Camshaft Broke while driving...What else needs to be replaced? - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

DamnedButDetermined · 08-19-2012, 06:04 PM

I am buying a 93 hatch soon, and the owner has been very forthcoming about the issues with the car. He was driving and all of a sudden he heard a loud noise and then engine had no power. He took the valve cover off the engine and the camshaft broke at the cam sprocket. I am going to take a much closer look when I go to buy the car but I was hoping you guys could give me some pointers as to what to look for. I am debating whether I should just replace the complete complete head or try and rebuild the head. The upper valve chain slapped around quite a bit and left marks on the block but it doesn't look too bad. I will get pictures asap of the valve cover removed.

Do you think there are problems with the block itself?
Will I not know until I completely remove the head?

Thanks,
Zac

DJ-of-E · 08-20-2012, 01:56 AM

You will not know the extent of the entire damage until you remove the head and inspect everything after a tear down. It could be the camshaft broke, or it could be something bigger.

The block should technically be okay, you just need to hand crank it if it feels off or not.

Bentleyness · 08-20-2012, 02:42 AM

i wouldn't even buy it really and look for a running one, unless its super cheap then go ahead.

cost me like 1000 for complete head work with new parts

Croustibat · 08-20-2012, 06:19 AM

I have a hard time believing the pistons did not smack the valves when it happened .

If you get the car, get a new engine, dont even bother with that one. You can disassemble it later and rebuild / sell it ( maybe - most likely you will bin it)

ch1873857 · 08-20-2012, 06:36 AM

let me try to visualise what i would see happening.

pressure from the camshaft to compress the valve springs comes from the chain and ultimately the crank.

if the cam snaps. IN THEORY: the front section of the camshaft still driven by the chain would still compress the valve springs and valvetrain like normal. the back section that is not connected would essentially be "free floating" under the cam caps and the springs 'should' take over and the camshaft would snap back to its normal state.

So I would see the cam breaking and the valvetrain that is not in time would decompress, clearing the piston. best way to see this would be to open the valve cover up and see at what position the valves are in on the broken section of the cam

hopefully this shines some light and gets you thinking so you know what to look for. valve springs move fast obviously. this action wouldve happened just as fast as if it would decompress like normal.

DamnedButDetermined · 08-20-2012, 10:54 AM

There are two ways i can envision as to how this engine damage occurred...
1...Best case scenario is that the cam just had a weak spot were the sprocket attaches and the pressure from the upper timing chain cause the sprocket to snap like so...
The exhaust cam broke at the sprocket so the entire cam shaft would no longer turn. Then the upper timing chain and broken sprocket released all tension on the lower sprocket so the intake cam would stop turning as well. This means non of the valves were operating at the time of the break so the tension of the springs and hopefully compression of the pistons should have moved all valves to the up position so they would clear the pistons.

2...Worse case scenario is that the oil passages that lubricate the exhaust cam had clogged up and were no longer shooting oil to the cam. After a while the came siezed up and stopped turning. The upper timing chain continued to spin the sprocket which cause the cam to break right at the sprocket. If that is the case then the cam would not have allowed the valves to go to the up position on the exhaust side and we could have some damage to the pistons and valves on the exhaust side.

I will be removing the entire head to verify this anyways but i am hoping for the scenario #1

The upper timing chain would have been spinning at a very high rate so I would imagine there has to be some kind of damage to the inside of the front engine cover from the chain slapping, but I don't know if anything down below would have been damaged.

Thanks,
Zac

DamnedButDetermined · 08-20-2012, 01:45 PM

Here are some pictures for you guys to look over. It appears to me that the lifters were all pushed up to the top so hopefully that means scenario #1 is what happened and nothing is wrong with low end of the engine.

Bentleyness · 08-20-2012, 01:53 PM

if you have time and money buy it for a lower price, and look for a running engine

P-Funk alot · 08-20-2012, 04:47 PM

ive never see this happen myself but these are interference heads iirc, so there is a chance that the piston slapped a valve but as soon as you pull it apart you will be able to see. regardless that head is probably scrap due to the fact of where it broke, any scarring on the cam journals cannot be repaired as there are no bearings, and from the looks of the break spot there has to be some (hopefully not but i doubt it). well i hope this helps some i am somewhat forced to believe that the bottom end is safe, but expect the worse and hope for the best.

ch1873857 · 08-20-2012, 05:39 PM

regardless. its an sr. that needs a head. the cam snapped most likely due to oiling issues. i wouldnt touch it with a 10 foot pole

*KiLLeR2001* · 08-20-2012, 05:46 PM

Quote:

Originally Posted by ch1873857

regardless. its an sr. that needs a head. the cam snapped most likely due to oiling issues. i wouldnt touch it with a 10 foot pole

Looks like a KA24DE to me...

Regardless, I would swap in another KA for the mean time. Then you can play around with that one and see what went wrong and what got damaged.

ch1873857 · 08-20-2012, 06:04 PM

right. it is. bah. who cares. didnt even pay attention. thought i read it was an sr in the OP.

P-Funk alot · 08-20-2012, 08:34 PM

i dont think its that serious. nissan shit is so easy, and its obvious he is looking to fix it so why not help him out instead telling him ways to not fix his problem. your pre fan boy, what happened to helping people out.

Bentleyness · 08-20-2012, 11:14 PM

U cant fix the head with damage to the cam housing like that. shops dont even wanna touch it just cuz its a waste of time and money.

buy a new head for like 100 bucks and you good to go. you can even use that exhaust cams with the replacement head.

Croustibat · 08-21-2012, 01:09 AM

Quote:

Originally Posted by P-Funk alot

i dont think its that serious. nissan shit is so easy, and its obvious he is looking to fix it so why not help him out instead telling him ways to not fix his problem. your pre fan boy, what happened to helping people out.

Because most of the time that kind of damage is either not fixable, or costs more than just changing the head/ whole engine. No fanboyism here .

P-Funk alot · 08-21-2012, 03:18 PM

i am all for changing the head my last comment was more directed at pulling the whole engine, and trust me i know any scaring and the head is scrap metal.

Butcher240sx · 08-21-2012, 06:39 PM

The cams can also snap if the head was ever warped too much and machined back flat. The cam towers stay out of alignment. I would pull of the head and check the block and pistons and throw another head on it.

08-21-2012, 06:39 PM	#17
Butcher240sx Zilvia Member Join Date: Oct 2010 Location: Houston Texas Age: 32 Posts: 156 Trader Rating: (0) Feedback Score: 0 reviews	The cams can also snap if the head was ever warped too much and machined back flat. The cam towers stay out of alignment. I would pull of the head and check the block and pistons and throw another head on it. __________________ Don't Mess With Texas

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08-19-2012, 06:04 PM	#1
DamnedButDetermined Zilvia Addict Join Date: Oct 2002 Location: Jax, Fl Age: 31 Posts: 626 Trader Rating: (1) Feedback Score: 1 reviews	Camshaft Broke while driving...What else needs to be replaced? I am buying a 93 hatch soon, and the owner has been very forthcoming about the issues with the car. He was driving and all of a sudden he heard a loud noise and then engine had no power. He took the valve cover off the engine and the camshaft broke at the cam sprocket. I am going to take a much closer look when I go to buy the car but I was hoping you guys could give me some pointers as to what to look for. I am debating whether I should just replace the complete complete head or try and rebuild the head. The upper valve chain slapped around quite a bit and left marks on the block but it doesn't look too bad. I will get pictures asap of the valve cover removed. Do you think there are problems with the block itself? Will I not know until I completely remove the head? Thanks, Zac

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08-20-2012, 02:42 AM	#3
Bentleyness Leaky Injector Join Date: Mar 2012 Location: chicago area Age: 24 Posts: 136 Trader Rating: (0) Feedback Score: 0 reviews	i wouldn't even buy it really and look for a running one, unless its super cheap then go ahead. cost me like 1000 for complete head work with new parts

08-20-2012, 06:19 AM	#4
Croustibat Zilvia FREAK! Join Date: Aug 2011 Location: France - Toulouse Age: 33 Posts: 1,050 Trader Rating: (0) Feedback Score: 0 reviews	I have a hard time believing the pistons did not smack the valves when it happened . If you get the car, get a new engine, dont even bother with that one. You can disassemble it later and rebuild / sell it ( maybe - most likely you will bin it)

08-20-2012, 06:36 AM	#5
ch1873857 Nissanaholic! Join Date: Sep 2003 Location: Andrews Air Force Base Posts: 1,843 Trader Rating: (0) Feedback Score: 0 reviews	let me try to visualise what i would see happening. pressure from the camshaft to compress the valve springs comes from the chain and ultimately the crank. if the cam snaps. IN THEORY: the front section of the camshaft still driven by the chain would still compress the valve springs and valvetrain like normal. the back section that is not connected would essentially be "free floating" under the cam caps and the springs 'should' take over and the camshaft would snap back to its normal state. So I would see the cam breaking and the valvetrain that is not in time would decompress, clearing the piston. best way to see this would be to open the valve cover up and see at what position the valves are in on the broken section of the cam hopefully this shines some light and gets you thinking so you know what to look for. valve springs move fast obviously. this action wouldve happened just as fast as if it would decompress like normal.

08-20-2012, 10:54 AM	#6
DamnedButDetermined Zilvia Addict Join Date: Oct 2002 Location: Jax, Fl Age: 31 Posts: 626 Trader Rating: (1) Feedback Score: 1 reviews	There are two ways i can envision as to how this engine damage occurred... 1...Best case scenario is that the cam just had a weak spot were the sprocket attaches and the pressure from the upper timing chain cause the sprocket to snap like so... The exhaust cam broke at the sprocket so the entire cam shaft would no longer turn. Then the upper timing chain and broken sprocket released all tension on the lower sprocket so the intake cam would stop turning as well. This means non of the valves were operating at the time of the break so the tension of the springs and hopefully compression of the pistons should have moved all valves to the up position so they would clear the pistons. 2...Worse case scenario is that the oil passages that lubricate the exhaust cam had clogged up and were no longer shooting oil to the cam. After a while the came siezed up and stopped turning. The upper timing chain continued to spin the sprocket which cause the cam to break right at the sprocket. If that is the case then the cam would not have allowed the valves to go to the up position on the exhaust side and we could have some damage to the pistons and valves on the exhaust side. I will be removing the entire head to verify this anyways but i am hoping for the scenario #1 The upper timing chain would have been spinning at a very high rate so I would imagine there has to be some kind of damage to the inside of the front engine cover from the chain slapping, but I don't know if anything down below would have been damaged. Thanks, Zac

08-20-2012, 01:53 PM	#8
Bentleyness Leaky Injector Join Date: Mar 2012 Location: chicago area Age: 24 Posts: 136 Trader Rating: (0) Feedback Score: 0 reviews	if you have time and money buy it for a lower price, and look for a running engine

08-20-2012, 04:47 PM	#9
P-Funk alot Zilvia Addict Join Date: Sep 2009 Location: 909 Age: 27 Posts: 790 Trader Rating: (7) Feedback Score: 7 reviews	ive never see this happen myself but these are interference heads iirc, so there is a chance that the piston slapped a valve but as soon as you pull it apart you will be able to see. regardless that head is probably scrap due to the fact of where it broke, any scarring on the cam journals cannot be repaired as there are no bearings, and from the looks of the break spot there has to be some (hopefully not but i doubt it). well i hope this helps some i am somewhat forced to believe that the bottom end is safe, but expect the worse and hope for the best.

08-20-2012, 05:39 PM	#10
ch1873857 Nissanaholic! Join Date: Sep 2003 Location: Andrews Air Force Base Posts: 1,843 Trader Rating: (0) Feedback Score: 0 reviews	regardless. its an sr. that needs a head. the cam snapped most likely due to oiling issues. i wouldnt touch it with a 10 foot pole

08-20-2012, 06:04 PM	#12
ch1873857 Nissanaholic! Join Date: Sep 2003 Location: Andrews Air Force Base Posts: 1,843 Trader Rating: (0) Feedback Score: 0 reviews	right. it is. bah. who cares. didnt even pay attention. thought i read it was an sr in the OP.

08-20-2012, 08:34 PM	#13
P-Funk alot Zilvia Addict Join Date: Sep 2009 Location: 909 Age: 27 Posts: 790 Trader Rating: (7) Feedback Score: 7 reviews	i dont think its that serious. nissan shit is so easy, and its obvious he is looking to fix it so why not help him out instead telling him ways to not fix his problem. your pre fan boy, what happened to helping people out.

08-20-2012, 11:14 PM	#14
Bentleyness Leaky Injector Join Date: Mar 2012 Location: chicago area Age: 24 Posts: 136 Trader Rating: (0) Feedback Score: 0 reviews	U cant fix the head with damage to the cam housing like that. shops dont even wanna touch it just cuz its a waste of time and money. buy a new head for like 100 bucks and you good to go. you can even use that exhaust cams with the replacement head.

08-21-2012, 03:18 PM	#16
P-Funk alot Zilvia Addict Join Date: Sep 2009 Location: 909 Age: 27 Posts: 790 Trader Rating: (7) Feedback Score: 7 reviews	i am all for changing the head my last comment was more directed at pulling the whole engine, and trust me i know any scaring and the head is scrap metal.