Timing belt gear wheel destroyed

[TC Baur MD]

While my daughter was driving my 87 325ic (m20) the car broke down. Turns out the timing belt came off but didn't brake but the timing belt Gear wheel got destroyed, see item 9 from realOEM photo and attached photos. It's now in three pieces. This caused the valves to slam into the pistons leaving smilies and at least 4 rocker arms to brake off. I'm going to replace the gear wheel and head but am not sure why this happened to start with. Do you think the Intermediate shaft, no. 10, seized up or the gear wheel failed due to fatigue? Before I start replacing parts I want to make sure this doesn't happen again. Any advice is appreciated.

http://www.realoem.com/bmw/showparts.do?model=BB13&mospid=47326&btnr=11_4365&hg=11&fg=25

[jo3y]

thats strange. I had a problem with the gear on the crank and the woodruff key way becoming elongating causing timing issues.

However, i have never had issues with the gear you have. Its possible the gear just gave out. I cant think of any reason for it to break other than just fatigue.

One thing you may find is that when you order your new gear is that BMW may have redesigned it, making it stronger. My thermostat housing i ordered new was a lot different than the stock piece i removed, with several upgrades.

What are your plans for the pistons?

[Exodus_2pt0]

Who did the timing belt last?

Only cause I see here is a tensioner that was over tightened, or maybe the camshaft seized?

I'll keep this on my mind, if I come up with anything else i'll post back. Either way though, if you throw a new head on i'm sure you'll be fine.

[TC Baur MD]

Good point on the possible redesign of the part. I'll check it out tomorrow. I knocked down any edges sticking up on the smilies used fine sand paper to smooth it out. After reading several threads it sounds like this will be ok.

[dashboardmonkey]

The stamped steel timing gears do not hold up well to the higher revs of an i car. It should have a cast gear that is more beefy. This is not the first i have heard of this happening.

[TC Baur MD]

Who did the timing belt last?

Only cause I see here is a tensioner that was over tightened, or maybe the camshaft seized?

I'll keep this on my mind, if I come up with anything else i'll post back. Either way though, if you throw a new head on i'm sure you'll be fine.

The PO did it last the last timing belt change. Overtightening the tensioner is a possibility. I did notice a ticking noise coming from the timing belt area a couple days before this happened. I was hoping it would go away. Wrong :(

[toointoxicated60]

The stamped steel timing gears do not hold up well to the higher revs of an i car. It should have a cast gear that is more beefy. This is not the first i have heard of this happening.

winner

[TC Baur MD]

The stamped steel timing gears do not hold up well to the higher revs of an i car. It should have a cast gear that is more beefy. This is not the first i have heard of this happening.

When I closely inspected the damaged gear it did look like there may have a older crack in the seam at the base of the gear but couldn't be 100%. This is very thin metal that takes a lot of stress. I'm surprised it hasn't happened more often.

[jo3y]

let us know what the new gear looks like when you get it. After thinking about this, i dont know because im sure weight is in the equation somewhere. Im curious to see if it has been improved

[jlevie]

When I closely inspected the damaged gear it did look like there may have a older crack in the seam at the base of the gear but couldn't be 100%. This is very thin metal that takes a lot of stress. I'm surprised it hasn't happened more often.

That says that you had the stamped sprocket, not the cast one. The stamped steel sprockets are a known failure item and it should have been replaced a long time ago.

[TC Baur MD]

That says that you had the stamped sprocket, not the cast one. The stamped steel sprockets are a known failure item and it should have been replaced a long time ago.

That's nice to know, thanks! At least there is a legitimate reason why there was a failure. Do you know what year they started replacing the stamped form to the cast one? I also have an 88 325i and am now worried about that one to. Good thing I bought two new sprockets. :D Oh, any trick to tightening the bolt that holds the spocket in place? I'm hoping that having the engine in gear will be all I need to do. Thanks in advance

[TC Baur MD]

Maybe inspecting and/or changing out the timing spocket needs to be emphasized to new E30 owners as an initial step to protect their investment. It did the same amount of damage to the engine that a broken timing belt would do, if not more.

[jlevie]

That's nice to know, thanks! At least there is a legitimate reason why there was a failure. Do you know what year they started replacing the stamped form to the cast one? I also have an 88 325i and am now worried about that one to. Good thing I bought two new sprockets. :D Oh, any trick to tightening the bolt that holds the spocket in place? I'm hoping that having the engine in gear will be all I need to do. Thanks in advance

I'm not sure when production changed but I think it was around 87.

The sprocket bolt doesn't require much torque. The resistance of the engine alone is enough.