Bank 1 out of time on "new to me" 3.6 engine - possible causes?

Hey folks, I'm doing a "minimal" recondition on a 996.2 2002 3.6 motor I acquired. The motor has been sitting for a couple years, unclear to me how well it was running prior to my acquiring it. "Ran when removed" Was stored properly. Had an RMS leak, oil cooler coolant leak due to oring failure, AOS check vent leak, and the IMSB is probably OE. Good leakdown across all 6 cylinders, 98% "wet". 70k miles, apparently. I'd thought internals were OK. I was just about to replace the IMSB today. When I went to lock in bank 1 TDC, I found that bank 1 seems to be just slightly out of time, a couple degrees retarded. I can get the cam locking tool into bank 1, but only if I advance the crank a few degrees past TDC, to the point where crank lock won't fit. Bank 2 is perfectly aligned one rotation later. Bank 1 cams are aligned correctly with each other, but just slightly off from the crank. I don't see any indication that the exhaust cam bolts behind the scavenge pump have moved, and it would be odd for it to move anyways in sync with the intake cam sword bolt locking it in. It's off so minutely I don't think it's a full tooth off, but not impossible I guess. I've spun it around a number of times, and it always winds up back in this position. Not sure what else to check for for causes at this point, before proceeding. To investigate further, and to complete IMS, I want to pull the tensioners, but normally/obviously I'd lock the motor to do so. If I lock only the bank 1 cams in place, and don't lock the crank, is there any risk of valve/piston interference, IMS chain skipping, other when I pull the tensioners for bank 1, IMS, and bank 2? Would it be better to lock the crank at its TDC, and leave the bank 1 cams unlocked, or lock the cams at TDC and leave crank unlocked? Not sure how people normally deal with taking apart mistimed engines safely. Don't want things flopping around on me! I will re-time it when reassembling obviously. Also, I don't mind re-timing the engine, but I'm curious as to next steps I should take to determine what caused this, before proceeding. I'd rather not have it reoccur, obviously! My thoughts on causes - Tensioner has failed (it's obviously dry of oil, but I'd expect spring to keep mostly it in place) - these are planned to be replaced as part of refresh, but I'm not sure if this is a failure mode that would result in a couple degrees of timing retard. - Chain has stretched - this seems unlikely on a 3.6 3-chain as I think they usually just break, but not impossible. - Chain guides have worn - possible, but can I determine this without opening the head? Is this likely to result in a consistent slip in timing like this? - Cams were "always" out of time - is this realistic? It's clear this motor has never been significantly refreshed, but service history isn't available. - IMS has actually failed - I can check this as soon as I can lock the cams and can open it but the motor spins fine, bank 2 is in time, and leakdown is fine. - Other? Can you "feel" a loose chain in a motor by massaging the crank a bit with cams locked? Seems like a good way to snap them I'd hoped to avoid a more invasive recondition, eg replacing all the timing guides etc, as I wanted to get it started first to evaluate where it was at, before proceeding with further investment in a refresh. Perhaps I was overly optimistic!

I do have a question for you (I don�t have an answer to your query).Did you drop the sump and see if you have any evidence of crank or rod bearing material?I have 2 of 3 engines that have bad crankshafts��😳. food for thought.If you have done so already enjoy your journey.Spare engine, or refresh to put in a car you have?

This will (sadly) be to replace my grenaded LN 4.0... it's a sad story I'll tell at some point Haven't dropped the sump (yet) but the oil coming out was fine (it was stored full), no glitter or sediment or chunks of surprise. Going to Blackstone for analysis shortly. I have a Mantis sump to put on it at some point, but will likely wait until installed, trying to minimize work on this motor until I know. The motors you have with bad cranks, were these motors you had run, or acquired secondhand and discovered the issue? Surprising either way!

One engine in a car I bought 1999 c4 cab with 125 ,000 miles,another core engine 3.4 that had intermix .Cracked cylinder head,both bad cranks.I have a boxster 2.7 longblock no glitter in pan,not torn down yet.I also have a 3.6 complete engine alleged rod knock.You might want to check for bore score from sump so you not in for a surprise later.Sorry about your 4.0.

Yeah I'll scope it from the back at some point once I pull the sump, but the top side bores look surprisingly good. Hoping this is a temporary solution - I just want to enjoy the car again for a bit! Will rebuild back to its proper state in the future, when I have time to do a full rebuild / send out case / etc. Right now more interested in safely "un"-timing it though!

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I am no expert on this but I have done my own IMSB and tensioners. If I had run into this problem I would lock the crank and modify the cam lock tool as required to be able to lock the bank 1 cams. Then do the work you are planning, put it all back together and see what you have.

I don't think you can properly modify the cam timing vis-a-vis the crank without major work on a 3-chain engine. Although, I would be willing to try this procedure before I dig in further. 1. Bring the engine to TDC overlap on the bank you are trying to change. 2. Lock the crank shaft with that pin. 3. Release tension on the chain by removing or backing out the chain tensioner. 4. Loosen but not totally remove the exhaust cam sprocket by loosening the four M6 bolts holding the pulley to cam shaft 5. Manually turn both cams to their proper positions and lock them with the timing tool blade 6. Re-insert the chain tensioner to apply tension to the chain. 7. Tighten the four M6 bolts at the Exhaust cam shaft sprocket Now your engine should be in time, with the exception of the length of chain between the IMS sprocket and the Intake cam. You might get lucky.

Thanks - given both the cams are off-center, I am not sure how I could modify any of my locking tools to support that. It would be easier to take an old crank pulley, drill it, and swap it on temporarily, I think, but that's a bit drastic! Surely someone else here has retimed an out-of-time motor before, and can set my mind at ease as to a safe position to undo tensioners with the motor only partially locked. I feel like I should be able to just undo the tensioners as long as crank is locked at TDC #1, and I might be able to modify a tool to lock bank 2 since it's just 180˚ out, just needs a thinner locking tool. Unlikely that bank 1 is going to spin and damage anything even if loose, it will just need to be re-timed. For that matter, I could probably lock at cyl 4 TDC, leave bank 1 loose, and then retime bank 1 when I'm done IMS, but I don't really want to bend any valves with an error. Just don't know how to work on bank 1 safely at the moment. I suppose pulling the bank 1 valve cover to see what might pop/spin on me with a locked crank might be enough to make a call.

Yelcab's advice is solid. That procedure worked for me when my timing chain skipped a tooth on bank 2

Thanks, I was considering doing that, but you shouldn't be able to advance the intake cam when the sword bolt is done up - was that for a 3.4L by chance? I think that would work on a 3.4 5-chain engine.

Quotes source post: 19207154

Missed this earlier, relying on email notifications while working. Thanks! Thinking about it, this will indeed put slack in the chain between intake cam and IMS. Which is fine for locking the motor, I guess, and then I can re-time it with new sword bolt in the intake cam. Will be interesting to determine if the chain is off a whole tooth (doubt it), or has potentially stretched (not sure how to check without a full teardown).

Looking at your post again, effectively it says "you can undo the tensioner for bank 1 with just the crank locked" which answers the original question of if that is safe to do (if done at TDC overlap on that bank). TDC overlap for bank 1 is when the locking tool fits, correct? Think so, based on Ahsai's post here . Basically the position you'd have cams in to time the motor. (I don't think I ever realized that you time this engine at current bank overlap, not compression, LOL).

Quotes source post: 19208224

The correct cam timing for all engines is verified at TDC overlap, not at TDC compression.