Hi guys, I have a new to me 1980 DT175 that I am doing some work on to make it rideable. When I got it I found the compression to be 55psi with signs of running out of oil causing damage to the piston and cylinder. I have bought a new piston for it, but it is taking weeks to arrive and it got me thinking whether or not I could fit a new cylinder + a new 66mm piston. I have found multiple sellers advertising DT175 cylinder/piston kits such as this one.  DT175 cylinder kit  which advertises as being suitable for 1979-1981 F, G, H motorbikes, but its absolutely not....

So can this fit my bike? If so what mods are required, it looks like I would need to change the stud nuts between case and cylinder unless I drilled holes in the fins, then it has a much larger inlet, so new reed block + carb connection boot?

Thanks in advance

You'll probably find piston pin height in piston is different too.

Cheap Chinese pistons often self destruct and take engine with it.

Similar listing on US ebay site says it won't fit the 1978 DT175 or the 79-81 "off road" models. Hate to say this but 78-81 DT175 and 79-81 "off road" model (we had the off road model in the US... called a MX175 but the MX does NOT mean the same thing it does in the UK) all take the same 2A7 cylinder. There is no difference!

So they are mislabeling the part... it either fits them all from 78-81 or it doesn't fit any... unless some country someplace had a different cylinder than most of the world.

I don't know what that kit fits but I suspect it's an 82 or later model that we never got in the USA. Have your cylinder reconditioned with a new piston and you'll be a lot of $$ ahead and about 1000 times more reliable.

Trying to make it work would not be worth the trouble and expense... probably need a new connecting rod along with other problems you already noticed.

Ok I thought this may have been the case, I wonder how many cylinders they incorrectly sell with all of them showing incorrect years. Seems a shame as buying a new cylinder would be nice, I’m not sure what a rebore will cost me in New Zealand 

at any rate, if you were to buy a new piston online, where would you get it from? something with oversized options

First step is find a reputable shop that knows two strokes and can do the machining. They can measure and help determine what oversize you'll need to buy. RT325 and others are in NZ and might be able to suggest a shop. Shop should bore to factory clearance specs... some places like to "add extra clearance" which is not good. They also should know how to chamfer the ports after machining to prevent ring snagging and/or premature wear.

There are lots of options for pistons... I'd stay away from Chinese pistons. Japanese name brands are often of excellent quality. You can also use a Yamaha Blaster (200cc 4 wheel ATV) piston if you trim the piston skirt slightly to match height of 175 piston. Blaster pistons are super easy to find here in the US.

Of course there are the two premium forged brands... Wiseco and Wossner. Wossner might be the better of the two.

Where exactly in New Zealand are you ?

Mark can the blaster piston be used in the ct 175 reed and piston port models or only reed…or none?

Would the kit fit a reed ct ? Looking at a $65 wiseco top end kit I see the ports in the piston and assume you would need the 6 bolt 2a6 or blaster head.

I first heard of using a trimmed Blaster piston from DVM...  he was heavily involved with the development and building of the sleeper pipes and had the best running CT3 I've ever ridden and it reportedly used a Blaster piston with skirt trimmed.

I've personally used modified Blaster pistons in a 76 and 80 DT175. 

Reed valve only.

The Chinese DT175 cylinders only fit Australian model bikes, that were updated versions of the DT175MX produced 78-81. It might be possible to fit one to an earlier motor, but it would be an awful lot of work, and probably cost more than getting a badly damaged cylinder re-sleeved.

Blaster pistons have longer skirts than DT and compression dome height is slightly different. They arent as strong as DT pistons, as the boost windows are bigger, but the ring pegs are further apart, so the boost port can be made wider.