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XS400J Maxim 82/83 DOHC engine rebuild

Discussion in 'The Garage' started by DynaGlide, Jun 15, 2016.

  1. DynaGlide

    DynaGlide XS400 Enthusiast

    I think if this were my own bike I would splurge on a bolt kit. Since it isn't I ordered through Fastenal just what I needed. Total was $25. Not much of a savings I know.

    I decided to measure the valve clearances and I can't get a 0.0015" feeler gauge under any of the 4 valves. I used the zip tie trick I read about to hold the valves in place so I could get the shims out and write down their thicknesses. I suspect the clearances are off from lapping the valves. I'll try the local shop to see if they have a significantly thinner shim I can borrow so I can measure which size I actually need for each valve.
  2. Doh! That's what I get for posting while having my first coffee, after only 4 hrs sleep... :zzz:
  3. OopsAboutThat

    OopsAboutThat XS400 Enthusiast

    Thanks Dyna for the awesome posts! This thread is definitely getting bookmarked. :bike:
  4. DynaGlide

    DynaGlide XS400 Enthusiast

    Happy to help!

    So I'm doing the valve adjustments now. This is tedious especially when you don't have any clearance on any of the valves. Luckily the local shop (Crossroads Cycle in Bailey's Crossroads, VA) was kind enough to lend me a couple shim sizes. Otherwise you have to go buy a kit with all the sizes and those are expensive. I didn't take any pictures but I'm sure there's a million guides out there for this. Rotate valve in question to be depressed by cam, find a way to hold it there (I use a zip tie folded over and taped), rotate engine so lobe is off the tappet/bucket and while the valve is held open you now have room to get the shim out. Take it out, mic it, put it back in, rotate again to get your valve holder out, rotate until lobe is off the valve bucket/tappet and measure the clearance with feeler gauges. To make it worse none of the shims are actually what they're printed on the back due to wear or manufacturing tolerances, and blindly guessing since I didn't have any clearance to start with made this job take a lot longer than it should have. I think I know which shims I need so I'll use some quarters as placeholders to get my shims out to swap at the shop so I don't have to make yet another trip. One of the shims they gave me to check with fits the front Intake, the other 3 I need to replace.

    Not much left to do still working on cleaning up the engine covers when I feel like it. That's another mindless job I've been avoiding.
  5. What a great thread to have followed, as living here in England, and riding a Canadian imported, 82 XS400J (12R) motor (5 speed gearbox) and it seems that mine, and the engine you stripped/rebuilt, are exactly the same? I do have a question to ask! The YICS system, used on these engines, would the YICS, having any blockages, in the ports, cause any starting problems?

    Great strip/rebuild, very informative!

    Merlin in the UK
  6. DynaGlide

    DynaGlide XS400 Enthusiast

    Well it's been a while but I finally feel like working on this again. Got the carb out and started figuring out what all is needed. I think I'm looking at two float bowl gaskets, a handful of screws to replace the ones that rusted out, and some bigger jets to accommodate some pod filters and a custom exhaust. This is a Mikuni BS34mm carburetor which is used on a lot of bikes of the era, not just Yamaha. The intake boots are pretty hard but it looks like for those I just need two o-rings to refresh them. Open to advice, this is the first carb I've worked on. I'll clear out the passages and soak as necessary.

  7. DynaGlide

    DynaGlide XS400 Enthusiast

    Hey Merlin,

    My understanding of the YICS system is that it is sort of secondary. .it's an auxiliary chamber for supposedly helping to fill the charge of the main combustion chamber. Anythings possible but I don't think there's really any ports to get clogged. Wish I was of more help but I'm no expert here just kind of shooting in the dark hoping to hit something.
  8. billday

    billday XS400 Enthusiast

    Just found this thread for the first time, I want to say thanks for the great photos and clear descriptions.

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