Bought a used 6 hours outboard but forgot to add engine oil

[99yam40]

Wow, good to know. I have a torque wrench and will use it instead of using my easy method to try turning the plug loose by hand.

not sure what you are saying here, but sounds like you think you need a torque wrench to take the plugs out.
you need a torque wrench to keep from over tightening things

[99yam40]

Lol, marina who sold me the outboard told me they could tell whats wrong when hooking it up to their computer.

ok so i was expecting computer can read some codes that caused the knocking if there is indeed bearings broken or loosed or piston rod expanding and shrinking.

i am hoping i can open up the powerhead and piston apart myself to fix it to save money if computer is no help.

I think they can see if the low oil pressure came in or is in if the start it up, but I have a bad feeling the motor will have to come apart to find what all is damaged from running with out oil

[zenoahphobic]

I think the points have been made. No alarm systems or plugged in computer is going to tell you what the damage is. Those things are simply designed to help around in helping find a "simple" or pending failure.
Your engine has undergone substantial trauma. You may or may not to get this engine to run for sometime, however the question will be long term reliability, least of which could be the risk of a catastrophic failure completely destroying the engine beyond repair.(engine worth even less than it is now).
The only way is to pull it apart and inspect. The use of cameras can help to minimise your effort.

[Yamaha18]

not sure what you are saying here, but sounds like you think you need a torque wrench to take the plugs out.
you need a torque wrench to keep from over tightening things

i meant I would try to test whether the 4 plugs are tight by unscrewing them by hand with my 5/8" plug removal socket. If I could not remove them by hand, then I know they are tight. If I can remove them by hand then I will tighten them and see whether the knocking sound disappear.

But, I will now bypass that step and use a torque wrench and try to tighten it to 18 pounds instead.

[Yamaha18]

I think the points have been made. No alarm systems or plugged in computer is going to tell you what the damage is. Those things are simply designed to help around in helping find a "simple" or pending failure.
Your engine has undergone substantial trauma. You may or may not to get this engine to run for sometime, however the question will be long term reliability, least of which could be the risk of a catastrophic failure completely destroying the engine beyond repair.(engine worth even less than it is now).
The only way is to pull it apart and inspect. The use of cameras can help to minimise your effort.

ya, it sure looks like I have to tear down the F70 to the piston and see whether the pistons are knocking or the bearings are broken or piston rings are broken. Camera is a smart way to check which piston is wrong and which ring is broken.

Ya, open up the flywheel, remove the powerhead and strip the F70 down to the rod and piston will take at least 4 hours if I am lucky. Manybe another 4 hours to put everything back after getting the new parts.

[99yam40]

my thoughts are, lack of oil will get the crank and bearings

[Yamaha18]

I am going to do 2 things: (1) compression test - will update soon, (2) ask Yamaha headquarter about getting a break on the repair costs (only used for 6 hours by prior owner and marina for test drive to show me the motor). - i still have the 3 years warranty.

[99yam40]

running a motor with no oil in it voids the warranty

[Yamaha18]

PTL - my 2019 Yamaha 70 hp 4 stroke (F70) survived my silly mistake - 10 minutes idling to rinse out salt on my DIY outboard motor stand without motor oil. https://www.youtube.com/watch?v=6hGaNG-rjxs


I will post the video with my motor with knocking sound soon.

I will also post video of the motor running at the dealership soon.

Cost me a trip to see the Yamaha dealer and $135 for a damage assessment.
Compression test done by Yamaha dealership registered at 205, 205, 200 and 200. Dealer mechanic started my outboard motor and no knocking sound at all. I was told I was very lucky, it does not seem to suffer any noticable damage. I asked whether it is necessary to hook up to their computer, but the dealer suggested not to bother.

I am grateful to this forum and all of you who commented!

[Yamaha18]

It won't hurt anything to add some oil.

If anything I'd add the oil just to get oil back on the cylinder walls, etc.

Cold starts, oil back in the crankcase causes the most wear (under normal conditions)


Just know that adding oil WILL hide piston ring wear and result in more compression (than if started "dry").

With the leak down test, there's NO cranking over, just getting to TDC on the compression stroke..
I would add the oil, spin it some (safety lanyard out so it doesn't start) and crank it some to get oil everywhere.

Then crank it up, and after warm, do your compression test..

I am forever grateful to your excellent tip here!!! I will post a video to help others to see how to wet the 4 cylinders with 4 cycle oil without starting the motor soon.

[TownsendsFJR1300]

Did they check the oil pressure?

THAT would tell if clearances in the engine (bearing area's specifically) are excessive..

Your real lucky about the compression/ rings/ top end!!

[Yamaha18]

No. They didn’t check oil pressure either, but told
me to go ahead and run the F70 and enjoy. Any issues just bring it back.

[zenoahphobic]

It is easy to think this was an overheat issue, that it wasn't, and then assume what damage occurs is the same.

Generally there would be no damage through excessive expansion causing seizure, so broken rings are extremely remote etc.

What you will find is damage through diminishing lubrication and not the binding grabbing between components through expansion, such as overheat between piston rings and cylinder walls .It is therefore highly unlikely that a compression test is of much use to detect lack of lubrication and subsequent resultant damage.

When lubrication is inadequate some components can wear differently as opposed to when they normally wear out at the end of their lives with adequate lubrication.

None of this damage was seen, or attempted to be looked at. Unfortunately most "shops" just want to get rid of the problem with doing the least. They should have at least looked down the plug holes with a borescope and taken oil pressure readings (called out for by members of this forum)! .......where is the peace of mind?

[TownsendsFJR1300]

Yup, for $135 and no oil pressure test?? Come on, friggin lazy...Screw in one gauge, some muffs with water and crank it up..


I personally, would be trading / selling that engine.

But that's me..

[Yamaha18]

It is easy to think this was an overheat issue, that it wasn't, and then assume what damage occurs is the same.

Generally there would be no damage through excessive expansion causing seizure, so broken rings are extremely remote etc.

What you will find is damage through diminishing lubrication and not the binding grabbing between components through expansion, such as overheat between piston rings and cylinder walls .It is therefore highly unlikely that a compression test is of much use to detect lack of lubrication and subsequent resultant damage.

When lubrication is inadequate some components can wear differently as opposed to when they normally wear out at the end of their lives with adequate lubrication.

None of this damage was seen, or attempted to be looked at. Unfortunately most "shops" just want to get rid of the problem with doing the least. They should have at least looked down the plug holes with a borescope and taken oil pressure readings (called out for by members of this forum)! .......where is the peace of mind?

I cannot agree with you more about their $135 assessment job. I was told when I got there these motors are built to last and Yamaha warranty is very good to its customers. The aged looking mechanic seems to know what he was doing and other mechanics also came to check out my motor to see and hear it running after it started up. I think everyone was curious and want to see how bad this new motor was damaged. They said I was not the first who ran a new motor without oil. They get these kind of appointments many times over the years. Many had to have the motors taken apart and fix things. I was very lucky.

My friend was annoyed when I asked him for help to install F70 to my DIY mobile outboard stand (up to 360 pounds) first to rinse out the salt water. He asked why not just installed on the boat and rinsed it? I had a couple reasons: (1) I want to test out my outboard stand before I move the 301 pounds old Johnson 90 onto it, see whether it will topple over? whether the motor vibration will cause the stand to be unstable, etc (2) Take pictures and videos to show case the beautiful lightweight outboard before I mount it to my boat.

Lessons learned!