No start...timing good...leak test bad...need help

[flaps10]

You wouldn't pet a cat backwards would you?

There is quite a bit of extra chain, especially the one from the crank to the IMS. The slack is always on the side of the tensioner, while the non slack side keeps perfect (cough) unison. Turning it backwards will pull the slack side tight, and allowing the "extra" chain to now destroy the relationship of the two gears.

If the tensioners were rigid it wouldnt matter much, but they are a combination of a not particularly ballsy spring and a piston trapping oil behind a check valve (I'm simplifying for purpose of the description) These tensioner are already a source of trouble (look up chain rattle on start up)

This pic shows the chain I'm referring to. The zip tie is near the point where the tensioner pushes



Even if turning it backwards wasn't enough to cause valves to touch pistons it would make it very hard to get consistent timing. You would have to spin it the correct direction several times in order to get it to settle in.

Once that zip tie was cut i put sharpie arrows on both ends of the engine to keep me from doing something dumber than usual.

[Jamesp]

Flaps10 Thanks for the picture and reply. I can not answer your question because I don't discuss cats on this forum. :chicken: Interesting point on reversing the tension in the timing chains. Do you think the force into the chain tensioner would increase somewhat if rotated backwards? I don't think that would actually break the tensioner if it did, and I think you are right, the valves would not hit the pistons.

[flaps10]

James I'm sort of winging here but the force generated by the tensioner just has to be enough to take up the slack. When they aren't pumped up with oil you can easily compress them against your bench with one hand.

With a static engine if you turn the crank backwards it would be the valve springs against the tensioner spring (plus quite a bit of chain drag). The cams would hold the IMS still until the slack side was pulled tight.

By comparison, my Triumph motorcycles are inline triples - sort of like half a "real" motor.
One cam chain, one tensioner which is a long but quite beefy spring. 9750 rpm as much as i like (and i do). Off topic but when you take a cane to the triumph triple it sounds similar to a nasty flat six. And stone axe reliable i might add.

[rah rah 986]

Is there anyone who can add to this thread that can shed some light on what might be causing the symptoms that I described in my original post? Your help is needed, and will be appreciated.

[JFP in PA]

Originally Posted by rah rah 986

Is there anyone who can add to this thread that can shed some light on what might be causing the symptoms that I described in my original post? Your help is needed, and will be appreciated.

Assuming the cam timing is where it is supposed to be, take a look at your crank position sensor, they can cause an intermittent non coding no start condition where the engine just spins over.

[flaps10]

Originally Posted by JFP in PA

Assuming the cam timing is where it is supposed to be, take a look at your crank position sensor, they can cause an intermittent non coding no start condition where the engine just spins over.

I was going to suggest the same thing. I would think an OBD2 reader might uncover that, but if you have the engine laying on the ground that is out.

I wonder if there is a way to bench test the sensor. Perhaps a resistance check with a multimeter while you whiz a piece of metal past the end. It's just a Hall sensor isn't it?

If the engine were in the car you could just swap it with a known good one, but again you'll have to reassemble the whole beast before that is an option.

Either way I'm tuned in for the fix. Best wishes to the OP.

edit: just re read JFP's post about it not pulling a code. That puts us back at bench testing or replacing with a known good sensor.

[JFP in PA]

Originally Posted by flaps10

I was going to suggest the same thing. I would think an OBD2 reader might uncover that, but if you have the engine laying on the ground that is out.

I wonder if there is a way to bench test the sensor. Perhaps a resistance check with a multimeter while you whiz a piece of metal past the end. It's just a Hall sensor isn't it?

If the engine were in the car you could just swap it with a known good one, but again you'll have to reassemble the whole beast before that is an option.

Either way I'm tuned in for the fix. Best wishes to the OP.

edit: just re read JFP's post about it not pulling a code. That puts us back at bench testing or replacing with a known good sensor.

The correct way to test a CPS is with an oscilloscope trace to show the pulse generation as the shutter teeth pass the sensor (which is a Hall Effect sensor).



The problem with diagnosing the CPS is that it can fail without throwing a code as the DME just thinks the engine is not turning and shuts off the fuel and ignition. Bench testing flakey units with a multimeter can be misleading; they can look fine, but still not deliver the pulse width required for the car to run properly. They are also heat sensitive, working when cold but failing when hot.