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Discussion Starter · #1 ·
Need to tap into your vast wisdom. I recently aquired a 67 daytona 500 motor held compression a little over 100 when i got it the sellers story didn't quite hold up and i was planning on taking the motor down anyways to freshen everything up, i ran into 20 over pistons no big deal, one is very clean/ almost looks brand new never ran on the other has its far share of carbon, upon removing the cylinder jug i measured and it seems as if the bore is 30 over and they took up the slack in the rings,im no machinist this is my first build of a motor, is this acceptable? very excited about the bike and the build. any and all info will be greatly appriciated, ive got the triumph workshop manul already and trying to make sense of everything.

Thanks in advance and look foward to seeing my very newb questions more frequently, i did search for answers didnt see many although useful info not the info i needed.
 

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I'd say you need to soon find your local machine shop cat. You need to know just what exactly you got. Measuring OD, like a piston, isn't so difficult but accurately measureing the bore is tougher. If you need new pistons, the commonly available Asian T100 ones are actually pretty good.
 

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I set up new pistons at .0045 clearance and I consider pistons with more that .008 clearance as worn out.
 

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I agree with Tony. I have seen .009 and .010 not smoke but I considered it a miracle. You definately want to make sure that it is right. I have never head of anyone effectively "making up the difference" with rings. At the very least you are gonna have slap, at worst you are gonna smoke like a Suzuki Water Buffalo.
 

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Discussion Starter · #6 ·
Sorry everyone my first post had alot of half info on it it was late and been working all day let me try to explain better. Thanks to everyone who has already chimed in. The cylinders are 20 overs, my concern is with the rebore size of the cylinder block, my manual says suitable rebore sizes for 20 over is 2.736ins, and for 40 over are 2.756 now my cylinder block is bored to right inbetween the two. im not sure if that is acceptable or not i know the piston needs a "c hair" of clearance but again im no machinist.
 

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The specified bore size in the manual is only good if your pistons measure the same minus the specified clearance. You should take your parts to some one who has the tools to measure properly and determine piston to cylinder clearance, taper and out of round.
Here is the basics. An outside mike is used to measure the piston and the mike is used to zero the dial bore gage. I dont really even have to read the outside mike as I am just using it as a gage represent the size of the piston. The dial bore gage sweeps the cylinder wall and shows the piston to cylinder clearance. you can measure 9 different spots in about 15 seconds for a thorough exam of the cylinder
 
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