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78 Nissan/Datsun 4-banger need help with timing!!!


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Hi there, new to these forums. I'm a full time college student of Automotive Technology and a classmate and I run a small shop on the side. The other day an older gentleman called us and said he's got a tractor with a 78 Nissan motor out of a 710 (Don't know much about it other then its a 4 cylinder and single over head cam) and said it needed valve seals. Cool. So we replaced the seals meaning we had to remove the cam and cam sprocket. we got it back together and it doesnt want to start, only backfire like its out of time. So we tried re-positioning the the sprocket on the cam dowel and still nothing. This is all new to me as I've been trained to work on newer stuff like Toyotas and Hybrids and the fact that there's not an  OBD2 plug in on this has me lost lol.

Any advice is greatly appreciated, thanks! 

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You can change the valve seals simply by taking the valve cover off and using a piece of rope and a large screwdriver. The cam does not need to come out at all.

 

 

First question. Did you properly block the timing chain tensioner from falling out when you removed the cam sprocket??? If NO then the damage is done.

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You can change the valve seals simply by taking the valve cover off and using a piece of rope and a large screwdriver. The cam does not need to come out at all.

 

 

First question. Did you properly block the timing chain tensioner from falling out when you removed the cam sprocket??? If NO then the damage is done.

 

Yes I took great care to make sure everything was in place and tight before start up. Even marked the cam, chain and sprocket and put it back on as it came off.  But still, nothing. I'm quite out of ideas - that's why I'm here.

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For someone that took the cam out to change the valve seals a simple 'yes' does not convince me you know what you are doing. Before going further I need to know for sure your tensioner is in place.

 

What did you use to block the tensioner? Was it something like this...

 

867D6CB0-62C5-46A8-99EE-4FD8ACC71794-329

 

 

If not properly blocked this is what you have down there...

 

tensionerout.jpg

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Perhaps you're answer is supposed to cover this, but it's not clear from what you said.

 

You have a tool like this that used?

 

31V0G12PR8L.jpg

 

And you jammed that tool in under the cam sprocket, before doing any further disassembly? Like this?

 

867D6CB0-62C5-46A8-99EE-4FD8ACC71794-329

 

FE8A322F-1117-4BBF-B70C-795F52B2F3D0-329

 

If not, the tensioner, down just above the crank sprocket, did this.

 

tensionerout.jpg

 

 

And you have a lot of work to do now.

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I mean I don't have that exact tool, I used a screwdriver handle to wedge it in place. It's all back together at this point and I'm about to turn in for the night, but just theoretically, if the tensioner did shift or move like the picture what's the worst case scenario? Broken tensioner? Or something more along the lines of a bent valve?

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If the tensioner did pop out, and somehow you got the cam chain tight enough, you are going to have to replace some parts, if you run the engine.  If you do not know if you did, you should check it first.   You have to remove the cam chain cover.

 

Having engine diagnose themselves with OBD2 is handy.  But you still have to have basic knowledge on how an engine works.  For example, when faced with a "crank, no start"  do you run to get all sorts of equipment, or do you just listen to the rhythm of the engine, and then smell the exhaust pipe for a raw gas smell?

 

Hint: After cranking, and a no start, if you smell gas, suspect ignition.  Do not smell gas after cranking, suspect the fuel injection. 

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@DanielC thank you, best constructive criticism I've had all night. So pull the accessories, drop the timing cover, inspect everything and replace anything broken, align chain with timing marks, put it all back together and fingers crossed it fires right up? Cool, sounds like I've got some wrenches to turn.  

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And generally speaking a scan tool is normally the last tool I grab for diagnosis. Always start with the sound (Ticks, knocks, etc.) then continue from there. Normally fuel system and then ignition, and then wherever it takes me from there. Lol I had a lady call me the other day and said her car was "acting funny". So I go take a look, first, not a drop of oil in it. And that's when I noticed the rod sticking out of her block lol

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Well you could look down between the chain guides below the cam sprocket with a flashlight. If you dd it right (and you may have) it may be alright. 

 

 

Set to TDC compression stroke on #1. Have the calve cover off and you'll see the cam lobes should be 2 (exhaust) and 10 o'clock on the intake for #1. Make sure you turn the engine only in the clockwise direction when setting TDC. If you overshoot, back up about a 1/4 turn and try again slowly.

 

This will move all the chain slack to the right side and tension the chain on the left. Now the sprocket can be checked for proper timing.

 

Look through the top hole to the back of the sprocket wher there is a small Vee cut. Behind it you will see a small horizontal etch line. The V must be below or slightly to the right of the horizontal line above it, as seen from the front.

 

You should see this. V notch just slightly to the right of the etched line. L16/18 sprockets are set on the #1 hole. L20B are factory set on the #2.

motorLcamtiming.jpg

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You did not say if you had the distributor out during the repair.

 

Also, you do know the distributor turns counter clockwise, right?

 

The first valuable thing you learned in your new profession is to pay attention during disassembly. Never assume something is right before you dig in. Maybe the old farmer had the distributor in 90 degrees out and now you've just set the firing order to factory spec. It aint gonna fire if that's the case.

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The distributor shouldn't have come out (but you never know, right?)

 

The distributor is not affected by removing it. It only fits back in, in one position. The timing would be out if it was removed by removing the timing adjustment screw. If unbolted from the timing cover it will be fine.

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Right, but the OP clearly has made mistakes during this repair so I fall back on my mantra, "assume nothing".

 

Also, these are old engines and I've seen many people with improperly timed distributors in running cars, so they've changed the firing order to accomodate (someone's) mistake. If the OP put the firing order to spec, but the distributor was, at some point, improperly timed (oil pump removed during previous repair?) then assuming that because the firing order on the cap is ok, it should run, is not going to work.

 

On a side note - even though flatcat's initial response was a bit harsh, I totally agree. A good mechanic won't rely solely on a reading from an OBDII diagnostic port. You have to pay attention and verify. Remember the old days when a repair manual showed you how to rebush an alternator or set the clearance on an oil pump? Well it seems they don't teach any of those things in "mechanic's school" now days. That's a shame.

 

Back to the cam timing. At this piont, the only way to be sure it's right is going to be starting from scratch. Find TDC, verify it, make sure it's TDC for #1, not #4. Set the cam and try again. If that fails, and there is a possibility that the cam timing was set incorrectly at some point during this repair, then it may be time to do some checking to see if a valve got bent.

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Yes, I am assuming it was running before, so it will still run if the distributor was removed and replaced.

 

I guess anything is possible when the cam is removed. Why it was removed to replace the valve seals is explained only by inexperience

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Things are going well. All the accessories are off and most of the timing cover bolts are out. No i did not remove the distributor and yes it ran before. Quick question, does the distributor and/or oil pan have to come off before the cover? This thing is covered in about 25 years of grass clippings and oil so its hard for me to tell what exactly has to come off first.

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