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Old 10-08-2013, 04:36 PM   #1
Heater Guy
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Default Zeroing in cam timing with timing belt

When I set the timing on my 2.5 L Subaru engine I can never get the timing marks on the belt to line up perfectly with the plastic cover marks.

On my chain drive Porsche engines, I can adjust the the cams to get them dead on by using the adjustment on the cam sprocket and a dial indicator on a valve. When the degree on the crank is at the set point and I have 1mm valve lift, I lock in the cam sprocket.

Using the plastic housing as a reference point doesn't appear the most exact way to make the adjustment.

I have seen the eccentric adjusters that can adjust the slack in the belt to make the timing adjustment closer but, if the eccentric should slip, there goes the engine. With the Porsche system, there is a series of off centered holes for a pin that when lined up will keep the adjustment from total failure if the locking nut should slip.

Is there a better way to precisely adjust the cams in the Subaru engine? Are all timing belts the same length? How do you compensate for a decked block?
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Old 10-08-2013, 06:08 PM   #2
Concillian
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All timing belts are the same length, and for a reason. As I recall, one revolution of the belt will result in all sprockets being one tooth different from where it started. In the event a sprocket tooth has a shape problem or deris or such, issues from abrasion will be mitigated by spreading over as much of the belt as possible.

There are adjustable centerline cam gears, but not any that I'm aware of that also utilize AVCS. Eccentrics is how it can be adjusted for decking, since it affects both intake and exhaust.

If you are competant in tuning, you could use your AVCS maps to adjust centerline, but you'd need to degree beforehand to know how much you needed. Also keeping in mind that AVCS maps are in crank degrees (double cam degrees). For example, if you needed to retard 3 cam degrees, you'd run one tooth retarded (15 crank degrees --> 7.5 cam degrees), then advance AVCS 9 degrees in all cells and tune from there. This potentially limits your max advance, since the stock USDM ECUs seem to limit at 25 degrees. Exhaust is opposite direction in AVCS maps if you have an 08+STi... you could use static adjustable cam gears for single AVCS cars.

HOWEVER, timing marks don't always line up on a freshly installed belt due to tensioner not settled yet. Try (after releasing the tensioner) turning the crank CCW 90, then CW 180, then CCW 90 to get back to the marks. That may bring the marks closer (unless it's decked).

Last edited by Concillian; 10-08-2013 at 06:24 PM.
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Old 10-08-2013, 06:48 PM   #3
Heater Guy
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I use a Stinger ECU which doesn't use the AVCS. I just blew a head gasket and getting ready to install sleeves which will hold the 26 psi boost. But, in the mean time I thought I would see if there was a better way of timing the cams other than using the grooves in the plastic housing. I guess for now that is my best choice (close enough is ok). Is there anyone that supplies replacements for the AVCS units? Like to get rid of the weight.
I am afraid that eccentrics can slip.
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Old 10-09-2013, 05:05 PM   #4
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If not using AVCS, then you can get adjustable cam gears, I think Brian Crower and Tomei make some. The centerline at 0 IS different from the AVCS sprocket (more advanced on intake at the very least.) So take some measurements of your current setup prior to swapping if you go this route.

You need to plug your AVCS oiling holes in the cams if you do this. Preferrably by welding, but some have tapped and capped.

Dropping AVCS also costs you ~4-700 RPM spool, but you're probably already aware of that.

Last edited by Concillian; 10-09-2013 at 05:16 PM.
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Old 10-09-2013, 10:37 PM   #5
Leafy
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If your timing marks arent at the same tooth for all the cams you haven't aligned the belt correctly. Sometimes the mark isnt printed exactly on the right spot with the cog on the belt to be 100% perfect in line.
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Old 10-10-2013, 12:21 AM   #6
Heater Guy
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Using the Subaru shop manual, I always count the teeth and spaces on the belt to be sure the marks are correct. Thanks anyway for the tip.
Concillian,
This is a 1,900 lb road race car. 25psi boost, 550 WHP, 476 ft-lbs torque. For the AVCS, we leave the oil pressure connected but no electrical connections. I checked Brian Crower and Tomei's webpages but, did not see any parts to replace the AVCS sprockets. I will call them. Thanks for the tip.
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Old 10-11-2013, 06:23 PM   #7
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Adjustable cam gears are NON-AVCS sprockets, they're listed on the BC site in the EJ205 section, but are applicable to all EJ engines if you delete AVCS.

To run NON-AVCS cam gears you need to plug the oiling holes at the end of the cam.
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Old 10-12-2013, 02:03 PM   #8
Bullit62
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Old 10-13-2013, 02:32 PM   #9
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http://www.subaru.com/content/downlo...IMING_BELT.pdf

Page 5 and 13 will show you the tooth count length. Good luck!
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