Well, She's hurt :'( -Mystery of the sudden #2 no-compression misfire solved

MikesFixedRoof

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Mar 23, 2009
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Queens, NY
So, about 3 weeks ago, I hop on the highway home just after getting gas. I accelerate rather briskly to a velocity somewhere near the speed limit :) . Then all of a sudden I notice a strange vibration. I notice the car is now struggling to do 60. I slow down, and then I hear it- an unmistakable misfire. Great. 30 miles from home, and this happens.
So I get off the next exit, try shutting it down / starting it back up at a light. Now, I know what a motor with no compression sounds like when you crank it, and that's what I heard. A chill ran down my back. "Oh no" I said to myself lol. At that point I realized it was bad, and there was nothing I could do about it where I was.
My initial guess was the hg (its original) but after I limped it 25+ miles to my shop, where we began the checks, I had no typical smoke, no coolant loss. Hmm. Spark? Yep. Fuel? yep. Compression? Cylinder 2 shows 24psi. I check it 2 more times. Still 24psi. * Sigh * I start taking it apart that night. Here's some pics.
 

MikesFixedRoof

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Mar 23, 2009
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:sarcasm: What ever could be the problem?
 

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MikesFixedRoof

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Mar 23, 2009
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So I brought the head to a guy who was recommended to me who builds race engines. Since the problem valve was an exhaust valve, he suggested upgrading them. So I had him get me a set of supertech exhaust valves, the brand he uses in race motors which are comparable to manley. He stripped it down, checked it for cracks, (thank god there were none). He checked the valve springs and said almost half were on the weak side. Told him to get me a set of new springs. All new seals, valve adjustment, and its now finished, waiting for me to go pick it up. Grand total is about 1000 bucks. :wtc:
 

92nsx

Supramania Contributor
Sep 30, 2005
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^^^ not that bad of price if that includes the parts. My labor bill alone on my head was a touch over 900. Parts extra ;)
 

toyotanos

What will we break today?
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Nov 29, 2008
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WhtMa71;1430202 said:
I dunno...but whatever it is, it's probably not that hole in the valve.

No, I think that one of those "speed holes" that is supposed to increase exhaust flow :sarcasm:

Impressive chunk, though.
 

Mr. Y

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Mar 31, 2005
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80 miles away from Kremlin
Sorry for hijacking, but I've burned valve some time ago too. It was built head bought from member here with O/S valves. One exhaust valve got hole and another (same cylinder #2) has cracks...
What is the reason? I suspect either bad valves or wrong working seat area (wrong valve job)...
 

MikesFixedRoof

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Mar 23, 2009
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92nsx;1430196 said:
^^^ not that bad of price if that includes the parts. My labor bill alone on my head was a touch over 900. Parts extra ;)

1,036 to be exact :icon_bigg yes it did include parts- upgraded (oe size) exhaust valves, all new springs, oem hg replacement kit (valve stem seals, cam seals, etc) + labor. I mean I didn't go crazy with it. Not building a race motor............yet :biglaugh:
 

MikesFixedRoof

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Mar 23, 2009
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Queens, NY
Mr. Y;1431019 said:
Sorry for hijacking, but I've burned valve some time ago too. It was built head bought from member here with O/S valves. One exhaust valve got hole and another (same cylinder #2) has cracks...
What is the reason? I suspect either bad valves or wrong working seat area (wrong valve job)...

Not at all :icon_bigg I appreciate all the comments. You know both the mechanic who owns the shop my car is at and the machine shop guy said a big reason for it is all the damn ethanol they're putting in the fuel these days. It makes the gasoline burn quite a bit hotter which puts a lot of increased stress on the valve heads/seats. The machinist said he just finish a head off a 2 year old nissan that had the same problem.
 

adampecush

Regular Supramaniac
May 11, 2006
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Edmonton
Channeling of the exhaust valves like that is generally caused by poor seating of the valve from manufacture/bent valve or deposits between the seat and seat face (bad gas, etc)...both resulting in the passage of hot gas when the valve is closed. The lack of contact between the seat and face prevents the conductive cooling of the valve, which is made worse by the constant presence of exhaust gas, causing it to overheat and burn away. While ethanol-blended fuels may cause the accelerated damage, it is likely that your valve would have been toast either way. Before re-assembling the head, ensure the valve seat is undamaged and there is no slag left in the valve port.
 

MikesFixedRoof

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Mar 23, 2009
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Queens, NY
adampecush;1432638 said:
Channeling of the exhaust valves like that is generally caused by poor seating of the valve from manufacture/bent valve or deposits between the seat and seat face (bad gas, etc)...both resulting in the passage of hot gas when the valve is closed. The lack of contact between the seat and face prevents the conductive cooling of the valve, which is made worse by the constant presence of exhaust gas, causing it to overheat and burn away. While ethanol-blended fuels may cause the accelerated damage, it is likely that your valve would have been toast either way. Before re-assembling the head, ensure the valve seat is undamaged and there is no slag left in the valve port.

I agree. Although nothing less than 93 goes in my tank, you can't completely avoid carbon deposits on 19 year old valves. Let's also remember that our antiques with their port fuel injection are more or less spraying hot fuel onto really really hot valves:: angry :::icon_bigg
 
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MikesFixedRoof

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Mar 23, 2009
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Queens, NY
gofastgeorge;1432778 said:
IMO, looks like not enough fuel (ran lean).
Really light color deposits, plugs & turbo inlet.

That had crossed my mind, even though the car always smelled like it ran on the rich side. Got a set of rebuilt stock injectors.
 

MikesFixedRoof

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Mar 23, 2009
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Queens, NY
Mk3runner;1435566 said:
get pics of install!

lol I'll work on that. Only have this one so far, about to put the head together a bit before putting it back on. So cleann! :icon_bigg . I was supposed to work on it today but the weather didn't cooperate :3d_frown:
 

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MikesFixedRoof

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Mar 23, 2009
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Queens, NY
You know, While working on the car the other day, I really started to think about the white color of the turbine / exh manifold outlet. What could have caused it? Is it really a bad injector? If the o2 sensor was faulty and leaning it out, wouldn't I have a check engine light? I really don't want to spend the money on a set of injectors, but I'd feel like a dick if I skip it put it back together and it's still running lean.