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God awful noise

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DeanBrantley

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So I went out and broke in my 2 brand new 720 engines in my speedster. After 1 tank of gas I refilled and throttled on. Then my port engine quits at WOT. I limp into a ramp and get towed home. When I get my speedster home I first start trying to get my port engine to run, no luck. Starboard starts fine. I can tell the starters dragging so I replace it and install a new ground wire. Now the starter turns great but engine still wont fire. Switch coils and rectifiers from starboard motor...same thing. Someone tells me I have a bad port stator,so I check with my ohm meter and get the same reading for both (even though its not what the tech told me the readings should be) I assume it cant be bad since the starboard engine is running fine. So then I changed all the plug wires and it starts firing but sounds like a weed eater, with a bad cam chain,running on one cylinder,while someone is throwing bolts down the intake. Oh yea, before it died on the water it blew the port steering nozzle right of the venturi along with the linkage I just had machined, don't really think that has anything to do with it. Any suggestions appreciated.
Also..checked compression both motors 120 on all holes/checked voltage to both rectifiers,11.94v/carbs getting gas
 
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I'd get a different gauge to check the compression, 120 is not right. Can you post a short video?
 
Have tried to post pics in past, site wont allow. Gauge is new 120-125, all holes from day 1. Both brand new SBT motors. Please tell me that's a good reading, that I didn't start out with bum motors in the first place. I just ran more electrical tests and they are weird. Both stators show .6 ohms on yellow/yellow black and 59 ohms on blk/blk red. So that looks ok? Batt shows 11.74v not so good. Both red rectifier wires showed 11.74 at rest, (I didn't know the rectifiers were energized with engines off). However with engines running, port shows low, between 7.5 and 9v, then when I shut it down would only read 8.4v static? Starboard ran from 15 to 19.5v running and went back to 11.74 at rest. Port engine still sounds like a chain saw
 
On both engines does the gauge read 120-125?
If so, the gauge is reading low would be my guess. The rebuilt engines you have should be closer to 150 range.
 
Your compression figure are not ideal, but its certainly good enough to run normally. New engines should have 150, and the figures might come up to that after they are broken in - but probably not. Here is a compression example:

150 / 150 / 150 / 150 = perfect
150 / 150 / 150 / 100 = bad
123 / 122 / 125 / 124 = good

The higher the better for compression figures, but having the numbers be close to each other is far more important than the actual figure. Anything below 100 lbs is an automatic fail.

As for your electrical tests, I think your digging too deep. Just use a spark tester and see if the results are good. If your battery is testing low, you should replace it before trying to test the engine at all. A low battery will mess everything up, as the compression numbers wont be accurate, and the engine may be relying on the battery for spark if the electrical system has problems. If you have compression, spark, fuel, air, and timing - then it runs. Start with that list and start eliminating them as a possible cause.
 
Take a video, upload it to youtube and share the link in your thread. If the thing sounds like a bag of marbles it's not good. Remove the spark plugs on both engines, turn the pto over by hand, do they both feel the same? Does one make noise where the other doesn't?

In my eyes 120 is done for an engine that is fresh, they should be with in a few percent of each cylinder per engine but since you're getting 120 across the board (as I stated before) I question the comp tester.

I've never built an engine that didn't test out at 150 before I fired it up
 
I didn't know, 150 psi. Yes all holes, both motors, 120-125. Maybe your right, faulty gauge. Ill get another in the morning and test again. Yes i agree about consistently close compression readings. So lets assume my battery's bad, still don't see that screwing up compression readings. As long as the engines cranking good. Though, we all know how temperamental these are when it comes to battery's. I have a new AGM in my other boat, I'll swap in the morning and recheck all my readings. Hopefully I won't scrap a brand new battery
 
I would just use jumper cables and hook the boat up to your truck (without the truck engine running). If the motor is cranking too slow, it might not build the compression up to give an accurate reading. New engines don't seal perfectly around the pistons, so slow cranking could cause inaccurate readings. Your reading could come up after it broken in, but unlikely. The compression difference from a new ring and a fully seated ring are usually close to the same, but not always.
 
Ok folks, Paul the Tech guy at SBT said 125 psi is fine as long as its uniform. I used another gauge, the readings were 125 all cylinders. New rectifiers and battery, the readings are quite different. Battery at rest 12.3v rectifiers at rest 11.9v engines running, depending on rpm, 12-15v. Of coarse the port engine hardly runs. Still sounds rotten. Tomorrow I'll post a you-tube link after I video it.
 
Is the pump hooked on? are you sure it's the engine and not the pump? How noisy? any chance exhaust is loose and you are hearing the exhaust noise (which is loud and sounds like a metal hammer?)
 
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When you say that it sounds bad, can you be more specific? Is there a loose bolt floating around in the crank? Is it piston slap? Rod play? Pre-ignition? Bad exhaust gasket? Loose engine mount?
 
If you still have not found the noise I would remove the pump and drive shaft to eliminate it as your source of noiseas ialonso said
 
Will take another day or so, Hermine took out my temp boat shelter and a lot of stuff from under the house, going to take a bit to clean up the mess, water came within a foot from flooding my shop. Doesn't sound like piston slap or exhaust, engine still runs (if that's the word for it) like crap
 
I think you should look behind the rotary valve cover, I cant think of any where else a sound like that would come from cause it doesnt sound like crank or rods, I hope.
 
Orion, the only thing is it ran tops for 2-3 hours so I cant see it being assembled out of time and I haven't heard of a rotax motor like these "jumping timing". Yea it does't sound like a crank or rod, have to find out this weekend, warranty's up on the 18th
 
Well,I jerked the motor today. Rotary valve looks brand new(cause it is). The rotary valve gear has some play, about 3-4 degrees, don't know if that's normal. If its not, than something is wrong inside the crank case. Motor turns counter clockwise fine, however it won't turn the other way.
 
It will cost ya some money for shipping, but I recommend sending it in for inspection by SBT. They know what to check and how. When it comes back, you can eliminate the internals as the problem. At that point its either an electrical issue, a carb issue, or restricted exhaust.
 
Yep, I did just that Orion, live on the river in Tampa so SBT is right close, drove it there. Anyways 82.2% sure its the Rotary Valve sacrificial brass gear, we will see soon.
 
Not anything I thought. while up around 5k RPM, had a rectifier malfunction, a steering nozzle blow off, motor died, Hydro-locked, and must of spun the crankshaft...we thinks. Then Jupiter aligned with Mars and electrons went back in their 1 dimensional holes. Got a brand spanking new 717 from SBT, no questions asked!! Thanks Bobby, Lynn and crew.
 
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