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Do not remove the belt yet..
The unique thing about this engine came to me earlier today. On almost every engine crank to cam speed is only controlled by the ratio of the cam and crank pulley sizes.
On this Isuzu engine the crank to cam speed is controlled the timing belt pulley ratio PLUS the ratio of the ratio of the intermediate timing gears that are located in the cylinder heads.
That 1/2 tooth discrepancy you see on the belt timing mark is due to a problem located in the other 1/2 of the timing system, phaser, incorrect timing belt or improper install.
So do not take off the timing belt until the other 1/2 of the timing system is inspected for abnormal ware and proper installation.
Pop off both valve covers and inspect the timing components. Verify that thier timing marks are aligned, the gears are fee of damage. You will need to rotate the engine 180° forward and back to see everything...look closely. Inspect the hydrolic timing belt tensioner (HBT) & phaser for proper alignment
When you performed the stethoscope test, what area was the sound originating from...was it at the top front area of the valve covers?
The sound to me seemed strongest on the driver side valve cover towards the back, but it is just so loud it very difficult to be sure. This is the same side that showed the 170 psi and same side where the cam doesn’t align to the timing mark. I haven’t counted the teeth on the belt yet.
So been busy at work and got a chance today to try and set the cam pulley on their respective marks. I started by aligning the passenger side cam. It sprung to the 12 o’clock no problem. I then tried to align the driver side cam to the 9 ‘o’clock to rotate 90 degrees to the 12’ o clock…..but it only aligned to 10 ‘o’clock not 9 ‘o’clock. I realized that the crank was not completely aligned to its mark. So I aligned it. However when I traded to rotate the driver side cam again it sprung once but not further! Too tight! When I move the crankshaft about 90 degrees the cams free up. What sequence of events did I do incorrectly.
Where did you come with the procedure to time a 3.5L GDI engine?
The 3.5L GDI does not have the same camshaft drive setup as a non GDI 3.5L engine so it is likely the GDI engine uses a different procedure.
I gather that much that the GDI is an obscure engine platform. No real leads really aside from some of the recommended steps here (highly appreciated).
The non GDI 3.5L has a 26 tooth Crankshaft timing belt sprocket and a 39 tooth Camshaft timing belt sprocket which produces a 1.5 to 1 ratio. The Intake Camshaft has a 40 tooth drive gear attached and the Exhaust Camshaft has a 40 tooth drive gear attached. The Camshaft timing belt sprocket drives a 30 tooth idler gear that in turn drives the camshaft gears, 40/30 = 1.33333 to 1. Therefore, 1.5 x 1.33333 = 2 which makes the overall ratio 2 to 1 as expected. Timing this engine is tricky because the procedure for the LH bank is not the same as the RH bank and cam sprocket to crank sprocket ratio is 1.5 to 1 as opposed to 2 to 1.
To time this engine you have to rotate the RH Camshaft sprocket clockwise several times to get to a point where the Camshafts spring to a neutral position and the timing mark on the head cover aligns with the alignment mark on the sprocket.
To time the LH (driver side) you have to rotate the Camshaft sprocket clockwise several times to get to a point where the Camshafts spring to a neutral position and the sprocket alignment mark matches a reference mark located at the 10 0clock position. Once the sprocket alignment mark matches the reference mark with the camshafts in the neutral position the LH sprocket needs to be rotated clockwise about 90 degrees until the sprocket alignment mark matches the alignment mark on the head cover.
Once the cams are in alignment and #2 cylinder is at TDC the belt can be installed.
I have never actually worked on a 3.5L GDI engine but I am reasonably sure the 3.5L GDI engine has a 26 tooth Crankshaft timing belt sprocket and a 52 Tooth Camshaft timing belt sprocket which produces a 2 to 1 ratio. The Camshaft timing belt sprocket is attached to the VVT phaser and the phaser drives the Intake Camshaft. There is a gear on the Intake Camshaft that drives a similar size gear on the Exhaust Camshaft, so the phaser is capable of changing the angle of both the Intake and Exhaust Camshafts at the same time. Since the timing belt sprocket ratio is 2 to 1, timing the GDI engine looks to be much simpler than the non GDI engine. It appears that all you need to do is line up the Crankshaft and Crankshaft timing marks and install the belt with #2 at TDC but I don't know for sure.
Thank you for the detailed response. I can tell you that the timing marks did not align previously. I then took off the timing belt. I aligned the marks as you described above. The tech that installed it incorrectly kept the old belt in the trunk which he apparently marked prior to taking off. When I lined it up and compared I confirmed that they both are 219 tooth belts and used the marks on the old belt to reference the new belt marks. It was obvious that the tech installed the belt in the wrong direction as I was unsuccessful to align. When I flipped the belt I was able to align all marks! I then installed the tensioner and after multiple rotations at the crank, all timing marks kept aligning spot on. I then proceeded to turn it on. The noise is gone!
My question now is how can I confirm that it is timed right? Is it enough that the cams and crank all keep aligning to their respective marks?
219 is the correct number of teeth for a 3.5L GDI engine timing belt so if the marks stay aligned after several rotations of the Crankshaft I think you have fixed the problem.
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