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Pinned Scraping & Fitting Gaskets (not head)

Discussion in 'Tech Tips' started by maelstrom, May 12, 2015.

  1. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    I just started doing this in preparation to fit all my covers prior to the next step. So I thought it might be interesting or useful for some members. Feel free to contribute what works for you.

    Now here is something we all hate. Lots of stories on the internet about this one. Beware the Ides of March and the evil Scotchbrites. Anyway this is just my two cents and I have never used Scotchbrites for this task. Like everything to do with a high performance motorcycle engine this is meticulous work. If you are the wham, bam I'm done sort of guy then read no further.

    I finish my gasket surfaces with 300 grit or higher wet and dry sandpaper and I use a flat object as my sanding block. I mean something flat not a piece of cork. Now to do this I cannot have clutch baskets etc in the way or it will not be possible to maintain a flat surface. If you cannot remove a protruding shaft then design a shape that will work around the perimeter and make a specialised sanding block for that task. I used a 12mm thick piece of Lexan about 200mm long and 50mm wide to do the clutch cover surface that you see in the image. You can use anything that is strong enough not to flex and is suitably flat. It has to be long enough so that both ends of your block are making contact with the surface to be sanded. This ensures that the block stays flat.

    First, remove any dowels and in the case of my Yamaha I threw them away since they are the thin walled variety. I bought a bunch of new ones a long time ago. I would sooner eat my own head than try to do this with dowels in place.

    Then I scrape the old gasket off with an exacto knife using a broad chisel blade. I keep the blade fairly flat and press my thumb against it to prevent the blade twisting. I also make myself as comfortable as possible and work very slowly. This means not working on the floor. If I had to do this on an engine that was still in the motorcycle then I would build a bike bench first. In the attached image the engine is in a stand. You do not need to try to remove all of the paper with the blade because you don't want to risk gouging the aluminium surface. Work like a surgeon not a butcher. Once that horrible task is finished it is time for the sanding.

    It is a dead simple task and you can use water to keep the paper wet. Of course you will need to use sponge, rags or similar to ensure that no grit or debris falls into the engine. Work around the surface focusing on those areas where there is still paper. It comes away very quickly leaving a clean and flat surface. I have seen people posting that you cannot use sandpaper but that is ridiculous. Of course you cannot use sandpaper if you plan to use your hands as the sanding block. You will notice as you make progress that the original milling marks on the surface will be revealed and they are a lot deeper than the tiny scratches left by your sandpaper.

    Then repeat the process for the matching part that mates to the surface that you just completed. Blow out the screw holes with compressed air and clean, clean, clean.

    Apply lithium grease to your new gasket and assemble.
    [​IMG]
    cheers
    Blair
     
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    Last edited: May 12, 2015
  2. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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    Good one Blair. Hadn't thought of using Lexan.

    Have never had to do this with a Japanese case (unless after welding), but English ones are a different matter. Years ago helped a friend with a 650 BSA rebuild. He had been putting thicker and thicker gaskets between the crankcase halves to stop oil leaking and the end float of the crank was a loud knocking. When the cases were stripped and placed on a surface plate there was a 1.5mm gap! No wonder it wasn't oil tight. Cases machined flat, correct gasket and end float, careful assembly and it is probably still holding oil now.
     
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  3. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Yes, had to deal with similar issues over the years; old Ducati singles spring to mind. You have to re-bush, hardchrome journals, restore tapers etc. I'm sure you know about all these activities :)
    Speaking of thicker gaskets, I bought some cover gaskets off eBay for my Yamaha. The seller assures that they are identical to original. No, they were thicker and made of rubbish. A common misconception that people have is thicker is better. I bought original ones and have had them copied by a small startup in the UK. I told him about the 250 forum and suggested doing them for all the 250s.
     
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  4. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Pulling off Flywheels:
    So you want to move on to your alternator cover gasket but unfortunately there is a flywheel in the way.
    Now there are special factory tools for this but sometimes you can improvise. So here is an example. This is my FZR400 Yamaha, but if you study the fitting of your parts and do a bit of searching on the web you can usually find all the information you need to design your solution.
    First of all, remove the bolt holding the flywheel in place. I used a rattle gun for that. Now the factory Yamaha flywheel puller is actually a 16 x 1.5mm bolt and it looks something like this (might not be genuine). There are also posts on the web suggesting that you can use the handlebar weight for the same purpose. I tried that but it was useless because you cannot transmit enough torque through the 8mm hex key.
    [​IMG]
    Now here's the thing. I used something similar, an M16 x 1.5 x 50 bolt (60c from my local hardware shop), but my bolt, much like the tool shown previously, has a slightly rounded end and the end of the crankshaft has a slightly concave end.
    [​IMG]
    Now that might sound ok but it means that when you try to pop the flywheel of the bolt is trying to spread the end of the crankshaft.
    [​IMG]
    As you can see the bolt is only pressing against the concave surface.

    Now that might be fine but I am a bit paranoid about things like that, so what I did was cut the head off an M10 x 1.25 socket head cap screw and put a slot into it.
    [​IMG]
    Then screw that into the end of the crankshaft until it is just proud of the end. Of course it could be flush, or even a bit under, it will still stop any tendency to spread the end of the crankshaft.
    [​IMG]

    Then I used my rattle gun to pop the flywheel off and finally I could sand the gasket surface. Sorry I did not take pictures with the flywheel still on.
    cheers
    Blair
     
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    Last edited: May 16, 2015
  5. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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