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  1. #1
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    Default 80" Shovel 8.5:1 Piston Swap

    Hello,
    Looking into swapping out the factory low comp 7.x:1 pistons for some 8.5:1 pistons in my stock 80" Shovelhead. Bike is a 1982 FXRS. Problem is it's a very low mile bike I got from the original owner and I would like to get some standard bore pistons. I can't seem to find very many 8.5 pistons let alone 8.5 standard bore pistons. Is it even possible to just pop some 8.5 standard bore pistons in or will I have to go overbore? I doubt a 7.5k mile motor needs it. Also will I need to have anything balanced? Just doing a mild build and can't find definitive answers thru research. Any advice appreciated.

    Thanks

  2. #2

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    not sure about the pistons and boring ect, but you should weigh each piston with rings clips and pin and make the new ones match the old ones.
    Be sure to match each one to their prospective cylinder.

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    Why do you want to swap? More umph get a better cam? i would leave a 7k motor sealed if it OK

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    ^^^^^^^^^^ Damn good question.....^^^^^^^^^^ I wouldn't fuck with it if it were me............ Just swapping the pistons will be of little power improvement........ In other words it's a waste of time and money..............

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    Quote Originally Posted by Tattooo View Post
    ^^^^^^^^^^ Damn good question.....^^^^^^^^^^ I wouldn't fuck with it if it were me............ Just swapping the pistons will be of little power improvement........ In other words it's a waste of time and money..............
    Yeah that's why I'm trying to gather info. See if it's even worth it? Originally wanted to just pop in Andrews #1 cam for low comp Shovels but can find very little real world feedback.

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    Quote Originally Posted by flatman View Post
    Why do you want to swap? More umph get a better cam? i would leave a 7k motor sealed if it OK
    Yeah I'm on that fence. I'm of the mind if you want a faster bike than buy a faster bike BUT I like Day 2 type mods and some drop in pistons and a cam are in that neighborhood. I agree about opening it up but the original owner I got it from had it opened to redo top end gaskets just for the heck of it. I was going to just pop in Andrews #1 cam for low comp Shovels which is based on their A2 cam but I can find very little real world feedback.

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    Your time and money would be better spent on a set of 9:1 or 9.5:1 pistons (from Wiseco, J&E, or maybe KB forged). Then use the A2 cam. It will be quite an improvement over your stock motor.

    You can hone your low mile cylinders with a micrometer adjustable hone (Sunnen, Lisle, etc.) and fit standard bore pistons. This ain't rocket science.

    Jim

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    Lets take a look at what the Acc. Program thinks ...

    Click image for larger version. 

Name:	Capture ACC PRO 1.JPG 
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ID:	99058

    Now for a bit of Hot-Rod ...

    Click image for larger version. 

Name:	Capture ACC PRO 2.JPG 
Views:	35 
Size:	189.0 KB 
ID:	99059

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    Quote Originally Posted by Dragstews View Post
    Now for a bit of Hot-Rod ...
    Holy smokes! Now that is some good info! Yeah seems I would be wasting time and money with the little I was thinking about. Hmm

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    Quote Originally Posted by moshumi13 View Post
    Yeah seems I would be wasting time and money with the little I was thinking about. Hmm

    Yep..............

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    Lower compression makes for less detonation and easier starting, nice considering the early electric starters weren't great.

    On an engine that young I'd be inclined to use up the stock parts first and just enjoy the ride then if you decide the bike is a keeper and you really want more ponies, build another engine since by the time you're done with a serious motor there won't be many stock parts left. Part of the "Harley tax" is the less original parts remaining the more capable the motorcycle.

    If it still has the excellent stock crossover exhaust I'd keep that and uncork it via pressing out the original baffles (if it has stock mufflers) by using a loose-fitting rod in a hydraulic press from the "engine" side and protecting the chrome on the outlet with a piece of scrap plywood etc.

    The stock carbs work decently with a rejet since factory settings were lean. We usually checked what (#60 thru 80, a set is dirt cheap) drill shank size fit the low speed jet then went up one at a time rather than buy jets. Grab drill bit with vise grips then spin jet between thumb and forefinger until it goes through, stroke back and forth a couple times to debur. Use hollow ground screwdrivers only on carb jets. Look at "gunsmith" screwdrivers and typical screwdriver bits for examples. Wedge style screwdrivers are best used as chisels and pry bars...

    The carb screws are JIS, not Phillips and the difference has wiped many a screw head. I went with socket head screws (which don't fall off a hex key during roadside bowl removal) because I hate cross tip screws. You can find metric matches via Ebay. Dunno if anyone still makes a kit. Vessel JIS screwdrivers work very well and are cheap.

    Some years had the accelerator pump cover with the check valve (good), and others had no check ball (less squirt, bad). If your pump cover rattles when shaken (must be pulled to check) it's the good one. This is what the good covers look like:

    https://www.dragspecialties.com/prod...umber=DS289096

    With the air filter off you can twist the throttle, see where it squirts (you can do this with the carb off the bike if you fill the float bowl) then drop the float bowl and twist the (pressed-in) nozzle until the aim is centered in the carb bore.
    Last edited by farmall; 12-20-2019 at 6:59 PM.

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    Drag's charts show that power can be improved considerably with very little work. (Although I think a stock motor is commonly known to produce 52 - 54 hp.)
    Because it's so easy and relatively inexpensive, I would do it now, and enjoy the change. I don't see any reason to wait, as farmall suggests. (And my Scots blood seethes when I have to take a new or near new or really nice motor apart to hop it up.) But I think it's always worth it, and a low mileage motor, no matter its age, will stand up to a good bit of roddin'.

    Jim

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    the current compression and cam sounds bout right for NOS and a blower.
    Dusty

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    Blowers are cool but when "shovelling" out that much cash the exclusive reason to keep a Shovel engine is because you like the way the heads look because more recent options can have many more cubes for much less money, and a race motor needs appropriate clutch, primary drive. transmission, starter suspension and brakes which is why fast FXRs have an FXR frame but lose a lot of original parts (like the whole drive train I have left over).

    I doubt OP wants to replace everything on that motorcycle and we shouldn't forget stock can be fun and reasonably durable.

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    Quote Originally Posted by farmall View Post
    On an engine that young I'd be inclined to use up the stock parts first and just enjoy the ride
    Yeah it's got a Super E a stock look 2-2 performance exhaust, Twin Fire 2, Progressive suspension. Day 2 stuff. It runs great. I'm just going to keep it the survivor it is. I have faster bikes.

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    Quote Originally Posted by moshumi13 View Post
    I'm just going to keep it the survivor it is. I have faster bikes.
    That's a very smart move,

    That's exactly why I didn't change my 79 FXS......... There wasn't any need to..........
    Attached Thumbnails Attached Thumbnails MVC-015S_zpsef848745.JPG  

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    Quote Originally Posted by JBinNC View Post
    (Although I think a stock motor is commonly known to produce 52 - 54 hp.)


    Jim
    Factory HP is rated at the crank, there will be about a 20% loss though the drive train before it gets to the ground ..
    The charts was generated using Rear Wheel Horse Power ... Could change the chart parameters to read at the crank ...
    Last edited by Dragstews; 12-21-2019 at 9:09 AM.

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    Quote Originally Posted by Dragstews View Post
    Factory HP is rated at the crank, there will be about a 20% loss though the drive train before it gets to the ground ..
    The charts was generated using Rear Wheel Horse Power ... Could change the chart parameters to read at the crank ...
    I bet running that simulation with a stock H cam would yield better hp numbers.

    Jim

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