M62 (non TU) Exhaust Cam Timing Question

[qcdstick]

I'm normally pretty good with this stuff, but this one has me perplexed so I wanted to bounce the situation off you guys to see if there is an explanation I'm missing to explain this.

Finishing a timing guide job on my winter driver (IE, bought cheap, used, and rusty) 1997 540i/6. Had to crack the exhaust cam sprocket loose for some reason I can't even remember right now (has been a side project for a few months). Both intake sprockets, and the opposite bank exhaust cam sprocket I did not touch. This particular engine hasn't seen regular love with good oil, and has the stains to show it, so it was pretty clear to see where the sprocket bolts had been (no staining, nice silver color under the bolt). I figured I would just line the bolts up so they again covered the non-stained parts and call it good since I hadn't ordered my GAS cam lock set yet.

All good in theory, but knowing I have a bigger M62 engine job on the horizon which will involve pulling and swapping heads, I decided to bit the bullet and order the GAS set now since I'll need it anyway. Pinned the crank, and the cam locks dropped perfectly on all 3 cams I didn't touch, but the exhaust cam I did was visibly way out even before tightening the cam lock. I wouldn't have been surprised to find it a little off, if I didn't hit things exactly lining up the bolts on the marks... But it was WAY off. Below picture is where things line up with all 4 cam locks fully on.

2019-02-17 16.48.20.jpg

As you can see, it is quite a few degrees off from where it was by the factory. Engine ran fine before I went in, no codes, so i'm confident it was in time before. I'm equally confident the timing is correct with the locks, as the exhaust lock fits fine on either bank with the sprocket in this position. Yet clearly the cam is in a different location than it was before I started, how can both of these be true? Only thing I can think is that I didn't re-install the sprocket in the same orientation, yet the slot spacing for the bolts appears to be uniform so I don't see how that should matter.

I can't explain this and it's really bothering me, any ideas?

[qcdstick]

Thought maybe I somehow "slipped a tooth" on the chain while the sprocket was loose, which could explain it. Snapped another picture from a straight on angle to see if the amount I am off equated to one tooth on the sprocket.

No dice, less than half the difference it would be different had I jumped a tooth, so looks like that isn't the reason. Again, this is a non-vanos engine, so that bit of play in the relationship between the intake and exhaust cams that could be present in the vanos on a TU engine should be a non-factor here, right?



2019-02-17 17.20.35.jpg

Going to stop for the day and keep thinking on it. Don't want to button it up and start it without figuring out what in the hell is going on here.

[jmc1590]

I'm not real familiar with the m62, but from the cam timing side of things - Is there a tensioner involved, like on the M52's? Could that explain the slight difference in sprocket location?

Interested in the outcome.

Sent from my SAMSUNG-SM-G900A using Tapatalk

[qcdstick]

I'm not real familiar with the m62, but from the cam timing side of things - Is there a tensioner involved, like on the M52's? Could that explain the slight difference in sprocket location?

Interested in the outcome.

Sent from my SAMSUNG-SM-G900A using Tapatalk

Yes, it tensions the "non pulling" (slack) side of the chain. Came around to TDC going the normal (pulling) direction. Did doublecheck tensioner was extended as far as it could be for what difference it could make. Bottom side of chain (this is the bank 2 side, US driver's side) was taut.

[geargrinder]

Yeah as long as the tensioner is tight it should be good. Having 3 blocks drop in and 1 need to fiddle the crank is normal, because no matter what arbitrary spot you stop the motor (TDC included, there's always going to be some cam ramps under pressure that make one or another cam want to roll a little bit. What you should find is that if you have to turn it back at all, that is just taking up slack

The only thing that surprises me is I didn't think it was the bank2 exhaust that you have to fiddle, I thought it was normally intake cam bank 1 that needed rolling, but perhaps that's different for non-TU, or maybe my old man brain is farted out.

It is always a good procedure to fit up the blocks, tighten the cam (doesn't have to be 100% final torque but 75% at any rate) then turn the whole motor through 720 degrees, and keep checking the manual tensioner as you turn it through to be sure its fully tight. The secondary chains you can't hand tension obviously but you want to be sure it looks like the tension-side (obv top/bottom changes between banks) is really tight. Thats the only thing that could get you, if the secondary slack is on the wrong side. Then as the motor runs that cam could be off a little bit.

If you did all that it should be good and indeed maybe its just chain 'stretch' (really: wear).

You didn't turn the motor over with that cam unbolted did you?

[jicaino]

You could have jumped 2. That'd explain the difference.

- - - Updated - - -

2 teeth in the secondary sprocket, that is.

[qcdstick]

Not really subscribing to the chain stretch theory personally, that's a LOT of stretch on a short chain, hell the primary chain I replaced with twice the miles of what this car has had virtually none. Also, the other bank is dead nuts on even with the old chain of the same age an operating conditions. Neither here nor there, I know chain stretch has been tossed around on here in various threads with all manner of opinion on it which is fine, just doesn't check out with my own observations.

I for the life of me can't remember why I cracked that sprocket loose in the first place. Had nothing to do with getting the locks to line up, at the time I didn't even have them yet. I was thinking maybe it was to make more room to slip the primary chain into the U guide, but that makes no sense because the primary chain runs on the intake cam. Furthermore, the last engine I did, I know damn well I got the chain/guides replaced without touching ANY of the sprockets. I'm sure I had a damn good reason, but hell if I know what it was!

I think jicaino might be on the right track. Maybe I took the entire sprocket out and when it went back it was in a completely different orientation, I thought I left it engaged with the chain but hell I don't really remember for 100% sure. Only thing that makes sense to me though. I should have marked one of the slots and made sure that same slot in the sprocket went in the same place. I was pretty subscribed to the theory of matching up the marks and being good to go at the time, perhaps without thinking that it may index slightly differently if not careful to install as it was.

Hopefully I didn't bend a valve turning it over with it that few degrees out of time. Might get out the compression gauge and see if I can move the needle turning it over by hand before going farther with re-assembly. Won't mean much, but if I can manage it on one bank and not the other that's a pretty big clue... Don't want to have to do the head, but I'll be doing 2 already in the next few months so what's a 3rd? Got a free motor/automatic trans with what should be a good bottom end (someone screwed up the timing job) and my heads off my high mileage car that the bottom end went out of. If I ever get to it. Stupid procrastination!

[geargrinder]

Yah you might have a point. Might re-lock and pop the sprocket off and try all the positions. It can’t be on backwards, right? The backside is gonna have a big circle of varnish mark right? You didn’t take any pics before did you? The sprocket does have a mark on it... if you could ID what spot that was in before you’d be able to see if it’s different now.

[qcdstick]

Not really, closest I have and unlikely to make out much on it? This is blown up to 100% from a much larger picture. Just took it because I thought the inside of this engine was gross. Didn't take 1000 pictures this time like I did on the first one I did. Can see some markings on the cam, but i can't tell where the holes on the sprocket are unfortunately. Also, not sure the engine is even TDC in this picture as it was just after the valve covers came off.

I kind of hate that I looked it up, because apparently it hasn't been a couple months, this picture was end of September! F' me.

2018-09-30 20.56.242.jpg

It would be quite obvious if the sprocket was backwards, the discoloration is very pronounced. If I didn't have the upper timing cover back on already i'd probably play around with the sprocket. I have all of $1100 wrapped up in the entire car (not counting my time) so if some damage was done it isn't the end of the world. I'm confident it's timed correctly now, don't see how it can't be, so probably time to just button up and move on...

[geargrinder]

Agreed. It’s prob fine unless you made some other big mistake that none of us can think of! Doesn’t seem likely.

[jicaino]

I think the 2 teeth theory covers it pretty sensibly. Although you might be right. Do you have access to one of those cheap boroscopes? snake cam, etc? They're like 5 bucks and come with a side mirror and all. You could stick one down a spark plug well and see if the valve events resemble what they should be doing.

[qcdstick]

I think the 2 teeth theory covers it pretty sensibly. Although you might be right. Do you have access to one of those cheap boroscopes? snake cam, etc? They're like 5 bucks and come with a side mirror and all. You could stick one down a spark plug well and see if the valve events resemble what they should be doing.

I do actually. But I don't think I'd see if it was bent that way. Maybe with a really powerful light, but that would require pulling the exhaust manifold which is a huge PITA on these cars.

[jicaino]

Mine has 5 tiny but ultra bright leds in the face. I thought all chinese snakecams were created equal.

[qcdstick]

I don't think lights on the camera side would really tell you much about the seal. I was speaking of a light on the other side of the valve from the camera.

[jicaino]

I don't think lights on the camera side would really tell you much about the seal. I was speaking of a light on the other side of the valve from the camera.

Right, we're talking minor discrepancy if anything, so it will be easier to spot with a leak light.