The exhaust is a WES From Sammy Miller.
As people are asking about the YZ case on the TY here are the Mods that need to be made to the
YZ125 case to make it work on a TY
This Picture shows the Hole that needs to be moved. The Gasket is from a YZ125 layed over a Stock TY Case
I find that it is easier to grind away the front side of the hole first. Then build back up with the JB weld
and then to re drill the hole in the right place
This Picture shows the three places that needs to be filled in the YZ case to fit
And here is the spot to be filled at the top of the case
And here are the two places that need to be filled on the Bottom and back edge
I use JB weld to fill in the spots that need it and the Hole that gets moved. I use clear tape to the edge of the case to build a Dam so the JB weld flows and stays where it is needed. Be sure to roughen up the case first in order to get a good bond .I use a small grinding wheel in my drill. JB weld take about 24 hour to really set-up hard so take your time. After the JB weld is hard use a file to flatten out and you may need to add more JB weld in order to get things nice and flat
JB weld is a epoxy that when hard can be drilled or machined, So any epoxy that can be drilled and machined and will hold to metal should work.
Lay a TY175 gasket over the YZ125 case in order to see if the fitment is good.
If your TY175 has the foot peg mounts under the engine then you need to grind away the bump on the bottom edge of the YZ case that you filled in, you do not need to grind away all of the metal from the bump just enough to clear the foot peg mount.
The Rod for the kick starter return spring needs to be shorten by 0.400 inches in order for the YZ case to fit sorry no pictures of this. I use a cut off wheel in a small hand grinder to do this, just cover the clutch and kick start gears first so no grinding dust gets where it should not.
All mentions of top, bottom, front or back are for when the case is mounted to the engine and not for the orientation in the Pictures
The YZ 125 clutch cover from a 1974 is the same as the TY175, Both have a oil pump.
The 1975 YZ 125 clutch cover bolts right on with only the mod to the kick start return spring rod.
The 1976 to 1979 YZ 125 clutch cover will work with the above mods.
Now this is info for the US models but as all TY 175 engines are the same it should work on all the other as well