Mechanical Timing Issues 5VZ-FE

I have a non-running 1996 Tacoma with 5VZ-FE (280k). Compression test showing low compression on all cylinders (75psi average dry). I suspect the head gasket is ok (no coolant/oil mixing). Because compression was low on multiple cylinders, I figured the timing belt had jumped. However, I verified timing marks on both cam sprockets and crankshaft (notch on crank pulley at zero). To verify mechanical top dead center, I used a rod (down the spark plug hole) to verify cylinder 1 was at top of compression stroke when timing marks were in alignment. I discovered when cylinder 1 was @ TDC the crank shaft timing marks were off about 20-25 degrees on the crank pulley.

If cylinder 1 is @ TDC, shouldn’t the timing marks all line up? My next step is to disassemble the front of the motor and pull the crank shaft pulley to verify the woodruff key is still there. Before I do that, I wanted to ask the question here to see if that’s even possible or likely. Has anyone had issues with the crankshaft woodruff key coming out? In my case, it would explain the mechanical timing being off and low compression. Any help would be greatly appreciated. Thanks,

 

I don't think a woodruff key can come out unless it is shattered into pieces. I don't have anything else to add other than I think you might be on to something with the timing mark -- I would assume that it should align with 0 at TDC.

 

The only way the crank pulley would spin would be if the woodruff key sheered which I highly doubt. Much more likely the belt slipped a couple teeth.

 

The serpentine part of the harmonic balancer has slipped on the rubber hub. You need to replace the harmonic balancer.

 

I don't think the harmonic balancer has slipped or the timing belt jumped. If I rotate the balancer so the timing mark is at zero, the timing marks on the cam sprockets are also in alignment. However, the #1 piston is not at TDC. What else would cause this?

 

Your engine was running well at some point before this happened? Was is it a sudden change in performance?

 

All that means is that the correlation between the camshafts and the harmonic balancer is correct. Everything is timed off of #1 piston/crank on TDC. I suggest putting #1 on TDC using your wooden dowel and retiming the camshafts then roll it over by hand a few revolutions then retest your compression, Ill bet that you will recover up your lost compression. This is a non interfearance motor.

 

I'm not quite following this.

If the crankshaft timing mark is not lining up with zero when #1 is at TDC, then something is off with the harmonic balancer. It's connected directly to the crankshaft, which is connected directly to the pistons.

What's the history of this motor?

 

Thge inner portion of the harmonic balancer is keyed to the crankshaft and cannot shift unless the woodruff key is missing or sheared, very, very rare. The outer part of the balancer is pressed onto the inner part with a rubber ring in between. The outer part has slipped.

 

The engine started losing power over a span of a few months. It ran smoothly with no codes, no smoke, no overheating... just extremely low on power. It progressively got worse until it would no longer run. Service records show the timing belt and front crank seal were replaced a few years ago.... so the crank pulley + lower timing belt sprocket have been off the truck.

I think the only explanation is a failed woodruff key. The harmonic balancer and cam sprockets are still in alignment with all timing marks... However, cylinder one is not at TDC (20-25 degrees off) when timing marks are all in alignment. The only thing that would cause this condition is slipping between crank pulley/sprocket and the actual crank shaft. Searching on this site, failed woodruff keys on the 3.4L motor are not a thing.

 

I would say "at this point" it looks like the key.
A forum search might not pick it up but "shearing" the key is not uncommon. It happens when the HB bolt is not tight enough or has loosened. The key does not extend very far into the HB hub.

 

One more.
The above is assuming your TDC locating operation is accurate.
The outer ring/pulley can "move" and sometimes come off.

 

Lets hope that it isnt the key or the groove or the lower sprocket. I have seen where the key gets pushed out the back when the lower sprocket goes on and if an impact was used to tighten the HB bolt you would never know. A new HB bolt is cheap insurance.

 

Appreciate the information. Next step is to verify if the woodruff key is still there and intact. It's very possible the HB nut was not torqued properly during the previous timing belt replacement. I'll dig in next weekend and report back.

One more question. With the crankshaft off 20-25 degrees, would that be enough to explain the low compression and no-start condition? Thanks

 

To answer your question... maybe. I think there are multiple issues. If the HB has slipped and the prior tech timed the timing belt based on a slipped HB it would have run poorly all along but you say she had gradually degraded performance so I think that that isnt the issue. If the crank sprocket has moved for some reason that could explain the issues but I think you would have tripped a code or 2. My fear is that you go to all the trouble and expense to put this right and she still doesnt start or run right.

 

I don't buy the timing is off. To OP I don't doubt your skills but I doubt you would have bad timing and no codes. Starting from the beginning. Are all the cylinders low on compression or just some?

 

yea but how I don't get. The balancer balances, no timing takes place because of it's position. Only the measurement for co witnessing by timing light. Which by the way, do you have one?

 

that is LOW compression!
have you had the leak-down testing to verify it is NOT losing compression that way?
i am no expert... just learning as it goes lol ... the 'trusted' expert highly-paid pro's out there seem to be no more, unfortunately
my rig is/has been acting strangely also after hitting 280k in the rockies and i am just a bit concerned about it all and what needs to be checked + done to make 'er chipper again
could be engine related, could be fuel pump related, could be something not even on the radar...

...keenly anticipating any follow-up on this condition, brober34

 

Yeah, the only thing (so far) that would explain the slow degradation in performance is if the woodruff key sheared and the crank sprocket has slowly shifted along with the HB. The HB outer ring shifting wouldn't change performance unless it was timed with it shifted, which doesn't make much sense since they should be using marks on the sprocket. And that would not explain slow degradation.

Interesting mystery to follow along with . . .

 

Quick Update: I pulled the harmonic balancer to examine the crankshaft timing belt sprocket. It appears the timing gear is gouged out on either side of the woodruff key…. Indicating there had been movement between the crankshaft and the timing sprocket. The crankshaft bolt was not very tight (I suspect it was not torqued properly previously). Mechanical timing being off this much was likely causing low power and low compression. Has this happed to anyone else?

Next step is to pull the timing belt and replace the crank sprocket and woodruff key. Fingers crossed the crankshaft is not damaged. Appreciate all the help.