Koni yellow vs. Bilstein strut diameter difference

[AlfaBMWGuy]

A few months ago I bought Koni yellow sport struts (86-1519) and shocks (80-1868).  My mechanic is now installing the struts.  He was having difficulty in getting the struts down the tubes where the Bilsteins go down perfectly (which is what I'm swapping out because of the harsh ride).  He measured the diameter of both with a digital caliper and found that the Koni (39.6) was a full millimeter wider in diameter than the Bilstein (38.6), thus explaining the difficulty in getting the Koni inserted in the tube.  He said that the existing lubricating fluid in my tube still looked good and no visible rust inside the tube.

 

He's concerned about two things:  1) Not being able to get it fully down and then if it gets stuck, needing to source a new strut tube assembly and 2) if he does get it down, he thinks ever getting it back out won't be a possibility.

 

Also on at least one of the Koni struts there was a sloppy weld he needed to file down just to get as much progress in inserting it as he has made--apparently Koni QC isn't up to Bilstein standards, at least Bilsteins from a couple decades ago.

 

Have others seen this difference in diameter (has anyone else measured?) and/or had any difficulty in getting Koni yellow struts into the stock tubes (mine is a '74 tii)? Just trying to get some feedback before biting off on doing something that likely won't be reversible.

 

Thanks,

Gary

Edited December 20, 2021 by AlfaBMWGuy

[2002iii]

Don't shove them down if they are to tight, you'll ruin a good set of tii struts.

 

The first thing I would do is check the part #s to make sure you got the right ones. If they are the correct ones then I would call Koni or whoever you bought them from.

 

What Bilstein's are you taking out? There are different versions with different stiffness levels. You might want to get the oem spec ones.

[AlfaBMWGuy]

Thanks.  I am not sure if these are Bilstein HDs or Sports (B6, B8, whatever the terminology is) that are being removed.  They were replaced more than 20 years ago a couple owners back and there is no record/invoice for them--I bought this tii back in August.  Is there a part number on the struts themselves to differentiate them?  Would be nice if Bilstein used different colors like Koni does, but I guess they consider the yellow part of their brand identity.

 

On my last 2002 bought in 2017, I bought Bilstein HDs and even those in combination with Ireland Engineering stage 1 springs were stiffer than I prefer, although it handled great of course.  This time I researched and decided on the Koni yellows because of owner feedback and also went softer on the springs than the ones from IE--I went with Eibach because they were noted for having a slightly better ride than H&R.

 

The part number on the box for the new Koni struts is 86-1519 as I indicated above.  They were purchased through BluntTech, my regular supplier.  Is there a difference between part numbers for tii Koni struts and regular 2002 Koni struts?

 

Thanks,

Gary

Edited December 20, 2021 by AlfaBMWGuy

[AceAndrew]

I have brought this up a number of times (linked the most recent), there are semi-uncommon instances where ID of the strut tube and the OD of the Koni's are not compatible.  It's fairly well known at this point, but the fact does get buried by conversations comparing performance....not fit.

 

For giggles/last-ditch-effort, I ended up turning down the OD of the Koni insert on a lathe...still no bueno.

 

 

[AceAndrew]

9 minutes ago, AlfaBMWGuy said:

  Is there a difference between part numbers for tii Koni struts and regular 2002 Koni struts?

 

no, this is not a 2002/2002tii difference ... this is a manufacturing production run difference (this issue...when I've cataloged them, do seem to be more common to later years).

[AlfaBMWGuy]

Thanks Andrew.  So is the incompatibility due to the strut tube or the Koni's (even being the correct part number)?  Because the Bilstein's fit without issue and are a full mm less in diameter, it would seem to be a "Koni issue"?   But, maybe most of the strut tubes were a tad bigger (maybe based on year or supplier) so the problem with manufacturing a slightly bigger diameter strut doesn't come up often?  Bilstein just figured out and accounted for this difference in 2002 strut tubes while Koni did not?

 

-Gary

[AceAndrew]

31 minutes ago, AlfaBMWGuy said:

Thanks Andrew.  So is the incompatibility due to the strut tube or the Koni's?

 

Your logic follows the same conclusions I came to.  It's both Koni and BMW's strut housing manufacturer working the max/min of their respective tolerances; perfect storm.  Couldn't say if Bilstein accounted for it, or just specified different internal tolerances (plenty of crusty engineers would add a LITTLE extra margin without being asked to).

[PapaG]

I had this exact issue. I ground off the lumpy weld at the bottom of the Konis and took off some of the paint/powdercoat, then just kept at it till it slid nicely into the tube. I didn't mic it, and the only "structure" I took off was a bit of the weld at the bottom. It ended up sliding right in, with fresh oil, and I am confident it will slip right out when and if that is necessary.

[bergie33]

Gary, I have my '74 tii strut housings out of the car and a set of new Koni's in the box. Mine are the same part numbers as yours.  I'll try to see tonight if I have the same issue as you, or at least get a measurement on the Koni tube diameter.  Stay tuned...

Edited December 20, 2021 by bergie33

[AlfaBMWGuy]

6 minutes ago, PapaG said:

I had this exact issue. I ground off the lumpy weld at the bottom of the Konis and took off some of the paint/powdercoat, then just kept at it till it slid nicely into the tube. I didn't mic it, and the only "structure" I took off was a bit of the weld at the bottom. It ended up sliding right in, with fresh oil, and I am confident it will slip right out when and if that is necessary.

Thanks.  There is some hope then.  I don't mind disfiguring the Koni's since they are hidden anyway and at this point, they brought this fate on themselves 

[AlfaBMWGuy]

8 minutes ago, bergie33 said:

Gary, I have my '74 tii strut housings out of the car and a set of new Koni's in the box. Mine are the same part numbers as yours.  I'll try to see tonight if I have the same issue as you, or at least get a measurement on the Koni tube diameter.  Stay tuned...

That would be greatly appreciated in terms of another data point.  If you had a good caliper accurate to tenth of a mm, I'd ask you to measure the diameter of your Koni's.  Without that though I think there isn't the precision to make that a worthwhile data point.  Thanks!

Edited December 20, 2021 by AlfaBMWGuy

[PapaG]

As Ace says above, it is most likely just some tolerance stackup between the very old BMW strut and the new Koni. I just made sure that anywhere I ground the paint/powdercoat all the way down (just a few spots here and there) I liberally coated it with oil. I just don't think it will be a problem.

[Mike Self]

If it's a tight squeeze and you're gonna "persuade" 'em in with a little lubrication assistance, I think I'd use wheel bearing grease, as it is more likely to cling to the insert's entire length, where oil will tend to puddle at the bottom. 

 

When I redid my front suspension and replaced the ball joints, I filled the space where the ball joint's castle nut is inserted with wheel bearing grease so I can get the thing loose when I have to do ball joints again.

 

mike

[Tommy]

7 hours ago, PapaG said:

I had this exact issue. I ground off the lumpy weld at the bottom of the Konis and took off some of the paint/powdercoat, then just kept at it till it slid nicely into the tube. I didn't mic it, and the only "structure" I took off was a bit of the weld at the bottom. It ended up sliding right in, with fresh oil, and I am confident it will slip right out when and if that is necessary.

This and cleaning and honing all the shit out of the strut tube. I have also drilled and threaded a hole at the bottom of the tube so incase the shock got stuck I could use M8 bolt to press it out. 

[AlfaBMWGuy]

Thanks for the added advice Mike and Tommy as well as to the others who have helped me out here.  Much appreciated.  The FAQ comes through again with timely guidance!

 

Cheers,

Gary