1990 150 HP V6 Leak Down Fail. Help!

[dieffer]

I purchased a used 1990 Forester Fish n Ski with a 1990 Johnson 150 HP V6 VRO outboard. Engine fires when high idle is lifted. Took it to a mechanic, and he suggested a leak down test. His report was that it showed 18-20% loss in all 6 cylinders, and 2 of the spark plug threads are stripped. He didn’t give me any additional info on where he heard air leaking from. Just says given the numbers, engine is shot and would likely require a total rebuild. Is this accurate? Or is it possible the problem isn’t as bad. Prior to purchase, boat was stored unused in a garage for 8 years, and seller reports no known mechanical issues before that. Help!

 

[flyingscott]

What is the compression? What was done to the motor before starting it after 8 yrs?

 

[dieffer]

Don’t think mechanic did a compression test prior to leak down. Nothing was done to it other than hooking it up to fresh gas as far as I know. Previous owner put muffs on it and fired it up. Would only run at high idle.

 

[racerone]

Stripped sparkplug threads ( in my opinion ) suggest someone was struggling with this 30 year old motor.-----Taking sparkplugs out 3 times a day to try and figure this motor out.------Lots of boats are being dragged out of storage for eager buyers today.-----I would pull a cylinder head for plug thread repairs.----Inspect cylinders walls.-----Head gaskets are cheap.

 

[flyingscott]

How did he do a leak down test on 2 stripped spark plug holes?

 

[dieffer]

How did he do a leak down test on 2 stripped spark plug holes?

Sounds like they're not totally stripped but almost there. I just tried and you can screw a plug into it but the threads are almost gone.

 

[flyingscott]

Sounds like they're not totally stripped but almost there. I just tried and you can screw a plug into it but the threads are almost gone.

If it cant be torqued they are junk. Do what racer said

 

[dieffer]

How did he do a leak down test on 2 stripped spark plug holes?

Update: apparently cylinders 1 and 5 weren't testable (according to him) because of the stripped threads. I put spark plugs in and was able to torque them. Cylinder 3 was 30% loss, rest on port side were 18-30% loss. He seems convinced the pistons need to be re-ringed/needs new pistons. Wasn't able to indicate WHERE he noticed/heard air leaking out....

 

[flyingscott]

You have to replace the pistons. Do not replace just rings on that motor and you have to do all 6. But pull the heads first.

 

[racerone]

Putting new rings in worn out ring grooves is a waste of time on those crossflow pistons !!

 

[Faztbullet]

Fix the heads, decarbon it and run it. Doubt its 20-30 % if so the cylinders have major damage. Most people dont know how to do a leak down on a 2 stroke properly.

 

[dieffer]

Fix the heads, decarbon it and run it. Doubt its 20-30 % if so the cylinders have major damage. Most people dont know how to do a leak down on a 2 stroke properly.

I’d want to make sure to put new gaskets in correct? Do they just go in or is there additional adhesive needed?

 

[Faztbullet]

I would pull the heads, inspect the cylinders for damage, if old gaskets are not damaged coat em with AV sealer and test run it. If compression is good 95 psi or above and close to each other. Go thru thru the carbs since it has set 8 years, replace all fule lines , flush oil tank if still has VRO...JMO

 

[dieffer]

Fix the heads, decarbon it and run it. Doubt its 20-30 % if so the cylinders have major damage. Most people dont know how to do a leak down on a 2 stroke properly.

Could you elaborate on "decarbon it"? What would that entail? I've got the starboard head popped off and there aren't any cracks in the block or evidence that I can see of serious (or any) scoring.

 

[oldboat1]

Done right, thread repair kits work fine.

 

[RBoyd1971]

Could you elaborate on "decarbon it"? What would that entail? I've got the starboard head popped off and there aren't any cracks in the block or evidence that I can see of serious (or any) scoring.

How about posting some photos of the inside potion of the heads and the cylinder walls.

 

[dieffer]

How about posting some photos of the inside potion of the heads and the cylinder walls.

Here you go! I should add that all these photos are of the starboard bank of cylinders. Haven’t had time to get the port side head off yet.

 

[racerone]

Some will argue.----I see scoring in one of the cylinders.----Not a good sign.

 

[RBoyd1971]

Some will argue.----I see scoring in one of the cylinders.----Not a good sign.

Here you go! I should add that all these photos are of the starboard bank of cylinders. Haven’t had time to get the port side head off yet.

Well, not too bad. I do see some light scoring. Also see what looks like etching where there was some patches of light rust on the cylinder walls at some point. With that said, based on looks I would think the compression should be good enough to run ok.

 

[racerone]

Yes it will run.