Wiseco, Johnson & ring end gap

CorB

Petty Officer 3rd Class
Joined
Aug 6, 2003
Messages
76
Hi there,<br /><br />I have a '78 55 HP Johnson.<br />I had it rebored, because I had too much piston ring end gap and eventually too much piston to cylinder clearance.<br />I've ordered 2 Wiseco 0.030" oversize pistons (3.217" bore size) and gave them to my machine shop to rebore the powerhead.<br /><br />Now I've measured the piston ring end gap. Three rings measure approx. 0.024" and one ring measures approx. 0.022". I measured evenly in both cylinders on top & bottom so I assume the cylinders are round & evenly.<br /><br />My oem Johnson manual calls for a ring end gap of min. 0.007" and max. 0.017" and Wiseco says 0.004" x bore size, so that will be 0.004" x 3.217" = 0.012868" minimum ring end gap. Wiseco didn't describe the max. ring end gap, only the minimum.<br /><br />So my readings don't fall between the specified tolerances although Wiseco doesn't provide a maximum ring end gap.<br />I don't know anymore what is wrong or right. Did my machine shop rebore too much (they had both the pistons), or do these Wiseco's cause the problem, or don't I even have a problem at all?<br /><br />Some help is greatly, very, very appreciated!
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: Wiseco, Johnson & ring end gap

Your end gap is fine. The old .007 to .017 went away long ago. The ring material today is nothing like the older rings.<br /><br />Find out what your shop used for a "finished bore size". 3.217 is a bit on the tight side. It'll work but you need to break the motor in very slowly and carefully. I would like to see it at 3.2175 to 3.218.<br /><br />Good luck!
 

Hooty

Rear Admiral
Joined
Oct 2, 2001
Messages
4,496
Re: Wiseco, Johnson & ring end gap

Even after break-in be very aware of the need to bring the engine up to operating temperature before any hammerdown boating.<br /><br />c/6<br />Hooty
 

CorB

Petty Officer 3rd Class
Joined
Aug 6, 2003
Messages
76
Re: Wiseco, Johnson & ring end gap

Dhadley, Hooty,<br /><br />Thanks a lot for your replies, I'm very happy with your answers. <br />Even a manual isn't always enough, it's nice to get in touch with experienced people like you through this forum, the value of it is priceless!<br /><br />I don't know the exact finishing bore, but the machine shop used the range between 3.217 - 3.218 as mentioned by Wiseco. I will ask them to be sure if I'm on the safe or on the cautious side.
 
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