Common problem? 33-cube Johnrude Twins

[Chinewalker]

I've had two of these in the shop lately with low compression issues. Both look to have been overheated, which in and of itself would account for the low compression, BUT, both were non-rebuildable due to the cylinder sleeve seperating from the cylinder! Both blocks had both sleeve separated in the same area - exhaust side, from about the 7 to 10-o'clock positions, which resulted in about .040" to .060" out-of-round. Was this a common issue with this style motor? One was a 1985 Evinrude 20, and the other was a 1986 Johnson 30.
- Scott

 

[R.Johnson]

Re: Common problem? 33-cube Johnrude Twins

Scott: I personally have never run into this, but it makes for an interesting problem. I would wonder how hot the engine got in the erea of exhaust flow. The machinery handbook says aluminum melt's at 660 degree's C. Did it get this hot in that erea, and start to seperate from the cast iron sleeve? How much support is in this erea to surround the sleeve? This would be a good guestion for Dhadley.

 

[Chinewalker]

Re: Common problem? 33-cube Johnrude Twins

Thanks R.J.,
There is what appears to be maybe a 3-16-inch to 1/4-inch of casting behind the sleeve. Not much support, .ie webbing or the like. Doesn't look like it melted, rather more like it simply distorted and pulled away from the sleeve. The sleeve, in turn, bulged out a bit in that direction, making the bore out of round. Only other motor I've ever seen anything like that on was a 1980s 8hp twin that had been used extensively in salt water. Corrosion got between the sleeve and the casting, pushing the casting outwards.
- Scott

 

[R.Johnson]

Re: Common problem? 33-cube Johnrude Twins

Scott: Have you found any thing more with this problem? How did you ever happen to get hit with two of them?

 

[Chinewalker]

Re: Common problem? 33-cube Johnrude Twins

Hi R.J.,
Not sure. I just had my service tech shoot down another block due to cracks in the port webbing! I've got one more block to tear down and I hope it's rebuildable.
- Scott

 

[Chinewalker]

Re: Common problem? 33-cube Johnrude Twins

Got my block back last week and assembled the motor over the weekend. One minor exhaust leak due to that nearly impossible to reach nut behind the throttle linkage not being tight enough, but other than that it ran like a top! Put about an hour of break-in time at high idle, in gear at the dock. I ran the tank dry, so I have to pony up an arm and maybe even a leg to refill that so I can put more time on it...
- Scott