N62 timing chain

[Bimmer7410]

Good evening.
I have an non-running N62 engine that I have been taking apart as a project. The engine has zero to very little compression on all cylinders.
Today, I was able to remove the valve cover (after being stuck with multiple stripped valvetronic bolts) and found, to my surprise, that the timing chain was completely off the camshaft!
I was wondering if anyone else has seen this before, or any insight as to what would cause it? My search had came up empty so far.

[andrewwynn]

Usually after the chain guides fail the tension can't hold then the chain can come off a sprocket

[Bimmer7410]

Originally Posted by andrewwynn

Usually after the chain guides fail the tension can't hold then the chain can come off a sprocket

Figured as much. What Im really trying to find out is if I can simply re-time the engine using the AGA tools and replace the chain guides. I'm not yet sure that no head damage occurred, but I'd think if the chain just popped off during running that the valves could be OK?

Also, theres no compression on the other side, but that side (passenger) actually has the chain on the cam gear. The dig continues

[andrewwynn]

The chain goes in one loop. If off anywhere it's not going to turn. No turn no valve motion. If the valves don't close can't have compression.

The bad news is that I've seen 2-3 M62 that have had chain derailment and always bent valves comes out of it. We pulled four heads from several engines pulled out all the valves that were bent and found some unbent valves and did some swapping to restore one of the motors.

It's easy to set timing and then you can do the compression test to confirm if valves seat or not.

You can use a block of wood as a spacer if your guides are completely gone just for the purpose of getting the chain on to set timing for testing before you bother to replace the guides

[TX4.6X5]

Very rare on any engine that loses a chain during operation to NOT damage the valves. Even if its not listed as an interference fit assembly, even by the manufacturer.

[Bimmer7410]

Originally Posted by andrewwynn

The chain goes in one loop. If off anywhere it's not going to turn. No turn no valve motion. If the valves don't close can't have compression.

The bad news is that I've seen 2-3 M62 that have had chain derailment and always bent valves comes out of it. We pulled four heads from several engines pulled out all the valves that were bent and found some unbent valves and did some swapping to restore one of the motors.

It's easy to set timing and then you can do the compression test to confirm if valves seat or not.

You can use a block of wood as a spacer if your guides are completely gone just for the purpose of getting the chain on to set timing for testing before you bother to replace the guides

Concerning the chain loop: on the N62, there’s supposed to be two chains connected to the crankshaft gear. Popped off on one side doesn’t explain why the other side also has compression, unless I’m missing something.
Also forgot to mention that the chain caused some very fine metal shavings. Haven’t found out if the shavings came from the chain itself or from it hitting the inside of the housing, but we will see.
Agreed with the rest though. I’ll rent the AGA tools and get the timing set, then go from there.

[andrewwynn]

Metal shaving is aluminum from the chain guide frame. When the plastic disintegrates the aluminum frame will start to shred. Also when the chain eventually derails it will chew up the chain cover also aluminum.

Compression comes from crank turning not cam moving. If cam not moving you can have or not have compression depends if valve is permanently open or closed (or bent= open).
Sent from my iPhone using Tapatalk Pro

[Bimmer7410]

Originally Posted by andrewwynn

Metal shaving is aluminum from the chain guide frame. When the plastic disintegrates the aluminum frame will start to shred. Also when the chain eventually derails it will chew up the chain cover also aluminum.

Compression comes from crank turning not cam moving. If cam not moving you can have or not have compression depends if valve is permanently open or closed (or bent= open).
Sent from my iPhone using Tapatalk Pro

That part I got. But the crank is turning on the passenger side.
All in all I’ve got some work cut out for me. I’ll have to remove the whole front portion of the engine to get to the timing chain/tensioners. Thank goodness I have the internet to rely on for little gotchas. Thanks for your help

[oldskewel]

Originally Posted by Bimmer7410

... I’ll rent the AGA tools and get the timing set, then go from there.

On the timing tools, you might at least take a look at eBay clone options, if you're not planning to go into the business of N62 rebuilds.

I bought the eBay china brand set for my M54 this summer, and recently sold it on craigslist, for not much less than what I paid. Helped the guy out, cleared my garage of this set I would probably never use again, and recovered some of my investment.

But I don't know if eBay versions for the N62 exist yet.

Sounds like an interesting project. Nice that you can take it slowly on this. That's what I did on my M54 this summer. Conversely, the guy who bought my set chose to buy mine because he could just come and get it, vs. waiting for shipping from eBay, and he wants the whole thing all done in a few days. Not so fun.

[andrewwynn]

I've used German auto solutions (often called GAS and they are incredible however it's a very simple process to hold the cams locked to 0° so the most basic design will do the job.

Are you saying the main chain came off the cam gear on one side only but is still somehow pulling through if you turn the crank? FYI you see used "crank" in place of "cam" ? If somehow the chain fell off one of the cam gears vs the crank gear there is a good chance only damage on valves of one head and could save a lot of work only re working one head.

Experience has shown that every time a cam is not turning but crank is, you will bend valves but it's often a subtle damage: the pieton interference is not by far so it tends to only bend the valve not damage the Piston so it's not terrible to fix.

I've only worked on the M62 and the N62 has a far more complicated valve train but I'm pretty confident the weak link is still the valve and the eccentric levers and such will survive. Do some googling about N62 and timing chain break/valve head repair to confirm.

It probably adds 3-4 hours per head to deal with the N62 valve train. The M62 is brilliantly simple by having only variable cam on the intake and no variable lift. Probably the best bang for buck motor for DIY fixing.