Yamaha 60 2 stroke rattle

[Jacob555]

My Yamaha 60 autolube has always had a certain rattle to it.
It's been fine all summer though with many trips, pushes the boat at 40mph no problem, good compression etc, just sounds like a box of spanners. It's not bothered me too much as it was just a cheap stop gap engine (built 1989) to get me out on the water while I wait for the right 4 stroke 40 to come up for sale. Now, having gone all summer without it missing a beat and realising its not as bad on fuel as I thought it would be, I'm thinking of keeping this motor and ironing out some of its little annoyances.

I'm used to 4 stroke engines and to be honest thought that the noise it was making was normal 2 stroke rattle. Imagine my surprise when, last time I put it on the water, it was ticking over on fast idle to warm up and suddenly stopped rattling for a few seconds (it was still running) and sounded all lovely and smooth and nice!

The fact that it is now an intermittent rattle tells me something is wrong and hence may be fixable. Any ideas what this could be?

The rattle is a plasticky tappety, fluttering noise, quite loud compared to the rest of the engine at tickover. it sounds like an old 1.1 fiesta with worn out tappets.

Now, when I first got this motor, I went mad and disconnected the autolube system and premixed it as the engine was of unknown provenance and I mistrusted the autolube. Following the advice of a local (non Yamaha) outboard specialist I did not set up the tank oil to circulate the pump as I was told running it dry would do it no harm and if I wished to reinstate the autolube I'd just need to reconnect the pipes and prime it and it would all be good to go again. When I got sick of poisoning myself and passengers with 2 stroke fumes on 50:1 premix I refitted and primed the autolube system, which seems to be pumping oil in OK, though I am still doing a 100:1 premix in the tank to be on the safe side.

Could this horrendous rattle be a dodgy automix pump? Could they all sound like this? I had an Optimax 225 that sounded similarly horrid at tickover and then found out they all have horrible rattly pumps at tickover.

Any ideas?

[Nos4r2]

It's probably piston slap. If it was anything else it'd have gone pop by now.

[Jacob555]

I've found and rectified the fault!
A loose bolt had fallen down and jammed between the powerhead and the undertray. It was transmiting the vibrations from the powerhead to the aluminium undertray which was rattling arround badly making all the racket. Now I know why they isolate the undertray and the cover which clamps to it from the rest of the motor with rubber bushes. That was also why the motor sounded OK from cold. It wasn't that it was cold, more that it had been tilted up and towed down to launch, so the loose bolt had fallen back out into the main cover somewhere, then when tilted down it took a few minutes for the bolt to work its way back down to the bottom of the undertray again and start rattling.
Sea trials this afternoon! (any excuse)

[gibbo500]

Nice one, great engine.

[Observer]

Yeah but where does the bolt come from?

[outboardtech]

jacob555 mate these engines r pretty bullett PROOF . I have many customers with these engines and to be HONEST THE ONLY THING THAT GOES wron is DIRTY FUEL . . If you have good compressions on all cylinders you have nothing too worry about . Ok you found a bolt in the lower pan which is a common thing and caused by the two stroke engine vibrating away . this is possibly a 10mm bolt come off the front of the reed valve assy . I have seen this before and once again nothing too worry over . two stroke bangers are goinng to run rough as all old outboards do . if you have GOOD compession , good spark , good fuel she will RUN FOREVER . those are the THREE golden rules for a two stroke engine Cheers baz

[Jacob555]

The bolt came from the clamp assembly which holds the cables in place where they go into the undertray. I dropped it when I mounted the engine on the boat but just replaced it and thought no more about it as at the time I couldn't fish it out, though I could see it wouldn't do much harm where it had ended up and was in a hurry to launch. I couldn't believe a discarded bolt could make such a racket. It was a seriously harsh mechanical sounding rattle.

[9D280]

Know the feeling... I spent hours fishing out dropped fasteners from the tray of my old Suzi.

It's one of the good points about a clamshell - Nowhere for dropped suff to accumulate..... but the down side is when you are fixing something "en route" & what you just dropped goes in the drink!