Building a 904
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Author:  Bill Sargent [ Tue Oct 16, 2018 11:35 am ]
Post subject:  Building a 904

And so it begins .....
File comment: Underside of nose
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File comment: Top of nose and roof
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After many years planning and gathering parts my 904 build has started in earnest. Martin and Walker in the U.K. is building the roller, which I hope will be delivered in 12 to 18 months for me to complete things like drive train install, wiring etc. Lay up of body parts started on Monday and chassis fabrication will start in a few weeks.

This build will differ from all prior M&W builds (~ 20 since 1999) by the use of a two liter Porsche 4 cam motor, a 904 transmission and correct suspension uprights.

The week after Rennsport I also started the rebuild of the motor, with Jacques LeFriant doing the work. Jacques was kind enough to mentor me by allowing me to assist with tear down, procurement and eventual reassembly.

Before starting this thread I consulted with the Registry trustees since the car, even though it will be built with a Porsche drivetrain and many other original parts, will be a replica. I received their approval.

This will be a long running thread as M&W only build about 1 car a year. Thanks for following along!

Author:  Brad Ripley [ Tue Oct 16, 2018 1:02 pm ]
Post subject:  Re: Building a 90faux

Bill, Sounds like another one of your great projects, long distance from China. Keep us up to date with progress reports.

What was the approval you got from the Registry trustees?

Author:  Bill Sargent [ Wed Oct 17, 2018 10:39 am ]
Post subject:  Re: Building a 904

Hi Brad,

Not so many years ago there was a high level of concern among the trustees about replica cars. This concern extended to not allowing them to be discussed in forum threads, attending events etc. Even though I am building a replica I felt the process might be of interest to Registry members as the chassis is being made off factory blueprints, I am using a Porsche 2 liter 4 Cam motor, a reproduction 904 trans case and reproduction factory suspension parts. So before starting this thread I corresponded with the trustees to inform them about the build and request their concurrence to start a build thread in the projects section. They were kind enough to give me a green light.

Author:  Greg Scallon [ Wed Oct 17, 2018 11:42 am ]
Post subject:  Re: Building a 90faux

I give you a green light too, Bill! :-). Looking forward to seeing this build progress. If it's anything like your cabriolet build, it'll be fascinating.


Author:  Bill Sargent [ Wed Oct 17, 2018 11:43 am ]
Post subject:  Re: Building a 904

Prior to Rennsport Reunion I shipped my 4 cam motor down to Jacques LeFriant for a preventative rebuild. The motor was running well, but I found an exhaust manifold stud pulled from the head - and it was partially under an oil return tube. This meant the motor had to come out and the head would need to come off to make the repair. This, plus the fact that the motor had about 40 vintage race hours on it since the last refresh prior to my purchase, made me decide that a preventative tear down made sense.

The motor is a 587/1 out of an early C Carrera II coupe. It had a major rebuild by Jacques and Stan Gold’s mechanic in early 2004. At that time a Crower crank, Pauter rods, Mahle pistons reworked by Whal and new Carrera II cylinders were installed. At some point the valves were replaced with custom ones that had stems about 8.5 mm diameter (stock stems are are 9 mm intake and 11 mm exhaust). Valve sizes were enlarged to 50mm intake and 42 mm exhaust. Intake cams were changed to dot 2 while exhaust were left stock with dot 1. The sum of all these changes produced a 904 street spec motor that dyno’d at about 160 flywheel hp.
File comment: Motor prior to tear down
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The Monday after Rennsport we started the tear down. The first step was to check the valve timing to have a baseline.
File comment: Checking the 1-2 cylinder intake valve timing.
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Motor was then torn down over the course of Monday and Tuesday. Jacques had me doing the dirty work.....
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Cam shafts Valve Drive shafts are removed and tie wrapped together to keep the shims in place. Jacques also has nice aircraft plastic storage trays with spring lids to keep parts for each intake and exhaust valve together.
File comment: Tie wraps on cam shafts to keep shims in correct places.
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Then the heads come off and the shroud is next.
File comment: Heads off.
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After the heads and shroud are off the pistons and rods can be removed. The case can then be split. In the photo below the intermediate shaft has already been removed.
File comment: Case split, crank still in case
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By this point the motor is pretty well disassembled.
File comment: Guts!
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File comment: Case and bare heads. Valves and springs removed. All parts for each valve kept together.
DB0AEAF0-FD74-4E43-A817-B82186B6C577.jpeg [ 315.89 KiB | Viewed 710 times ]

In the next post I will describe the condition of parts and what will be replaced etc.

Thanks for following along.

Author:  Bill Sargent [ Fri Oct 19, 2018 12:02 pm ]
Post subject:  Building a 904

This post will cover the internal condition of the motor after tear down and inspection. The motor started life as a 587/1 in a early C carrera II coupe delivered in August 1963 (per Heinrichs Carrera book). It had an extensive rebuild in 2004 by Jacques LeFriant after its purchase by Stan Gold as a spare motor for his 904 (904-006) to use for vintage racing. The goal was to produce a 904 street spec motor. At that time the following was done:

- Crower billet crank, new bearings
- Pauter rods (CrMo), new bearings
- New valves, guides and seats. 50mm intake, 42mm exhaust. (904 valves are 50mm intake and
43 mm exhaust). Odd size stems ~ 8.5 mm intake and exhaust. Exhaust were bimetal.
- New carrera II cylinders
- New pistons machined by Wahl (ex Mahle employee who sold his own design pistons) on new
Mahle blanks – essentially 904 pistons with deeper valve pockets
- Heads X-rayed
- Solex P40 replaced with Weber 48 IDAs
- Dot 1 intake cams replaced with Dot 2 (higher lift)
- Carrera II flywheel replaced with 904 flywheel (lighter).

After rebuild the motor dynoed at 163 crank hp compared to a stock Carrera II at 130 hp.
File comment: Original carrera II crank on left (with fixture to allow it to stand upright) and Crower billet crank from my motor on right.
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File comment: Pauter rods
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File comment: 904 flywheel, some of the valve drive shafts and the layshaft.
BAE8C1C9-27B5-44BF-A6BB-77592D67AF1F.jpeg [ 134.79 KiB | Viewed 657 times ]

The motor then was used for vintage racing in Stan’s 904 for about 40 to 50 hours. The motor was torn down again in 2009 after something happened in the 1-2 cylinder intake valve train. It was bad enough to crack small parts of the cam enclosure part of the head in two places. This damage was repaired by welding. We theorize that an over rev may have allowed a drag lever to float enough for a lash cap to escape its home on a valve stem and wreck havoc. The valve drive “C” shaft pinion gear and its matching ring gear were pretty chewed up and were replaced. The damaged C shaft is shown below. Crank and rod bearings were replaced, but nothing else. The motor reassembled and dynoed again, yielding 164 crank hp.
File comment: Damaged “C” valve drive shaft removed from motor in 2009. Note that new motors have a matched set of shafts with the same number on every shaft, preceded by a letter A thru F. In my motor all the original shafts were number 371. You can see C371 etched on the shaft.
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File comment: Valve drive ring gear from another motor. Note B443 etched on the gear. Every original shaft and gear in this motor would have had 443 on it. Note broken tooth and grinding. Gear was welded to the cam shaft and grinding was needed to get it off. This motor needed the B shaft replaced and what ever happened was bad enough to severely crank the head on that side.
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The motor was then vintage raced in Stan’s 904 and RS60 for about another 40 hours prior to my purchase. I then put about 1000 road miles on it. Motor was running well prior to this tear down, with the exception of occasional plug fouling – which Jacques traced to too cold heat range spark plugs.

So at this tear down the motor had 90 to 100 vintage race hours and about 1000 road miles since the 2004 major rebuild. We found the following:

- Leak down 3% to 8%. Valve timing all within 3 degrees (factory spec is within 4 degrees) –
some closer than others. Intake valve lifts ~ 11.75 mm.
- Case main bore still standard, but a little tight (0.02mm) on the center main – likely due to a
little case shuffle. Rest of case in good shape. See Photo below.
- Crank mains near low limit but look good. Will need to closely measure mains and a bearing set
to decide if we polish and stay std or grind first under. Crank rod journals std and look very
- Rod big ends still std. little end bushings slightly oval.
- Very little valve guide wear, but all valve stems slightly tapered – 0.01 to 0.02mm. 2 x intake
valve heads pretty pounded – knife edges. Rebuild justified on this alone. Exhaust valve heads
looked good. One chamber in one head had minor foreign object damage (small dings) – likely
something to do with the 2009 event? See photo of intake valve head with knife edge.
- All valve drive shaft splines not overly worn. Estimate 2 degrees rotation (problem over 4
- All valve drive gears look good. Valve drive shaft bearing seats all worn 0.01 to 0.02 mm. Valve
drive shafts and gears good to reuse.
- We found the valve drive gears that are normally pressed onto the cam shafts had been brazed
to the shaft – likely preventative to keep them from spinning – but the sign of a turkey. See
photo below. OK to reuse, but if one of the gears is ever damaged, the cam shaft will probably
need to be sacrificed to save the gear. So a new cam shaft would be needed.
- Cam lobes looked good with no visible wear (they fit on cam shaft and can be changed out).
Reuse. Same for drag levers.
- Intermediate shaft gear looked good. Seat for 2 x valve drive gears was a little scored - like one
gear may have had a burr. Bearing seat worn 0.01 to 0.02 mm.
- Piston wear within acceptable limits to reuse. Rings need replaced.
- Cylinders worn oval enough to require recoating or replacement.
- Oil pump – very worn – likely never replaced.
File comment: Foreign object damage in one chamber
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File comment: 50 mm intake and 42 mm exhaust valves. Note sharp edge on intake valve head indicative of valve being pounded into the seat.
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File comment: Turkey modification- note gob of brazing at junction of cam shaft and valve drive gear on shaft. What appears to be a chip out of one of the ring gear teeth is some oil and the way the light hits it - not a piece missing.
5F82AA99-2381-4122-8E91-38B0E77B8E76.jpeg [ 278.45 KiB | Viewed 657 times ]

So for those that say carrera motors are fragile, this one at least says different. Bill Doyle recommended rebuilding a 2 liter motor every 40K to 50K miles or every 40 racing hours (assuming it was built correctly in the first place). So here we have a motor with ~100 vintage race hours with only bearings replaced after 40 hours. And it is not in bad condition. Gregory Campbell has had similar experience with the 2 liter flat fan motor he races in his Elva.

We will do the following for this rebuild:

- Closely measure crank and a set of Std bearings to see if the main journals can stay Std or if we
need to grind them first under and renitride the crank. Polish rod journals.
- Replace rod little end bushings. May machine big ends to take Toyota clevite bearings – lots
cheaper than Porsche rod bearings.
- Ream valve guides to 9mm (currently ~8.5 mm). Purchase custom Ti valves with 50 mm intake
and 43mm exhaust heads. Install beryllium seats. (About $2,500 to $3,000 all in including
installing new seats). May clean up cylinder sealing surfaces in heads.
- Install oversize bearings machined to size for all valve drive shafts.
- Hard chrome intermediate shaft gear journal and machine to size. Install oversize bearing
machined to size.
- Replace rings
- New carrera II cylinders from Millennium (who make cylinders for L&N) – about $3500
- Purchase new oil pump (~ $4,000) or rebuild old one with new gears and center case that
Jacques has made (Parts + 3 days labor to match gears to new center case). Leaning toward
new while Euro is weak.
- Install a time sert in the one exhaust manifold stud that pulled from the head. Check all other
- New gaskets, stainless oil return tubes, replate fasteners and find some original fasteners for
more visible ones,
- Swap Weber 48 IDA for Weber 46 IDM. Found the Weber 46 IDM carbs several years ago and
had Pierce Manifolds in Arizona rebuild them.
- General cosmetic clean up.
- Install reproduction Speedco distributors with 123 electronic guts. Possibly also install a
Winterburn CD set up (like Jack Walther did on the Dean Jefferies Kustom Karrera). Have
original distributors rebuilt and keep on shelf.

The rough estimated cost for the rebuild, including parts and labor is $20,000 to $30,000. Which is about double a comprehensive pushrod motor rebuild needing the same kind of work. The main drivers for the higher cost compared to the pushrod rebuild are the custom valves & seats, new oil pump, more expensive bearings and more labor hours for machine work and reassembly. Shipping to/from Seattle adds another $1,500.

At this point I must thank Jacques for allowing me to work with him in his shop to disassemble the motor and for being so giving with his time to educate me. I asked a LOT of stupid questions. Olivier Auvray, a 4 cam mechanic from France, was also there and helped with the mentoring. Thank you Olivier.

Hopefully this thread will provide some hands on education about the 4 cam motors. My next few posts will cover various parts that have been purchased or fabricated over the last few years for the 904 chassis, suspension and body build.

Thanks for following along.

Author:  Bill Sargent [ Wed Oct 24, 2018 7:18 am ]
Post subject:  Re: Building a 904

One major item that I needed to procure for the 904 build was a transmission. The 904 transmission used the same internal parts as the 911 type 901 transmission with the exception of the input shaft which had second gear separate from the shaft and a different reverse lock out part (same as 911R). Internal parts were easy - Ralfy in Alaska had a low miles 68 911 transmission that he sold me the internal parts out of. We purchased the input shaft from Tom at Carquip and Jacques Le Friant supplied the reverse lock out parts.
File comment: Parts laid out for the transmission build. 904 case to the right, early 911 case to the left. 904 input shaft on the edge of the yellow cloth. Also using a GT Torque biasing differential in the transmission. Lobro half shafts, not the original Nadella
904 Trans build starting.jpg
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File comment: 904 (and 911R) reverse lock out part
904 & 911R Reverse lock out parts.JPG
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The case itself, nose cone and shift linkage parts are all 904 specific. Unlike a 901 transmission, which has the shift shaft in the nose cone for 911 use, the 904 has the shift linkage come out the bottom of the bell housing in order to have a shorter shift shaft in the mid engine configuration. The 904 transmission also has bosses on the sides of the bell housing to allow it to mount to the chassis, with the rest of the transmission extended rearward with no support at the nose cone end. The photos below show the 904 transmission case, parts to mount the transmission in the chassis and shift linkage parts.
File comment: Side view of the case. Triangular boss with 3 holes on the side of the bell housing is where the mount to the chassis is bolted.
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File comment: View of case showing reverse lock out mount hole - round hole near fins.
DSC08026.JPG [ 137.61 KiB | Viewed 580 times ]

File comment: Bottom of case. Square hole on bottom of bell housing is where shift linkage comes out.
DSC08078.JPG [ 151.26 KiB | Viewed 580 times ]

File comment: 904 nose cone. Original on left. Casting to be machined on right. Speedometer was driven off transmission nose. I will probably use a GPS speedometer.
IMG_0666.JPG [ 199.12 KiB | Viewed 580 times ]

File comment: Two black parts are the mounts that bolt to the side of the bell housing to mount the transmission to the chassis. Shift linkage parts are shown below them.
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File comment: Additional shift linkage parts
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File comment: Internal shift rail parts that are 904 specific.
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File comment: Clutch throw out bearing lever and shift linkage parts
904 clutch lever and shift linkage parts.PNG
904 clutch lever and shift linkage parts.PNG [ 102.03 KiB | Viewed 580 times ]

Complete 904 transmissions are not readily available as you might guess. Freisinger in Germany had one for 120,000 euros. Stan Gold had a spare for his 904 at $65,000. Neither were within my budget. Fortunately a couple of 906 enthusiasts in France have reproduced the 906 transmission case, which is the same as used in the 904. They made 3 aluminum (as used in 904) and 5 magnesium (as used in 906) back in 2015 and I purchased one of the aluminum cases, a nose cone, the shift linkage parts and internal shift rail parts. I estimate that once Ralfy builds the 904 transmission for me I will have about $23,000 in it - including all parts and labor. Not cheap, but way less than an original.

The next post will discuss front suspension parts. Thanks for following along.

Author:  Vic Skirmants [ Wed Oct 24, 2018 8:11 am ]
Post subject:  Re: Building a 904

I see you changed the title of the post. Too many people couldn't figure out "faux"?

Author:  Wes Bender [ Wed Oct 24, 2018 10:40 am ]
Post subject:  Re: Building a 904

... or they couldn't pronounce it correctly...

Author:  Vic Skirmants [ Wed Oct 24, 2018 1:06 pm ]
Post subject:  Re: Building a 904

Wes Bender wrote:
... or they couldn't pronounce it correctly...

:D :D

Author:  Bill Sargent [ Wed Oct 24, 2018 10:14 pm ]
Post subject:  Re: Building a 904

Vic, I felt the need to be more inclusive; I was worried only Jacques might understand 90faux :D !

And now for a teaser of more to come, a photo of the factory 904 chassis assembly bench. Raceline Fuestel in Germany purchased it from Porsche many years ago.
Porsche Factory 904 Frame Bench.jpeg
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We are in Da Li, Yunnan province China now for a long weekend.
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Thanks for following along.

Author:  Bill Sargent [ Sun Nov 04, 2018 10:09 am ]
Post subject:  Re: Building a 904

904 suspension parts are something that I have been working on for a few years since they not normally reproduced. The 904 was the first Porsche not to use trailing arm front and swing axle rear suspension (per Wikipedia - anyone know otherwise?). Coil springs are used on all four corners with an unequal a double A arm front suspension. I have not seen a name for the rear suspension but I am sure someone on the board can tell me what it is. The rear suspension has an A arm at the top and three other locating links, two running forward and one running laterally from the bottom of the upright to the rear bulkhead. This suspension was carried forward and used for the 906 as well.

A factory diagram of the 904 front suspension is shown below:
File comment: Top view of front suspension
904 front suspension 1.jpg
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File comment: Front view of front suspension
904 front suspension 2.jpg
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M&W supply the front A arms with their chassis, so that part is easy. The hard part is the front suspension upright. For years Barrie (owner of M&W) has used modified early 911 front suspension parts, but these are becoming both more rare and more expensive. Various people have made cast and heat treated CrMo uprights over the years, but for a critical part like this a forging is more desirable. Barrie had a factory drawing for the 904 front suspension upright so I placed it into CAD:
File comment: 904 front upright factory drawing
904 front upright drawing Clean.JPG
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File comment: 904 front upright rendered in CAD. I use Autodesk Inventor and then export in the file format needed.
904 front upright Original Version - 21Aug15 (2).JPG
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The next question is how to get them made. Barrie plans to get them CNC machined in the UK using my CAD file, either from billet CrMo or titanium and use them on his cars going forward. Prior to Barrie making this decision Jacques hooked me up with a fabricator he knows who was making a small run in forged titanium. The finished product is shown below - forged Ti upright, machined steering arm and aluminum brake caliper mount.
File comment: Test forging of the titanium uprights.
Front Upright Test Forging - Dec16.jpg
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File comment: Finished forged titanium front uprights. Not cheap, but also not something you want to have fail....
904 Ti Uprights.jpg
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Rear suspension uprights were a little more difficult as I have never seen a factory drawing and neither has Barrie. Fortunately a prior M&W customer in The Netherlands had a set that he loaned Barrie to duplicate. Barrie used Ben Coles in Birmingham to make the aluminum castings.
File comment: No 3D printing in sand - Ben does things the old school way.
904 Rear Susp Uprights - Casting Boxes at Ben Coles - Aug2016.png
904 Rear Susp Uprights - Casting Boxes at Ben Coles - Aug2016.png [ 962.59 KiB | Viewed 364 times ]

File comment: Raw rear suspension upright casting
904 Rear Suspension Uprights - first Castings at Ben Coles - Oct2016.png
904 Rear Suspension Uprights - first Castings at Ben Coles - Oct2016.png [ 241.7 KiB | Viewed 364 times ]

File comment: Fully machined rear suspension upright
904 Rear Upright Castings machined - photo 4 - 2Dec16.jpg
904 Rear Upright Castings machined - photo 4 - 2Dec16.jpg [ 306.92 KiB | Viewed 364 times ]

The only 904 rear suspension uprights I have seen advertised recently are currently in the classifieds section of the Registry from Classic Parts in Germany - NOS for $15,000. Barrie got his done for about 20% of this price - but he made enough for several cars.

Below is a partially assembled 904 rear suspension prior to installation in Gregory Campbell's car. Original cars used Nadella half shafts, just like early 911s. But they had a larger diameter half shaft with a sliding section for racing. A set of the racing Nadella half shafts is for sale on E-bay at the moment for ~ $5K, but I will pass and use the more reliable Lobro half shafts like later 911s used. The rear parking brake assembly is virtually the same as the 356C and early 911 unit.
File comment: Rear suspension partially assembled prior to installation on Gregory Campbell's car - which he had at Rennsport VI
Gregory Campbell 904 - Rear Suspension 2.jpg
Gregory Campbell 904 - Rear Suspension 2.jpg [ 87.87 KiB | Viewed 364 times ]

The next post will provide some info on making a proper reproduction 904 chassis. A couple of companies (Beck and Rock West Racing) offer 904 replicas, but use tube frame or a combination of tube and box section chassis. M&W, Duel Motorsports (Netherlands) and Raceline Fuestel are the only companies making a correct chassis, with M&W the only company offering complete cars on a regular basis. More on this in the next post.

Thanks for following along.

Author:  jim nelson [ Sun Nov 04, 2018 10:53 am ]
Post subject:  Re: Building a 904

Very cool. I appreciate the time and effort it takes to reproduce bits in exotic materials, as we’ve had to make a number of things in the ex-Alesi Tyrrell 018 that I’ve been restoring. No parts manual, no workshop manual, but in touch with a number of ex-crew members with knowledge that’s priceless. And, like all race cars, different versions of the same bits as development progressed. Thousands of parts. Occasionally a bit daunting, until you break down what you need to do into manageable tasks, and then stay on task. Hard to not get distracted by the next in line thing to do. Watching this thread with great interest, it’s a pleasure to see a pretty close build of a great car.

Author:  Bill Sargent [ Sun Nov 04, 2018 11:33 pm ]
Post subject:  Re: Building a 904

Hi Jim,

WOW, restoring a Tyrrell without a parts or workshop manual (or drawings) is in another league compared to what I am doing. I guess you are into lots of measuring or laser scanning parts to get them into CAD for reproduction. Feel free to hijack this thread for a post on parts you are making.

We thought about laser scanning to get the chassis rear bulkhead right, but opted for a more low tech method that appears to be workable. More on that in a post to follow.

Author:  Adam Wright [ Tue Nov 06, 2018 11:08 am ]
Post subject:  Re: Building a 904

Bill Sargent wrote:
904 suspension parts are something that I have been working on for a few years since they not normally reproduced.
Thanks for following along.

My problem with my build was having to lower all 4 shock towers to fit under the 904 bodywork, which was very tight. With the help from Elephant Racing I was able to get the shocks short enough, while still allowing almost full travel. I was talking to Chuck Beck about my build and told him I was using a 914, he said you can't, the shocks are too high. I told him I was lowering all 4 towers, he said I was crazy. Maybe I am.
Please keep posting pics of your build Bill, nice to see a 904 build not bound by budget concerns.

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