Carb Adjusting and Overheating Issue

[JFrog]

Re: Carb Adjusting and Overheating Issue

Hey Capt,

Oh, nope, didn't try a second test with motor oil.

How much motor oil should I squirt in?
Should the numbers change?
What happens to tell you if its leaky valves, worn rings or both?
Are those the only two things that cause a drop in compression?

Thanks,
Keith

 

[JFrog]

Re: Carb Adjusting and Overheating Issue

Either way, won't I need to be taking the head off?

 

[JFrog]

Re: Carb Adjusting and Overheating Issue

Are there any other things that can cause a loss in compression?
Cracked head? Something else?

Thanks,
Keith

 

[captmello]

Re: Carb Adjusting and Overheating Issue

Not much oil, maybe a tablespoon. The oil helps seal up leaky rings and if the compression jumps with the oil, that would be a sign that the rings are worn out. If the compression doesn't go up, or just a little, that would be a sign that the valves are leaking. I'm not an expert, but being that your compression numbers are relatively close, I would think either your rings are worn, or perhaps, your timing belt may have jumped a tooth, causing bad valve timing, or you are not testing correctly and you're getting fairly consistent but low numbers.

This is why, another test is needed with the oil added.

imo.

 

[JFrog]

Re: Carb Adjusting and Overheating Issue

Sounds good, I'm going to go ahead and test with the oil and see what happens.
Honestly, I'm really hoping that it doesn't change with the oil. That way I know it's either the valves or the timing belt. Hopefully it's the timing belt which I'll just change.
If not though, to fix the valves and/or rings, the head needs to come off, correct?
Thanks,
Keith

 

[Alan Lloys]

Re: Carb Adjusting and Overheating Issue

The spec for compression as I recall is 128 psi minimum.
Note that this is on a warm engine and you will get a lower number on a cold engine. I measured mine cold and got 125 psi evenly on all cylinders.

Replacing the piston rings is probably more complicated as you not only need to remove the heads but also need to disconnect the connecting rod from the crankshaft to be able to remove the piston. I will imagine this will require removal of the engine from the boat.
If you have an issue with a valve you should be able to remove the head for repair with the engine still in the boat.

 

[JFrog]

Re: Carb Adjusting and Overheating Issue

Hey guys,

Well, after blowing oil all over the place I have new numbers...lol

This is on a cold engine:
#1 170
#2 220
#3 179
#4 180

So I imagine that since my numbers went up, it's the valves and/or timing belt...correct?

Thanks,
Keith

 

[captmello]

Re: Carb Adjusting and Overheating Issue

no, I'd say your rings are worn. However, there's no saying it won't run for many more years as is. I'm not sure that is the reason for your performance issue, but you must take that into account.

If it were me, I'd continue to try to get it to run better and see what happens. Rebuilding that motor will cost you a lot of cash. The fact that you don't have a lot of experience with these motors doesn't help. They need to be highly tuned to put out the power you need. Go back to the tune up and see where you get. If you need help with specific tasks, don't be afraid to start a new thread.

 

[JFrog]

Re: Carb Adjusting and Overheating Issue

Woops, you're right, I misread your previous post about the symptoms.

Alrighty, I'll go ahead and put everything back together, set the points and dwell and see where that gets me.

Thanks,
Keith