how much should a piston cost me?

[massimofinance]

I am rebuilding my Evinrude outboard, two pistons were ruined (right bank), they wound up costing me $80 each, plus rings for another $15 each, at the local boat dealer. Is this a standard price? While I have the head off and half of it apart, I might replace the left bank as well (compression was 110 on that side, compared to 75 and 25 for the right bank), but if the parts cost this much, I might live with 110 compression, does anyone think I am nuts, should do it differently, buy the parts online, other advice? (what's a good place online for evinrude parts?)<br /><br />Thanks!

 

[Dhadley]

Re: how much should a piston cost me?

Im sure this will get moved but in the meantime --<br /><br />Most oversize pistons today come with rings, wrist pin and locks. The 95 you were quoted is a tad high by about 6 bucks per piston. Youll have the motor completely apart so you may as well do the rest. Since it was the starboard side we assume the damage was from coking. This means the other side will probably measure out of spec also from the added combustion heat.<br /><br />The biggest thing is to correct the cause of the problem. An off hand guess would be that the motor is set up in the low 5000 range, probably 5200 or slightly less. Once you get it back together, set it up for 5800 with an average load. That will relieve the stress and reduce the combustion temps. Make sure the cooling and fuel delivery systems are in proper working order and you use Champion plugs and fresh 87 octane.

 

[Dhadley]

Re: how much should a piston cost me?

Coking is that black sticky carbon like substance you see on the piston. It causes the rings to stick in the grooves and eventually the piston will lose enough support that it cocks far enough to shear off the end of the rings.<br /><br />Coking is directly related to combustion temp. The higher the temp the faster it appears. High combustion temp is most related to engine set up. If the motor can only rev up to, say 5200 rpm instead of 5800 rpm the combustion temp will be higher. Thats known a "lugging" the motor. Its very hard on it thru the entire rpm band. Other things influance combustion temp too. Like the wrong spark plugs and / or the wrong grade fuel. Fuel that isn't fresh, things like that.<br /><br />Once the motor is apart a machine shop will measure the cylinders to see if they are in spec or not. With all this added combustion temp its hard to imagine they will be in spec. Most likely youll bore it to the first oversize and repalce all 4 pistons.<br /><br />Setting up the motor to be able to reach 5800 rpm has to do with the mounting height on the transom and the prop. <br /><br />Higher octane will hurt more than help. Assuming the motor is a stock motor and not modified for high performance.

 

[massimofinance]

Re: how much should a piston cost me?

Hi, thanks for the answer! (The price difference is not bad; I will stick with my dealer)<br /><br />Does coking mean the engine runs too hot? When you say measure out of spec, is that related to the compression test?<br /><br />Regarding correcting the problem, are you suggesting I adjust the carbs to 5800? (5800 what?) (sorry for my lack of engine knowledge)<br /><br />Also, is it fair to assume I can use a higher octane as well? Should I be buying a pre-mix (this engine is a two stroke)<br /><br />Thanks!

 

[JB]

Re: how much should a piston cost me?

Moving to JohnnyRude Troubles