Evinrude 1972 25HP Sportster 25202R Help Needed

[prdevoe]

[FONT=&quot]I found an old Evinrude outboard of my grandfather's in my Dad?s stuff (both have passed away) that I have slowly been working on the past year. I know a little about outboards which I have mostly learned from all the great folks on iboats and from borrowed library books etc. I have cleaned/rebuilt the carb on it and repaired the fuel pump. I checked the cylinders? compression (114 and 111). I then noticed that the upper spark plug socket threads were pretty thin. I read about heli-coil and timeserts and decided I wouldn't try to tackle that just yet. The next thing I did was to check the sparking and found that only one plug was sparking. I then checked the coils and the condensers (which I knew nothing about before reading several iboats forums) and figured out one of the plug wires was corroded. I removed the corrosion, rechecked the sparking, and they both were firing. I then noticed that the spark plugs were Champion J6C instead of the J4J plugs that are listed for the outboard. My questions are: what is the difference between J6C and J4J plugs and why might my grandfather put the wrong plugs in it? Could the J6C plugs have stripped the spark plug threads (doesn?t make sense to me since the thread size should be the same)? Should a novice like me try the heli-coil or timesert fix or should I try to remove the cylinder head assembly and have it worked on by a machinist? Are there other options I should pursue? I guess I am looking for advice on how to proceed.[/FONT]

 

[F_R]

J4 and J6 refer to the heat range of the spark plugs, J6 being the hotter. Otherwise, they are exactly the same. Heat range refers to the temperature of the tip of the plug when running, not temperature of the spark. Too hot can glow and pre-ignite the fuel, causing severe engine damage. Probably not going to happen on most motors, but the 25 is a high performance engine and you ought to use the correct plugs, not just anything that fits the hole. BTW, over-tightening the spark plug is what strips the threads in the head.

Find a good used (or new) head if you can. But remember the 25 is different than the 18 or 20hp, and not interchangeable, though they look the same. It is difficult to get a heli-coil in straight when doing it free-hand, and much more difficult on that one because they go in at an angle. Best to let a pro do it unless you are able to deal with the angle situation. If not installed at the correct angle, it will leak around the plug's threads and gasket. Be sure to use a new head gasket and torque the bolts to the proper value.

 

[prdevoe]

Thank you F_R for the guidance on both the spark plugs and the cylinder head repair. I will definitely get the right plugs going forward. I have searched several sites as well as eBay for the cylinder head and they are all indicating the part (383535) is obsolete. I have been able to find the gasket however. Any idea where I might look for the cylinder head or am I now limited to getting the old one machined out? Anything I need to be particularly aware of if/when I remove the head? Thank you.

 

[F_R]

Yeah, probably in short supply because so many people think they can get 25 horses from their 18 by just changing the head (no way). Some Evinrude dealers have access to a database that will search for a part in other dealers' stock. It's worth a shot. Also try a want ad on the classified ads pages at www.aomci.org The ad is free.

 

[oldboat1]

sure the threads are stripped? (not sure what you mean by thin threads in a socket.)