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I have a 98 Nissan sentra i was driving down the road and i heard a clunking noise and my vehicle diedtried to restart the vehicle and all i can hear is the starter spinning i was just wondering of anyone would know what this might be.
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Hi I'm new here, have a 99 sentra with a stock GA16DE and I'm desperately trying to figure out why this happened to me too. When the engine died, there was a metallic whirring sound. When the mechanic took off the rocker cover and the cylinder head, he found some broken pieces of metal in there. I was not there when he found them but I'm guessing he found them in the cylinder head somewhere in the recesses under the camshafts.

I have two photos of them below. The bigger piece looks like it's part of something to hold a 3/8" diameter pin. The 2 smaller pieces for a smaller pin?

The mechanic can't recognize them. Does anyone know what the broken pieces are? He's checked the piston rod bearing, replaced the piston rings (lots of black gummy stuff in one of the cylinders) and put the cylinder head & rocker cover back on. The engine could start but within a minute, there was a loud metal on metal clunking sound. Can't tell which part of the engine it came from. Is there some broken part somewhere in there?


 

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It may be pieces from the timing chain guide assemblies. You'll have to remove the front timing cover to verify this. If that's the case, then the timing chain probably skipped several teeth which may have caused several valves to get bent.
 

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It may be pieces from the timing chain guide assemblies. You'll have to remove the front timing cover to verify this. If that's the case, then the timing chain probably skipped several teeth which may have caused several valves to get bent.
Thanks rogoman. I combed thru the timing chain section of the FSM... the parts blowup diagram ... but couldn't see anything that looked like this piece. Went to the mechanic's today & examined the timing chain assemblies - nothing. Surprisingly, I thought it was a pretty simple setup.

Anyway, I forgot to say in my earlier post that he showed me a spark plug with no gap from cylinder #2 ... said the piston was hitting the electrode. He even put it back in after opening up the gap, put it back in & started the car. Idled nicely and then he revved the engine & soon enough it stalled again with the same clunking sound. Took out the cyl#2 plug & it lost its gap again.

I mentioned he had checked the piston con rod bearing yesterday ... found nothing wrong. So we really don't know why the piston is hitting the plug. Today, he screwed on another rocker cover. Showed me mine, and pointed to the plastic seal rings that lined the holes thru which the high tension cable connect to the spark plugs ... he said they were disintegrating and bits had fallen into the combustion chamber and may have caused the damaged to the plugs. Huhhhh ????

Anyway, started the engine with the diff rocker cover, revved the engine up to 5k. Repeated few more times. It seemed to work ... we examined plug #2 & found the gap intact!

I still think there's something wrong somewhere down there in the piston-crankshaft connection. Perhaps I'll take it to another mechanic for a second opinion.

Btw, he also changed the upper timing chain tensioner. He's not familiar with the B14 & there I was with the FSM in my Android phone showing him how to align the 3 sprockets of the timing chain :p
 

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oh no!!! was cruising down the highway today ... max 3000rpm. Suddenly, the engine felt hesitant & then started being jerky. I suspected that one of the spark plugs lost its gap again.

Crawled to the mechanic's and the examined the spark plugs. Guess what! Yup one of the plugs indeed lost its gap. BUT no ... it was not the one in cyl #2 ... was the one in cyl #1

He stuck a skinny magnet-tipped tool down into the combustion chamber & came up with broken bits of metal similar to what I posted earlier.

I am convinced something in the cylinder head has broken to pieces & the fragments are dropping into the combustion chamber thru the valves when they open. I thought it was the pistons hitting the spark plugs ... perhaps because of failed bearings at the con rod or the piston head pin ... but why different cylinders? Instead, I believe it's something in the cylinder head that's broken & causing this problem

Has anyone opened up the cylinder head & perhaps worked on the valves before? Is there any component down there that looks like a sleeve for a pin or a rod? The fragments look like they came from a broken cylindrical thingy ... perhaps a sleeve of some sort. Do the valve "legs" have a sleeve?
 

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oh shit ... i think i found it. It's the valve guides! The valve "stems" go into these guides

Does anyone have experience with the entire valve assembly? How can the valve guides break into pieces? It seems they've broken in cyl #1 and #2 ... dunno which or how many of the valves ...

Is it a big job replacing the guides?

 

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Considering you have to heat up the head to 230 - 248 degrees just to remove or install a valve guide, yes it's going to be a pain. The head needs to come off, you need to find a way to heat it up, you have to knock the old guide out (or in your case whatevers left), heat it back up, install the new guide. Ream out the guide to 5.5 - 5.515 mm.

But it's not so bad, at least the lower timing chain cover doesn't have to come off, that's a 10 hour job.

NOTE: don't forget to get a new head gasket, and the FSM says to always install new valve oil seals. In the photo you posted, those two things are marked with a black circle with a white X.
 

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Considering you have to heat up the head to 230 - 248 degrees just to remove or install a valve guide, yes it's going to be a pain. The head needs to come off, you need to find a way to heat it up, you have to knock the old guide out (or in your case whatevers left), heat it back up, install the new guide. Ream out the guide to 5.5 - 5.515 mm.

But it's not so bad, at least the lower timing chain cover doesn't have to come off, that's a 10 hour job.

NOTE: don't forget to get a new head gasket, and the FSM says to always install new valve oil seals. In the photo you posted, those two things are marked with a black circle with a white X.
thanks b13er ... i guess I'll have to pass on that because I have neither the tools nor the expertise. I've asked around a few mechanics & they have no clue how the guides could've disintegrated :crying:
 

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What happens is they wear, and the valve starts knocking around. I guess your valve was knocking around so hard it finally cracked the guide.

Your picture just doesn't look anything like the valve guide in the fsm photo though. It almost looks like a camshaft bracket or a connecting rod cap, except for the fact that the half broken off bolt hole is perpendicular to what it should be on either of those two, and on top of that it has that piece protruding out making an L shape. You think it would be easy to identify, but I've been looking in the fsm to no avail.

I'm starting to wonder if something broke in the throttle body, or egr, and then got sucked through your intake in to the engine, and that's why I can't identify it by looking at the cylinder head and block components. You didn't have the air filter off while the engine was running and suck something in to your engine did you?

Did you discover more pieces to the puzzle, if so post another pic please. You said it looks like cylinder 1 and 2 had broken ones, how could you tell? What did you take the head off again?
 

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you said he took off rocker cover and cylinder head. was this a typo? Only reason i ask is because after you had a second issue, but it was #1 spark plug that lost its gap, the mechanic used a magnet and pulled metal out of the cylinder. if the mechanic pulled the head off, the first time, he should have seen any metal in the cylinder. And i would assume if there was a problem with the head, he should have seen that too.

if you are mechanical at all, you should be able to pull the head off yourself fairly easily.
 
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