2-stroke clatter trap -- why so loud?

[jiminmontana]

Thanks to everyone helping me get my well-used 1958 Evi, 35 hp Lark running at 39 mph.

I shut her down on Sunday because the mild tap that I heard while poking around above idle turned into a distracting clatter when wide open.

Power is surprisingly strong. Carb seems to be 100%. Seal kit for Lower Unit working well. VERY little smoke. Just a noise issue that says , "Got a problem in here."

Everyone knows 2-strokes are loud, largely due to the skirt of the piston being loose by design. But what are the typical causes of too much clatter?

Thanks!

 

[Al-53]

Re: 2-stroke clatter trap -- why so loud?

I can't answer your question...the top dogs will..but have to ask..what boat do you have it on to do 39mph....a john boat.....wish my 35 would get me to 39mph....lol

good luck with the motor..hope you get the answer and all is well...

Al

 

[Daviet]

Re: 2-stroke clatter trap -- why so loud?

What oil ratio are you running?

 

[jiminmontana]

Re: 2-stroke clatter trap -- why so loud?

Running 24:1 gas to oil. Added 8 oz SeaFoam to 6 Gallons.

On a 12.5 foot fiberglass flat-bottom boat. GPS said 37 - 39, depending on wind. Pics are on my blog, called "Ann's boat", is a 1958 Seagull, I hear. Maker on title is listed as "GFO". Out of business now.

I was thinking that maybe it clattered because a governor or something had been modified and let the motor run too hard. RPMs unknown, but seemed really fast, more than 4500, I think.

I better take it to a mechanic, huh?

 

[Fisherball]

Re: 2-stroke clatter trap -- why so loud?

My 1981 70 hp 2 stroke developed a "clatter" after years of running great that turned out to be a piston slap. That's when 1 ring disintegrates & the piston wobbles side to side as it goes up & down. Check your compression, if that's the problem there will be a difference between the cylinders, if you only have 1 cylinder, it will be low. That may not be your problem but it does cause a loud clatter. This winter I get to learn how to rebuild a 2 stroke motor.

 

[F_R]

Re: 2-stroke clatter trap -- why so loud?

They rattle for a very good reason: They are made that way. If you were to take the cylinder head off your 35 and attempt to move the piston back and forth, you would be shocked. The piston skirt fits fairly close, but the head end is loose as a goose. Not only that, all the bearings are roller bearings and do not have a sheet of oil to quiet them.

They are engineered to run wide open all day long and survive on practically no oil, compared to 4-strokes. The noise goes along with the design requirements.

 

[jiminmontana]

Re: 2-stroke clatter trap -- why so loud?

THANKS, F R:

I hope that it's normal operating noise, but just need someone who KNOWS to look at it. If I get my wife and son stuck 3 miles from now-where, that will likely be a long day for all.

I appreciate your input.