3 5/8 big bore evo..help?
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Stage IV
Joined: May 2010
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3 5/8 big bore evo..help?
i am new to hdforurms and this is my first post. ive got a 98 dresser that had a screw sucked into the intake, and made it all the way into the cylinder.. needless to say that piston/cylinder was toast, as well as the rod. ive decided to do a 88 inch big bore when i go back together. i am a machinist and i am gonna bore the cases myself. my question is... is there a specific tolerance the case must have in relation to the case bore/cylinder skirt... how much clearence does it need?! will the studs need to be plug welded and redrilled? should a torque plate be bolted to the cases before they are bored? for any of you that tell me to send it to a professional, save your breath. i want the satisfaction of doing it myself, and i am a professional as far as being a competent machinist, there is just no instruction or directions that i have been able to find anywhere for the specific job at hand.
Road Warrior
Joined: Nov 2008
Posts: 1,595
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From: Vancouver Island British Colombia Canada
As far as torque plates, yes!! For your clearance question, I can't answer that.
Replace your inner cam bearing with a torrington! The makers of the big bore kits should have all spec's that you will need I would think.
Replace your inner cam bearing with a torrington! The makers of the big bore kits should have all spec's that you will need I would think.
Club Member
Joined: Jun 2007
Posts: 45,429
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From: Bedford UK
Welcome to HDF.
From what I can make out there are two sources of a big bore kit. One is a Harley specialist who will machine your cylinders and fit larger liners, the other is an after-market company like Axtell, Wiseco and Sputhe, who sell cylinders with matched pistons. Either should tell you the size you need, especially when you buy from them!
Keep us up to date with your progress!
From what I can make out there are two sources of a big bore kit. One is a Harley specialist who will machine your cylinders and fit larger liners, the other is an after-market company like Axtell, Wiseco and Sputhe, who sell cylinders with matched pistons. Either should tell you the size you need, especially when you buy from them!
Keep us up to date with your progress!
Last edited by grbrown; Jun 19, 2010 at 05:15 AM. Reason: Expanded.
Seasoned HDF Member
Joined: Nov 2009
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From: Farmington ,MS
Every pic I have ever seen of cases being bored, they used a jig that was made just for that purpose. Jig costs about a grand.
http://www.handsontools.com/JIMS-140...n_p_19743.html
Getting your cases bored costs about $275... may want to rethink that "satisfaction" thing. Just saying
http://www.handsontools.com/JIMS-140...n_p_19743.html
Getting your cases bored costs about $275... may want to rethink that "satisfaction" thing. Just saying
Last edited by Tom84FXST; Jun 19, 2010 at 06:31 AM.
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Stage IV
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well i bought the v-twin motor shop 3 5/8 kit pre fitted with wiesco pistons. i measured the skirt of the factory cylinder and it was 3.675" od, the case bore was slightly egg shaped ranging from 3.690 to 3.695.. so thats .0075" clearence per side roughly or .015" larger diameter on the case. the new cylinder skirt is 3.875, so that means if im right i need to make the cases .200 larger diameter to a grand total of 3.890". the 3 5/8 cylinders have a lot heavier wall it seems than the factory stuff. my new worry is that im going to be cutting into the case wall on the cam side of the rear cylinder making it slightly thinner. the JIMS case boring tool mentioned by TOM84FXST wouldn't even work in this application because the maximum diameter you can bore with it is 3.8125. im also still curious about the stud location, i should still have plenty of meat left between the bore and the stud, but it also looks as though the holes in the new cylinders are on a slightly larger bolt pattern, and the alignment pins look different as well.
Club Member
Joined: Feb 2008
Posts: 18,575
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From: Norfolk, VA
well i bought the v-twin motor shop 3 5/8 kit pre fitted with wiesco pistons. i measured the skirt of the factory cylinder and it was 3.675" od, the case bore was slightly egg shaped ranging from 3.690 to 3.695.. so thats .0075" clearence per side roughly or .015" larger diameter on the case. the new cylinder skirt is 3.875, so that means if im right i need to make the cases .200 larger diameter to a grand total of 3.890". the 3 5/8 cylinders have a lot heavier wall it seems than the factory stuff. my new worry is that im going to be cutting into the case wall on the cam side of the rear cylinder making it slightly thinner. the JIMS case boring tool mentioned by TOM84FXST wouldn't even work in this application because the maximum diameter you can bore with it is 3.8125. im also still curious about the stud location, i should still have plenty of meat left between the bore and the stud, but it also looks as though the holes in the new cylinders are on a slightly larger bolt pattern, and the alignment pins look different as well.
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