M70 valve timing relation to chain tensioner

[diegokarol]

Hi guys. I’m on the process of banjo bolts work and intake manifolds clean in Bmw 850. As intakes are already removed I would like to checks valve timing. My question is how is chain tension is related to the camshaft timing? As old tensioner spring might loose tension. Should I replace tensioner spring before timing reset? Thanks for advice guys

[Ericks2002]

I don’t think chain tension matters in that regard because it just needs enough to make sure the chain doesn’t skip a tooth.

The spring is only there for preload until oil pressure builds. Also if you think about it when an engine is brand new timing is set with just the tension of the spring.

The actual timing is set by the slots in the camshaft sprockets not the chain tension.

I think either way you would be fine setting timing with the old or new spring

[diegokarol]

Thanks for reply. I would like to checks timing with flywheel pin. Could you please advise where exactly is it? Any picture would be great. If it’s just minimum different between camshafts is worth to play with? How much tolerance is for timing set. I mean if bank2 is correct and bank1 is just twisted minimal in the tool?

[cartoonz]

Thanks for reply. I would like to checks timing with flywheel pin. Could you please advise where exactly is it? Any picture would be great. If it’s just minimum different between camshafts is worth to play with? How much tolerance is for timing set. I mean if bank2 is correct and bank1 is just twisted minimal in the tool?

Uhh... the whole reason for this exercise is to set the cam timing perfectly for optimal operation. When you have essentially 2 independent engines on a common crankshaft, why would it be ok for one of them to be off?

IF you know what you are doing and have the right tools, this is a straight forward process to set perfectly. If you don't know what you're doing and/or don't have the correct tools - find someone that does.

Bottom line, do it right - with the right tools. If you do not, that engine will never run properly.

[diegokarol]

Thanks for advice. I’m looking for quality set of camshaft locking tools in Uk. I found two procedures for timing m70 engine. One from Bentley with front upper chain cover off and other procedure with front upper chain cover which looks easier but not perfect.

[cartoonz]

All you need to do this is the valve covers removed. You do not have to take off front covers, not upper - and definitely not lower. You will, however, want to look at the sprocket bolts you can get to and those you have to "pre-loosen" during the rotations (tighten the same way)
You need ONE locking tool and one pin. You do bank one, then bank 2.
You need to set it, then rotate the crank 2 complete turns, lock it again and recheck. Do this for both sides.
I have multiple sets of cam locks, but I do not actually use them both at the same time to set the cam timing - only as a final check.
You CANNOT set both cams at the same time, so do not even try. Bank 1, then Bank 2. (I technically *could*, but even I won't)
Rotate crank after each adjustment, recheck.

[diegokarol]

Great advice. This is what I was looking for. Last question please. Should I replace tensioner and tensioner spring before timing or tensioner is not related to the timing? Many thanks

[cartoonz]

No. ...and do not try to adjust it either.

[diegokarol]

Clear reply. Thanks a lot for help. Have a great weekend guys 👍

[diegokarol]

https://www.bimmerforums.com/forum/s...44vop0u8P9iG2w

[diegokarol]

Bank1 timing is out, bank2 is spot on. Is that common issue for chain stretch?

[CD05001CIA]

Bank1 timing is out, bank2 is spot on. Is that common issue for chain stretch?

I think it is more likely that either the six bolts that secure the cam gear to the cam were not torqued to spec. or were not set up properly the last time the procedure was done.
There are exactly TWICE as many teeth on the cam gear as teeth on the crank gear, that is why the crankshaft goes around twice each time the cam goes around once. It is critical to keep the timing chain in tension, that is why you physically turn the crankshaft in ONLY one direction, AND if you miss Top Dead Center on the crankshaft mark, you go TWO revolutions of the crankshaft and try again. I take out the spark plugs so that I do not have to fight against compression of the cylinders when rotating the crankshaft manually.

[diegokarol]

Thanks for advice. Already set timing but I tightened to 10nm for the moment. What is the torque specification for camshaft sprocket bolts to camshaft? Bentley says 15nm,is it correct? It’s a lot of torque for m6 bolts in my opinion. I’m waiting for advice before I torque it that much. Thanks guys for all help 🙏

[cartoonz]

15nm is way too much for those, they will snap right off ( they are only 8.8 bolts) 9.9nm (10) is recommended.

6mm 10.9 bolts will take 14nm
6mm 12.9 bolts will take 16.5nm

[diegokarol]

That means Bentley provide wrong info. That what I thought. Thanks for reply Cartoonz👍