Yamaha DT400 help

[plagrone]

My room mate just picked up this bike for about $200. Good compression, been sitting in a barn for 15 years, lights and gauges have been removed, and there's a nice rat nest in the battery box.

What are the go-to things that need to be done before a bike like this should be run. I'm talking more model specific stuff, not the standard: oil, chain, cables, plugs, filters, tank, etc.

Anybody familiar with these? I know old RDs should have some seals replaced before running, is it the same with a DT?

 

[SONICJK]

Replace crank seals, and clean it up

 

[VonYinzer]

It's such a ridiculously simple motor, why not tear it down and replace all seals and gaskets? For less than $100 and an afternoon you'd basically have a fresh motor (as long as the cyl and rings are kosher).

 

[xb33bsa]

do a case pressure test tells you where it leaks if it does

 

[DesmoBro]

Leave it alone get it running, rip it then replace seals bearings etc later on.... I thought i would replace all the seals first missed a washer along the way and the case blew apart when i went to kick it the first time...same bike...so if you need a parts motor...pm me

 

[xb33bsa]

+1 for sure get it running first, if it has issues then pressure check, before you blindly tear it apart
if the motor turns over now,it may be fine,doesn't hurt to pull the pipe and look in the cylinder with a flash lite

 

[DesmoBro]

Also if you do plan for a rebuild you will need to make (or buy) a puller & press. The cases have the crank bearings pressed into them and the crank are pressed onto the bearing....basically its a huge pain in the ass

 

[plagrone]

Leave it alone get it running, rip it then replace seals bearings etc later on.... I thought i would replace all the seals first missed a washer along the way and the case blew apart when i went to kick it the first time...same bike...so if you need a parts motor...pm me

This is the plan. Get it running first. Thanks, I'll keep you in mind.

Also, the bike is going to need to be %100 rewired

This is a bad omen:

I don't like seeing that symbol on anything electrical

 

[VonYinzer]

What's so wrong about rebuilding? So it takes some time and effort. It's a 35 year old engine that as far as the owner is aware, has never been properly serviced. I get trying to get it running I suppose, but at some point it WILL need a rebuild. So why not do it now?

 

[xb33bsa]

jeezuz why fix what isn't broken,those things are as reliable as a stone hammer, unless it has rust inside,chances are it will run perfect,forever,without any serious work

 

[DesmoBro]

What's so wrong about rebuilding? So it takes some time and effort. It's a 35 year old engine that as far as the owner is aware, has never been properly serviced. I get trying to get it running I suppose, but at some point it WILL need a rebuild. So why not do it now?

The rebuild will run at least $200 (probably more like $700)which is what the thing cost....and unless the tools and everything are in hand ready to tear it down i would just wait the longer it sits apart the easier it is to lose that washer... Also it is a simple bike so if you tear into the engine you may as well do a full restoration then when its done its done and looks new

 

[plagrone]

My room mate doesn't want to delve into it, his last project was a 1984 500cc v4 Magna, and it left a bitter taste as far as engine work is concerned.

If it exhibits symptoms of bad seals, we will deal with it then

 

[makotosun]

Good bike. I have a 78. Motor is different a bit from the 75-76 model, but same general design.

Go to www.yamaha-enduros.com and sign up - free and there are PDF versions of the factory service manual there. Also a forum with folks to give some guidance.

The electrical on that year is fairly reliable. Lots of parts still available from the dealer, and then goe e-bay or nwvcp.com for NOS stuff.

You can look at my rebuild thread here: http://yamaha-enduros.com/index.php/forums-community/kunena-2014-01-06/restorations/34-1978-dt400e-monoshock-re-do#78

First place to start is a really good carb cleaning then get it running.

 

[plagrone]

Thanks for the advice. Btw, I took the exhaust off and peeked inside. This is a piston off my spare cb360 engine, the dt400 has similar, but much lighter streaking on the sides of the piston. Is this okay?

 

[plagrone]

Sorry for even asking. Did some research on my own. Probably caused by overheating/poor lubrication?

 

[makotosun]

Most likely too lean of mixture. Could be run out of two stroke oil too. Remember, as you increase the amount of oil in the mix,the gas gets leaner - same when you increase airflow (such as using a Uni-filter over stock. Leases gas = leaner. Almost always better to be rich and foul a plug than lean and hole a piston. Don't ask me how I know . . .

I had a piston that looked much like that one in a DT400, which ran just fine. Obviously not what it should be, but these bikes tend to run quite well when pretty loose on the tolerances.

When you clean the carb, really soak it (Berryman's non-California formula is best) just replace the main and pilot jets. Under $10 for the pair and most bike shops should have them in stock. You can't get a carb rebuild kit for the 400's that I have ever seen, but most all the parts are available from Sudco. If it runs, but won't idle, probably the pilot jet is plugged.

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