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1977 Johnson 200 bore

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mdr584

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"Can anyone tell me what is th

"Can anyone tell me what is the allowable tolerance for the bore before it should be rebored oversize...How much out of round...what is maximum clearance...? I believe the bore is 3.500"...

Thanks,"
 
"David, according to my notes

"David, according to my notes a cylinder should be honed or rebored if it is out by more than .003" for inline models and more than .004" for V4/V6 models (which would apply to your motor).

If it is rebored for oversize pistons, you are to leave a .003 to .005" clearance between the new bore diameter and the oversize piston.

OEM pistons/rings for your model came in standard, .020 over and .030 over"
 
If my 77 200 Johnson is a 3.50

If my 77 200 Johnson is a 3.500 bore (as I believe it is) then if it measures more than 3.503 it needs to be rebored...correct..?
Anybody know for sure what the actual bore size is...?(still waiting for the manual)

Thanks guys
 
"should be honed or rebored if

"should be honed or rebored if it is out by more than .003" for inline models and more --
------If it is rebored for oversize pistons, you are to leave a .003 to .005" clearance between the new bore diameter and the oversize piston.
--that ,dont sound right to me..--"
 
This is simple----The standard

This is simple----The standard bore from the factory is exactly 3.500" you over bore to 3.520" or 3.530" I do this work myself.The new O/S pistons are sized to give the proper piston to bore clearance.Now new OMC factory O/S pistons give you a clearance of 0.009" and WISECO give around 0.005".You need a true / O/S / round hole to give good engine performance.Hope this is clear.
 
"London, just so I understand

"London, just so I understand as well, because like JWB the notes in my manual sounded a bit confusing.

You are saying that you bore exactly to the oversize and that the OEM pistons are made with the allowance required for clearance - whereas the notes in my (old) manual may be indicating that older pistons were exactly the bore diameter and you needed to bore a little extra to allow for clearance.

Do I have that right?"
 
"THE NEW BORES are 3.500"

"THE NEW BORES are 3.500" and pistons are something in the order of 3.495" I discussed with OMC rep as to why the new O/S pistons are 0.009" ---did not really get a good answer , but it may have something to do with expansion rates of the alloy.As you well know pistons also taper about 0.010" top to bottom to allow for expansion.Pistons seem to be really sloppy when cold but they " grow " to the cylinder when running."
 
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