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86-95 Trucks & 4Runners 2nd/3rd gen pickups, and 1st/2nd gen 4Runners with IFS

Timing Jumped?

Old 05-25-2019, 01:16 PM
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Timing Jumped?

Performed a leakdown test.

Cylinder 1, 3, 5, I can hear air coming through the egr tube.
So burnt exhaust valves in all 3 cylinders in line. (Valve cover is off and I can confirm that valves are closed and TDC)

I pull the timing cover off, put cylinder no.1 TDC and the cam (the one with all 3 dead valves) doesnít line up...
(Those yellow dots should both face towards the sky)


My truck had broken down on the highway.

Did the T-Belt jump?
How do I know if the camshaft sprocket just isnít lined up with the camshaft? (Previous owner could have taken off the cam and put it back on incorrectly)

Also there are rubber shavings everywhere and even rubber ďnoodlesĒ, is this normal?

Last edited by SrgntSlaughterr; 05-25-2019 at 01:18 PM.
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Old 05-25-2019, 03:12 PM
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Originally Posted by SrgntSlaughterr View Post
...
How do I know if the camshaft sprocket just isnít lined up with the camshaft? (Previous owner could have taken off the cam and put it back on incorrectly)

Also there are rubber shavings everywhere and even rubber ďnoodlesĒ, is this normal?
Well, the cam timing is definitely off. I would be tempted to ease off the tensioner, get the cam timed correctly, then repeat the leak down test. Your burned valve diagnosis may, or may not, be correct.

1. The camshaft sprocket is lined up on the cam by a "knock pin" that fits into a hole in the camshaft, and engages in a slot in the sprocket. http://web.archive.org/web/201204051...67timingbe.pdf If that pin is missing (or bent enough) there is nothing to hold the sprocket in alignment with the cam. If you rotate the camshaft sprocket to arrow-up, and the valves on #1 are not both closed, you'll need to look into that. (hint: to remove the camshaft sprocket bolt, you can hold the cam with a wrench on a 27mm hex cast into the middle of the cam.)

2. Rubber shavings and noodles are definitely not normal. Your belt is being eaten. More importantly, it looks like your belt is just too narrow. It should span almost, but quite, the width of the sprockets (if you measure the width of your belt, someone might have one lying around to compare it to). You may have the wrong part.

3. You will almost certainly need to replace the belt (I'd try to confirm the burnt valve diagnosis first; that may influence your decision to go forward). If you do, put your hand on the idler pulleys and turn them gently. If you can feel ANYTHING, there is a bearing issue, do replace them. They're not expensive, and often come in sets with the timing belt.
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Old 05-25-2019, 03:32 PM
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x2 on what Scope103 said.

To me, it looks like your timing belt ripped apart on the back side in such a way that it looks like a too narrow of a belt, but was originally correct and shaven down to what you see.

All of those stringy bits of rubber and all that rubber dust you see in the pictures used to be part of the timing belt. Try and see if you can find a reason for the back of the belt to be shaven off like that to prevent a new belt from doing the same.

There is a pretty good chance that the timing belt started failing and got to the point where it jumped time, causing your issues.

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Old 05-25-2019, 07:17 PM
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I'd be looking hard for a mis-aligned pulley somewhere. Something caused the timing belt to drift sideways inboard and chew itself up on the inside edge. A cockeyed pulley would do that - doesn't take much, might not even be obvious to the naked eye. I'd put a straight edge across each pulley face and check to see that the face is parallel to the front of the engine. Also check for wobble on any of the pulleys.
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Old 05-25-2019, 07:27 PM
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old87yota probably has it correct. You could ease the tensioner, re-set the cam timing, and then pull the belt to the forward side of each of the sprockets and idlers. In the process of re-doing your leak-down test, you'll turn the crank shaft a few revolutions. Does the belt stay put, or track back toward the engine? This could be a more sensitive test than a straight edge, but if the belt moves you may still need the straight edge to find where the problem is.
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Old 07-16-2019, 04:50 AM
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Hey guys sorry I havnít replied. It was a broken cam sprocket!!!! The guide ring on the back snapped off.

I ended up having to lap all the valves. Put the passenger head on with a new HG, manifold gasket, and stretch bolts. Then grind valve shims to get the clearance within spec. I have the valve cover back on. Timing is set.

I only forgot one thing...
I never pulled out the exhaust donut between the crossover and manifold and the old one wonít come out.
Iím thinking Iíll just red rtv it and bolt it up. Here are pics, itís a tight fit now since the head is back on.

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