dt400 pistons

[ya me hauler]

awhile back i read a few paragraphs from someone who seemed to know alot about dt400s .I have a 75. had broken piston . not having alot of $ I bought a used dt400 piston from a 78. all together and running ok but seeme to lack comp. did a leak down test dropped below 90. inspection show , most of the hone work I did untouched. I have a better hone and want to try again. whats the most clearance I can run on this engine 4 thous.? I only run this a few hours a summer when I take dirtbiking trips. thanks

[johnmumie]

Check out fellow member amcfrek...........

[amcfeek]

check the ring clearence with a feeler g.i dont know what the clearance should be but id bet the rings are sad.. if the piston is fine chck the rings it sounds like the rings are not making contact on the walls ..

the big bore from what i got asking around can take as much as 5k of slop and still run alight and wont seize when pushed ,3 k is nominal but 4 is about fine as they like to swell pistons up the way it is .. air cooled...
you can either find you own .75 over mx 400 piston made like 1 year 75 or kick my ass for mine .. i bought a nos for mine , as i have a 75 and a 78 that are both .75 , and infact if you were using the stock 75 piston it will have the L shaped rings wich are a hard find ... rings are the same from dt it yz and mx 400's the 77/78 is the most common parts in ebay {pistons are different}
the dt and the it/yz400 used a different piston , as the connecting rod is different the mx400 and dt 400 share the 498 connecting rod the yz/it400 used the 214 rod wich is longer then the 498 rod .
piston fit from dt400's from 75 to 78 and are pretty much the same .as the 75 were a bit lighter and had th dikes rings i can show you a pic as i have one here..the pisons ugly but the bore is fine ..

for better you can open up the window in the piston a little bit , then you can do some mild port work ..open up the exhaust port a few mm {2mm each way isnt all that much and should clear up the cylinder liner alighnment} polish the exhaust and whala..
oh yeah drop the intakes floor a few mm to get the piston to open up the intake sooner my plans for my dt engine i was kinda blessed with . they do run alright..