Valve timing conundrum
12-17-2015, 04:18 PM
#1
Rennlist Member
Thread Starter
Valve timing conundrum
Ok, working on Dougs951S's '86 NA just now, we have an issue that's stumping us. Posting on his behalf cause at the moment he's looking stuff up. Sorry for long post but there are important details along the way.
We did the timing belt and balance shaft belt a couple month ago and it ran fine, it was all lined up, he put a couple thousand miles on it between now and then. But it came apart recently for a water pump job (See the other threads he made).
This morning the belts went back on, and there's interference between a valve(s) and a piston(s) unknown exactly which one, just that spinning it over by hand causes resistance, all plugs are out so we know it's not compression.
At one point we lost the alignment because the crank was spun with the belt loose and it skipped teeth, so we had to manually align the crank and cam back to TDC using various marks. Along the way there was interference...we were using a ratchet to spin the crank and would stop when there was resistance and fiddle with the cam until it was out of the way. Within a few minutes it was all back at TDC and we put the belt on, tensioned it, and then it got weird....
We spun the crank over by hand probably 5-10 times, no issues. No interference, plugs were out and we heard the airflow like you would expect. Then.... stop. Hit interference??? Yep, put the cam at TDC first based on it's mark, and the crank was more or less also at TDC. I say "more or less" because if the error on the cam TDC mark was +/- 2 degrees, that's an error of +/- 4 degrees for the cam which accounted for why it was off. But it certainly wasn't off by an entire tooth. We pulled the crank gears off the front of the engine and the woodruff key was fine, just to ensure that the TB drive gear hadn't moved relative to the crank itself.
So...does that pretty much mean that a valve got bent during all this? It baffles me that a ratchet on the crank could cause that, rotation very slowly. Either that, or a valve is stuck in a guide, or a valve spring is broken? We just want to hear what you guys think before the cam tower or head comes off.
We did the timing belt and balance shaft belt a couple month ago and it ran fine, it was all lined up, he put a couple thousand miles on it between now and then. But it came apart recently for a water pump job (See the other threads he made).
This morning the belts went back on, and there's interference between a valve(s) and a piston(s) unknown exactly which one, just that spinning it over by hand causes resistance, all plugs are out so we know it's not compression.
At one point we lost the alignment because the crank was spun with the belt loose and it skipped teeth, so we had to manually align the crank and cam back to TDC using various marks. Along the way there was interference...we were using a ratchet to spin the crank and would stop when there was resistance and fiddle with the cam until it was out of the way. Within a few minutes it was all back at TDC and we put the belt on, tensioned it, and then it got weird....
We spun the crank over by hand probably 5-10 times, no issues. No interference, plugs were out and we heard the airflow like you would expect. Then.... stop. Hit interference??? Yep, put the cam at TDC first based on it's mark, and the crank was more or less also at TDC. I say "more or less" because if the error on the cam TDC mark was +/- 2 degrees, that's an error of +/- 4 degrees for the cam which accounted for why it was off. But it certainly wasn't off by an entire tooth. We pulled the crank gears off the front of the engine and the woodruff key was fine, just to ensure that the TB drive gear hadn't moved relative to the crank itself.
So...does that pretty much mean that a valve got bent during all this? It baffles me that a ratchet on the crank could cause that, rotation very slowly. Either that, or a valve is stuck in a guide, or a valve spring is broken? We just want to hear what you guys think before the cam tower or head comes off.
12-17-2015, 10:08 PM
#4
Rennlist Member
Remember..a 4 stroke engine has to rotate 720 degrees. I have another engine that all the marks lined up in, but the timing is off by 180 degrees, because someone rotated the crank 360 degrees during the building process...So what I'm saying here is, that even with all the marks lined up, you can still be off...disconnecting the cam belt won't get it, because it is out of phase with the crank. you'll have to pull the cam tower, since you can't just pull the cam cover, and back off all the valves until they are are all seated like on a regular engine, and then start over.
12-17-2015, 10:27 PM
#5
Rennlist Member
On a lot of 4 stroke OHC engines, the #1 cylinder cam position must be in "Bunny Ears" with both valves closed, the #1 piston on TDC (dowel method) and all marks lined up..Bunny ears is where both cam lobes, I&E, are pointed up and off the lifter. Then you can still be 360 off, because the crank might be on the exhaust stroke instead of the intake stroke. This will cause the engine not to start, because the wires are 180 degrees out of phase. Once that has been done/ corrected, the engine will operate normally..until the cam is disconnected from the valve train, the crank rotated another 360 degrees and all is put back together. And this can all happen with all the marks lined up properly. The only key to this is even with the distributor rotor in the right spot, on #1, you can still be 180 off on the wires. Hello, Is VAN listening? Maybe he can shed some light on this too...
12-17-2015, 10:28 PM
#6
Drifting
If the timing marks are lined up then maybe sticking valve. Maybe a price of debree made it way into the spark plug whole when you were turning it over. Broken camshaft keyway? Broken camshaft?
12-17-2015, 10:38 PM
#7
Drifting
On a lot of 4 stroke OHC engines, the #1 cylinder cam position must be in "Bunny Ears" with both valves closed, the #1 piston on TDC (dowel method) and all marks lined up..Bunny ears is where both cam lobes, I&E, are pointed up and off the lifter. Then you can still be 360 off, because the crank might be on the exhaust stroke instead of the intake stroke. This will cause the engine not to start, because the wires are 180 degrees out of phase. Once that has been done/ corrected, the engine will operate normally..until the cam is disconnected from the valve train, the crank rotated another 360 degrees and all is put back together. And this can all happen with all the marks lined up properly. The only key to this is even with the distributor rotor in the right spot, on #1, you can still be 180 off on the wires. Hello, Is VAN listening? Maybe he can shed some light on this too...
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12-17-2015, 11:12 PM
#8
Rennlist Member
Dear Humboldt..Man I really hope that you are right on this one, but my Effe'd up Nissan only has one mark on the crank and the cam..and it's still 180 off on the timing. and the distributor only fits on one way (indexed)...Color me stupid? When we put the P-car engine back together, we religiously followed the book, and all the marks were lined up. Going to have a better (more experienced) guy look it over prior to the install anyway. It seems all right..no interference on several ratchet turns of 720 degrees or better...fingers crossed...
12-17-2015, 11:32 PM
#9
Three Wheelin'
Wait, before you go further. Let's make sure you have everything lined up. No way you could have mistakenly damaged internals by hand cranking -- it takes more than that, rest assured. You (odonnell) and Doug are experienced minds so let's work through this and we'll figure it out efficiently.
Can you confirm everything is lining up at TDC: 1) front engine timing gears lining up with timing belt cover and front end indicators. 2) flywheel notch under car is lining up in the port hole. 3) a wood dowel (or socket extension) is showing TDC inside #1 cylinder spark plug. 4) There's one more, I think. Oh yeah, the view port you can see from left side of car, behind intake. I personally haven't had luck with this one. I didn't see any mark despite knowing it was at TDC.
If everything is showing TDC, it should be fine. Line it up and start her up, you can't go wrong. ...Otherwise maybe something is over my head?
Like I said it takes more than a hand-crank to destroy an engine -- you would know it because it takes at least as much torque as a common bolt, which is higher than you torqued I am almost sure. I doubt you bent anything.
Can you confirm everything is lining up at TDC: 1) front engine timing gears lining up with timing belt cover and front end indicators. 2) flywheel notch under car is lining up in the port hole. 3) a wood dowel (or socket extension) is showing TDC inside #1 cylinder spark plug. 4) There's one more, I think. Oh yeah, the view port you can see from left side of car, behind intake. I personally haven't had luck with this one. I didn't see any mark despite knowing it was at TDC.
If everything is showing TDC, it should be fine. Line it up and start her up, you can't go wrong. ...Otherwise maybe something is over my head?
Like I said it takes more than a hand-crank to destroy an engine -- you would know it because it takes at least as much torque as a common bolt, which is higher than you torqued I am almost sure. I doubt you bent anything.
12-17-2015, 11:36 PM
#10
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Can anyone please shed some light on this? How on earth could we have rotated the motor through 7 to 10 full turns of the crank ( so, several full cycles on all cylinders) and then magically hit valve interference when the timing didnt skip teeth and neither the cam not the crank slipped it's key? I'm absolutely baffled and honestly really pissed off as I've put a ton of money and time into this NA recently and it's been one setback after another. Somebody please help me.
Right now we are in the process of taking the cam tower off to check for a broken valve spring or something or that nature. Running into trouble there as well with a stripped plug that refuses to budge on the cam tower and the 5 bolts inside the cam tower that also refuse to break free (not stripped yet).
As far as everything being lined up properly, I can confirm the cam was definitely at TDC. The crank was slightly off, but both Michael and I agree that the timing couldnt have been off by more than 1 tooth and I know that it takes an error of 3 or 4 teeth to actually hit interference.
Again what I'm having trouble swallowing here is we spun the engine over MANY times with absolutely nothing slipping before magically we had valves touching pistons.
Right now we are in the process of taking the cam tower off to check for a broken valve spring or something or that nature. Running into trouble there as well with a stripped plug that refuses to budge on the cam tower and the 5 bolts inside the cam tower that also refuse to break free (not stripped yet).
As far as everything being lined up properly, I can confirm the cam was definitely at TDC. The crank was slightly off, but both Michael and I agree that the timing couldnt have been off by more than 1 tooth and I know that it takes an error of 3 or 4 teeth to actually hit interference.
Again what I'm having trouble swallowing here is we spun the engine over MANY times with absolutely nothing slipping before magically we had valves touching pistons.
12-17-2015, 11:43 PM
#11
Three Wheelin'
You might be baffled but I would be very, very surprised if this isn't correctable.
Unless something would have fallen inside to jam things up.
Edit - that's correctable too :/
Unless something would have fallen inside to jam things up.
Edit - that's correctable too :/
Last edited by bonus12; 12-18-2015 at 12:00 AM.
12-17-2015, 11:46 PM
#12
Drifting
Thinking about it...even if the marks are 180 on the cam to the crankshaft and the #1 is still at TDC then it's still in time. A Honda can mess up because I'm thinking of a DOHC and having one cam 180 off from the other. My bad. I don't see how it can be off if the marks line up either way. The piston doesn't care if it's an intake stroke or a power stroke, it just goes up and down.
12-17-2015, 11:53 PM
#15
Drifting
Take the back camshaft cover off and turn the engine over, or back and forth. Make sure the camshaft isn't broken buy verifying it's rotating at the rear.