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hutchwilco

Trouble fitting a new timing chain - VQ25DD

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Hi all,

Currently in the middle of replacing the timing chain on my VQ25DD (2002 M35 Stagea).

While I've got the engine at TDC, and the crankshaft mark and intake cam sprocket marks lined up with the old chain markers. I've found that the top stretch of old chain between intake cam sprockets was too spread apart, so that the new chain can't reach the last tooth to make the new chain marks align with the sprockets.

Hopefully the photos make it clear what I mean. Comparing that section of the old and new chains you can see the difference in length of about half a chain link. The two photos of the cam sprockets show one mark lined up, and the other as best I can make it reach - one tooth too short for the sprocket mark.

The best thing I can think to do is stow the tensioner on one or each of the cam chains and that might give me enough play to nudge the chain over that last tooth. 

Any better ideas or if this is ok to do, or even work as I'm hoping?

hoping @scotty nm35 might be able to weigh in...

Also looking for recommendation on the silicone/rtv product to use to reseal the case on when the time comes.

cheers!

 

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This looks fun. Can you document it on here please?

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This might be a silly question (as I don't know these motors at all), but in your chain side-by-side photo, you have 2 pink marks on the top (new?) chain lined up with 2 orange marks on the other chain. I can see the 3rd mark on the top chain is orange.

So whilst all 3 marks on the bottom chain are orange, is there any possibility that you're lining up the wrong marks there?

With the silly question out of the way - I note that the cam gears have slotted holes. Would these be to provide you with the 1/2 a tooth's worth of adjustment to account for chain stretch?

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This looks fun. Can you document it on here please?

Yep plan to, once it’s done. Taking photos along the way.

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This might be a silly question (as I don't know these motors at all), but in your chain side-by-side photo, you have 2 pink marks on the top (new?) chain lined up with 2 orange marks on the other chain. I can see the 3rd mark on the top chain is orange.
So whilst all 3 marks on the bottom chain are orange, is there any possibility that you're lining up the wrong marks there?
With the silly question out of the way - I note that the cam gears have slotted holes. Would these be to provide you with the 1/2 a tooth's worth of adjustment to account for chain stretch?


No such thing as a silly question.
Photo colour may be misleading, the old chain is two pink for cams, one orange for crank. The new chain is the same but old chain has slight colour fade.

As it happens, I’ve resolved the issue by slightly rotating the cams as required using the hexagonal ring. This is actually mentioned in the manual I just found for the 2003 G35 coupe. Just have to be very careful you’re not turning the cams to break a valve.

I also realised each intake and exhaust cam sprocket marks align with subtle bumps formed on the inside of the rear chain case at TDC. This let me determine that the LHS cams were slightly off mark while the RHS were on mark. Made it easy to choose which one to turn to fit the chain and also have some confidence you’re within reasonable margin of safety as you move the cams a degree or two.

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