Engine 04 GT timing chain issue

I would call and talk to somebody at MMR.


Your symptom — slack on the passenger chain while the driver’s side is tight with both tensioners pinned — means one chain path is longer than the other before oil pressure hits the tensioners.
That difference almost always comes from cam-gear phasing, guide height, or a mismatch in head or block geometry.



Head and gasket geometry


Trick Flow heads sit the cam a little higher than stock Romeo heads, and any decking or gasket thickness difference changes the chain span slightly.
Even ten thousandths of an inch can create noticeable slack with the tensioners locked.
If one head or the block was surfaced more, that’s often enough to make one chain seem short and the other long.



Adjustable cam gears


Aftermarket Fidanza adjustable gears are known to have dowel slots that don’t line up perfectly with OEM specs.
If one gear is clocked even a degree off, you’ll see one chain pulled tight and the other hanging loose.
Also check that the dowel pins are fully seated — they can hang up on paint or burrs and throw off phasing.



Camshaft base circle and grind differences


Reground Modular Head Shop cams can have smaller base circles, which changes how the chain loads before oil pressure builds.
It’s not uncommon for one cam to preload the chain differently if its grind differs slightly between banks.
That’s magnified when you lock the tensioners and take oil pressure out of the equation.



Guide standoff height


Inspect the MMR guides to be sure each lower post is fully seated and the upper bolt boss hasn’t bottomed out.
If a guide sits even a millimeter proud, it shortens that side’s chain path and tightens the opposite bank.
That one shows up a lot when aftermarket guide kits are mixed with factory dowels.



Verification steps


Before releasing the tensioners, verify true TDC with a dial indicator on cylinder one — don’t trust the balancer mark.
Lock the crank, install the primary chain only, and confirm that slack sits on the tensioner side of each chain.
If the right side is loose and the left side tight before releasing, your cam gears are probably clocked unevenly.


Pull the tensioners and guides, release the cams, and lay the chains side-by-side to confirm identical length.
Rotate the cams slightly toward each other — if the slack evens out, that confirms gear indexing or dowel misalignment.


Measure the distance between cam centerlines across both heads to see if one head was surfaced more than the other.



Common fixes


Builders often:
• Re-index one Fidanza gear by a single tooth to equalize preload (then re-degree both cams).
• Temporarily swap in OEM gears to check whether the issue is gear machining vs. engine geometry.
• Shim a guide or change gasket thickness to equalize chain span once degreeing confirms both cams are correct.



Bottom line


On a hybrid build like yours, this isn’t a bad tensioner.
It’s almost always cam-gear indexing or head/block height variance upsetting chain preload.
Once both cams are properly degreed and the tensioners are released, oil pressure should balance the system.
If it still doesn’t, one of your adjustable gears isn’t sitting at a true zero reference.