shoggoth80 Posted February 20, 2006 Share Posted February 20, 2006 Hey all... JUST registered with the site. I have a 1976 DT400 that I know next to nothing about, and would like to pick some brains if I may. 1) Has anyone here ever owned one, and could lend advice? 2)If so, have you ever converted the engine to premix by using a pump block off plate? Any issues with under-oiling in this situation? 3)Can the compression release unit be safely removed, and blocked? I have NO experience with compression releases, all I know is that they are typically used to make starting the bike easier. 4)Have you ever used a different model cylinder (ie: MX, or YZ 400 models)? 5) What would you recommend to make the bike more spirited, and streetable? This is a street-tracker project in the works. I got the bike really cheap, and the motor needs a rebuild... I am already sourcing pieces for this, and happened across a pretty good deal on a used (2nd overbore) YZ400 jug from a breaker yard. Any and all input would be really appreciated. Thanks in advance for any info you can lend! Link to comment Share on other sites More sharing options...
Moderator YamaHead Posted February 21, 2006 Moderator Share Posted February 21, 2006 Regarding the compression release......they can be easily removed & blocked off with a spare spark plug in most situations. I would think the YZ barrel should work as long as the bolt pattern is the same......might also want to do some research on Bore/Stroke numbers comparing the DT to the YZ.....making sure the con-rod is the right length. Link to comment Share on other sites More sharing options...
shoggoth80 Posted February 22, 2006 Author Share Posted February 22, 2006 Regarding the compression release......they can be easily removed & blocked off with a spare spark plug in most situations. what about the space where it bolts into the cases? the cable runs down in there, and what would i do with that? snip it? leave the calble end to flop around? no... couldn't do that. put it out, and use a short bolt to plug? for the jug: could use same idea. while a spare plug would work, it'd llok pretty bugly poking out of the side of my cylinder like that! ha ha! bore/stroke: well, the YZ400's had the same bore... which leaves me under the impression that the stroke has to be the same, since the engines have the same displacement. Link to comment Share on other sites More sharing options...
Moderator YamaHead Posted February 23, 2006 Moderator Share Posted February 23, 2006 The bore may be the same....but they could arrive @ the same displacement by having a slighty different stroke & making up the difference with the con-rod length.....somethin' to think about anyway. Link to comment Share on other sites More sharing options...
shoggoth80 Posted February 23, 2006 Author Share Posted February 23, 2006 The bore may be the same....but they could arrive @ the same displacement by having a slighty different stroke & making up the difference with the con-rod length.....somethin' to think about anyway. maybe, although i imagine it as unlikely. i wished i had a site that would give me part numbers. i emailed the yamaha dealer that is closest to me (their parts department anyway), and fired away a few questions. even if the con rod is a different length i'd be willing to bet the bottom end bearing is the same. with what little i could dig up it seems like i lot was shared between the DT/YZ/MX series bikes in terms of internal specs/clearances. Link to comment Share on other sites More sharing options...
Moderator YamaHead Posted February 23, 2006 Moderator Share Posted February 23, 2006 You're probably right there Shogg Here's a site that's been handy for me, in terms of sourcing factory parts......MotoGrid Beats the heck outta paying those ridiculous dealer prices! Link to comment Share on other sites More sharing options...
shoggoth80 Posted February 24, 2006 Author Share Posted February 24, 2006 they do appear to use the same bottom end bearing, there are a bunch of internal bottom end part numbers that are shared... which is always promising. Link to comment Share on other sites More sharing options...
Moderator YamaHead Posted February 24, 2006 Moderator Share Posted February 24, 2006 Good news Indeed! Link to comment Share on other sites More sharing options...
shoggoth80 Posted February 25, 2006 Author Share Posted February 25, 2006 well, the dealer was amazingly not helpful... the parts department guy claims that he doesn't have info, or access to info for older bikes. somehoe i think that is BS, but whatever. looks like i do this the hard way! i won that YZ clinder on auction. trying to imagine what could be different as far as bore/stroke numbers.... but i honestly believe that they are the same... same bore would pretty much have to equal the same stroke... unless a shorter rod was used and a longer piston, or longer rod/shorter piston... either way with enough research, it should pan out. the YZ jug idea was suggested by one of the guys from motocarrera, so perhaps this was a more common mod to do "back in the day" to get some more oomph out of the DT series machines? who knows... i DO know that the early DTs and YZs use the same part number for boyesen power reeds. that makes getting that part set up pretty smooth. what would be schweet is if i could find a boyesen RAD valve to accomodate the reeds... but it would be tough to find one with the right size, and bolt patterns i imagine... i can always shoot another email to boyesen for that... would definitely add more grunt to the powerplant if they had something that would work. the question now comes down to heads... i have one that has some slight scoring inside, could be cleaned up with sandpaper, and one that has a small screw imprint in it (it was embedded in the piston!), with no other marks on it. which would serve as a better unit? i am under the impression that the screw imprint is less offensive, since the scratch/score marks on the other head look like the result of really sloppy decarbonizing, or broken piston ring pieces. should i trim down the fins on the other side of the head to accomodate the YZ pipe (while the pipes on both the YZ, and the DT exit at the same side, they cross over opposite sides of the head... one is a straight shot back, and the other crosses over close to the rear of the frame)? maybe just get a YZ400 head? i don't thing the combustion chamber is shaped differently. although more research may be needed here. this is a pretty adventurous and ambitious project, since i am bringing a bike back to life from virtually nothing. should be fun to watch the transformation process, as well as a major learning experience. should i use aluminum, or steel to block off the compression release unit? o-rings almost seem a no brainer to add in there for extra security, and dirt cheap to boot. maybe make little copper crush gaskets? Link to comment Share on other sites More sharing options...
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