timing belt, water pump, & cam Q's [Subaru]

[porcupine73]

I finished checking the valve clearances and now have some questions about changing timing belt and water pump:

• 2000 Subaru Outback 2.5L 4cyl gas non-turbo
• Crank is set at #1 TDC

Engine layout is (according to OEM manual):
#3 #4
RH LH
#1 #2
radiator

This may be a dumb question, but, is it bad for the cams to roll backwards? In the process of removing the timing belt, the LH cam rolled backwards about 30 degrees, so I rolled it forward back to where it was.

Then, I had to remove the LH cam pulley to replace the water pump, and in doing that, the cam rolled forward about 30 degrees. When I install the new timing belt, I'll have to get that cam back to its original position, so should I turn it forward about 270 degrees to get back to the original position or is it OK to roll it backard? [I'm guessing forward?]

Now I'm hoping that since crank is at #1 TDC, that cylinders #2 and #4 (LH) are not at TDC, and thus the turning of the LH cam and the corresponding opening/closing of valves won't have a risk of the valves hitting the pistons.

I don't know if this is a valves and pistons non-interference engine; the diagrams in the OEM service manual would maybe seem to indicate the pistons are dished where the valves are located.

Thanks in advance for all your help! Louis

 

[Eddie]

According to Subaru ALL 2.5L engine ARE interference engines. That is why it is strongly recomended to lock the camshaft before removing the belt. You can nick a valve if the cam rotates. In addition; it usually is the idler that is removed/loosened to replace the WP and not the cam gear. If you are using a OEM belt then it has white lines on it. The white lines show where the alignment marks on the cam, belt and engine marks should be. Hope this helps and you have not problems because of the cam rotating. Ed

 

[Eddie]

If you are still in doubt, go to www.endwrench.com for pictures & How To do it.

 

[UncleS2]

There are some good Subaru forums out there- here's one of the best, IMO.

Link: http://www.ultimatesubaru.net/forum/

For more goto Yahoo or Google & search "subaru forum". Good luck.

 

[jamesn]

the white marks on the belt make it pretty easy. i was amazed at how long a subie timing belt really is. you could jump rope with that thing.

 

[edhackett]

#2 will be at TDC on the exhaust stroke, you must roll the cam backward.

Ed

 

[porcupine73]

Thanks for all the help guys. Thanks Eddie for the link to EndWrench; it's very informative. Thanks Stuart for the Subaru forum link - good idea!

EndWrench shows the DOHC version of the 2.5L where the cams should be locked together during timing belt work.

Mine is the SOHC version, so I don't have to worry about the valves hitting each other, but I do believe I have to worry about the valves hitting the pistons, esp. if #2 is indeed at TDC on the exhaust stoke as edhackett mentioned. I didn't see any cautions in the OEM service manual procedure for timing belt replacement about locking the cams on this engine.

Anyway, I guess I'll put it back together and then maybe do a cylinder leakage test on #2 as EndWrench says to see if any valves might be bent or nicked. I told a friend who builds race cars that and he said it might be hard to tell because with the engine cold there might be leakage around the rings. He also said that unless I really plowed the valve into the piston with a lot of force they might have touched but not done any damage.

Thanks again for all the help, Louis