Lost compression

[amanick]

I bought a project boat with a Volvo aq125a engine.I checked the compression from the get go and it was good on all 4 cylinders #1 was at 140 through 160 on the other 3. I was doing some other checks on it since all it done was turn over and not start. During that time it would just back fire and not engage so i ordered a carb kit to rebuild the carb. The starter went out on it while I was trying to get her to turn over. I replaced the starter and she turns great problem is I double checked my compression on the again and they are all at 30 psi across all 4 cylinders. I got good spark but no backfireing any longer or compression. anyone that can give me some input I would appreciate it.

 

[Don S]

Re: Lost compression

Are you doing the compression tests with all the spark plugs out while cranking?
Since this is happening to all cylinders, you might want to check the schrader valve in your compression tester. If they don't hold pressure, you get low readings.
Have you done any timing belt work on the engine since the last compression test when you had good compression?

 

[amanick]

Re: Lost compression

yes i took all the plugs out and checked it. I will tighten the Schrader valve on the compression gauge hose and recheck after the rain quits.Just baffled me why it would just drop like that on all 4

 

[amanick]

Re: Lost compression

No Don I haven't done any timing work on it at all. My goal was to get it to run and go from there with it to see what condition overall the motor was in.

 

[Don S]

Re: Lost compression

I will tighten the Schrader valve on the compression gauge hose and recheck

t may not be that it's loose, it could just be leaking. There should be 2 schrader valves. One for the release, and one in the hose.

 

[amanick]

Re: Lost compression

I went back out and checked the compression again. The gauge is good no air leaks in it. Turned the motor over for 25 seconds each cylinder and got a 30-40-30-30- reading. any suggestions?

 

[amanick]

Re: Lost compression

failed to mention that the gas in the carb is blowing out of the carb as well when im turning the engine over

 

[YZ165]

Re: Lost compression

+1 to what Don said. Sounds like a timing issue to me...

 

[destroyer_85_golf]

Re: Lost compression

did you try putting a little oil down the cylinders to rule out the rings you dont say how long the motor sat between when you had 140 to 160 psi till you had 30 to 40 psi. id at least rule out rings and then definately look into the timing or make sure that you didnt knock anything down the intake when you took the carb off to rebuild it which would keep the valves from seating all the way.

 

[Don S]

Re: Lost compression

failed to mention that the gas in the carb is blowing out of the carb as well when im turning the engine over

Either it's jumped time, or things are rusting inside and the valves can't close all the way, or the rings are rusted. Who knows.
Understand, there is no ez button you push to find the one and only answer for your problem and some simple adjustment screw you turn to fix it.
You could have several things wrong combined together causing your problem, but you are there and can see, feel, hear, and smell what is going on. That's some of the many things marine techs use is troubleshooting problems.
Since we aren't there, you have to tell us what is going on.

 

[amanick]

Re: Lost compression

I didn't put oil in the cylinders yet to check the difference in the compression. I only had the boat for a couple of days so far so going slow with checking it out. I checked the compression the day i got it and it was good. After I replaced the starter that went bad from trying to crank it over is when i noticed that the engine wasn't backfiring any longer and i could tell we lost compression by the way the engine sounded as that was the next day. I got a gut feeling that the timing may have jumped. I did look at the belt and they seem fine.I have to get a timing light and see how it lines up. I took the carb off in one piece and the only thing that could have possibly went down the intake would have been a small piece of the gasket. I guess after i check the timing i can take the intake manifold off and look inside.I appreciate every ones input as I am new to all of this and my mechanical skills arent the greatest.

 

[Robj]

Re: Lost compression

I do not know this particular engine, but if it i a typical volvo rubber band engine, I would bet that the belt jumped. You need to pull the front cover off and check the alignment.