Koni Yellow inserts are retrofitted into modified front shock housings.
Low pressure gas, rebound adjustable, pn 8641-1224-Sport.
{ed: ***** See post #71 for a concise How-To using the latest methods ******}
This project was motivated by the need to replace aging original shocks while skipping the Bilstein circus and the Boge price.
Koni does not offer a e31 application (see bmw app info at the bottom of this post), but ever since RF days, people guessed that the e32/e34 insert could be adapted someway, somehow.
The Koni fronts were part of a complete suspension retrofit: Mtech springs front and back, CSI rear bar and E32 front bar.
I proceeded fearlessly knowing that Wokke has been there, done that.
Wokke revealed two incompatibilities and provided a solution, which I'll call the Nut Job.
The first incompatibility is that Koni insert is too tall to fit entirely within the stock shock housing vacated by the Boge insert and therefore the retainer (gland) nut on top was extended in length.
The problem with this approach, that troubled both Wokke and myself, is that there is a half-inch loss of suspension travel between the gland nut and the bump stop.
Although I was prepared TIG in hand to proceed, I instead ended up recovering all of the missing travel by recessing the insert down through the base of the housing.
This also allows me to use the e34 nut unmodified.
What is supremely significant is that this alternate method brings off-the-shelf Koni's further within the capabilities of DIY'ers.
The second incompatibility is that the stock housing has a constricted diameter over about 4" of length, below the spring perch.
There is no explanation for this other than it was clamped as part of the manufacturing process.
The Koni shock is 46mm diameter (hence the B46 family designation) and so an expansion tool was created using 1-7/8" tube.
The tool is pressed down into the housing and then retrieved using a slide hammer.
{ed: I backed into this slide hammer method and there is an easier alternative.
If you cut the bottom of the housing first, then the expansion tool can be hammered/pressed out using say a 1" dowel catching the far edge.}
The Koni now fits snuggly in the housing but can be inserted and removed with minimal effort.
This Koni number gets you the 14mm rod and top nut which matches the outbound Boge.
There is another e34 app part number that will get you 12mm.
Note on the housing, the number of threads used by the outbound e31 gland nut. About 5 threads.
The fully seated the insert extends 5/8" (0.625) above the top of the tube.
However, this is not the loss of suspension travel with respect to stock, because the stock Boge insert also rides above the end, due to a lip that is clamped by the stock gland nut.
AND the e31 gland nut is thicker than the e34 gland nut.
Down at the bottom, the insert diameter reduces down significantly to a pedestal.
We use a core bit on a drill press to open up the bottom of the housing and allow the insert to seat further down in the housing, supported further out in its diameter.
A jig was fabricated to cantilever the tower under the drill press and guide the core 1-3/8" bi-metal core bit into the center of the housing bottom.
The inside edge is deburred using a reverse-taper rotary file.
For now I'm leaving the end open, but I will likely go in later to weld in a cap, allowing the tube to be oil-filled and sealed from moisture.
The end result is that the insert sits low enough that the stock e34 gland nut grabs 4-1/2 threads.
The top of the e34 nut ends up at exactly the same height as the stock e31 nut.
{ed, Dec 2016:
*** ATTENTION *******
Use a thread lock compound, medium/blue such as Loctite 248. Otherwise, that suspension rattle/knocking?, it's the result of the gland nut having backed off allowing the insert body to slam up and down in the tube by say 1mm.
********************
}
The rebound rate is adjustable after installation.
The fixed compression is said to be comparable to stock.
I don't have the -1224S data but this curve (from a Koni 1198 Sport on the rear of my MBZ) gives you
an idea of the soft fixed compression rate at the top and the range of rebound at the bottom (soft, medium, firm).
The low gas pressure allows the front to match the drop in back from the new M-tech springs all around.
My brief easy-cruise road test took me on a suburban beer run, 2 miles of freeway, a casual canyon, six speed-bumps and a squirrel.
I did not detect any dramatic differences from stock. Comfortable.
**** Koni app info ****
This project uses 8641-1224 Sport as found on 740, late 750 and late e34.
Last edited by Hyper; 07-12-2017 at 10:48 AM. Reason: Pic link repair, re PB affair
Amazing.
And you still can make them harder if you need.
You are all in. I'm sure it rides better than billy.
Congrats....
I Will be looking closely at this. I hope someone can find the compression rate, and the range of the rebound rates.
The original plan was to run thru Jay's shop with a Koni, a Billy, a used Boge and an M-tech rear.
Just too tight on time now. Maybe later if I get overly ambitious. Wouldn't be surprised if Jay had the Koni info already.
What rears would you use with these?
E30 1992 335 Cabriolet - Transplant nearly finished
E31 1992 850ci - Hartge H8 6.0 conversion
E34 1995 540A - Stock, low mileage, hi spec and soon to FI'd
E36 1994 M3 - GM LS3 Transplant
E38 2001 735 - Daily driver
E46 2002 330 Cab - Stock
M62B46 with TTV flywheel, dual plate clutch and 6 speed box sitting in a corner waiting for me to decide where to put it.
Yes you caught me leaving out that detail.
Rear was done with Mtech springs (33531138738), Mtech shocks (33521137474), and the CSI bar (33552227321).
Last edited by Hyper; 07-12-2017 at 10:53 AM. Reason: Pic link repair, re PB affair
What about e34 stuff in the rear? Like adjusteble konis?
Great writeup, I will for sure try to do the same on mine this summer.
I have one question, my car has M-suspension. Is there any difference between my struts and yours and is the technique applyable to mine?
Prompted by the billie chatter this week...
Route: SFbay to Idaho Falls, seventeen hundred miles out and back. July 2013.
Front: Koni inserts, E32 bar, Mtech springs, fresh arms.
Rear: Mtech shocks, CSI bar, Mtech springs, original bushings.
245/45-17 all season.
Result: Very happy, not a single triffle. Luv'it. Was pleasantly surprised by how well it handled the Donner Summit road surface.
Koni fronts is a $400 solution. Jan 2013.
*** Warning, requires tools and skill to do a housing mod. Liabilities and support?...You're on your own. ***
Never thought about it. My trajectory was to do M-tech springs and dampers all around, but sub'd Koni's in front due to cost considerations.
Great, useful question. Don't know.
Last edited by Hyper; 07-12-2017 at 10:55 AM.
IMHO, When you factor in labor, billies still sound like a better option. I can get a round peg to fit into a square hole, but why not buy a round peg and make it easy.
Jeremy Smith
94 840Ci
98 Porsche 986
02 Mini Cooper
13 Ford F150 Platinum
IMHO, When you factor in labor, billies still sound like a better option
I remember from my Maser days that guys kept trying to come up with a better/cheaper solution for front brakes. I can remember month-long projects that were deemed a success because of a $100 savings...
Of course in this case, the added benefit of adjustability is a good thing. Been loving mine for the past couple of years now (RIP Randy - and thanks!)
I anticipate you have yet to use the Koni rebound adjustable dampener. IMHO, the Koni is worth the effort no matter what the actual cost. After all, once the dampeners are installed every time the tire goes around you will feel the difference.
- - - Updated - - -
Totally different rear suspension!! Using the E-31, M-Sport rear suspension upgrade as a package is the only way to go since it is an BMW M-Division engineering suspension package.
Oxford Green Metallic, Parchment leather, 854 badge, EDC stock struts, M-Sport springs, 3.91 LSD, CSI rear sway, 18" M-Pars, M-Sport wheel w/flappy paddles, CD-43 head unit, Strong Strut brace, Euro FTPs, CSI rear defuser
Previous -
'70 2002
'92 525it e34 - Touring
'97 530i e39
'06 325xi e91 - Touring
Hyper used the M-Sport front springs and I assume he desires, as other, to avoid the extra cost of the Euro M-Sport front struts at something like $650-700 each side. Also, the nice touch with Koni Sport strut cartridges is the adjustable rebound. However, if you don't have access to the tools or a shop that can fit the Koni's you can't go wrong with the complete Euro M-Sport suspension setup either!! That I'm aware the M-Sport Suspension kit p/n: 33 32 9 059 315 is NLA so it can only be purchased in individual parts.
Bump, This is good stuff and more than worth consideration for anyone wanting a super Sport ride.
Well, I am deep into an upper and lower control arm replacement and and discovered that my 1995 Boge shocks with 110,000 miles on them are toast. Not really a surprise at this age.
A search of my usual suppliers pelican/autohausaz/ecs comes up nada for front shocks of any kind. Which makes this Koni option seem pretty real. But it looks like a set of Konis will run about $400, who knows what the Bilstein/boge prices are.
My concern is ride. My 840Ci is my luxo barge. I have a 911 with a suspension that already knocks my teeth out, and I only need one car like that. I am more concerned about maintaining a comfortable ride. My wife has giant boobs and she has to wear a steel reinforced bra in the 911. Alright I lied. She doesn't really have giant boobs. But you get the picture.
So, the question is......How are the Koni's comfortwise? I also read the guy in the US that revalves the bilsteins passed away. What the heck are the options these days?
1995 BMW 840Ci
1999 Porsche 996 Cabriolet, 6 speed
1974 VW Westfalia P27 Deluxe camper
1974 Mercedes 280C
I just bought a set of Billy's from shock warehouse, they weren't overly expensive. Billstein will revalve, there should be form linked on this thread by Olin. They come Sport, people have revalved to Comfort, but the preferred seems to be in the middle, HD. Mine have been sitting in the box for 3 months, I think you've given me the motivation to get them sent in.
Jeremy Smith
94 840Ci
98 Porsche 986
02 Mini Cooper
13 Ford F150 Platinum
HD will still rattle your teeth IMO. I like it but it's no wagon.
What "thumbs up" really means
I just read a bunch of threads on this shock issue, and I now understand why they refer to Bilsteins as being a circus effort. It can take 10 weeks to revalve. Aside from the excessive time, I am sure they charge a fee, and there is the cost of shipping them back and forth. Circus.
After reading this thread more carefully, it doesn't seem like the mods required to allow the Koni's to be adapted are that difficult to do. Basically you need to ream out the strut tube with a strong piece of pipe, and drill a hole in the bottom of the strut endplate to let the Koni insert sit down a bit lower. Once this is done you can easily change out replacement struts in the future.
I would be interested in hearing from anyone else who has gone the Koni route regarding their experience.
1995 BMW 840Ci
1999 Porsche 996 Cabriolet, 6 speed
1974 VW Westfalia P27 Deluxe camper
1974 Mercedes 280C
I had good service and excellent results getting the Bilstein's on my '85 M635 rebuilt (could have been re-valved at the same time ..... if I had wanted) at the Bilstein site in Poway, CA in 2011.
Turn around was 4 weeks, and pricing was (IIRC) roughly $100 each at that time. http://www.manta.com/c/mmn6lpl/krupp...ein-of-america
================
1985 M635 (gone but not forgotten)
1994 850CSi (also gone but not forgotten)
1985 M635 (current obsession)
Well, I am going the Koni Route. The OP of this thread lives pretty close and will loan me his tooling to modify my strut tubes. My car is in pieces in my garage, so the possibility of a 4 to 10 week downtime is not looking very attractive.
I bought two Koni's for a total of $340 shipped to my house.
I like the Koni option to dial the ride in, and the ability for an inexpensive and fast future replacement cartridge.
1995 BMW 840Ci
1999 Porsche 996 Cabriolet, 6 speed
1974 VW Westfalia P27 Deluxe camper
1974 Mercedes 280C
I understand ..... time is money
Good luck with your Koni conversion.
================
1985 M635 (gone but not forgotten)
1994 850CSi (also gone but not forgotten)
1985 M635 (current obsession)
The OEM Boge shock is very different from the usual BMW strut cartridge, . In fact you really can't call the Boge a cartridge. The Boge strut housing is filled with oil, and inside it are the guts of the shock, while the replacement shocks are a self contained unit that sits inside the Boge housing. Not oil filled like the Boge tube.
It appears to me that the Boge shock should be rebuildable. It looked like some new rubber O rings, a bit of oil and you should be good to go. I tried to undo the 9mm nut on the bottom of the Boge shock, but it just kept spinning. So I never got to see what was inside.
Does anyone rebuild these?
Edit: following are dimensions of the Boge shock tube on my '95 840Ci:
ID of tube at threaded opening: 49.9mm (this area of tube is machined slightly wider than the remainder of the tube.)
ID of remainder of tube except at crimped portion of tube 49.58mm
ID of tube at crimped portion: 47.04mm (My ID guage couldnt read this far down so I took the OD at the crimp and subtracted the pipe wall thickness)
OD of tube except at crimped area 55.42mm
OD at crimped part of tube: 52.88mm
Depth from bottom of tube to opening at threads: 433.38mm
Calculated tube wall thickness (OD-ID) X 0.5 : 2.92mm
Last edited by Cefalu; 01-08-2014 at 11:07 PM.
1995 BMW 840Ci
1999 Porsche 996 Cabriolet, 6 speed
1974 VW Westfalia P27 Deluxe camper
1974 Mercedes 280C
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