Piston crown condition

[Dellquay]

Hi, whilst putting my carbs and fuel pump back on today (Merc 60hp 2 stroke 1988) I thought it would be a good idea to replace the spark plugs and whilst they out I stuck my endoscope down into each of the cylinders to have a look at the piston crowns but I'm a bit concerned now and don't know if I'm making problems up in my head.

I have attached the images to see if any of you can tell me this is normal or not? The pictures start from cylinder 1 through to 3. Cylinder 1 looks normal in my opinion with a black crown but as you progress through the images the piston crowns get cleaner and there looks to be a rusty coloured mark that's worse by cylinder 3.

The motor was serviced in April and is well looked after. Compression is 120psi on each cylinder and apart from a fuel issue last Tuesday she was flying along and always has done.

Is this anything to be concerned about?

 

[fastjeff]

She's burnt alright. At the very least you'll need to rip it down and replace the top piston.

Jeff

 

[Dellquay]

Thanks for the reply Jeff, you have helped me out so much lately. Would she still get good compression and run fine with a burnt piston? I'm now thinking did this happen last week when I had an issue with fuel delivery and was running lean for the 20 minute journey home, or is this a more long term issue? Also is this a power head off job to replace pistons?

Thanks for all you help

Rich

 

[racerone]

Serial # of the motor ?------With compression at 120 PSI I think it might be normal.-----Have you replaced impeller ?----Are there any bypass covers on this motor to look at piston rings ?

 

[Dellquay]

Serial number is OB240262. I'm just in the process of taking the exhaust cover off today to see if I can get a view of the rings. I replaced the impeller, housing and gaskets in April and she pumps water well, sometimes a little weak on tickover but I put that down to what looks like an undersized impeller in my opinion.

 

[racerone]

Hopefully you are not using oil injection on that motor ?-------Why would you install an " undersized " impeller ?

 

[Dellquay]

I binned the autoblend and mix 50:1 in the tank. I have installed the correct impeller but it just looks undersized to me compared to my old DT40. I have manged to free up all of the bolts on the exhaust plate which was a miracle in itself as they were pretty tough to budge but looks like the throttle and gear controls bracket needs to be loosened to make room for the plate to come off. Just letting those bolts soak now and the BBQ coals are nearly ready so time to crack open a cold one and back to it later today.

 

[Dellquay]

So with the exhaust plate off you can get a sight on the rings on each piston as you turn the crank clockwise. I have attached pictures from cylinder 1 to 3 in order. I've cleaned all the surfaces and while I was scrubbing I noticed a hole where it looks like a thermostat would fit. I have read on other threads that this model doesn't have a thermostat or poppets and I can't see anything in the parts list when I search. Does that sound right or has someone taken it out in the past and not replaced it? Would seem a bit daft to do that.

 

[racerone]

Pistons / rings look in very good condition.----I would even say low hrs on the motor.------Put cover back on and enjoy it.

 

[Dellquay]

Gaskets were ordered today so I'll have to wait a week but weather looks crap next week anyway plus I'm back to work after only doing one day a week for the last 2 and a half months. Do you know of these models had a thermostat and/or poppet valves? Like I said, I heard these models had neither but there is a very suspicious looking home for one under the exhaust plate.

 

[racerone]

Early versions did not have thermostats.-----Then some did.------If your serial # parts list does not show it then leave it out.

 

[faztbullet]

I don't see what Jeff was seeing but those look very good. Only thing I would do is add Qiuckleen to fuel