Hello everyone,

I have had a 1979 dt 175 for about 10 years now and I love it. It lost compression last year and finally had the guts to remove the cylinder and piston. I thought I was going to find a disaster, but the cylinder and piston are not scratched or damaged at all. The both have never been removed and the rings look shot. I do not have a proper caliper to measure the bore but it has never been modified. It clearly needs new rings but I am not sure which direction to take. I want to have a professional do the machining, but should I move up to a larger piston and have the cylinder bored or should I just have it honed and install slightly larger rings? Is there such a thing as larger rings for the original piston? What are my options? This is clearly the first time I have attempted to dig this deep.

Ok you don't seem to know much so.

1when you say it lost it compression what do you mean? all of a sudden or what? and what indicates "It clearly needs new rings"

2 rings come in sizes to match the bore,though new rings have more strength to seal. ( I won't bother with telling you about end gaping the rings yet)

3 you ned to have it measured to detrmin if it needs boreing.

Posting a few good pictuers would help.

Before the compression went to hell the throttle cable stuck completely open and the kill switch would not stop the revving. I pulled the spark plug wire which ended the deal but following the event the bike would not kick over. I replaced the cable but am now dealing with the aftermath. The rings look to be worn and the edges are pretty sharp and blackened. I will post pics sometime tomorrow. The piston does not show any wear however. The pin holding the piston on the shaft was very scored and super hard to remove. I have already ordered a new pin and bearing. When would a bore need to be done?

Your easiest option ( assuming the crankshaft and seals are ok ) is to rebore and fit a new piston and rings . My first bike was a '79 DT175MX . Great bike and pretty simple to fix , but you should get a workshop manual . They are available and are a great help . Best of luck .