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Did you mean the valves hit the tops of the pistons ? if so this is usually caused buy a t/belt breaking while driving or sometimes you may loss a few teeth on the t/belt and it can skip on the t/gears throwing off the timing enough to let the pistons hit the valves( if the belt tensioner failed it could allow the belt to slip around on the t/gears ) check the t/belt condition.
yes i meant pistons. what about over reving the motor would that cause time to be off?timing chain looks good and all teeth look good. so prob the tensioner?
Ok , this motor has a timing chain ( not a t/belt ) correct ? a tensioner prob could cause a chain skip. allowing the timing to be off enough for the valves to be hit. over reving can cause a condition known as valve float where the valves open farther then normal and the pistons hit them ( Ive done this before with one of my muscle cars ) since the head is off have you inspected for bent valves ? I would do a valve job since the head is off. also replace all components involved in the timing chain system. how do the tops of the pistons look ? hopefully no holes in them. I recently drop an exhaust valve (# 1 cyl ) at freeway speeds in my 69 chevelle. that little piece of metal tore that motor to pieces.
yes a chain.. the head is brand new from the machine shop. I am trying to get this car running so i can sell. it is a manual and my bro in law didnt know how to drive it and it stopped running on him. I just changed the head from the old one due to th old valves being burnt has 190000 on it. any sugg????
Let me make sure I am reading the scenario correctly… You replaced the old head with a fresh one. timing set up proper and car running fine. someone else drove the car and it came back non operational. you pulled the fresh head and found the pistons had smacked the valves. if this is the case then you will need to inspect the new head for bent valves and address that. I would definently change out all the components of the t/chain assembly when you put it back together ( obviously making sure all t/makes are lined up-cam/crank ) 190.000 miles is bound to wear out the t/chain components.
There really is only one thing that can cause that and that is the engine not being mechanically in time, if you just did work on it then that’s where you start as that would be the most likely cause of the problem. BTW as for ‘over revving’ the fuel is cut to the engine by the computer once it gets to the redline to help preserve the engine. Good luck.
the motor seems to not have spark. what could cause spark plugs to be burnt up after only a few days? would the fuel also be cut off on a manual trans if it was slammed into 4th gear going 80mph. i am thinking maybe the motor was flooded with fuel and was knocked out of time some how and maybe the spark plugs burnt up. I there any way to check for bent valve rods with out pulling the head apart….
Some pistons are cast with four imprints making it look like marks from the pistons hitting the valves. Not sure if the Nissan engines are like this.
More importantly, are the valves bent?
Ok… based on your newest post I will assume that the ” new head ” is still on the motor. if the t/chain is still attached as when the car was driving I would manually rotate the engine to line up the t/marks and see if they are correct. it they are not then you probably have some bent valves. next you can pull the valve cover and rotate the engine to close both valves on a cylinder ( make sure both valves are completely closed ) then you need to hook up a air line to the spark plug hole ( I usually use the quick disconnect line from my compression guage for this) attach the air line and listen for any air leaking from that cylinder. you may need to pull the exhaust manifold ( which I believe is pretty easy on these ) but any bent valves and you should have air escaping. a compression check of each cylinder should also give you answers. otherwise the head will probably need to come off.
In the case of your car several things could have happened…..
The t/chain could have broke… I believe you said it was intact
the t/chain could be stretched from age .. possibly jumping on the t/gears
there could be a t/chain tensioner that failed causing the chain to become loose and jumping on the gears9 times out of 10 when you do a lot of work like that it’s something that you may have inadvertently done. I strongly suggest you go back over the work that you did just to make sure everything is where it is suppose to be, plugged in, and assembled correctly.
Engines burn pretty clean these days, but in the distant past, I’ve had piston crown deposits from fuel and oil ash that accumulated to the point that the valves were hitting and packing the deposits. These were generally fully worn out engines that I pushed beyond any expected service life, and yours might qualify for this description.
Valves hitting pistons means a timing issue. If the car has a solid metal chain and not a rubber belt the chances of it ever going out of time as a result of driving habits are so low it’s probably not measurable. In order for a car with a metal timing chain to slip out of time would require a significant amount of teeth to be missing from the gear so that there would be a point where the chain for a brief moment had no teeth in contact with it.
My gut diagnosis is the timing was not set correctly when the head was installed.
Now there are 4 other possibilities.
1. You were sold the wrong head. Maybe you got a head for a 1.8 and installed it on a 1.6.
2. The head guy installed the wrong valves, or lifters causing them to stick out too much.
3. The head guy put the wrong cam in. The lobes are oversized lifting the valves out too far.
4. Valve float: My first car was an 87 pontiac sunbird with a OHC engine. One day the engine lost all power and could barely get to 20MPH.I took it to the stealer and he suspected valves were not staying in contact with the cam lobes as a result of worn engine or revving too much. (Hey I was 16!) At the time I didn’t think about it but valve float sounds like that’s what was happening in my case.
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