78 xs 400 E rebuild and modify

Left piston measurements
20170403_121026.jpg
20170403_120942.jpg


Right piston measurements
20170403_121252.jpg
20170403_121321.jpg


Why the hell are the specs high from factory specs? Expand from constant heat?
 
Standard is 69mm, first over is 69.25mm You need to check the bores for these numbers. If the bores are 69mm and don't have any big gouges in them you may get away with just a hone and new rings.
 
xschris said:
Standard is 69mm, first over is 69.25mm You need to check the bores for these numbers. If the bores are 69mm and don't have any big gouges in them you may get away with just a hone and new rings.
Click to expand...
OK thanks. I can only measure 1.5cm deep on either side of the cylinder, with my micrometer. Is there a way to measure the middle without spending that money on one of those bore gages?

What if I measured the piston at the top. Then insert into the cylinder half way, and use a feeler gauge to measure the difference?
 
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You could take the jugs to a shop and have them check the bores or cut something to 69mm and see if there is any play. I would do it the correct way. If the motor is apart you want everything done the best it can so you won't need to do anything for a long time again. Top end parts are not cheap for these bikes and are hard to find.
 
So made a 69mm dowel. No play. The jugs still have a slight bit of cross hatch. So I ordered some new rings and a complete engine gasket set. I can borrow a honing tool from the local auto store. So just have to figure out how that will work.

I checked the clutch
20170403_214008.jpg
friction plate is .14mm from spec
Still usable?
20170403_214023.jpg

Clutch plate still within usable specs
20170403_214105.jpg

Springs within spec
 
On the steel plates you need to check for warp. Place each plate on a flat surface and look for any spaces. I use a scotch brite pad to clean them. If you still have cross hatch marks in the travel zone you only need a very light hone.
 
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I will watch as many videos as I can on honing before I go ahead with it.

Also i borrowed a valve compression tool that only compresses the top half of the spring and I can't get the valve container out. I suppose I need one that holds the valve from the bottom and compresses the valve?
 
Just do it the old school way if you are trying to get them off, I promise you won't break them. Place head valves down on thick cardboard(important), place appropriately sized deep-well socket over cup, smack top with hammer. One good whack is all it will need, the spring and cup will compress but the valve will stay put and the retainers will just fall off. You'll still need a proper compressor to get them back on, but for removing them it works fine.
 
Thanks for the old school tip.

What do you think of this valve compressor tool?
https://www.amazon.ca/gp/aw/d/B000P0VTG4/ref=ox_sc_act_image_1?smid=A3DWYIK6Y9EEQB&psc=1

Might as well get one if I need it to put em back on.

I've never lapped valves but from the vids I've watched seems pretty straight forward job.

In the meantime, I'll prbly try and figure out exactly what cosmetic parts I want for this bike. Pull the wire and everything off the frame. Sand blasting and a powder coat is prbly the best option for the frame. But is there a more cost efficient way to for someone without those means? I suppose I can get a quote from someone. Well see.
 
I would use a cleaner and a soft hand brush. You don't want to rip a seal or pull out any wires.
 
Im getting ready to lap the valves this wknd. I have only removed one valve spring so far. The manual says remove the valve seal before the valve itself? So I slide the little circular spring off the seal. So you can't just push the valve stem through the the seal? Do you use pliers to pull the seal up off the valve stem?
 
Don't get pliers anywhere near the valve stem.
On a quick glance the Haynes manual does not appear to specify that the valve seals must come off before the valves. The valve spring retainer has to come off first, followed by the valve springs. That's not referring to the circular springs around the valve seals.

The seals shouldn't need any disassembly or huge force to remove. The little circular springs can stay on. The seal should come off with a bit of a wiggle and a pull.

Make note of which valve comes out of which hole and put it back where it came from.
 
BBS360 said:
Don't get pliers anywhere near the valve stem.
On a quick glance the Haynes manual does not appear to specify that the valve seals must come off before the valves. The valve spring retainer has to come off first, followed by the valve springs. That's not referring to the circular springs around the valve seals.

The seals shouldn't need any disassembly or huge force to remove. The little circular springs can stay on. The seal should come off with a bit of a wiggle and a pull.

Make note of which valve comes out of which hole and put it back where it came from.
Click to expand...
OK thanks. I'll just leave the valve stems in place and push the valve out.

Maybe I'm miss interpreting this? This is from the manual I downloaded from here
tmp_10840-20170408_0758281798993151.jpg
 
Valid point I suppose, unless you're replacing the seals.
I'd replace them. You have the head apart now. Possible they may have been damaged already with the removal attempts.

Looks like they're using pliers to grab the split collets while compressing the valve springs. That'd be ok but you don't want to risk scratching the valve stem once it's exposed.
 
BBS360 said:
Valid point I suppose, unless you're replacing the seals.
I'd replace them. You have the head apart now. Possible they may have been damaged already with the removal attempts.

Looks like they're using pliers to grab the split collets while compressing the valve springs. That'd be ok but you don't want to risk scratching the valve stem once it's exposed.
Click to expand...
I haven't actually tried to remove the valve or seal yet, just the spring is off one.

I suppose I might as well replace them.
Do you or anyone have anything to say about Viton? They have seals for these bikes.
 
I put viton valve seals on both my bikes. There was an ebay seller with them listed for a pretty good price.
Also have viton butterfly shaft seals in the carbs of both bikes. Ordered those from Thailand.

All of them seem like fantastic quality but I haven't run the bikes long enough to make an informed recommendation.
 
Pulled all the valve springs out today old school style with a hammer. I cut a notch in a socket I'll be using with a clamp to reinstall. Valves all within specs. Lapped valves. Intake didn't even look like it needed it. I assume exhaut valves and ports are always going to have more build up?

Also tried soda blasting with a gravity fed sandblaster. Works real well. But you need a lot of medium.

20170410_133232.jpg

20170410_133224.jpg


Also pulled the swing arm. Cleaned the dust covers and bushings. Forced the old grease out and reinstalled. No free play.

Still waiting for rings and gaskets. Going to also have to wait for valve seals if I replace them.
 

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