Hi, I have a TY 175 Whitehawk and when I removed the head and barrel for a rebore I noticed that the head bolts had been modified and cut down as the stud holes in the barrel were a smaller diameter than the head.

Does anyone know if this means I have a DT175 head or did the TY175 have different variations?

It's  probably a 200 cc whitehawk, instead of short studs and sleeved head bolts they had full length studs and ordinary nuts on the head. Have a look at the spigot on the barrel, if its very thin its a 200cc barrel 

A DT175 barrel has different finning to a TY175 barrel.

A DT175 head has different finning to a TY175 head and has two plug holes.

A DT175 head and barrel is held on the same as a standard TY175 head and barrel is held on.

Your next question is probably going to be where to get an oversize piston from for your big-bore motor. For that answer, you'll need to take some measurements.

Bore diameter (accurately) or read the numbers on the piston crown.

Piston pin centre to crown dimension.

Was there a spacer under the barrel?

Thanks for the replies, there wasn't a spacer under the barrel I will do a bit of investigation and let you know, cheers 

Hi please find photos of the barrel.

I have already had the rebore and it is out to 67mm.

I'm not sure what that would make it cc wise

A standard TY175 motor is 66 mm bore and 50 mm stroke which is 171cc swept volume.

Your cylinder at 67 mm bore and 50 mm stroke has 177cc swept volume.

After seeing your photo (showing 8 mm studs a lot longer than standard studs), I suspect that your crankcase cylinder mouth was earlier enlarged to match a bigger cylinder sleeve to allow the cylinder to have a bore somewhere in the range 70 mm to 72.5 mm and that "200cc" cylinder was later replaced with the standard cylinder that you are showing. If this is the case then it would be interesting to know if there has been something done to match the diameter of the standard cylinder sleeve with the enlarged crankcase cylinder mouth.