Timing Question

[jforand]

I realize this is a bit of an amateur question, but I did not see anything in my google search of the forum and I also did not really see this mentioned in the manual, both were surprising.

Do the timing belt marks line back up as they are positioned in the install? Has anyone experienced or noticed this?

Installing the timing belt on a DOHC EJ2.5.

I think every one knows you put the engine at TDC and then you line up the marks on the sprockets such that the single marks line up with the cover marks and the double marks line up on the inside edges of the intake and exhaust sprockets. When installing the belt they have you put the dotted line centered over the crank pulley and then all of the marks align with each cover mark (top of intake pulley and side of the exhaust pulley).

OK

So, with all happy it makes sense to turn the engine over by hand and see what happens. Not sure why but after a couple revolutions without any issues I thought I would send the bent around for a full revolution and see what happens. The timing belt marks do not return to the initial install position, which surprised me. The marks on the pulleys match back up with every second revolution and are perfectly opposed every other revolution between those just mentioned. So mechanically I think the timing is perfect and the belt simply 'walks' around the pulleys such that eventually every cog on the belt will hit every cog on the sprockets. This would be very similar to the way certain rear-end gears will have the same teeth always mesh and other ratios migrate so that every tooth touches every other tooth.

[NevaLift2Shift]

I realize this is a bit of an amateur question, but I did not see anything in my google search of the forum and I also did not really see this mentioned in the manual, both were surprising.

Do the timing belt marks line back up as they are positioned in the install? Has anyone experienced or noticed this?

Installing the timing belt on a DOHC EJ2.5.

I think every one knows you put the engine at TDC and then you line up the marks on the sprockets such that the single marks line up with the cover marks and the double marks line up on the inside edges of the intake and exhaust sprockets. When installing the belt they have you put the dotted line centered over the crank pulley and then all of the marks align with each cover mark (top of intake pulley and side of the exhaust pulley).

OK

So, with all happy it makes sense to turn the engine over by hand and see what happens. Not sure why but after a couple revolutions without any issues I thought I would send the bent around for a full revolution and see what happens. The timing belt marks do not return to the initial install position, which surprised me. The marks on the pulleys match back up with every second revolution and are perfectly opposed every other revolution between those just mentioned. So mechanically I think the timing is perfect and the belt simply 'walks' around the pulleys such that eventually every cog on the belt will hit every cog on the sprockets. This would be very similar to the way certain rear-end gears will have the same teeth always mesh and other ratios migrate so that every tooth touches every other tooth.


It's normal that the marks on the belt won't line up after a revolutions, if there are 250 teeth on the belt, it would probably take 250 revolutions to make the marks on the belt match the gears. The marks on the cam gears and crank gear are the most important. If you want to verify, find a copy of the original service manual and there is a tooth count diagram to verify everything after you have turned it. Set your marks on the gears, then count the teeth, if they are correct, you should be good to go.

I attached the timing marks from the EJ205 manual I have.

130447

[jforand]

Most appreciated. yes, I have that pic in the manual. I believe that you are spot on. I did notice that the belt's dotted line was one tooth behind the TDC mark after a single full belt (not the engine crank) revolution. So, as you say one tooth/revolution would take the full number of belt teeth converted to belt revolutions to get the belt back to home. The important thing is my crank and cams line up every second spin of the crank, a perfect 2/1 relationship as it should be on a four cycle engine.

[NevaLift2Shift]

Most appreciated. yes, I have that pic in the manual. I believe that you are spot on. I did notice that the belt's dotted line was one tooth behind the TDC mark after a single full belt (not the engine crank) revolution. So, as you say one tooth/revolution would take the full number of belt teeth converted to belt revolutions to get the belt back to home. The important thing is my crank and cams line up every second spin of the crank, a perfect 2/1 relationship as it should be on a four cycle engine.

Yep, you got it. Better to be safe than sorry on these engines.

[flynntuna]

Here's a video that helps explain timing marks
https://youtu.be/0Hss0kCj3s4