broke the motor, what do you think?

[Mr.Finesse]

Here's the scenario. I just bought an 18' F/S with a 88 Johnson GT 150 VRO that has been bypassed. When I bought it, the compression on all cylinders was around 85, normal for this age and condition of motor. Took boat out for first time, cranked right up, ran like a top both at partial and full throttle, GPS with a 20 pitch 4 blade stainless prop was 55 mph, everything seemed right on. That trip put about 15 minutes on the motor, maybe a little more.

Have the boat out a second time, same thing, everything went well, running well no problems, about another 15-20 minutes on the motor, mostly at partial throttle.

Boat out for third time, about 20 minutes of partial throttle and then about 2 minutes of full throttle and PERCLUNK!! chokes and dies. Water poring out of carbs, stumbling idle, then freezes up.

I have pulled the motor and taken it apart. Middle cylinder, starboard side, ate its con rod bearing, added a new port on the intake side of the block, cracked the cylinder sleeve(hence water poring out of carbs), chewed up the cylinder head and pretty destroyed this block beyond any hope.

I have not taken the lower unit water pump out to check the impeller, I may find my answer there, but betting that wont be it. Tell tail stream was flowing well. And there was copious amounts of water poring out of the bottom carbs when I restarted the motor trying to get a little closer to the dock.

Question! what in Sam hill could have caused this? over heat? I know fuel mix was okay, had Seafoam in it too.

 

[jawsnatcher]

I thought anything below 90 meant it was on its way out

 

[Strato-G]

Was oil added when replacing gas in tank>>>>>Add oil to gas tank when VRO is bypassed????? emoGeezer emoUSA

 

[silvertalon]

Check the inside of all pistons for black burnt look above the wrist pins. Probably didn't overheat tho. As your horn would have gone off. Check all the crank end caged bearings and rod surfaces. If they all look good (no pitting, bluing), probably had a rod bolt let go. You will need a crankshaft and block. I happen to have an 84/85 XP 150 block and crank. The block was bored in 1 hole and honed. It may need to be honed again if surface rust. Crank is from the same block and will also need to be cleaned up with Crocus Cloth. Also have the heads. Don't know about the rods, maybe. After tomorrow, I wont be around until the 6th or 7th. If interested, send me a text at 352-364-2436 and I will get back to you. I'm in the Hixson area.

 

[Mr.Finesse]

oil was mixed in gas, don't think it was a lubrication problem. Don' think it was an over heat either. Thats what has me confused. Thanks for the offer Silvertalon. I already picked up a an 84 gt 150 for $700 including a stainless 22 P raker 8-O The compression on that one is all around 75. its tired I know, but if it gets me through the summer and fall, Ill rebuild it in the winter and have a fresh motor. I can rebuild lowers too, so now I have two lower units, probably will sell one to supplement rebuild. Also will be selling the raker to supplement.

 

[Mr.Finesse]

jawsnatcher - 5/26/2016 7:54 AM

I thought anything below 90 meant it was on its way out

you're pretty much right, that goes for most two strokes, but not on this specific motor. This motor shares many parts with much more powerful motors, to get this one down to 150, they used lower compression heads, this motor would have around 90 from the factory. If I put the 235 heads on it, it would jump up the compression immediately. So ~85 is a nice healthy GT 150, ~75 its getting tired. less than that considerable loss of power would be felt I believe.

 

[silvertalon]

Mr.Finesse - 5/27/2016 2:56 AM

oil was mixed in gas, don't think it was a lubrication problem. Don' think it was an over heat either. Thats what has me confused. Thanks for the offer Silvertalon. I already picked up a an 84 gt 150 for $700 including a stainless 22 P raker 8-O The compression on that one is all around 75. its tired I know, but if it gets me through the summer and fall, Ill rebuild it in the winter and have a fresh motor. I can rebuild lowers too, so now I have two lower units, probably will sell one to supplement rebuild. Also will be selling the raker to supplement.

IMO; I'd pull the transfer port covers and look at the rings. Or better yet, pull the heads and exhaust cover and de carbonize the motor (scrape out all the carbon from the exhaust ports and pistons, and exhaust cover. I think a steady diet of carbon gard in your fuel will prevent further ring sticking and perhaps free them up for better performance. you should also install a service port valve on your fuel primer (if so equipted) so you can thread on a can of carbon free, power tune etc. Yamaha sells a de carb kit called 'Ring Free' . I hear it really works on older motors! Good Luck...

 

[Mr.Finesse]

My plan more specifically for this motor, is a basic go through before I run it. Its taking a lot of patience though lol. But, I'm going to rebuild and clean the carbs, pull heads and de-carb the cylinder walls, pistons and rings aggressively with open heads to have maximum access to carbon, reseal lower unit, fresh water pump, new thermostats, new plugs, and link and sync timing. That should hopefully get me a reliable motor through the rest of this year. Then I will likely have this motor torn down for a complete rebuild to totally restore full power and economy of engine.