Koni front inserts, revisited

[Bryson]

Looks like an insert to me. If we can crack it open and get a look at the damper plates and shims, we could source off-the-shelf stuff and play with damper rates. It's actually not so hard to do if they are built with fasteners but requires lots of time and testing

[Max Lumens]

IMHO Hyper's technique is a stroke of genius, great way to accomodate a longer shock. A guy ought to be able to widen the crimped portion of the strut tube with a tailpipe expander tool, cheap and easy device. Might take a little heat, since the wall thickness is a bit more than muffler pipe material.

https://www.google.com/search?q=tail...a&channel=fflb

[Hyper]

...a stroke of genius...

It was a refinement of the original premise set out by Wokke, that there was a Koni out there that almost fit.

[Cefalu]

Actually, I would say he is a genius. I just returned from a trip to his house where he machined my old strut housing to be fit with a new Koni insert. In his shop were various electronic projects he was working on. Projects like a more modern ECU for his car. Yes, an ECU. I didn't pry, but clearly he is a product of the Silicon Valley electronics world. He is working on some pretty amazing electrical projects.

But, my struts are done and I am just waiting on my Koni inserts to show up. I am posting some additional shots of the process.

Part of genius is keeping it simple. The bimetal core bit was, well, just that. I didn't realize it was just a plumbers/electricians hole saw. I had two boxes of Milwaukee ones in my garage. The reverse taper rotary file threw me too. It is also stupid simple, available anywhere. Pics of both are attached.

The coring process takes maybe 5 mins, including the time to bolt it to the drill press. The actual coring part couldn't have taken more than a minute. First a pilot hole was bored. A drill bit walked on the surface so a v shaped bit was use for the pilot hole. I don't know what you call the bit, but I have attached a picture in the drills chuck. Then the coring bit went to work. Technically, the aluminum jig that is bolted to the drill press only holds the strut up. It is not needed to bore the hole since the coring bit has a center guide drill bit. If you were careful, you could do away with the drill press and do it freehand without the jig. But the drill press is easier/faster/safer.

Next is the widening of the tube. Hyper shows what the pipe looks like in his earlier post. It was a simple matter of using a small sledge to drive it inside the strut housing then driving it back out with a steel dowel from the opposite end. And yes, you could probably bring it to a muffler shop and have them open it up a bit.

Done.

Forums like this don't readily allow a persons character to be observed. I am happy to report that Hyper is a genuinely nice person, and a darn smart guy who is a real asset here. This Koni retrofit has just made off the shelf Koni's a relatively easy option for those with a little bit of mechanical ability. Luckily I was able to do my part in return favor, I agreed to take a giant bag of freshly picked ripe Oranges! Nothing like home grown Oranges, they are good too.

[Fatandre]

Yeah, Hyper is a top guy.
I bought from him the handle fix and its amazingly good work and was just around 190 dollars shipped for two.

[Max Lumens]

It was a refinement of the original premise set out by Wokke, that there was a Koni out there that almost fit.

There are plenty of aftermarket shocks for e32 and e34 cars, and I had looked into using them years ago. I even had a pretty slick extension collar nut drawn up, but cost was pretty high and I lost interest. It was pretty sharp of you to notice that tip on the bottom of the Koni unit and realize that you could drill a hole to accomodate it. Adding the extra space at the bottom of the strut instead of the top was a great idea. I'm going to try it some time just for grins, even have an old 3/4" radius bullnose diamond router bit to relieve the top edge with.

The only thing I have minor curiosity about is the nature of that protrusion on the bottom of the shock. Most replacement cartridges end in a simple cap and sit flat on the bottom of the strut. I expect it's just a design quirk with Koni and there's no structural impact; after all, the shock isn't load-bearing, and you don't have to crush it into place in the tube with a lot of torque.

[Hyper]

The Koni application differs from the Boge, in that the stock design has the internals secured by the gland nut clamping down on a flange at the top end.
The Koni has no such flange and therefore positioning and gland nut tightness necessarily depends on the bottom end bumping up against something.
This would be true for the e34 app as well as this e31 mod and therefore the loads on the insert and gland nut are as the Koni people intended.
Just speculating, but the plug at the bottom of the Koni shock would allow a mass produced standard engineering design to be quickly targeted to the final length of a particular application (by chopping).

The stress on the e31 housing changes in that, uninstalled, the housing is now in tension to the degree the gland nut puts the cartridge in compression.
Installed, static loads now have the opportunity to travel from the top of the housing, thru the cartridge, to the remaining perimeter of the bottom cap.
Since the housing cap does not directly contact the knuckle/base, the load then transfers back into the outer tube and on its way to the knuckle/base as before.
Iow, the Koni insert is not trying to separate the tube from the base.

So the key difference is that the housing bottom cap and weld is now expected to take up some static load whereas before it was handling purely dynamic loads transmitted by internal hydraulic pressure.
Imo, the cap and welds are rather thick and sturdy and I would not expect them to fail.
And if there is a weld failure, then the insert simply bumps up against the knuckle/base about an eighth inch lower.

My only concern is with securing the gland nut per the Koni design. It would be nice to lock it, say thru compound or wire, independent of cartridge compression.

[Cefalu]

It seems to me that the steel protrusion welded onto the bottom of the Koni could probably be cut off with a grinding wheel. As Hyper noted, the Koni is probably a universal cartridge. If that is the case, the bottom steel plug of the Boge housing may not need to be drilled out if you trimmed the protrusion off, which is the hardest part. It may be the case that you slap an e34 nut on top, trim off the nub at the bottom of the shock, have a muffler shop expand the tube a lttle and that's it.

One thing to remember, is a shock offers little resistance to force in compression. The spring is the primary load path between the car and the suspension when the car is forced down onto its suspension. However, once the car has reached it's lowest point and begins to rebound upward, the load path transfers to the shock's rod in tension. Now the e34 gland nut sees an upward force from the shock below. This is the long way of saying I don't think the bottom plug of the Boge tube experiences very much loading as a result of the dynamic load of the Koni Shock.

But I bet Hyper is right about the Koni Shock being generic. A phone call to Koni could probably determine which application was modified by the addition of the nub welded to the bottom, and just order that one and save the trouble of trimming it off.

We might get this mod reduced down to a super easy process.

Next Guy's turn.

[Hyper]

... the Boge housing may not need to be drilled out...

No.
This not the case and, as I explained yesterday, the reason I lost my piloting on the core bit.
I first tried drilling to recess just the Koni pedestal, but had not gained enough threads to properly secure the gland nut at the top.
So I had to widen the hole, moving the support point further out and up the sloping bottom of the insert, thus gaining critical thread count at the gland nut.

And my discussion above was about what happens after static loads are transfered to the housing by the spring.

*** edit ****
And I did not mean to imply that an end user could/would/should modify the insert, but rather that the Koni factory could do so as a final step in production.

[Cefalu]

OK, I finished my front axle refurb yesterday. It involved new upper/lower control arms, sway bar links, rotors, pads, and Koni shocks. My car is a 1995 840Ci with 110,000 miles, BMW dealer maintained its whole life prior to falling into my hands about a year ago with 105,000 miles. I was hearing faint clunking in turns so I figured control arms were getting tired. I discovered after I got into the repair that my shocks were totally worn out and had to be replaced and found this thread.

My post repair impression? I was not expecting this big heavy thing to steer so nimbly. It's really a surprise. The closest thing I can compare it to is a 2002 E39 BMW 530i I sold a few years back.

Anyway, here's the Koni content. The Koni conversion was easy. It involves two procedures for the conversion which Hyper explained earlier in this thread.

The first is to slightly enlarge the Boge OE strut tube ID by driving a piece of pipe inside the strut housing and removing it. Hyper used a piece of piece of pipe with an OD of 1-7/8". A piece of 1-1/2" schedule 40 galvanized water pipe from any builders supply (United States) has the same OD. The second step is to drill a hole in the bottom of the Boge OE strut tube to allow the nub on the bottom of the Koni insert to protrude through a little, which allows the Koni insert to sit a little lower in the OE Boge strut tube. It was suggested that a muffler shop's mandrel might be able to increase the Boge OE strut tube ID. The muffler shop I brought mine to could only reach 2" deep inside the tube and you need to reach in about 8", so they couldn't do it.

What I discovered is the second step of drilling the bottom of the Boge OE strut tube is optional owing to the special design of the Koni insert. However, drilling a hole in the bottom of the strut tube does allow you to drive the piece of pipe back out from inside the strut tube, rather that use Hypers slide hammer procedure. All said, drilling the hole is easier in the long run.

But, I say the hole is optional because the Koni strut requires a spacer ring to be used on top of the strut insert, which can be omitted if you use the OEM e31 gland nut. The benefit of using the OEM e31 gland nut is the gland nut hole fits tightly around the Koni insert and restrains the insert from lateral movement inside the OE Boge strut tube. And I was able to get 7 turns on the gland nut which I was only able to get 3 with the e34 gland nut. But the OE e31 gland nut has an ID which is slightly smaller than the OD of the Koni insert. You must shave .39mm from the ID of the gland nut, but you will get a tight fit which keeps the new insert tightly restrained from lateral movement inside the OE Boge strut tube. However, you will probably need to remove the nub from the bottom of the Koni shock in order to get the Koni shock to sit low enough in the OE Boge strut tube, and be able to get enough spins on the gland nut.

NOTE: I did not use the Koni supplied spacer ring shown in the second picture. If you use the e34 gland nut you need this spacer. I re-used my e31 gland nut which seats snugly around the Koni insert as shown in the 3rd picture. Instead of using the Koni spacer ring I fabricated a shim from a 1-1/2" SAE washer to replace the Koni spacer, since the Koni insert sat too low in the strut tube for the e31 gland nut to bear down on the top of the insert.

I am posting photos which explain it better.

[Bryson]

Very clever! So to recap, you did not drill a hole at the bottom of your strut tube, you shaved off 1/4"? of the nub, then used the bored out e31 gland nut? It wasn't totally clear what we're looking at based on the photos and description

Thanks for taking the time to share!

[Cefalu]

I did drill a hole in the bottom of my strut tube. It wasn't until later when I received the Koni insert that I was able to understand how the top of the insert was made and that I could use my e31 gland nut to attach to the Koni insert at a lower position on the insert. This entire game is all about getting enough spins on the gland nut in its attachment to the Boge OE strut tube. When Wokke first attempted this approach, he had to fabricate a custom gland nut because the new insert protruded too far above the Boge OE strut tube and he could not use any OEM gland nut. Hyper solved this problem by using a Koni insert which could be recessed lower by drilling a hole in the bottom of the Boge OE strut tube.

Drilling a hole in the bottom of the strut tube allows the insert to sit ( 7/16" ) 11mm lower in the strut tube. See the photo I took of the ruler at the bottom of the tube. This actually caused my insert to sit too low in the Boge strut tube to allow use of the e31 gland nut. I had to fabricate a shim to compensate. But an e34 gland nut works fine this way as long as you use the Koni supplied spacer which is 10mm tall which is what Hyper did.

The length of the Koni insert, as manufactured, from the bottom of the nub to the ring at the top which the e31 gland nut connects to is (17-3/8") 441mm. If you partially trimmed the nub at the bottom of the Koni insert you will shorten the length of the Koni insert by (1/4" ) 6mm, giving you a length of 435mm. The inside depth of the Boge OE strut tube is 433mm.

This leaves the ring at the top of the Koni insert, 2mm above the top of the Boge Strut tube. This is the perfect height to attach the e31 gland nut and get enough spins on the gland nut for its attachment to the Boge strut tube.

One potential possibility regarding trimming the nub at the bottom of the Koni insert will be the loss of the Koni warranty. However, the possible loss of warranty may be outweighed by a persons concern over drilling a hole in the bottom of the Boge OEM strut tube. To each his own.

[Bryson]

Thanks for the clarification, just what I expected. Thanks again

Of note, not drilling the bottom of the strut tube would allow you to fill the OE boge tube with oil for better heat transfer in heavy use situations. This is not relevant to the bilsteins due to the inverted strut tube, but is relevant to the konis

[duje]

Thanks for the clarification, just what I expected. Thanks again

Of note, not drilling the bottom of the strut tube would allow you to fill the OE boge tube with oil for better heat transfer in heavy use situations. This is not relevant to the bilsteins due to the inverted strut tube, but is relevant to the konis

That's what I did with Boge inserts, filled the tubes with motorcycle fork oil left from fork overhaul.

[Fatandre]

So you can fill the boge again?

[duje]

So you can fill the boge again?

No, I bought new Boge inserts, and filled with oil the space between the insert and OEM strut tube, for better heat dissipation.

[Hyper]

I will be in there next month with my TIG and will compare the e31 nut w/insert mod vs e34 nut w/housing.

[Cefalu]

Here are the wrap up pictures.

First pic, OEM e31 gland nut and cap. Note how far down the e31 gland nut engages by counting the remaining threads.

second pic, new rubber bumper. Refitting the gaitor over the teflon ring was the most time consuming part of the job.

Last pic, pretty much all done. New rotors and pads too.

[Max Lumens]

Good stuff, thanks again. This gets better and better with each new revelation. Sounds like Konis are a viable option with hardly any effort. And if 1.5" pipe works as a bore expander, so much the better. You could find a chunk with both ends threaded, would give you a tapered thread area to start into the narrow section and allow you to screw a cap with a center hole onto the outside end, to slide-hammer it back out of there.

[danieldd]

Reviving an old thread as I have pursued this course of action and retrofitted my strut tubes with the Koni inserted mentioned earlier in this thread. I did not have a drill press, so I fabricated a jig of sorts to hold the strut tube and I hand drilled the required 1 3/8ths hole in the bottom of the strut tube without incident. I also employed a 1 1/2 inch galvanized plumbing pipe to enlarge the flats and used a slide hammer to retrieve the pipe.

Up to this point, things have been rather smooth until I found that the threads on my strut tube were preventing the new E34 gland nut from starting. Thanks to several suggestions on this board, I was able to clean up the threads and successfully screw on the gland nut.

Once I finally inserted the Koni shock and installed the Koni supplied spacer ring on top of the insert, I found I could only get 3 complete turns on the gland nut. This was by hand, so I haven't yet applied any real force on the gland nut, but I don't expect it to turn much further. Ideally, I would like to get more turns on the gland nut, so I entertained the thought of reducing the thickness of the Koni supplied spacer ring, but I cannot do that with any degree of precision as I do not own any milling equipment. If I could remove approximately 2mm from the shim, I could get additional turns on the gland nut. I'm not a mechanical engineer, so I don't know if this would compromise the Koni insert as removing 2mm would bring the gland nut clearance to less than 1/2 mm to the top of the Koni insert.

I tried calling Koni this afternoon (they are in Kentucky), but I called after hours, so I will have to wait until Monday to see if they have a shim that is less than 10mm thick. Three turns on the gland nut may be sufficient - but I don't claim to know if the resulting forces encountered when driving the car would compromise the effectiveness of only 3 threads to keep the gland nut from coming loose.


Lastly, I would like to add that if I delete the Koni supplied spacer, I can get a full 4 1/2 threads on the E34 gland nut. This may be the same as what hyper alluded to in his 1st post of this thread. Could it be that I can install the Koni insert without the spacer? The supplied Koni documentation is sparse at best - a series of pictures. I don't do well with just pictures - I need descriptive text to go with the pictures

Any thoughts or suggestions would be greatly appreciated.

[Cefalu]

See my post #35, with pictures. I used the e31 gland nut and didn't use the Koni washer. Fits perfect.

As I noted, you do have to open up the inside of the e 31 gland nut a tiny bit to make it fit.

[danieldd]

See my post #35, with pictures. I used the e31 gland nut and didn't use the Koni washer. Fits perfect.

As I noted, you do have to open up the inside of the e 31 gland nut a tiny bit to make it fit.

Saw your post and I appreciate your information in this thread. However, I was not able to purchase replacement e31 gland nuts as they appear not to be available. My existing gland nuts had to be cut off due to the corrosion of the nut.

[m6bigdog]

Saw your post and I appreciate your information in this thread. However, I was not able to purchase replacement e31 gland nuts as they appear not to be available. My existing gland nuts had to be cut off due to the corrosion of the nut.

Take the strut, gland nut, Koni spacer and the strut cartridge to a local machine shop and ask them to machine the spacer enough minimize the crush length of the spacer.
Enjoy.

[Cefalu]

You could also open up the e34 gland nut strut hole enough to match the OD of the top of the Koni strut, then it would fit on top of the Koni strut like my e31 did. I am sure a dremel and file wouldn't take too long.

The benefit to the gland nut capturing the top of the strut like this is the strut is restrained from lateral movement.

[danieldd]

You could also open up the e34 gland nut strut hole enough to match the OD of the top of the Koni strut, then it would fit on top of the Koni strut like my e31 did. I am sure a dremel and file wouldn't take too long.

The benefit to the gland nut capturing the top of the strut like this is the strut is restrained from lateral movement.

Your suggestion is valid. I don't think a dremel and a file would accomplish the task. I have included a picture showing how much material I would have to remove from the gland nut to adhere to your suggestion. The gland nut material inside of the spacer would have to be removed and then I could use the nut without the spacer.

I do have a friend who has a mill and a lathe, so I might approach him and see if he can do it for me...