70mm Piston Installation
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Thread: 70mm Piston Installation

  1. #1
    Senior Member elime's Avatar
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    70mm Piston Installation

    I finally talked myself into installing the 70mm piston on my parts bike. I am not sure I did the right thing as it was a very sweet running machine but it is done now so no need to dwell on it.

    I was going to post pictures of the change but reality is that it is no more than a base gasket change and there are already plenty of pictures of that. So instead I thought I would concentrate on the cylinder itself and different stages along the way.

    I spent $13.50 on the cylinder and honestly, I think I overpaid. I sprayed degreaser on it before I took the picture. My mistake. Not a true "before picture".
    DSCN0025.JPG

    Cylinder cleaned up and rust hand sanded from inside cylinder. The cylinder is mounted to a board and ready for the hone. One can see this has been sitting around a while and is badly pitted.
    DSCN0042.JPG

    The pitting cleaned up very early in the honing and I think a 67.5mm piston would have worked. It seems most pitting just isn't that bad.
    DSCN0044.JPG

    Final hone. Tried for the cross hatching -- could have been better but it will work OK.
    P9080011 (2)(A).jpg

    I lapped the gasket surface to make it flat and clean. I placed a stock sized piston in the bore to show how much bigger the new bore is. I don't have any pictures of the outside of the cylinder but trust me, it is every bit as clean as what you see here.
    Std piston 70mm bore (2).JPG

    So that is it. So far I have 8 miles on it and my concern for the thin walls seems unfounded. I am doing a "hard break in" which is WOT followed by a shut throttle followed by WOT again followed by a shut throttle and repeat , repeat, repeat for 25 miles while using dino oil. Change the oil at the 25 mile mark and continue using dino oil for the next 1000 miles and you are done and can change to synthetic if you desire. I will most likely stop break in around 15 miles but will stay with the dino for at least 1000 miles. (Is 25 miles necessary? I bet 4 or 5 miles is plenty.)

    As for increase in performance -- reports to follow. It seems peppier but it is hard to tell if that is placebo or real. I have to go for a ride in the hills to truly evaluate it and that will come after the first oil change. Tony
    Long live the internal combustion engine!

  2. #2
    Senior Member Ski Pro 3's Avatar
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    The first few miles will make or break the ring seating. I think you did it right.
    You may want to take a compression test reading, then take one at 1,000 and then the next couple oil changes to see if it continues to seal, or you got it done with the break-in.
    elime likes this.
    The bear slayer!

  3. #3
    Senior Member admiral's Avatar
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    I'm always interested in watching yours and TW-Brian's engine rebuild threads. I may actually learn something, though I don't always know it at the time.

    Last night I removed the remains of the dead Mayflower engine from the frame. When removing it I was surprised, some oil poured out onto the floor when I tipped it. The surprising part is I thought all the oil had been spewed out of the bleed screw area. So far the only real damage is the piston and cylinder. I looked real hard at the connecting rod wrist pin and it looks fine from my untrained eye.

    I now have to buy a honer (I can say that right?) and the measuring devices. Pretty sure my carpenters ruler isn't set up for the tolerances I need to be measuring! Doing this is above the hammer technology I possess! I'm not 100% sure the head didn't receive any damage, but by-gosh I can't see any. And I used a flashlight and everything!

    I don't think I'd take apart a good running stock engine just for the piston upgrade, but you guys keep pumping out these wiseco pistons got me thinking to fix my damaged cylinder and make it into a wiseco beast!

    Thanks for posting this stuff. It really helps and motivates!
    Dryden-Tdub, elime, Gerry and 2 others like this.


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  5. #4
    Senior Member elime's Avatar
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    Quote Originally Posted by admiral View Post
    So far the only real damage is the piston and cylinder. I looked real hard at the connecting rod wrist pin and it looks fine from my untrained eye.

    You jog my memory: Around 1985 I bought an essentially new 1957 Johnson 7.5 hp outboard motor a guy had lent to his brother who thought mixing oil with gasoline was foolish lubricating overkill. Long story very short the piston over heated and transferred aluminum to the cylinder wall which made it look terrible. After a little honing with a flex hone the soft aluminum was gone and the cylinder -- to my surprise and relief -- look great! A new piston and set of rings along with getting a hole welded shut and the little motor was back in business.

    So see if the walls are truly damaged. Maybe it just needs cleaning and a new piston and rings.
    Long live the internal combustion engine!

  6. #5
    Senior Member jtomelliott49's Avatar
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    Hey Admiral, this is the new "wife's bike". Didn't you recently post that she rode your TW and liked it????? Just sayin'.
    Tom in Wichita

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  7. #6
    Senior Member admiral's Avatar
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    Quote Originally Posted by jtomelliott49 View Post
    Hey Admiral, this is the new "wife's bike". Didn't you recently post that she rode your TW and liked it????? Just sayin'.
    He he! I get to keep the new TW. She just discovered she likes riding. The Mayflower was always going to be rebuilt, if anything as a spare for Moab. We know some people need a spare (me, Fred ). When I get done fixing the old TW, it will mainly be a spare for me as Mrs. Admiral wouldn't be comfortable riding in our normal habitat (to rough).

    Of course my plans for a spare TW may be a little "less manly"! Mrs. Admiral is already talking about which parts she wants painted pink!


  8. #7
    Senior Member jtomelliott49's Avatar
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    Hahahahaha... You must be very comfortable with your manly man-ness to paint your parts pink. lol
    Tom in Wichita

    78 Moto Guzzi SP1000
    87 Yamaha TW200
    99 Yamaha TW200
    03 Honda Shadow Spirit (girlfriend's ride)
    74 Moto Guzzi Eldorado Police model (in many pieces)

  9. #8
    Senior Member admiral's Avatar
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    I meant on the TW!


  10. #9
    Senior Member Fred's Avatar
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    Kris, have you considered going with a pink urban cammo motif? Stylish yet not excessively feminine..images-3.jpegimages-2.jpegimages.jpeg
    admiral likes this.
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  11. #10
    Senior Member Dryden-Tdub's Avatar
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    Quote Originally Posted by Fred View Post
    Kris, have you considered going with a pink urban cammo motif? Stylish yet not excessively feminine..images-3.jpegimages-2.jpegimages.jpeg
    What!!!???? The only way it could be MORE feminine is if it were sponsored by Tampax!



    Tom
    Last edited by Dryden-Tdub; 10-03-2015 at 04:28 PM.
    admiral, TW-Brian and Gerry like this.
    Never, in the history of mankind, have lives, less lived, been so well chronicled.

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