Rattling sound from engine + tachometer dancing - Suzuki DT65

[Sealfie]

Hi!

Ive got a strange problem with my Suzuki DT65 -92. When I reach around 3000 rpm I get this knocking/rattling sound from my engine. And as that happens the tachometer starts dancing up and down (with the engine at constant rpm). However, the engine runs fine but I dont like the sound and not knowing the rpm above 3000 rpm.

At first I thought some bearing had gone bad and that the tachometer-issue wasn't related. But after testing many times it seems that the sound and the tachometer-issue are correlating.

Note: Ive tested both with gear and in neutral, doesnt matter.

What could be the issue here?

[Solarman]

Not sure what you're hearing? Try turning flywheel back and forth to see if you feel any play, or slack? If you still can't tell, remove plugs and using a plastic drinking straw touch top of each piston, rotate flywheel again b&f at different positions to see if pistons move equally when flywheel is turned.

You should also inspect the magnets in the flywheel, if loose, repair or replace, before they eat your magneto.

I would not run motor until you can find the source of the noise.

Good luck. Post back when able to let us know what you find out.

[Sealfie]

Not sure what you're hearing? Try turning flywheel back and forth to see if you feel any play, or slack? If you still can't tell, remove plugs and using a plastic drinking straw touch top of each piston, rotate flywheel again b&f at different positions to see if pistons move equally when flywheel is turned.

You should also inspect the magnets in the flywheel, if loose, repair or replace, before they eat your magneto.

I would not run motor until you can find the source of the noise.

Good luck. Post back when able to let us know what you find out.

Its not hearable at low rpms. Maybe I can post a clip tomorrow in zipfile. It sounds just like something is loose. Imagine that u have screw loose in the engine area and that its vibrating as soon as u go for a higher rpm, thats what it sounds like (and ive ofc checked if something really is loose).

I turned the flywheel and couldnt feel any play or slack. But I will doublecheck with a plastic drinking straw, thanks for the tip!

I assume I need to remove the flywheel to check the magnetos or is there any other way to check?

[Sealfie]

Ive finally managed to upload a video:

https://youtu.be/durFnINgHdw

Turn up your sound and listen carefully, a little bit harder to hear on the video then in the reality.

Havnt been able to lift the flywheel yet, but from what I could see from the top it seems the magnets are in place.

[Sealfie]

Update: Ive now checked if there is any play between the flywheel and the pistons. There is no play at all, checked all three cylinders.

[Solarman]

I can't tell from the video. Is there any side to side play in the flywheel (top of crankshaft movement)?

If you can't find the source, maybe take it to a local mechanic, and have them listen to it?

Good luck. Post back when able.

[Sealfie]

I can't tell from the video. Is there any side to side play in the flywheel (top of crankshaft movement)?

If you can't find the source, maybe take it to a local mechanic, and have them listen to it?

Good luck. Post back when able.

There is no side to side play in the flywheel, not even the slightest. I let a mechanic hear it. He said "dont worry" but he couldnt say what the sound was. However, I fixed the problem with the tachometer, was just oxide in the main contact to the engine, its working perfect again.

Guess im just gonna leave it

[Sealfie]

Well, fyi I know now what the sound was. It looks like a piece of the cylinder lining at the intake port had come of and fallen into the crankcase and sat there for a while. The piece was pretty large and when I was driving the piece came into the cylinder area and destroyed the top piston, piston rings and scared the cylinder slightly. Total destruction, full of metal on top of the piston. The powerhead was doomed as soon as the piece came of and I have no idea why it did. There was no problem with the cooling, oil (2,5% in the gas tank) and I always let the engine get warm before revving over 2000 rpm.

[Sealfie]

Pics:

https://ibb.co/f9z7tF
https://ibb.co/bSmntF
https://ibb.co/ijERLv

[Solarman]

Yes, looks bad. However, if you dig deeper it might be possible to re-sleeve cylinders (at a local machine shop), and replace pistons and rings (if still available)? Not sure if any other problems? That could be the straw that breaks the back.

Good luck. Post back what you decide on. Might be worth investing in another motor instead.

[Sealfie]

Yes it might be possible. But as for now I dont know what damage it could have caused in the crankhouse. In the other two cylinders the pistons also have some metal dust on them (really small). My assessment is that the powerhead is scrap due to its age, its just to much money and effort to fix it. Im selling the engine in parts.

Ive managed to borrow another much smaller engine (Yamaha, 20 hp) so I can atleast go out for some fishing.

One man said that these engines were known for its cylinder lining, that it could come of. Dont know if thats true. However, next boat will probably be a Bella 512 with 2 stroke Yamaha. Even if Suzuki probably can provide the same reliability as Yamaha I would not buy one only because I know what happened to the last one.