Broken chain tensioner after new cam install....

[wakdog]

So i dropped my car at my mechanics today to have my M50B20 cams installed into my M50B25, went to pick it up this arvo and when i get there they basically tell me that its going to be best to just pick up another engine...

From what I can see the timing rail guide (attached to Part 7 in the diagram)


has been obliterated and there is plastic everywhere (yet its not brittle when i pick up the remaining bits...).

The problem here is the cost of a replacement engine VS cost of labor to access the part and replace it...

Is there anything that they could have done to cause this that may put them at fault? Im really not keen on having to fork out for the labor on this and then have to buy another engine ($1k in oz).... From doing a little reading, they should have turned it over by hand first before cranking it to make sure that the tensioner was functioning correctly?

[luckysnafu]

If it wasn't broken when you dropped it off and it was when you picked it up I don't see how it isn't the fault of the mechanic. They should own up to what they did and fix it for you on their dime.

What did they tell you happened?

[328ijunkie]

Yeah they broke it.

[ForcedFirebird]

They broke it and it's not that hard to pull the timing cover and repair it.

[e30serg]

Did they remove the head? How many miles on the engine? My guess is they dropped the head onto it and cracked it, then it broke when the motor ran. That part sticks out quite a bit if you take the head off. Like this, on my s52 build.

[wakdog]

They didnt remove the head, motor has about 115k miles on it...

[wakdog]

If it wasn't broken when you dropped it off and it was when you picked it up I don't see how it isn't the fault of the mechanic. They should own up to what they did and fix it for you on their dime.

What did they tell you happened?

They told me they had it all together, started it and within 20sec it snapped it and got real noisy from lack of chain tension...

[e30serg]

I'm wondering if they could have stressed that rail while messing with the timing chain. I can't remember if it's possible to bend it from above with the head installed. Or, could the tensioner be putting too much stress on the rail if there's no chain to push against it?

[ForcedFirebird]

I'm wondering if they could have stressed that rail while messing with the timing chain. I can't remember if it's possible to bend it from above with the head installed. Or, could the tensioner be putting too much stress on the rail if there's no chain to push against it?

Maybe. Hard to say unless they are BMW-specific mechanics. You wouldn't believe the stuff we see in our shop from general repair shops. Sad, really.

[328ijunkie]

^This. How did they take the cams on/off. Ive seen some shops leave the primary tensioner in place and smash the main cam gear off breaking the tensioner and other stuff in the process

[wakdog]

^This. How did they take the cams on/off. Ive seen some shops leave the primary tensioner in place and smash the main cam gear off breaking the tensioner and other stuff in the process

They are a BMW specialist, they have done upwards of 15 cam swaps/head swaps on m5x motors, this is the first one they have had this issue with...

[328ijunkie]

^ive done 30+ cam installs and broke a customers upper chain guide (plastic piece for secondary chain) a few weeks ago... Stuff happens when youre working on these things. They should fess up to it. These chain guides dont just explode randomly.

[ForcedFirebird]

^ive done 30+ cam installs and broke a customers upper chain guide (plastic piece for secondary chain) a few weeks ago... Stuff happens when youre working on these things. They should fess up to it. These chain guides dont just explode randomly.

This.

I had a helper break the tensioner when he was helping me remove the head on an m54, bought a new one and replaced it on my dime.

[wakdog]

spoke to them again and they have pulled the head, all of the exhaust valves are bent :(

Hopefully ill be able to get them to cover labor and ill just supply any parts required...

[e30serg]

Going for a head rebuild then? Did they own up to it? If rebuild, replace the upper tensioner too. Might as well. Also, don't forget the oil check valve that's in the head. It gets installed from the bottom. Do the valve seals, etc too. Good luck!