How big is the cylinder to piston clearance?

[DJ]

Re: How big is the cylinder to piston clearance?

Dhadley,<br /><br />1/2 to 1 HP used to be the difference between rowing and riding.

 

[Dhadley]

Re: How big is the cylinder to piston clearance?

Do you think it happened when it overheated?<br /><br />Did it happen something like this -- cruising along in the mid range and all of a sudden you felt a vibration. Pulled back on the throttle and the motor quit but the hot horn sounded. Pulled the hood off to take a look and sure enough, the powerhead seemed hot. Pulled the thermostat out and restarted the motor. It idled funny but got better the longer you ran it. <br /><br />Maybe when it first quit the starter seemed to be dragging. Anyway after sitiing a while it started and ran OK once you got going. Took it easy and it ran good enough to get home.

 

[DJ]

Re: How big is the cylinder to piston clearance?

Dhadley is right. I knew exactly when my head gasket popped. I had been in some weeds and the hot horn went off.<br /><br />Just after that, it didn't run right-lack of power.<br /><br />Actually, I couldn't even see where the gasket leaked, although I knew it did because the cylinder was washed down and a new one fixed it.

 

[Goodoleboy]

Re: How big is the cylinder to piston clearance?

My manual says that a good sign of water leaking into cylinder is the spark plug will be clean as new.<br /><br />I may have missed it some place, Perhaps you have already coverd that.<br /><br />Good Luck!

 

[Mark42]

Re: How big is the cylinder to piston clearance?

Dhadly, it happened like this: Crusing at 3/4 throttle motor was fine. Ran full throttle through some chop really shaking things up and it started to run rough, so turned back into the bay and into calm water. Noticed temp guage was up to 120 so I stop and check for seaweed but don't find any. Starts easy but stalls when put in gear. After a few tries it gets going. Head toward marina and its fine, so I cruise past and get a mile or two away when I start running WOT and top speed is down about 2mph. Temp is back up to 120 so I stop again check for clogged intake, but it's pumping water fine, but getting warmer so I shut off and remove the thermostat because I figure they may not be opening fully. Start back up and head toward marina. 10 minutes later doing about 12 mph, the motor looses power and the boat drops off plane and I idle into marina running very rough. <br />It never got hot enough to sound the horn. <br /><br />I expect to see a blow through mark if the head gasket was leaking. You know, exhaust mark, oil mark, but I don't see that. The gasket seemed to be sealing, but I'm not that familiar with water cooled two strokes. Just the air cooled kind on dirt bikes and lawn mowers. Even so, if it was sucking water, wouldn't there be some rust or something on the gasket metal ring?<br /><br />I just got home from working on my friends tractor, tomorrow family is visiting so maybe I'll get an hour or so to drain the carbs and see what comes out.

 

[AMD Rules]

Re: How big is the cylinder to piston clearance?

Sorry to hear about your motor troubles Mark. As you are aware, I can relate all too well. Hope you get it all sorted out & back on the water.

 

[rodbolt]

Re: How big is the cylinder to piston clearance?

it only takes one overheat to destroy it. ya dont always get a second chance. your motor is a lost foam casting that does not use a water jacket divider on the exhaust. however we do see the occasional pin hole in the castings. the plugs will tell the story especially in salt water.but just looking at the pics that motor was run with water in the cylinders. water is vary abrasive and will steam clean the pistons and cylinders. the rods will tell the sory of if it was a lubrication failure as will a look at the piston skirts. the compression ring on the gasket is stainless and not supposed to rust. you may or may not see a blown head gasket. looking at the green around the coil secondary towers ya need to tigten up a bit with the corrosion preventative maint .

 

[seahorse5]

Re: How big is the cylinder to piston clearance?

Bottom cylinder problems can also be caused by running without a thermostat or with one stuck open, not allowing the motor to warm up fully.<br /><br />Due to that particular engine design, "cold" water hits the lower side of the bottom cylinder first, and without any restriction from a thermostat, it can distort the cylinder and is also very common to have cold seizure on that piston as mentioned earlier.

 

[Mark42]

Re: How big is the cylinder to piston clearance?

Originally posted by rodbolt:<br /> ...looking at the green around the coil secondary towers ya need to tigten up a bit with the corrosion preventative maint .

Rodbolt, thanks for all the great info. FYI that green stuff is actually blue Triple Guard grease used in the boots as per the spark plug kit instructions (new plugs and wires in spring). It just looks green in the pic for some reason.

 

[rodbolt]

Re: How big is the cylinder to piston clearance?

wow<br /> good for ya and shame on me. someone who will actually follow the instructions . I hope the rebuilder does ya right if it was a flaw with the product.

 

[Mark42]

Re: How big is the cylinder to piston clearance?

FYI I drained the lower carb and all that came out was gas. Good to see it was tinted green from the VRO pumping oil. Didn't drain top carb because I would have to take off the air box and I want it to look as original as possable when sent back to the shop. But because the fuel has common pump and lines, if water was in the top carb, it would certianly be in the lower. Especially seeing as water is heavier that gas it would tend to settle in the lower part of the manifold feeding the lower carb (just my speculation).<br /><br />At this point the season is shot for me. I just want to get the powerhead back, wash and wax the boat and store it for the winter. There is always next season.