Help me determine what went wromg on my engine!

[Lavish]

I have a 1975 Mercruiser 140 I/O that has no compression in one cylinder. I turned it over with the valve cover off, and I can see the valves moving. How can I determine what is wrong?

I want to know if it's in the head or the block. I would I determine if it'd the valve or the rings?

The cylinder next to it is 30lbs lower than the other two. Not sure if this means a head gasket problem.

Please help me with figure out how to do some tests to figure out what went wrong.

Thank you.

BTW. The engine will start but pops out the carb, and flames out of the exhaust. Making me think it's in the valves? Thanks

 

[Bifflefan]

Re: Help me determine what went wromg on my engine!

Pull all the plugs and do a compression test.
On the low cylinders do a "cylinder leak down test".
This tool you can rent at AutoZone or someplace like that. Follow the directions with the tool.
This will tell you where to look for the problem.
I cant see being a block or head persay issue, but a valve, head gasket or rings or piston is a good bet.

 

[JustJason]

Re: Help me determine what went wromg on my engine!

google "leakdown test" and you'll find all the tools you need and how to perform the procedure. That's your next step to isolating your compression problem.

 

[picklenjim]

Re: Help me determine what went wromg on my engine!

If you have "NO" compression in one cylinder than it would be useless to do a leak down test. Sounds to me like a valve or valves are hanging in the guides or bent. Poping back out the carb means an intake valve isn't sealing and fire out the exhaust means an exhaust valve is not sealing. May as well pull the head and have it serviced. More than likely the problems in there. Pistons and rings are probably fine.

 

[Lavish]

Re: Help me determine what went wromg on my engine!

Ya they told me at the auto store not to do a leak down test. Instead they gave me a hose to hook up an air line from my compressor to see where the air is leaking.

I am having trouble determining if the bad cylinder is at top dead center to do the test. As I have no way to turn the engine by hand. The crank shaft pulley is blocked by the front motor mount. SO I cranked it over with the starter and made sure to stop it when both valves weren't compressed. I hook up the hose, and air just goes in. I guess I can hear it at the carb, I didn't check yet to see if I could hear it out of the exhaust.

Should I just pull the head? Will I be able to tell if there is a problem once the head is pulled?

 

[chaparall villain 2]

Re: Help me determine what went wromg on my engine!

there are a number of scenarios that cause vale problems but all will cause loss of compression if one has just a little bit of carbon or a chunk of something on the valve seat it wont seal but alot of times you cant see a valve thats not sealing properly ... i would pull the head and take it to a machine shop to have it vacuum tested ... they can tell if and which valve is leaking by testing this way

 

[HT32BSX115]

Re: Help me determine what went wromg on my engine!

Once you determine that you have no compression on a cyl and it's clear that the valves are moving,

You WILL be removing the head. You wasting your time speculating what the problem is until the head is off.



Regards,


Rick

 

[Lavish]

Re: Help me determine what went wromg on my engine!

Thank you. I am going to go out there and pull the head to see what's going on, and talk to a machine shop Monday.

 

[Lavish]

Re: Help me determine what went wromg on my engine!

I have the head removed!! And I think I found the problem, the exhaust valve.

Here's what I did.

I took off the intake/exhaust manifold, then removed all the rocker arms and pushrods. After that I KNEW the valves should be closed. I put the air line back on. and air was flying out of the exhaust port, not the intake that I could feel.

That cylinder had the most carbon in it. It was really caked onto the piston top also. That exhaust valve looked the most carboned up out of all of them too.

 

[alien4fish]

Re: Help me determine what went wromg on my engine!

congrats on finding the problem!!now get that thing serviced at the shop and get back out on th water

 

[Lavish]

Re: Help me determine what went wromg on my engine!

Ugghh. I just found the mainifold with a huge crack along where it mounts to the head!!

I assume this is what would have burnt a valve out??

 

[JustJason]

Re: Help me determine what went wromg on my engine!

sure could have, especially if it was leaning out a cylinder.

 

[picklenjim]

Re: Help me determine what went wromg on my engine!

Intake manifold or exhaust manifold?

 

[Lavish]

Re: Help me determine what went wromg on my engine!

Here is the manifold. It's the intake/exhaust manifold from a 1975 Mercruiser 3.0L I/O.

I'm hoping I can weld it. I know where to go in town that does cast welding. I hoping I can do that, and maybe pressure test it afterwards?

Has this been done before? or is it a no-no?

 

[HT32BSX115]

Re: Help me determine what went wromg on my engine!

Here is the manifold. It's the intake/exhaust manifold from a 1975 Mercruiser 3.0L I/O.

I'm hoping I can weld it. I know where to go in town that does cast welding. I hoping I can do that, and maybe pressure test it afterwards?

Has this been done before? or is it a no-no?

It cracked because someone did not drain all the water out prior to a Freeze.....and may be cracked internally too..... no one can weld in there......

You're wasting your time welding it. It will crack again. The cost to get it welded correctly by someone that has all the equipment is probably more than just buying a replacement manifold.


Check the block carefully. It may be cracked as well.

 

[Lavish]

Re: Help me determine what went wromg on my engine!

Ya when I bought it I was told the water wasn't drained. I had hoped I got lucky, but apparently not. The block had a freeze plug out, hopefully that saved the block.

 

[picklenjim]

Re: Help me determine what went wromg on my engine!

I would recommend you have the head disassembled, inspected, a valve job and resurfaced. That cracked manifold sucks but that isn't why you had no compression in one cylinder. You have another problem.

Like HT32BSX115 said you would be wasting your time trying to get that manifold fixed.

 

[Lavish]

Re: Help me determine what went wromg on my engine!

Ya I've decided to buy another one. The head will be going to a mach shop. It had two burnt up valves, and the one cylinder that had no pressure had no valve seat in it. I hope the piston and cylinder wall are ok, I haven't inspected them yet.

 

[picklenjim]

Re: Help me determine what went wromg on my engine!

If it was running and not getting water in to the oil the it's probably alright.

 

[HT32BSX115]

Re: Help me determine what went wromg on my engine!

freeze plug out, hopefully that saved the block.

That's not what "freeze" plugs are for and they won't prevent a cracked block.

You will be lucky if your block is NOT cracked.