Vw 1600 fox will not go into reverse

This sounds like a broken motor mount. When a mount breaks, the engine and transmission (since they're bolted together) twist slightly on the remaining mounts under the hood. This slight movement causes the shifter inside the car (which has stayed in place) to be "off" slightly at the transmission end. It's a pretty easy fix for you mechanic.

check the clutch cable for frayed and jammed and holding the pressure plate off. if hydraulic ,check that the clutch master is releasing the fluid ( blocked compensating port
If there is no problem in either system then it looks like a clutch kit is required.

Shifter Cable or linkage needs to be adjusted and or replaced.

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Bring it into VW the shifter has to be reset and the hard plastic bushing that make the shifter work have to be replaced. There is a special toolVW uses to reset the shifter on these vehicles NOT ALL SHOPS HAVE IT. This is a no brainer. If the Dealer is gonna ask a fortune to repair it(Which they shouldn't) You can purchase this tool on line and with the shop manual you can do this yourself.

The firing order is 1,3,4, 2. Look at your distributor ,, there are four connectors on the ouside on the distributor cap and one in the middle. The coil wire goes in the middle. The #1 spark plug connector usually is the one that is closest to the master cylinder,#3 is closest to the rafdiator,#4 is closest to the front of the head and #2 is closest to the rear of the head. make sure rotor and distributor are carbon free. Other wise it may not start and if it does it will run rough. Replace if the items are full of carbon

Hi Wesley,
From your description, it sounds to me like you have a broken piston ring. If this is the case, you're looking at a major repair... Not that the engine has failed catastrophically, but that to replace components such as piston rings, your looking at yanking out the engine and busting it down. Might as well call it an overhaul.
Get a second opinion, ok buddy?... this one is mine.

get a new timing chain then tune it up

there is a problem on the shift gear or shift lever check and adjust ,this is in the transmission assembly.

check engine to transmission mount.

Yes, but... I'm guessing you're likely trying to install a more powerful engine, such as the VW 16v from the later Scirocco mk2 ('83 to '89, and I think the 16v was available from '85 or '86). The basic blocks are very similiar; on earlier engines most if not all bore, stroke, and bearing dimensions are the same in same years and displacement, allowing one to use Audi connecting rods (stronger the the VW rods), and some other assorted benefits. Your first major complication is the crankshaft. The VW engine and transaxle is oriented transversly, the Audi's is fore and aft. Different transaxle and entirely different clutch mechanism. The Audi's clutch is fairly traditional, but the VW's is sort of reversed, with the pressure plate operated by a push rod running throught the center of the mainshaft. Result of which is; the crankshaft nose is different. You'll either need to machine the VW crank to mate to the Audi clutch assembly, or swap the Audi crank into the VW block. For reference, I strongly recommend Bentley Repair manuals; these are basically factory manuals sold to the public. For more and better information as to your specific intent, I suggest you try to find local VW or Audi clubs, or a really experienced VW/ Audi repair shop. A good mechanic who has been worked on these machines for years can probably help you get targeted on exactly what you will need to acquire to do the exchange. As I said, it's helpful that VW and Audi are so closely related, I'd guess it's a fairly simple process, bearing in mind that "simple" in context means an engine teardown and rebuild, installing the correct fuel injection and engine management components in the Fox, etc. And finally, if you do this swap; don't forget that more power brings other complications. You'll want to upgrade your brakes at least, and probably other suspension gear. Hope this helps, good luck.