1982 Porsche 924 TrackBuild, Should it Stay or Should It Go?

Stupid question: in your new rear subframe, there's the large center element with a big hole in the middle...what's that for? The factory torsion tube/driveshaft is above it.
Thanks for the answers re imperial vs. metric hardward. It may be apocryphal, but I think I read that during the Concorde program, the French said they wanted Bristol/Rolls to re-engineer the Olympus engines from Imperial fasteners to metric. We can imagine the words used at Filton to say "ain't gonna happen". Thanks, John

Finally got round to checking this out Robin - massively impressed with your work and immensely jealous of your design skill! If you fancy a change of scenery, there's plenty to do round mine  

Andy

So what is that big circle with the hole in the middle of the new subframe for? Driveshaft? John

Thanks Broady!



Ah, not sure how I managed to miss answering that in my last post! jonomisfit is absolutely right, it's for the exhaust to pass through. I really want to make sure that no part of the car sits lower to the ground than the floor pans or front subframe so the exhaust will pass through there to keep it up out of harms way.

A little bit of an update:

I finally managed to get some welding gas and decided to distract myself from the subframe briefly by getting the rear bearing carriers sorted. I had a pair of mk1 Audi S3 front uprights kicking around from an old project which I'd decided to use the centre section of as a pre-machined bearing housing. I did try and swap them for mk4 golf or audi A3 ones as the S3 items make a nice upgrade for the lower spec cars if they're lowered, as they have the geometry corrected for the lower ride height of the S3. Sadly it got to a point where it wasn't worth my time so I just butchered the S3 ones.

The first job was to get the drive flanges out of the uprights to give me space to get in and cut off the superfluous bits. I thought the was a good excuse to finally make a press frame to work with the porta-power I own but never use. I'd grabbed some really heavy duty steel from the scrap bin at my old work (with permission) when some stuff got ordered wrong and thrown straight in the scrap. Some of it was used to reinforce the doorway of the unit and add some security, and the rest I'd kept with a press frame in mind. It's massively overkill for the 10 tonne ram of the porta-power, but it was free, so who cares. At least if I ever decide to get a bigger ram it'll be up to the job with a tweak or two:



Which let me squish out the drive flanges to be left with a pair of these:



A while with an angle grinder later:



Then a while in the lathe to take all the unwanted features off, and just leave a lip at the rear edge



Tap a laser-cut profile over it up to the lip, weld the hell out of it, then press out the old bearings outer race, repeat the lot as a mirror image and you're left with a pair of these:



I left the bearings in until after the welding to try and minimise distortion and it seems to have worked, they certainly appear to still be round and parallel sided but I don't have much in the way of specialist bore checking kit. Once the initial corrosion was cracked the old bearings pressed out very smoothly, hopefully the new ones will go in similarly. The welds are actually kind of behind the bearing and I haven't taken it back very thin, so hopefully haven't messed up their shape.

With those done, I welded the rest of the rear subframe before starting fun and games with a few strategic cuts and welds to get it back to the shape I wanted it, as the heat of welding all the top surface without it supported by the cars shell warped things a fair bit. In hindsight this was obviously going to happen, the design's very weld heavy and it was probably a mistake to weld one side in place and the other unsupported as it encouraged it to all banana pretty badly. I'm happy I've got it back how it should be now though and no weaker thanks to careful thought of where to make the nips and tucks. I should have got some shots while doing the tweaks but I was in a head-down-get-on-with-it mood with headphones on and didn't think to take photos:







I think the end result looks quite cool, it's a shame it'll all be hidden under tatty bodywork. The next job for the back end is to make the bits that will join what I've done already: the rear arms.


Speaking of arms, I also found time to send some of these off to our friendly local laser cutters:



Which allowed me to collected this little lot earlier today:



Those will let me have another go at the front arms, this time with the M18 lower ball joints matching the strut inclination angle from the word go, instead of the 5/8th ones mounted horizontally the old ones were cut to suit. The eagle eyed of you may notice that there's actually the parts of the 3 arms there. I thought this time I'd get enough done to have a spare in case anything goes wrong with the first.

So I'm now 4 arms and one front upright away from being able to put the car down on 4 wheels, I'm genuinely excited by that thought, I think it's been 2.5 years since I first cut up the original front subframe and killed the possibility of having 4 wheels fitted at once!

To be honest I probably didn't think about it as much as I maybe should have, but after the fact I'm happy they're well stuck on there. Most importantly they do seem to be cast steel not cast iron; they're not brittle, they spark like steel and they give off curly 'cuts' of swarf, not just powdery chips. That's from memory though and I must admit I wasn't looking out for whether they were iron or steel, I'd just assumed that they would have used steel for a part like this, you've got me thinking I should double check on some of the off-cuts before I put them into any use. I did do a little test weld on the off-cuts and when I attacked it with a hammer it broke through the weld before the metal of the part. I kept a close eye out for any oddness around the weld but it seemed quite normal. On the back face the edge I was close to burned back just like I'd expect and the pool seemed to flow into the housing fine.


I managed a bit more over the weekend. I stuck together the second upright:







Then although I forgot to take any photos of the process I repeated the chopping up that I'd done on the other side to angle the balljoint to face the top mount.

Then I cleaned up the track rod end adapters I'd made ages ago for the front subframes 'plan a' which was abandoned before this thread started. In the end these turned out to be right for the new set-up too. They're M14x2 one end and left handed 5/8th UNF the other end, with a hex in the centre and a fair bit of length to make up for how much narrower an escort is than a 924. A few seconds in the lathe with some emery cloth and they're looking good again. Finally I threw a little primer on them and uprights as well as the rear subframe to keep them from going orange:

Could I ask where you get your laser cutting done ? Can't be a million miles from me (near Wells) but been quoted a stupid amount of money for a cut piece of 1mm sheet so time to investigate options.
How's progress anyway?
James

Thanks Broady and Oioisavaloy.




All the bits in this thread have been done by Luffman Engineering, who are based just off junction 27 of the M5, so the wrong side of me for you unfortunately. There's a couple of bigger guys in Bristol (SSC Laser and Precision Profiles), but I don't know how they'd take to smaller orders. For small batches Luffmans and Laser Industries (Saltash/Plymouth based) have always been good to me. I suspect all of them will have minimum orders though, and I don't know how any are with selling direct to the public. I've always put a few orders through them through work before getting my own bits done, which probably helps with the price too.

HI Robin,

Any update's on the Porker ?