Big Bore - sleeve wall thickness..??


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Hi all,

Just trying to figure out the wall thickness of big bore sleeves.
I have been going through a basket case "special" that I picked up a while ago & it came with 2 sets of barrels. 1 set has sleeve's that are standard bore 75.00mm ID & 82.7mm OD, the other set are 80mm ID & 85.10mm OD, obviously these have been sleeved at some point - out of curiosity just wanting to know what the wall thickness of LA sleeve's are for these bikes..??
Any input appreciated....:thumbsup:
Thanks scabber - yeah I'd worked out the current wall thickness of these sleeves. As the OD is obviously different on these sleeves to the OEM set that I have, I was just wondering what the "standard" oversize sleeve wall thickness is...LA sleeve/Mikes etc...its no big deal just curious.
Probably no help but there have been more than a couple shops that made (make) big bore kits. I think until MikesXS commissioned the "big fin" cylinders they all just punched out the stock cylinder. IIRC the limitation is that after a certain size you have to remove metal from the upper crankcase to get it in. Wiseco pistons were (are) popular on big bores.
Hoos racing sells big bore kits. I have an NOS big bore kit installed in the cylinder and machined with pistons for a 256 engine can't remember who did it, Big swede?? If I get a chance I'll look at the paperwork and measure the sleeves.
Just to be sure, aren't the original oem liner's boreable to get you somewhere around 700cc, after that the oem liner needs to be removed, the jug itself bored for the 750cc liner's and then the new 750cc liner bored for correct piston wall clearance?
78mm is the max over bore for stock liner(good old ductile iron sleeves would be useful at that bore size) while 77mm would be on the safer side of preventing liner distortion
Measured that big bore kit I have, sleeves are 80mm inside 85mm outside Big ass high compression pistons are marked JE on the bottom. I think this kit is old school race parts.....
Calculating the cc's isn't to hard. pi x the radius squared is the are of a circle. Multiply the area by the stroke gives you the cc's of one cylinder, X's 2 is the total cc's
77 devided by 2 gives you the radius, 38.5 Radius x radius is 1482.25. The 1482.25 x Pi of 3.14 is 4654.265. This is the area of the bore. X this by the stroke of 74 = 344415.61 X 2 is 688831.22 cubic mm. To convert to cubic cm then devide by 1000, or 688.83 cc's. Using the same formula the 78mm bore is 706.83 cc's
The 77 bore you can call a 689 the 78 bore a 707.
On Mike's 750 kit the piston is 80 mm, this gives you a cc of 741. His first over for the 750 is an 81 mm piston and gives you 762 cc's.
Using the stock stroke, bore vs cc's

75 654
76 671
77 689
78 707
79 725
80 744
81 763
82 782
83 801
84 820
85 840
86 860
87 880

Took me a while to dust off my rusty spreadsheet skills and figure out the open office spread sheet, by then XSLeo answered the questions. :doh:
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Thanks for the info lads, was just making sure there was plenty of strength in the sleeves. I will have to check these out for ovality and source some piston kits for them.
gggGary, I agree on most of your calulations but the 75 mm bore of the stock cylinders are marked 653 cc's right on the cylinders. ! cc won't make any difference but that's what the cylinders read.
I've been waiting for that comment. :laugh: Spread sheet comes up with 653.84yada, yada, I set it to round to a whole cc, usual rounding algorithm is 4/5, what does your math show?

My rounding algorithm today involved pumpkin and pecan pie, burp. I feel a nap coming on.
Were you also waiting for the "some of those are impossible" comment? 87mm is the maximum piston and even that requires the Heiden big bore cylinder block and a lot of machining. Heiden says you have to leave out the dowels on the mounting studs because the 91mm O.D. sleeve runs right up to the studs. If you want to go bigger than 880cc you need a stroked crank (and all the cylinder height/cam chain length issues that go with it). A member here is building one of those, might be time to bump that thread for updates.
gggGary, I agree on most of your calulations but the 75 mm bore of the stock cylinders are marked 653 cc's right on the cylinders. ! cc won't make any difference but that's what the cylinders read.

Never let a sleeping dog lie.


Guess they were more accurate with their math when it came to keeping the EPA happy.

GreasyC you are right I just ran off a list of sizes numbers without considering physical impossibilities.
Just bringing up an old thread, what's the minimum wall thickness would you think, I spotted some Wossner pistons on the Internet today they are 82mm, I have two sets of barrels both measure around 85mm which would only leave 1.5mm wall thickness, I'm trying to work out the cheapest way of my rebuild as I've basically gone through 2 engines this year
Max bore on stock liners about 78mm m/l 700cc My engine guy whines that even then the liner is getting flexy.
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