1980 volvo penta aq145a, cant get this thing to run woth a darn.

[zmboats]

How about the engine earth cable is it good?

It is. All of the connections look pretty good

 

[stelican]

What do you mean by a leak down test please?

 

[kashurst]

At first, I couldn't even look at the throttle without it stalling. For whatever reason, it doesn't do that any more and I can rev it without issue. As far as the floats are concerned, they do have fuel in them, I don't think that the float valves are sticking. I guess I could check by hooking up an electric pump and washing down the carbs to see if there is fuel leaking into the intake manifold. I have verified that the excellorator pumps are working. I would have to check the fuel pressure to verify that the lift pump is working correctly, but I don't have the right fittings to work with the banjo bolts that connect the fuel lines to the carbs, so I will have to rent or buy a better fuel pressure tester and check that.

I am confused now. The engine clearly starts and runs to a point, and if you open the throttle it revs up without issue.
So what are the remaining problems?

 

[zmboats]

What do you mean by a leak down test please?

A leakdown test is when, rather than testing how much compression each cylinder will produce, you test what percentage of a given air pressure each cylinder will maintain. You do this by setting the piston in the cylinder that you are testing to the top of it's compression stroke, ensuring that all of the valves are fully closed and then introducing air via an air compressor into the cylinder (usually around 100 psi because it makes the math easy) and seeing what percentage of the air that you are introducing is being maintained in that cylinder. Doing this tells you much more than a compression test because you can also find what component of the engine is leaking compression. You generally want to see that you are maintaining around 90 percent of the supplied air. I am loosing between 30 and 70 percent depending on the cylinder, past the piston rings and i am also loosing some past the valves.

 

[zmboats]

I am confused now. The engine clearly starts and runs to a point, and if you open the throttle it revs up without issue.
So what are the remaining problems?

It is still running very rough, and it is cutting out and doesn't have enough power to get on step most of the time.

 

[Refueler]

A leakdown test is when, rather than testing how much compression each cylinder will produce, you test what percentage of a given air pressure each cylinder will maintain. You do this by setting the piston in the cylinder that you are testing to the top of it's compression stroke, ensuring that all of the valves are fully closed and then introducing air via an air compressor into the cylinder (usually around 100 psi because it makes the math easy) and seeing what percentage of the air that you are introducing is being maintained in that cylinder. Doing this tells you much more than a compression test because you can also find what component of the engine is leaking compression. You generally want to see that you are maintaining around 90 percent of the supplied air. I am loosing between 30 and 70 percent depending on the cylinder, past the piston rings and i am also loosing some past the valves.

So ... to me not a motor mechanic .... if the pressure leakage is so variable across the cylinders - surely that says Hey - time for rebuild ?

But wouldn't air pressure be lost anyway - as the rings and valves are not prefect seals and rely on the speed of pistons / ignition cycles so compression is not lost in that tiny milisecond ?

 

[zmboats]

So ... to me not a motor mechanic .... if the pressure leakage is so variable across the cylinders - surely that says Hey - time for rebuild ?

But wouldn't air pressure be lost anyway - as the rings and valves are not prefect seals and rely on the speed of pistons / ignition cycles so compression is not lost in that tiny milisecond ?

Yes. That's why when you do the test you are only looking for 90 percent air retention

 

[Refueler]

Yes. That's why when you do the test you are only looking for 90 percent air retention

OK .. and you had 30 - 70% loss ??

 

[zmboats]

OK .. and you had 30 - 70% loss ??

Yes.
#1- 30% loss
#2- 50% loss
#3- 70% loss
#4- 60% loss

 

[Refueler]

Yes.
#1- 30% loss
#2- 50% loss
#3- 70% loss
#4- 60% loss

So we have either ring blowby or valve seal problem ? If the sump oil is still good .. and no sign of oil in exhaust - then likely valves ?

 

[zmboats]

So we have either ring blowby or valve seal problem ? If the sump oil is still good .. and no sign of oil in exhaust - then likely valves ?

Mostly a ring problem cylinder #3 had some leakage past the valves but it was massively leaking past the rings, I could have blown up a balloon in a couple of seconds from the PCV vent.

 

[Freebee]

But you say the engine has stood unused for some years,its possible the rings are just gummed up...its probably not economically viable to rebuild this old engine.

 

[zmboats]

But you say the engine has stood unused for some years,its possible the rings are just gummed up...its probably not economically viable to rebuild this old engine.

I have run the engine enough to know that it is not something that would work itself out. I can replace the entire bottom end of the engine including main bearings, rod bearings, rings, all seals and gaskets and throw in some parts for the outdrive for around $600. I will lap the valves while it's apart and should be good to go for quite a while.

 

[Freebee]

I can replace the entire bottom end of the engine including main bearings, rod bearings, rings, all seals and gaskets and throw in some parts for the outdrive for around $600.

That's great but missing off your list is new pistons, and a rebore??? it would be annoying to take it all apart and put it back together to find new rings in worn bores don't fix it.

The first thing before spending any money is check the exhaust manifold and exhaust port in the head, the one nearest the outdrive, for corrosion or previous repairs as the engines are notorious for big holes appearing in the last exhaust port/manifold caused by water coming back up the exhaust, Ive seem them bodged with bondo before now.

 

[stelican]

To true re corrosion.

 

[zmboats]

I can replace the entire bottom end of the engine including main bearings, rod bearings, rings, all seals and gaskets and throw in some parts for the outdrive for around $600.

That's great but missing off your list is new pistons, and a rebore??? it would be annoying to take it all apart and put it back together to find new rings in worn bores don't fix it.

The first thing before spending any money is check the exhaust manifold and exhaust port in the head, the one nearest the outdrive, for corrosion or previous repairs as the engines are notorious for big holes appearing in the last exhaust port/manifold caused by water coming back up the exhaust, Ive seem them bodged with bondo before now.

I intend to disassemble the engine before ordering parts incase there is something wrong with it that I can't see. I had a look in the cylinders with my inspection camera and they look beautiful. I can still see crosshatching on all of the cylinders which tells me that there is very minimal ware on the cylinder walls. I am confident that I can hone them and be good there. As for the pistons, I won't know until I remove, inspect, and measure them. If they are still in spec than no problem, if not than I will get new ones. I condenser any engine rebuild under $1000 a fairly cheap rebuild. And older engines are much cheaper to rebuild than new ones. The timing set alone for my truck is $2500. So in perspective I am more than willing to spend the money to have a new bottom end in a boat that I will be trusting my life to out in the ocean. Rather than going with a used engine that I have no background on.