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Thread: 7080 ratio

  1. #1

    Join Date
    Sep 2014
    Posts
    23
    Location
    Michigan
    Mower
    LawnBoy

    7080 ratio

    My newly acquired LB 7080 ser. 5950878 says 1/2 pint per gal. on the motor. Researching the mower, various sites say 32:1. Could this mower have a "transition " motor from 1969? One source says its a D-431, other says D-432. Is there a difference? Newbie to vintage LB's needs help. BTW, my free curbside LB Scamp still purrs like a kitten and mows tall grass like no 4 stroke ever could even after eighteen years. Love it.

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  3. #2

    Join Date
    Sep 2014
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    23
    Location
    Michigan
    Mower
    LawnBoy

    Re: 7080 ratio

    BTW, I'm not disputing the sticker on the motor- just trying to find out for sure why the different info.

  4. #3

    Join Date
    Apr 2016
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    121
    Location
    Texas
    Mower
    LawnBoy

    Re: 7080 ratio

    It was made in 1970 and 71, should have a D-432 with a 2 ring piston and all-needle bearing connecting rod, so 32 to 1 would be the correct ratio. The difference between the D431 and D432 would be earlier D431 would have a 3 ring piston and plain bearing wrist pin and it should be run at a 16 to 1 ratio. A general rule of thumb is any D series made in 1970 and beyond will probably be a 32 to 1 machine and the extended snout crankcase was no longer available on residential D series engines post 1970.

    Edit, Just wanted to add that it could be a transitional machine, we've seen extended snout crankcases on 1970 residential machines before. They probably just used whatever is in stock during the changeover. I would just count piston rings to verify the ratio since yours could be a 1970 model.

  5. #4

    Join Date
    Sep 2014
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    23
    Location
    Michigan
    Mower
    LawnBoy

    Re: 7080 ratio

    Again, newbie to vintage LB. Describe extended snout crankcase please. And thank you for the info.

  6. #5

    Join Date
    Apr 2016
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    121
    Location
    Texas
    Mower
    LawnBoy

    Re: 7080 ratio

    The extended snout is just the extra cast aluminum that extends down to the bottom of the muffler plate and contains an extra bronze bushing for crank support. On the 1970 and on residential mowers this extra support and bushing were eliminated. I'll post a side by side pic if I can. Photobucket does not work for me anymore so not sure about posting a pic, but I'll try.

  7. #6

    Join Date
    Sep 2014
    Posts
    23
    Location
    Michigan
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    LawnBoy

    Re: 7080 ratio

    Thanks again. Will to go to the shed and check when I can. Honeydo list just reappeared by magic. Funny how that happens when I get spare time...sigh.

  8. #7

    Join Date
    Apr 2016
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    121
    Location
    Texas
    Mower
    LawnBoy

    Re: 7080 ratio

    When you look under the deck just check the opening where the crank extends through the muffler plate (engine mount plate). If yours has the extended snout you will see it extend an 1/8" or so below the plate opening and the oil seal will be right there, it will be a nice snug fit right into the plate opening. If you don't have the extended snout there will be a huge opening where the crank comes out of the plate, and no support, or oil seal visible. In the pic below you can see the extra aluminum extending down below the engine mounting flange. You can remove the muffler and look through the exhaust ports to check the number of rings the piston has. If 2 rings, it's a 32 to 1 machine, if 3 rings it's a 16 to 1 machine.
    Attached Images Attached Images

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