1979 IT400 rebuild - Two steps forward, one step back

[GaryInVA]

I was looking for a two stroke bike that I could teach my teenage son how to work on a motorcycle. I came across an add on the Yamaha Enduro forum from a guy in California that had a (he said) 1978 IT425. It used to be his late fathers and had been sitting in a garage since 1998. After doing some research I figured it was actually a 1979 IT400, they didn't make a 425 in 78. He was asking $600 for it. Sat for sale for 6 months with only a couple of inquiries. The engine is stuck on the bike and no one wanted to mess with it. I exchanged a lot of emails with the guy and finally told him I couldn't afford the price plus shipping to Texas ($570). Two weeks later I get an email saying I can have the bike for free if I can get it out of his garage.

Been talking to my brother during this whole process and he told me he'd pay for the shipping as a Christmas present. Bike arrives a couple weeks later.

Give it a little wash and here's what we are work with. We've been working on this for a while so I'll start posting pictures and a little story of our progress (and taking two steps back).

 

[Sparkyduc]

I was looking for a two stroke bike that I could teach my teenage son how to work on a motorcycle. I came across an add on the Yamaha Enduro forum from a guy in California that had a (he said) 1978 IT425. It used to be his late fathers and had been sitting in a garage since 1998. After doing some research I figured it was actually a 1979 IT400, they didn't make a 425 in 78. He was asking $600 for it. Sat for sale for 6 months with only a couple of inquiries. The engine is stuck on the bike and no one wanted to mess with it. I exchanged a lot of emails with the guy and finally told him I couldn't afford the price plus shipping to Texas ($570). Two weeks later I get an email saying I can have the bike for free if I can get it out of his garage.

Been talking to my brother during this whole process and he told me he'd pay for the shipping as a Christmas present. Bike arrives a couple weeks later.

Give it a little wash and here's what we are work with. We've been working on this for a while so I'll start posting pictures and a little story of our progress (and taking two steps back).

I can hardly wait, I had a 1978 IT250

 

[GaryInVA]

After a good wash, I told my son to figure out what he'd think is the proper order to take apart the bike to get down to the cylinder head. I let him figure out how to take off the seat, tank, exhaust pipe.



Down to the engine now. I walked him through taking off the head of a two stroke properly. Off with the head and we find this.

 

[Jim]

Down to the engine now. I walked him through taking off the head of a two stroke properly. Off with the head and we find this.

Is it stuck?

 

[GaryInVA]

Is it stuck?

My oh my was it stuck. I've got a bunch of pictures to post of us getting it unstuck.

These pictures are old, as it's been a long process finding parts for this engine in that it's a one year model and I've had to find them mainly in Europe and through forum people with a bunch of old OEM stock.

 

[Signal]

The head should clean up, with a central spark plug combustion chamber its pretty easy in a lathe. I have a friend with a DT 400 to restore. No where as nice as yours. Thanks for posting.

 

[GaryInVA]

So we spent the next month soaking the cylinder, then using a large wood dowel that we beat with a big hammer. We could get it to move a couple mm every day. You can see in the picture above that the piston was stuck pretty high with no ports showing. After much oil and hammering here's what we ended up with.



Here's the spacer I had to place under the cylinder so that we could continue to pound out the piston after it reached BDC and was still stuck.

 

[Raymond]

At least you got the bike for the right price, great project for your son. Is he enjoying messing about with this ancient device?

New set of rings and she'll be fine . . .

 

[bosco659]

Looks like a great project. Maybe that’s something I should look for as next winters project. I’ll follow this with interest.

 

[atom4488]

...that bore and piston don't look all that bad. I'd assume that a bore and new piston would be in order, but I have seen far worse cylinders get resuscitated. Following with interest!

 

[Charles13]

These are such great bikes even by today’s standards; totally controllable, unstallable bottom end torque and great handling. I can’t wait to see the results

 

[Raymond]

These are such great bikes even by today’s standards; totally controllable, unstallable bottom end torque and great handling. I can’t wait to see the results

I had a DT400, 1977-79 with the same engine. Wish I still had it. So much torque it was an honorary 4-stroke.

 

[Its been a long time]

I had a DT400, 1977-79 with the same engine. Wish I still had it. So much torque it was an honorary 4-stroke.

Remember them well. Anything two stroke these days from the 70's seems to be silly money. Prices are dropping but anything two stroke still seems be asking daft prices. How much stuff actually sells for, I don't know.

 

[GaryInVA]

The intake manifold was of course cracked because it is dry rotted. No cracks that went all the way though into the throat. A replacement manifold is about $100 and I wanted to put my money towards piston, rings, rod, bearings, and such. So I asked a bunch of questions on a Yamaha Enduro forum and one person told me he has had good experiences with a black rubberized superglue. I do plan on getting a new intake after I actually get it running, one of the first things on my list.

The way the manifold looked along with the reed cage all rusted.


After a good soak in Evaporust.



Condition of the rubber on the intake manifold.



The black rubberized superglue I used.



Intake after applying black superglue.



I sealed up all the big cracks on the manifold and it survives me twisting and bending the rubber.

 

[Charles13]

I wouldn’t trust that manifold, you wouldn’t want that new piston to tighten up

 

[GaryInVA]

So I had to search for a piston which is not available anywhere because of it being a 1 year motor. The IT400 and YZ400 pistons and rings are the same size, the only difference is that the IT piston has a window in the rear skirt while the YZ has a cutout. I ended up finding a set of first over YZ piston and rings that a guy on the Yamaha Enduro forum had. Got those secured and then started looking to get the cylinder bored to fit the new piston. Nobody around here in Central Texas would bore a two stroke cylinder. Was recommended on the Enduro forum to use Bill Bune in Minnesota. They do a lot of two stroke snowmobiles and are very reasonable in price.

Packed it up, paid the man online and a couple weeks later this came back.



Here's the only first over piston I could find for it at the time, one for a YZ400

 

[Jim]

Did you chamfer the ports after you got it back from the machinist?
Sorry if that's an obvious task, just not sure your level of experience with 2 strokes.

 

[GaryInVA]

Did you chamfer the ports after you got it back from the machinist?
Sorry if that's an obvious task, just not sure your level of experience with 2 strokes.

That's one of the reasons I chose Bill Bune to do the work. They do a ton of two stroke cylinders and chamfer the ports. If you zoom all the way in on the ports you can see the chamfers.

 

[atom4488]

That's one of the reasons I chose Bill Bune to do the work. They do a ton of two stroke cylinders and chamfer the ports. If you zoom all the way in on the ports you can see the chamfers.

Oh yes, definitely see the chamfers of the port openings. Nice work by Mr. Bune.

 

[Jim]

Ol' dipshit here didn't zoom in...
I see 'em now.