ddrag2 Posted July 21, 2014 Share Posted July 21, 2014 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. Link to comment Share on other sites More sharing options...
dt502001 Posted July 22, 2014 Share Posted July 22, 2014 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. Link to comment Share on other sites More sharing options...
ddrag2 Posted July 22, 2014 Author Share Posted July 22, 2014 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? Link to comment Share on other sites More sharing options...
KevtheRev Posted July 23, 2014 Share Posted July 23, 2014 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 . Link to comment Share on other sites More sharing options...
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