78 xs 400 E rebuild and modify

Its a great idea if you arent using a starter to utilize the space in some other way. I dont know about the heat though. It might be enough to melt the battery case. I use a AntiGravity 4 cell battery and it looks like you have enough room in your electronics pan for one.
 
Bad idea. Heat and lack of air flow will kill the battery quick. I would look for a cool open place. Also a battery with more AH. 1.3 will work if your bike has minimal lights and can start with first kick on a cold day. I used a setup like that with my 80 sg for a few years but that bike had a factory TCI and was very easy to start. But I got tired of kicking altogether and put the factory e-start back in. So much easier!!!
 
I failed to really mention that is a bad idea ... I thought about using the space for a tool kit or something, but even thats a terrible idea. Its just too hot.

It is always nice to have the starter though. I kick my bike 100% of the time, but I have needed the E-start when its cold because I literally ran out of energy to kick.

My bike struggles to start when its below 50*F/10*C and I can imagine that you would still be riding in those temps where you live. All of my old bikes are much harder to start when its cold, except the K100 but only because its fuel injected. The battery I use is just enough to get the engine cranking and youll have about 15-20 seconds of E-start power before the battery is drained. Points ignitions will work with a battery drained to as little as 10v, probably less, but an electronic ignition will not fire below say 11.5v

When its a few degrees above freezing youll be glad to have the E-start lol. Its saved me a couple times.

If you want to shed as much weight as you can, its the first thing Id remove. Riding the bikes I own, the XS is plenty lightweight the way it is. The sportster literally feels like Im sitting on a steam train.
 
The sportster literally feels like Im sitting on a steam train.

(thread drift "on")
That was precisely my sentiments about my '84 sportster, it seemed to embody the word "contraption." As if the parts were just barely working together and just looking for any reason to start working against each other. Where the XS, despite its similar vibes, seems to be a happy assembly.

(thread drift "off")
 
I have the cylinder block back from the machine shop. The piston clearances are in spec. The rings are measured and have the proper end gap and fitted on the pistons.
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Im still waiting on some parts before I rebuild the motor.
-pistons pins and clips from Yamaha
-and basket full from Yamibits

I originally had planned on painting the engine, but, Ive decided not too.
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I think leaving the bare,scarred, oxidized, scratched, semi polished metal exposed better suits the grumpy personality this bike has had.

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In these pic, you can see it looks like someone painted the back half of the top half of the case. There is no over spray so Im not sure why,who or when it was painted.
 
Cases where painted from the factory. This was to help reduce oxidation. By 82 the sohc xs400 motors where fully painted black inside and out to reduce this even more. Although I think the inside coating was more of an epoxy or some sort of powder coat as it's very hard as it has to stand up to oil and high temps.
 
Little update...

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That's everything I needed from Yamibits

The engine is now fully rebuilt.
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The wires from the stator are new and with new heat shrink on. Kept the neutral and oil switch wires. New heat shrink tho.

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Also new rear wheel bearings and seals

Finally got the angle right for my tail end.
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I'm going to reuse these tabs I cut off and weld them right at the joint where the hoop and framf meet. I'll use them for mounting turn signals.

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I also might attach the Yamaha symbols from the tank to the electronic/battery tray, once built.

Next on the to do list is weld up the frame and another cross beam for seat mounting purpose, also those little tabs. Then prep the frame and all other parts I intend to paint.
 
Putting together the next list of items the bike is in need of.

It would seem there really isnt a rebuild kit for these gas caps
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all those rubber gaskets are quite dry rotted.

I can purchase an aftermarket cap, seems cheaper and easier that way.

Does anyone know how remove the key mechanism from the one I have and place it in a universal one?
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Only so I can keep the yamaha key, I have, in use. Ha
 
Those new gas caps you see on EBay are complete junk. They are very thin stamped metal, like a escutcheon for a bathroom faucet. I have one and it will stay in the package forever.

You can search for a Yamaha key by using the 4 digit number that will be stamped into the lock cylinder. Theres merchants on EBay who may have factory keys and you give them your 4 digits and the will cut a key for you.

The 4 digits will be stamped on to all your locks. Ive had to buy used key sets and ignitions before.

Ive gotten super lucky and found exact original factory cut Yamaha keys simply by typing something like " Yamaha key #1234" in various searches.
 
I ordered a new rubber seal for the gas cap from MikesXS. The 650 one fit perfectly.
That and some rust removal and my stock gas cap was just like new.
 
I ordered a new rubber seal for the gas cap from MikesXS. The 650 one fit perfectly.
That and some rust removal and my stock gas cap was just like new.

Thanks, I do see that part.

In my case, the cap has 3 separate rubber gaskets and a felt one as well. All are dry rotting. MikesXS has 2 different ones listed.

https://www.mikesxs.net/yamaha-xs650-gas-cap-seal-to-fit-76-84-650-s.html

https://www.mikesxs.net/yamaha-xs65...dels-oem-341-24612-01-00-256-24612-00-00.html

Will both of these work with my '78?

The 2nd link being the one that houses the metal spring holder?
 
The ones for the 80-84 "specials" should fit. I have them on all my bikes. Some are almost 10 years old now. Still like new. I do store the bikes very well tho. You should only have the rubber seal and the 3 hole gasket. Yours rubber seal looks like it's in 3 parts now.
 
Update on the bike...

Havent done much in the last month but managed to make a electronic tray this wknd.

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Turned out decent enough.

I used 16 gauge steel. Built up the box. Then puzzled over a way to mount it. Folded up a bracket that hooked onto the tank mount. Then the rear, I folded a couple more brackets, welded them in place and welded two nuts on the brackets. Then line it up on the cross member and drilled 2 holes. Fits well and holds everything I'll need.

Is it good idea to leave the front of the tray open, in order to keep air flow going in and out the back?

Hoping next wknd to start painting the frame and some parts. Got a basket full of parts I need to order, which will make this a roller again.
 
Make sure you have lots of air flow or that battery will go fast. The rectifier needs it also. You may want to mount that on the bottom.
 
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