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  1. #1

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    Default 3 1/2" bore cylinders in 3 5/8" bore cases? Shovelhead question.

    I bought a non-running 79 fx shovel to have some fun with. Good compression on rear cylinder, front is dead. Pulled the top end apart and noticed S and S connecting rods, flywheel, piston, and cylinders. Its the big bore kit, 3 5/8" bore with .060 pistons.

    Here's my trouble: I can't find .070 over pistons and rings for the 3 5/8 bore (ring gap on new .060 rings is a good bit over spec). S and S said the .070 piston kit was in their catalog, but couldn't find them anywhere. Having the cylinders re-sleeved puts the project out of my budget for a bit, if I could even find someone to do it. I DO have a good set of 3 1/2" bore 80" cylinders. Can I run those cylinders on cases that have been bored to 3 5/8 to accept the big bore kit?

    Thanks everyone!

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    I don't recall a +.070 piston ever being available for the 3 5/8 bore. Plus .060 is the max.

    No sleeving those cylinders. They do not have enough meat at the fastener reliefs to make that possible.

    Some have installed standard cylinders on bored cases and got away with it. For me, an aluminum sleeve for the case would make me feel a whole lot better about doing it.

    Jim

  3. #3

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    My buddy said the same thing. I think machining a sleeve is the way to go.

    Thank you.

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    Sleeve should be a slip or light press fit in the case, with a lip to correspond to a c'bore or chamfer in the case mouth, to prevent the sleeve from slipping down and rubbing the flywheels. It should have two to three thou clearance to the cylinder spigot.

    Jim

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    Can your budget handle $350 for a new set of import 3-5/8" jugs .. ??



    VT No 11-0380

    Cylinders are stock height.
    *NOTE: 3-5/8" cylinders are drilled to use with 4-1/2" and 4-1/4" stroke.
    These are cylinders only. Order pistons and rings separately.

    BTY ...
    Having Big Bore Pistons at .060" over is down to it's last inch of skin ..
    With buying these new re-pop jugs your back at STD bore for 3-5/8"
    __________________________________________________ ____

    On installing a sleeve in the S&S jugs, I have done a few ...
    L.A. Sleeve makes two Sleeves for that bore size ...
    One (LA-310) has a 3/32" (.093") wall, can be bored to a .040" max os piston and the other (L-310) has a 1/8" (.125") wall , .060" max os piston ...
    Last edited by Dragstews; 06-01-2022 at 8:12 AM.

  6. #6

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    That might have to be the route I go. In addition to the sleeve I'd need to machine to use stock cylinders, I'd also need a stroker plate... on top of ordering new pistons and rings. J&P actually has a closeout sale on the repop 3 5/8" cylinders. $138 each. Got a V-twin manufacturing piston kit for $130 off eBay too. A bit more than I wanted to spend, but I think this is the best option given the cards I was dealt.

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    ...

  8. #8

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    The sleeves area a bad idea.
    By the time you pay the machinist for that foolishness , you could just buy the replacement parts and retain the big block performance.
    As any machinist worth his salt will tell you.

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    Now that modern hi-tech bore coating services exist I'd pass on sleeves but that's only worth doing in special cases. The nice part is you can bring a cylinder to stock bore without sleeving.

    I'd save my pennies and build it back large by whatever method.

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    Quote Originally Posted by farmall View Post
    Now that modern hi-tech bore coating services exist I'd pass on sleeves but that's only worth doing in special cases. The nice part is you can bring a cylinder to stock bore without sleeving.

    I'd save my pennies and build it back large by whatever method.
    ^^ THIS is what I was going to recommend. have the Cylinders Hard Chromed or Nikasil coated, Then re bore
    them. I have never done this with Harley Cylinders, But I have had jugs coated for motocross 2 stroke cylinders.
    They have a longer wear life than cast iron, so You will be spending less $$$ on maintenance.
    AT least check it out & get the cost. (It's been over 20 years since I had one done, so I have no idea
    what today's prices are). I forget which Piston Ring material is best with the coatings
    (Chromolly or cast?) So, Be sure to find out.

  11. #11

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    lol
    he isnt asking about sleeving the cylinders , hes asking about sleeves in the engine case to make up for the stock cylinders being used in big bore case'
    fucking read the post
    lol

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    In his first post, Yamalol did mention sleeving his big bore cylinders. I pointed out that it is not possible because there is not enough material there.

    The idea of having these cylinders Nikasil treated would be a way of saving them, if a proper size piston could be had.

    Jim

  13. #13

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    what I get from his first post, is that he cant find 70 over pistons for his big bore cylinders. he does have a set of the standard cylinders thus wanting to know if he could run those instead. To get buy on the cheap have you considered knurling the pistons? This would still leave you with the 60 over rings (maybe one of the manufacterers could get 70? , what is the ring gap now? Pistons have been knurled in years past but it is indeed kinda of a bandaid fix. Not sure shops even do it anymore, but a guy with a lathe could. 2 cents.

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    .

    The ring lands would need to be in good shape ..
    Be a waste of time on worn out pistons ..

    Hinda a lost art ....
    Last edited by Dragstews; 06-03-2022 at 1:45 PM.

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    Yeah, I haven't heard of anyone knurling pistons on anything newer than a shovel, and that was years ago. At best it was sort of an emergency fix to get you where you could go through the top end proper-like.

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    Quote Originally Posted by SteveJ View Post
    lol
    he isnt asking about sleeving the cylinders , hes asking about sleeves in the engine case to make up for the stock cylinders being used in big bore case'
    fucking read the post
    lol
    The Idea was for the "worn out" Big bore cases to be hard coated, not the stock bore ones,
    YOU Dumbed Down IDIOT.

  17. #17

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    I dont think its been mentioned , but remember to match the weight of the new pistons to the old ones (pins, keepers and rings) to keep the balance .

  18. #18

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    Quote Originally Posted by Revelator View Post
    The Idea was for the "worn out" Big bore cases to be hard coated, not the stock bore ones,
    YOU Dumbed Down IDIOT.
    This is even stupider than the original post.
    Get real.
    The op is so stupid that you cant figure out its a jap bike guy posting stuipid shit to watch guys like you make fools of themselves.
    Hers a clue knumbnuts:
    The poster has abandoned the thread.
    Easily one of the stupidest threads I have seen.

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    Hey Steve,

    I am sure everyone appreciates your experience and willingness to share. I would just like to point out you are coming on a bit strong for new guy. There is a shit load of experience on this board as well as a lot of guys like me who have been in and out of the hobby for a lot of years.

    Just say'n you might want to ease up a bit so people can appreciate what you are offering without the snark.

    But hey what the fuck do I know...

  20. #20
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    Having the cylinders re-sleeved puts the project out of my budget for a bit, if I could even find someone to do it. I DO have a good set of 3 1/2" bore 80" cylinders.
    States the core problem which is worn jugs in need of replacement or bore coating or sleeving.

    Can I run those cylinders on cases that have been bored to 3 5/8 to accept the big bore kit?
    Is a question re: the bored cases. The bolt pattern hasn't changed and the cylinder flanges are sufficient to support hot rod cylinders so they'll do fine with stock or anything in-between because Shovel flanges support the top end. Bolt whatever to the cases as the studs and flange/case interface take all the loads.

    The responses regarding those options were correct. The Shovel cylinder skirt not being supported by the crankcase it wouldn't matter what bore the case happens to be.

    OP did not post trollishly and it's common for folks with little Shovel experience to ask that sort of stuff. I'm a multibrand wrench and while old Jap bikes have sleeved alloy aircooled cylinders later machines often have watercooled cylinders cast en bloc like alloy auto engines and one familiar with those might not know how Shovels are done. Not everybody compares and contrasts engine designs though it's a good idea for any mechanic. Most of the old HD mechanics are dead and the rest of us have one foot in the grave and the other on a banana peel.

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