Odd knocking sound on 500EFI XR setup
 

Went and looked at a 2000 Donzi 38ZX this past weekend with about 378 hours on motors and drives. Motors haven't been touched except for valve springs replaced at 250hrs. When The owner started the motors up in the driveway on the hose there was a knocking sound that he said was coming from where the drive meets the motors and said that it was a normal sound while there was no load on the drives. It wasn't consistent, more random. Both motors/drives did it while idling and drives were in the down position. He said when there in gear the noise goes away, in fact I believe the noise went away when he rev'd them too but who know as the motors were louder and you couldn't hear much more.

To describe the sound it was like a knocking sound that I thought was coming from the motors but like I said it wasn't consistent, he pointed it out before I said anything about it. I think he describe the noise as where the motor meets the drive it kind of free floats and that when you get that noise, I don't know. Does anyone else have the same issue.

Coupler?

Universal Joint?

Probably just the backlash in the upper gear set. More pronounced in an xr with straight cut gears.

Unless you have extension boxes, where the motor meets the drive is in a splined connection at the coupler. There is no, or should I say, there should be no slop in that connection to cause a knocking sound .

Internal flappers make a knocking sound at idle

Didn't think of that Jason.

How were the gimbal rings? Did they have slop or have they been recently replaced? If they had been replaced, the previous sloppy action could have ate up the engine coupler.

Not sure on the gimbals. Aren't the flapper rubber coated? So this sound isn't normal? The guy seems like he takes care of everything the boat is flawless.

were the drives down ,gimble barring

Yes, it could be exhaust flappers, universals, gimbal bearing, broken tooth in upper. If the seller agrees to it, at least have a survey done on the mechanical side of the boat and save yourself a head-ache and money in the long run. If something is wrong with the boat, mechanical agree the seller pays for survey. If everything checks good and you buy the boat. Money well spent!!!
Mark

What are the odds that either the couplers, u-joints, or gimble bearings are bad in both motors?

Exhaust was my 1st thought, followed by drive gear noise. When on trailer, lots of weird noises.

This is a good point

Random clattering noise is probably(could be) internal anti back wash valves .If you can open the throttle a little and it completely goes away ,makes it more likely .A lot of the aftermarket stuff has no rubber edges on butterfly like merc does ..They can make nasty noise idling ..MO

Drives were down. About 2in off ground. Survey was done last year and everything checked out. I can post results.

If it's in the drive, you should be able to feel the tapping by putting your hand on top of the drive. Did it do it in gear and in neutral?

Easy enough to rule out internal flappers, just stick your hand in there and hold them open. You will get wet, but you will know. Don't stand there long enough to consume CO.

I took 2 little vise grips and put on my flappers so diddnt get all wet I thought there was something wrong when I heard mine .

It was in neutral.

If it has silent choice, then it's probably the anti-splash flappers are located down where the bullhorn connects to the transom assembly. They typically rattle at idle randomly and quit when revved. If it does not have the cast 2->1 bullhorn then other problems.The exhaust tip flappers are possible among the other things mentioned above.

It was surveyed, and the report showed nothing so who knows?

my capitains call has a nasty sound at times from the back splash flapper...sometimes if it shifted in the right spot it sounds nasty...

Did you buy it?

No, not yet but it is my 1st choice. I talked to the guy in Cleveland about his with the 525s, it has no AC so that's not gonna fly for me or the gf.

PM Sent

Remember AC only works with gen and shorepower. You can add it yourself for around $2K and a little work.

Gen or shorepower....:D

dometic makes a 12 volt ac system,will require a 3 bank batt pack tho.

Next time you look at it i would Pull the drain screwws on the drives. 2 on each ( if you haven't) That can tell a story about your purchase. XR's schread metal and sometimes you can just pull a screw and be sure. Bring an extra screw and throw it in while you inspect the one you pulled. and bring some white paper towels. you probly know this but i didn't at one time . Hope this helps