though, I'm leaning towards that I was running the colder of the two OEM plugs.

I'm pretty sure this is the incident that regapped the plugs. This is the first spot where the car started having issues. My AFRs for the rest of the session look like the first second of the graph rock solid right on target.

Yup, 20:1 ain't good

Sorry to hear it.

JamesShort wrote:

Well looks like two James' blew engines due to detonation/AFRs in 1 week. Do we get to share the burnt piston award this year?

There is still 9 months before the Xmas party, there is plenty of time for one of you to take the lead.

<--Former Burnt Piston winner

JamesShort · **Posted:** Mon Feb 28, 2011 9:33 am

I guess if you think about it, it is MUCH more impressive blowing up a BP miata engine than a Subaru, so I guess Milko is still in the lead

.

JamesShort · **Posted:** Mon Feb 28, 2011 9:34 am

James, after you swap bottom ends, do I get to put ANOTHER timing belt on an engine in your garage

.

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Well I went and broke my Miata

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