AQ125A Total rebuild???!!!

[steve242002]

Hi guys, I have a 1986 or so AQ125A. It runs pretty good but my compression is only at 80PSI across all four cylinders. I was reading in my book that it should be around 140to 170, give or take. I talked to my local volvo dealer and they told me it might be better to just buy a new engine rather then rebuild this one becasue it would be well over $3K. I am in to this darn boat/engine around $4K and have had it in the water one time, this last Saturday and had to get towed in due to an overheat problem. My question is do I have to use Penta parts or can I use standard auto parts like from NAPA. If so, should I bore over .010" and just replace rings or do I need to replace piston and rings, and rods, and so on. What type of car has the same block as the AQ125A block? Any suggestions would be great!

 

[Maclin]

Re: AQ125A Total rebuild???!!!

A compression leak-down test will let you know more about what is causing the low compression numbers. If the engine does not use oil or oil-foul the plugs then it might just be needing the head refreshed. A leak-down test introduces pressure thru the sparkplug hole when at TDC on compression stroke. Then listening for air hissing, if mostly thru the carb or exhaust then a head job may help. If the hissing can also be heard into the crankcase then rings are involved. I would do that test before dismantling anything.

 

[Don S]

Re: AQ125A Total rebuild???!!!

Have you tried a different compression gauge? I doubt you could even get one to start with only 80 psi compression. I've had trouble getting them started with 120-130 psi.

 

[steve242002]

Re: AQ125A Total rebuild???!!!

I have never done a leak down test and do not even know how to go about it. Do I use an air compresser and put in 100PSI or something like that? Also, I have not used another pressure gauge, but it does run really good, starts on the second tourn or so every time. Maybe i'll try another gauge. What would cause it to run so damn hot? What temp should the valve cover get to when it's running?

 

[Maclin]

Re: AQ125A Total rebuild???!!!

What are the "running hot" symptoms other than needing the tow?

As far as the leakdown test, you can look that up or talk to mechanic friends, but it is much like you described, just need the air fitting that srews into the spark plug hole.

But, It seems maybe your compression is actually ok based on the "running ok" comment. If it is running ok, just hot, then the compression is probably ok and your gauge is off or the test was not done correctly. I would not worry about the compression right now and focus on the running hot issue.

It has a closed (aka Fresh Water) cooling system from Volvo I believe. Look at the stickies topics at the top of the forum. I believe you will find cooling system troubleshooting guides.

There is a raw water pump that draws in lake water and circulates that thru a heat exchanger, which is like a radiator in a car except it has two sections. One for the raw water to circulate around in (that acts like the air flowing thru a radiator), and the other has antifreeze that flows thru the engine via the engine's "normal" circulating water pump. If raw water flow is not good then the antifreeze will not be cooled enough and it will run hot. There is a strainer for the raw water system that can clog up I think.

The antifreeze circulation is controlled by a thermostat, for a closed cooling system they are usually 180 degrees. You could use an infrared (IR) heat gun and aim it at the thermostat housing and see what the temp is there.

These are only broadbrush suggestions, dig into those topic links at the top of the forum.

 

[RogersJetboat454]

Re: AQ125A Total rebuild???!!!

I have never done a leak down test and do not even know how to go about it. Do I use an air compresser and put in 100PSI or something like that? Also, I have not used another pressure gauge, but it does run really good, starts on the second tourn or so every time. Maybe i'll try another gauge. What would cause it to run so damn hot? What temp should the valve cover get to when it's running?

Need a cylinder leak down kit. Kit includes adapters that screw into various size spark plug holes, and a manifold assembly with a gauge and sometimes a pressure regulator. You will need to roll each cylinder to compression TDC while doing the test to ensure that both valves are closed. It can be a bit tricky to do, because the crank needs to be perfectly strait up to prevent the pressure tester from forcing the piston down, and rotating the crank.

When you are doing your compression test, you are spinning the engine over about 5 revolutions with the engine at WOT, correct? You are using a screw-in style tester, rather than one of those hokey rubber-tipped ones you just stick in the plug holes, right?

When's the last time you replaced the impeller? How does the water outlet on the drive (resembles a flattened thermostat housing) look? Corrosion around that outlet, which is common, will allow the impeller to suck air. Volvo doesn't have a specification for valve cover temp.

 

[steve242002]

Re: AQ125A Total rebuild???!!!

The water system is running properly. I have replaced all the seals in the outdrive and the and the raw water inpeller. The circ pump is working good also. I removed the cap and can see the water circulating. I didn't do the compression test at WOT but would it make that much of a difference? Also, I forgot to mention that the oil in the head smell alot like gas. If I run it with the oil fill cap off and use a rag to block the hole the rag becomes saturated in oil and it smells just like gas, is that normal?

 

[Howard Sterndrive]

Re: AQ125A Total rebuild???!!!

Maybe i'll try another gauge. What would cause it to run so damn hot? What temp should the valve cover get to when it's running?

spending $10 on another compression tester would be advisable before talking about new engines.

VP drives like to suck air when the water intake connector on the drive corrodes at the clamp. (tons of threads referencing this)
Also make sure the baffle in the heat exchanger isn't busted.

Never seen a temp spec for a valve cover, but a faulty (plugged) oil cooler could certainly cause high oil temps and high coolant temps.

 

[RogersJetboat454]

Re: AQ125A Total rebuild???!!!

I didn't do the compression test at WOT but would it make that much of a difference?

Yes it can. Think of what an engine basically is; a pump. The throttle plate restricts air flow into the cylinders to regulate how much air is drawn into the pump. You need to have the throttle wide open to allow the maximum amount of air possible into the cylinders.

Also, I forgot to mention that the oil in the head smell alto like gas. If I run it with the oil fill cap off and use a rag to block the hole the rag becomes saturated in oil and it smells just like gas, is that normal?

This could be caused by a number of things. A carburetor with its float set too high, misfire or poor combustion, bad rings causing blow-by. Next time you go to do the compression test, do a warm WOT test first, and record your numbers. Then add a couple squirts of regular motor oil to the cylinders and repeat the WOT compression test. If your numbers jump up, chances are your rings are either clapped out, or there is so much gas in the oil it's washing the cylinders down, and preventing the rings from making a good seal.

 

[steve242002]

Re: AQ125A Total rebuild???!!!

OK, so I just redid my compression test with a warm engine and WOT, the compression is no 90 PSI. I connected my compression gauge to my air compressure and it's off my 10 PSI, so my engine is producing 100 PSI, still not very darn good. Is there a set of rings and bearing thast are not going to cost me 2000 dollars? :facepalm:

 

[RogersJetboat454]

Re: AQ125A Total rebuild???!!!

OK, so I just redid my compression test with a warm engine and WOT, the compression is no 90 PSI. I connected my compression gauge to my air compressure and it's off my 10 PSI, so my engine is producing 100 PSI, still not very darn good. Is there a set of rings and bearing thast are not going to cost me 2000 dollars? :facepalm:

Hate to be the wet blanket here, but if the rings are shot, chances are the cylinders are cone shaped too, and need an overbore. Did you try adding oil to the cylinders to see if the pressure jumped up? If you add oil and the compression jumps, you will be needing at least rings for sure.

 

[steve242002]

Re: AQ125A Total rebuild???!!!

Thanks for all the replies but I feel like my original question was not answered. What kind of car has the same rings and pistons as this engine block? Can't I just bore .010" and use oversized rings or do I need new pistons to be .010" over?

 

[Maityme]

Re: AQ125A Total rebuild???!!!

If you bore the cylinders to .010 over, you need to change pistons as well. A boat engine normally runs over 4500 rpm for long periods of time. A standard size piston with oversize rings will slap themselve to pieces. Volvo running specs for the AQ125 is 4200 - 5000 RPM.

 

[foolinwfire]

Re: AQ125A Total rebuild???!!!

Same year Volvo car models based on the B-21A engine design. How do I know, lets just say my timing belt needs replaced and I was looking for a comparable belt. AQ120, AQ125A,B and I belive the AQ140 are the same. The AQ145A,B are the B-23A engine design.