Crank / Balancer interface worn - anybody else seen this? Fix?

[jbfrancis3]

It was held by 4 long bolts, and so it could not spin around even without the dowel pin. The massive damper just oscillated back and forth with a loose dowel and causing the marred surfaces.

Duh, good point…🙄

[heinzboehmer]

Curious - do you have a single mass flywheel?



Me too! This fixes half of my problem. :-D

Nope, stock flywheel and clutch for the entire life of the car (125k mi).

[sapote]

It looks like it was run without the dowel pin for a period of time. I'm not 100% certain but I don't think you'd get those long scoring arcs with only a little bit of play in the dowel pin hole.

It was held by 4 long bolts, and so it could not spin around even without the dowel pin. The massive damper just oscillated back and forth with a loose dowel and causing the marred surfaces.

[cobra]

If you find a shop with a lathe they could carefully center it and then take a skim cut like you're suggesting just to clean up the surface. It will probably take 30 minutes to properly indicate and 20 seconds of cutting!

I wonder if it's worth the effort?

[digger]

I do recall noticing the elongated shape of the hole on an undamaged balancer, but yeah this hole is definitely a little damaged. I'm very hesitant to attempt to recondition that surface on my own, on either part, unfortunately. The surface looks scored but it's smooth to the touch. I think the marks might actually be from heat. I do have a bunch of parts at a local machine shop for cleaning and measuring but they don't have a mill so they can't chuck it up and take a quarter thou off the top. I need to find a new shop.

would be a fretting type action (relative movement back and forth), there is probably a bit of stick slip going on due the angular torque pulses the damper is trying to absorb. Is the damper in good condition from a rubber perspective if its worn out the torque being transferred across the interface can get extremely high (i.e. enough to snap cranks due to fatigue)

[yellowltd]

Dang, I had to check you on this and you're right. Wow.
https://www.ecstuning.com/b-genuine-...waAsXtEALw_wcB

It's crazy. They used to be $750~ish for quite a while. Right now the VAC damper is technically cheaper, which hurts my soul. Ross (in Australia) also makes a damper for about $675 shipped.

[yellowltd]

The radial elongated hole in the vibration damper is normal though does appear light damage in the hole tangential direction from the movement (dowel is a locator only), the gear can be replaced for about $100 or through surface grinding (cheaper) or you may be able to lap it yourself on a surface plate a fine sandpaper after you remove the dowel pin but there may need to be too much material removal to clean it up adequately its hard to tell from pic. You would want to address the surface on the vibration damper as well so you have a good uniform surface for the friction surface as that's how the load is transferred. I would take it to a machine shop and have them fix it as new ones are very expensive like $1,000

I do recall noticing the elongated shape of the hole on an undamaged balancer, but yeah this hole is definitely a little damaged. I'm very hesitant to attempt to recondition that surface on my own, on either part, unfortunately. The surface looks scored but it's smooth to the touch. I think the marks might actually be from heat. I do have a bunch of parts at a local machine shop for cleaning and measuring but they don't have a mill so they can't chuck it up and take a quarter thou off the top. I need to find a new shop.

[yellowltd]

It looks like it's moving slightly from the enlarged hole. Might want to consider pulling, check and replace the rod bearings too if you've been driving the car hard.

I actually have the entire engine apart, and most of it is at a machine shop for proper measuring. And yes, I was beating the snot out of it. 😀

[yellowltd]

It looks like it was run without the dowel pin for a period of time. I'm not 100% certain but I don't think you'd get those long scoring arcs with only a little bit of play in the dowel pin hole.

I think when the rotation is caused by harmonics at a (relatively) high frequency, it can make a wear pattern like that. But you're right it looks like it was just spinning.

[yellowltd]

Is that a hairline crack in the balancer dowel pin hole?

No it's actually a little piece of debris. And now I'm looking at the dowel, and seeing a similarly shaped mark, and wondering if that's the cause of all my troubles here. Good eye.

[yellowltd]

The dowel pin hole seems to be enlarged and loose. If this is true then you might need a new one.

You are not wrong. Or, to have the hole drilled slightly larger, and a new dowel made. Either way, can't really leave it like this.

[yellowltd]

Can't comment on the severity or fix for this, but my crank looks the same.

Pretty sure it had never been apart before I messed with it and it hasn't given me any issues sooo...

Curious - do you have a single mass flywheel?

Edit: Damn, the sprocket is only $112. I thought for sure it was going to be a lot more money.

Me too! This fixes half of my problem. :-D

[yellowltd]

That is weird, I agree. At the same time, a guy here (Pklauser) just posted a picture of his and it looks kinda similar, showing a wear pattern around the perimeter. https://nam3forum.com/forums/forum/m...ressions/page4

The dowel pin should prevent it from rotating and I don't see any obvious signs of wear at that interface. So if it's actually caused by sliding it must be some very microscopic movements.

If you are truly worried about it - you can replace that part. It's separate from the crank. Just remove the little bolt in the middle and it comes right off. There is another dowel on the back side between this piece and the crankshaft so don't forget that too. You will need to remove the vanos and exhaust cam sprocket to give enough chain slack to remove it. https://www.ecstuning.com/b-genuine-...t/11211401036/

The movement would have been very small. The engine had a noticeable harmonic vibration when decelerating through the 5-6k RPM range, it was well over 100 Hz. I'm confident these are related.

I knew the nose was separate and replaceable, I had no idea it was that cheap, I went ahead and ordered one. Thank you for that!

[Pklauser]

new ones are very expensive like $1,000

Dang, I had to check you on this and you're right. Wow.

https://www.ecstuning.com/b-genuine-bmw-parts/vibration-damper/11237834425/?gclid=Cj0KCQjwwY-LBhD6ARIsACvT72OsUpvxXhsz9qWSJrJ5d53YS0YJDlRjyxM2Agm5C_b8angVaqdXxlwaAsXtEALw_wcB

[digger]

The radial elongated hole in the vibration damper is normal though does appear light damage in the hole tangential direction from the movement (dowel is a locator only), the gear can be replaced for about $100 or through surface grinding (cheaper) or you may be able to lap it yourself on a surface plate a fine sandpaper after you remove the dowel pin but there may need to be too much material removal to clean it up adequately its hard to tell from pic. You would want to address the surface on the vibration damper as well so you have a good uniform surface for the friction surface as that's how the load is transferred. I would take it to a machine shop and have them fix it as new ones are very expensive like $1,000