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Noob with a seized 1973 Yamaha Enduro DT3 250

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Hi everyone,

 

This is my first attempt at doing anything with a bike, but I'm a quick learner, and I'm a technical person, so I should be able to figure this out.

 

I inherited a 1973 Yamaha Enduro DT3 250.  The previous owner had used it as recently as 2005, but as far as I can tell, the engine is seized up.

 

So this is what I've done:

 

I shift the gears so that it is in neutral, squeeze the clutch, and push the kickstarter down.  

The kickstarter starts vertical, and moves easily to horizontal, but just stops there.  I've put some pretty good pressure on it, and it ain't moving.

 

So I found this site:  http://www.dansmc.com/stuck_engine.htm

 

The bike will move in neutral.

The bike will not move in any gear.

 

The next step in troubleshooting is to pull the engine side cover off and try to turn the crankshaft bolt.  He says the crankshaft bolt is usually on the side with the alternator rotor.

 

Well, on the left side (while sitting on the bike) there is something that I'm guessing could be an alternator...it has copper wire wound around something anyway...

When I turn the bolt clockwise on that side, it won't budge no matter how hard I push, even if I squeeze the clutch.

When I turn counter-clockwise, I just remove the nut...

 

On the right side, there are a bunch of gears and what I think is the clutch (it moves when I squeeze the left handle lever)

The bolt directly under the engine on this side doesn't move in either direction, even if I squeeze the clutch.

 

It seams to me that the piston is seized.  So I removed the top of the engine, and sprayed a ton of WD-40 all around the edges of the piston/cylinder.

 

The kickstarter still won't move lower than horizontal.

 

Am I going in the right direction?  What is my next move if penetrating oil won't free this thing up?  There is no way I'm going to be able to build the grease fitting thing that the guy builds in the link I mentioned.

 

What are my options?

 

 

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Let the penetrating oil sit for a couple days then pull the top end. You'll need to have it bored and get a new piston, rings etc., but I would probably rebuild the whole thing for peace of mind.

 

Would I go to a bike shop to have it bored?  Where would I get a new piston and rings?

 

What exactly is meant by "pull the top end"?

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I cannot add much to the recommendation of letting the penetrating oil sit for a long period of time, that is the best option.  Diesel fuel works pretty well for me in the past.  In this video of mine you will see what "pulling the top end" means.  Also the bike in this video had a severely stuck piston (seen in the video) but I got it unstuck.

 

Top End Removal of a stuck piston

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It very well may be the bottom end. My bother picked a up an old RM 100 once, 1979 I believe. we thought it was just the piston, so we looked, found no rust, then pulled the cylinder only to find the whole bottom end was seized solid with rust. Needless to say we got her freed up and running in a day but I used 2 full cans of pb blaster(this stuff really works good to eat rust), a whole quart of marvels mystery oil and about a half gallon of kerosene and another half gallon of diesel. It ran like an animal but made a really bad grinding noise in the bottom end so we sold it 2 days later.

But yeah, try pulling the cylinder off, if it moves up and down with the piston stuck in place in it then your rings/ piston are seized, but if you can slide it right off and the piston slides out and stays put, it's the bottom end that's seized

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Is there rust in the cylinder?

I can't see any.  But I can't see any holes on the wall of the cylinder like I see in some pictures of other engines online, so I think the piston is all the way up.  Not sure if that means anything

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I cannot add much to the recommendation of letting the penetrating oil sit for a long period of time, that is the best option.  Diesel fuel works pretty well for me in the past.  In this video of mine you will see what "pulling the top end" means.  Also the bike in this video had a severely stuck piston (seen in the video) but I got it unstuck.

 

Top End Removal of a stuck piston

Great video and great site!  I'll be using your site as I stumble through this restoration!

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By the way, what is the best recommended penetrating oil for this kind of thing?

 

+1 on kroil, but it's on-line/order only.

 

I read on several machinists site that 50% acetone/ATF works just as good. Kroil looks like ATF, smells like kerosene, I suspect the name comes from kerosene + oil. I was just a bit sceptical about the home brew, and I've got enough kroil to last a long time. Then I read an article where they did a controlled test on identical fastners corroded by acid and time, then used a torque wrench. WD was lowest, the 3 in 1, then penn oil, then PB blaster was quite a bit better, then Kroil was a lot better, then 50/50 acetone/ATF beat the sox off of kroil.

 

Be careful with acetone though. Relatively safe for humans, but eats plastics. Kroil has never harmed anything I've used it on. Another thing I use when Kroil fails, it get the parts hot, and hit it with some beeswax and it really wicks in and works. Not sure how that will work on a cylinder. The beeswax will catch on fire if reheated, and could just when applied, not like gas where it burns your face off, but rid the area of oil rags and don't do it where you will get in trouble with a small fire. I've done it on tie rod end threads, close to the vehicle, and have yet to burn a car, and the garage, and the attached house. We don't like our house that much anyway. :lol:

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I got the cylinder off!

 

It took an entire can of WD-40, and some hammer taps, but it came off.  It was pretty difficult.

 

I don't see any rust on the cylinder or the piston.  The two rings on the piston look different.  One is completely flush with the piston, and the other one is expanded.  Not sure if that means anything.

 

The kickstarter still won't move though.  So I'm guessing that it is the bottom end that is frozen.

 

What is next for me?  How does one get into the bottom end?  

Do I take off the clutch and surrounding gears to get to the crankshaft? 

Will I need any special tools to pull the crankshaft?

 

I know from watching other videos that I should replace the piston, rings, and the (is it a bearing?) that connects the piston to the (is it a rod?).

 

When I'm fixing the bottom end, what parts are normally replaced?

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You're getting into some pretty major work with that bike.  Apparently, if you're sure it wasn't stuck because of rust in the cylinder, that the main bearings could have gotten some moisture down into the bottom of the motor and rusted them stuck.   Even the rod big end bearing MAY be rusty & BAD.  I'm not sure you'd have to replace piston and rings for sure yet, depending on how many miles it has and how it was treated.  They would have to be inspected and maybe the parts measured to be sure.  For the apparently stuck main bearings the WHOLE engine has to be taken apart, known as "splitting the cases".  This is not a job for someone that's never worked on a bike before.  Not that it's an insurmountable thing for you, you'll just be in virgin territory THE WHOLE WAY.   NOW would be the time to decide if you really want to take it all the way.  That decision is really up to you decided by how good of shape the rest of the bike is, how much money you want to put in it, how much time you have, if you have any emotional attachment to it, etc., etc.  If you really decide to do ANYTHING further on the bike, I really recommend you buy a manual.

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You're getting into some pretty major work with that bike.  Apparently, if you're sure it wasn't stuck because of rust in the cylinder, that the main bearings could have gotten some moisture down into the bottom of the motor and rusted them stuck.   Even the rod big end bearing MAY be rusty & BAD.  I'm not sure you'd have to replace piston and rings for sure yet, depending on how many miles it has and how it was treated.  They would have to be inspected and maybe the parts measured to be sure.  For the apparently stuck main bearings the WHOLE engine has to be taken apart, known as "splitting the cases".  This is not a job for someone that's never worked on a bike before.  Not that it's an insurmountable thing for you, you'll just be in virgin territory THE WHOLE WAY.   NOW would be the time to decide if you really want to take it all the way.  That decision is really up to you decided by how good of shape the rest of the bike is, how much money you want to put in it, how much time you have, if you have any emotional attachment to it, etc., etc.  If you really decide to do ANYTHING further on the bike, I really recommend you buy a manual.

 

Thanks for the reply.

 

I'm pretty much doing this for fun.  I've always wanted to restore an engine, and this was free and available.

 

The only thing I don't want to get involved in is buying expensive tools that I will probably only use once.  I don't mind buying parts and cheap tools though.

 

How do I find out for sure if the main bearings are stuck?  Should I try turning the crankshaft bolt like I've heard online?  If so, do I turn something on the side of the engine where the clutch is, or the other side?

 

Again, I don't mind splitting the case, but will I need expensive specialized tools, or is it something that I can do for around $100?

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Also,

 

Does anyone have a recommendation of what kind of manual to buy?  If I get this thing running I'll probably keep it forever, so I'll end up fixing probably everything else at some point, so the most comprehensive manual is probably the way to go.

 

Where would I find a manual for my '73 DT3 250?

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It doesn't matter which end of the crank you turn to find that out but if you've already got the cylinder off, you should be able to push the rod one way or the other to try to turn the crank, it's gotta be the main bearings.  That's pretty much all that's left.  Again, the manual specifies what tool(s) you need to split the cases.  But if you look closely at them in the manual, most of these type of tools just push on the end of the crank while pulling on the case to separate them.   I usually don't buy them.  I usually either make my own, (quite easy) or it's possible the cases aren't so tight as to need the tool.   I'm not even sure you could find the exact case splitting tool for a '73.  Maybe someone else knows a source for them.

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abe.com for  factory yammy manual, if there is a used one out there...

 

Money? He's got a coat and tie, he has plenty of money :lol:

 

I'd get the side covers off and see what you can see.

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