Knot 4 Me

Just as the title states, I developed a strange noise from back of engine after pulling boat to town to get gas. Last Wednesday I dropped boat off lift and idled over to the ramp to load boat on trailer. Everything normal on 2 minute trip to ramp and while loading boat. Make the 20 mile round trip to town to fuel up (not paying more than double at Marina than I can pay on road) and after backing down ramp to launch as soon as I went to turn motor over you could hear what at the time I thought to be the boat in gear and the props hitting something. WTF?! Double check everything...boat in neutral, drive properly trimmed down, boat plenty deep in water, etc. Pull boat forward and everything looks good at back of boat. Put boat back in and go to fire engine and same thing, "thwap, thwap, thwap, thwap...". I stick the boat in storage and call it a day. Saturday I bring the boat home and start the investigation working from the back of the boat forward. Pull outdrive. U-joints (perma-lube) are intact and move freely with no binding. Driveshaft splines look like new and have plenty of grease. I rotate drive by hand since it is in gear after pulling and drive rotates smoothly with no grinding, binding, etc. Stick a light up into transom assembly and can see the coupler splines look new and have plenty of grease. I stick my hand up through the bellhousing and rotate the gimbal bearing and it turns smoothly. Insert the alignment tool and the alignment is good and has not changed since last time I pulled drive. While the drive is off the boat, I pull the kill switch so the motor will not fire and turn the motor over a couple times. I now do not hear the noise. I grease the gimbal bearing, clean and grease the driveshaft splines and reinstall the drive. Next I drain the gear lube. Both magnets are clean and the lube still golden in color (Amsoil) with no evidence of water. Drive is refilled, muffs installed, water on, and fire engine. "Thwap, thwap, thwap, thwap...". Beer thirty.

Yesterday I have a buddy come over so I can get an ear near the drive while the engine is running. I hear no unusual noise in the upper with the engine running. I step back and have him put it in gear both directions. Drive goes right into gear with no unusual noises. Now I crawl as best I can in the bilge. It is a tight fit as the rear seating is over the top of the engine and the back of the engine extends underneath the swim platform a good bit. Buddy fires the engine again and it is clear the noise is coming from somewhere around the back of the engine or in the transom assembly. I can see the snout of the coupler (long steel hub) and best I can see/feel nothing has fallen onto it from above (if it had, it should have made noise with drive off). What little bit of the driveshaft I can see has nothing near it.

The big stumper here is everything is fine on shutdown at ramp and then 30 minutes later, after doing nothing but taking a ride on a trailer, everything is fubar. So, my question to you all is have you ever heard this type of noise before from the back on your engine. Again, it sounds just like the old playing cards in the bicycle spokes noise only a bit more metallic in nature. Can raising the drive all the way up in trailer mode tweak the gimbal bearing (has 400 hours on it) and now it is toast? The noise does not sound like a typical bearing noise and again, the bearing rotated smoothly by hand. I've never lost a gimbal bearing so I don't know what they sound like bad. What else could it be? I was thinking something with the flywheel/coupler/flywheel cover but if that was the case why did it not make the noise with the drive off the boat? I really don't want to pull the motor if I can avoid it.

Boat is a 2004 Chaparral 260 SSi, 496 MAG, Bravo III drive. Engine serial number OM683216 (for BUP! ). I don't have the drive serial number in front of me as the Simrek Halo drive shower wore the decal thru right where the serial number is. I'm sure I have it in my paperwork somewhere.

turbom700

Fire the motor up with out the drive off, Its fine to run it for a few seconds. See if the noise is still there.

This may sounds stuipd but have you closley inspected your serptine belt? I have seen where they look fine till you run them and they have a loose rip that gives you that smacking sound.

Eliminated572

Just shooting from hip here. I could have swore I had a rod knocking in an old s-10 but Oil pressure was good. Ended up the flywheel was cracked. Also changed in gear and out of gear as load changed. Severity increased with more load. I'd probably look toward coupler/flywheel and closely inspect that area. Only so many things it could be back there..... I also had a loose pulley throw me fits but you stated it was definitely coming from rear..... I thought also of internal exhaust flapper, but you stated it didn't do it while testing with drive off. Good luck

Knot 4 Me

Belt is good. No accessories are making the noise. Noise is emitting from back of engine area. Turning over motor with pulling kill switch results in no noise. I'm not firing motor with drive off as I have no fresh water flush attachment to supply water and I don't feel like wasting an impeller. With the drive on, before the motor fires you can hear the noise as the starter rotates the engine, The engine does not have to fire to hear the noise. I never lit it off at the ramp when it first did it on arrival back from gas station. I was hoping it was a water pump, power steering pump, alternator, etc. but no noise from front of engine.

Knot 4 Me

Thanks. Yeah my fear is it is in the flywheel/coupler area. You would think it would do it without drive installed but maybe the driveshaft being inserted in the coupler puts enough load on it to where the problem will show up. It sounds like the flywheel is hitting the flywheel cover. Like maybe a bolt has backed out. But man if that is the case why does it not do it with drive off? I simply do not have enough room to get any good view of the area with engine in boat. I barely have room to change the IAC on the engine it is tucked so far under the swim platform with almost zero overhead clearance. The worst part of pulling the motor will be the stupid 500 lb. if it's and ounce fiberglass rear seating/engine hatch. Thing is a cumbersome beast!

donzi matt

iTrader: (1)

If you are 100% confident it is from the back of the motor, take the belt off and fire it up without the drive on and see if the noise is still there. You won't hurt the water pump that way.

turbom700

You wont hurt the water pump running if for a few seconds with the water pump hooked up,

Other wise grab your garden hose shove it in water pick-up hole where your drive was, that will give it enough water to idle off of.

My guess is hub adapter just weird that it was fine one second not the other.

Knot 4 Me

Thought about cutting the male end off my hose and shoving it into the water pickup hose but just ran out of steam on Saturday. As donzi matt stated above, I could also just take the belt off. Sometimes the obvious eludes me which is why I need you guys to help me out!

buck35

If you have a cell phone with a camera you can reach down and take a bunch pics from different angles, maybe see something that way.

BUP

iTrader: (9)

Just seen this, funny you guys throw my name in the mix.

Here is what I would do -

You can take off the inlet or unhook the water inlet cooling hose and hose clamp a water garden hose inside that inlet hose. Turn water supply on and start engine ASAP make sure it pumps water. Of course leave Serp. belt on.

Or take off inlet coolling hose back side of water pump housing and buy a 3 feet to ??? however long hose to connect to back side of inlet water pump impeller housing and either adapt a garden hose inside your hose that you just added or drop that hose in a full bucket of water and keep filling the bucket while engine is running to cool the engine properly..

The testing end here - the outdrive still OFF so take an engine alignment tool and stab it like you are checking alignment - how well is your alignment ??? or is it way off ? next test is leave the alignment tool in and run the engine ? How well of a perfect circle is the engine alignment tool rotation while the engine running or is the circle egg shaped pattern when engine running ?

What kind of shape is your gimbal bearing and U joints ?

have you scanned the engine and looked for available power ?