70 lb compression on mariner 150???

[lookingforluck]

Re: 70 lb compression on mariner 150???

bump

 

[studlymandingo]

Re: 70 lb compression on mariner 150???

See if you can see inside the cylinder; look for scoring and scratches.

Beyond that, it could be time to pull a head.​

 

[Deepblue22]

Re: 70 lb compression on mariner 150???

I'm not the top expert but a couple things wont hurt to ask, they are nonengine and may be worth confirmation before digging into the engine:

1. confirmation of electrical function and that all cylinders are firing correctly, sometimes these motors start and run fine for a while and then after an hour or so the thing heats up and electrical components can fail in the field, starts surging or seems to lose power, and then they may work again when it cools off (I have a merc 90 that pulls this trick on me, i dont know exactly why yet)

2. does your prop have a break-free hub maybe it is spun.

3. 5100 seems fairly near the high end of the range too so if you were running 68mph at significantly higher than 5100 you may have overworked something?

 

[jdupree]

Re: 70 lb compression on mariner 150???

I don't know if this will help but I had a similar problem with running aground. Did you use your motor to get off the sand bar? I used my motor to get off a sand bar several years ago. When all of the sand is swirling under water your water pump is pulling it in to the motor. That would explain the sudden drop in compression. What happened to mine and I would guess with yours is that your motor was overheating as the sand was being pumped in. My cylinders were scortched from the overheating. If the pee has slowed down as you say, the impeller was damaged by the sand thus causing the overheat and low compression.

I would pull the heads and see what you have. I am guessing that the cylinders will have heat damage and scoring. When my motor was re-built, they pulled 2 ziplock bags full of sand out of the motor. I hope this helps because the symptoms sound just like what I experienced several years ago.

 

[lookingforluck]

Re: 70 lb compression on mariner 150???

What did something like that cost, for all six cylinders to get rebuilt?

 

[lookingforluck]

Re: 70 lb compression on mariner 150???

bump...

 

[lookingforluck]

Re: 70 lb compression on mariner 150???

Would replacing the head gaskets on this engine help with the compression and power loss? Is that something that isn't real difficult to do?

 

[Don S]

Re: 70 lb compression on mariner 150???

Would replacing the head gaskets on this engine help with the compression and power loss? Is that something that isn't real difficult to do?

No, head gaskets will not cause your problem, maybe one or two cylinders low, but not all of them.
Pull the heads off and inspect the cylinders. Without that, you don't even know if it's rebuildable or not.

 

[redjmp]

Re: 70 lb compression on mariner 150???

Quick and dirty check is to pull all plugs and plug one hole at a time with your finger and spin flywheel by hand and listen carefully for blowby. If everything is fine then you should not hear much if any hissing as you turn flywheel and the pressure should build up enough to blow past your finger. If you hear a lot of hissing and nothing leaks past your finger then you have scorched something.
Very unusual to read evenly across the board like that and even more unusual to still start and run fine.
If your checker has a brass extention tube, remove it as the extra volume it holds will cause your readings to be lower. Use the shortest hose possible.Removing mine will cause the readings on my merc 115-6 to climb by 20psi. and my 6hp to climb 30.
110 on your lawnmower might be low as well. Not unusual to be over 150.
If you ran through a sandbar, chances are that there is sand in your cooling passages and your peehole won't be flowing properly.

 

[lookingforluck]

Re: 70 lb compression on mariner 150???

When you say scorched, what do you mean and can I turn the flywheel by the battery?

 

[Don S]

Re: 70 lb compression on mariner 150???

You should be seeing 110 to 135 lbs. of compression, you are getting 70, no need to stick your finger over the holes and do anything. You don't have valves, so you have a ring problem. Pull the heads off and LOOK at the cylinders and see if they are damaged. If not, then put some new head gaskets back on it, put the heads on and torque them and give a decarb a try. May be just stuck rings.
If there is scoring in the cylinders, perhaps your oil pump gave up. I doubt your motor compression problem had anything to do with your grounding. But if the blades on the prop were bent, that could lower your rpm.

 

[redjmp]

Re: 70 lb compression on mariner 150???

When you say scorched, what do you mean and can I turn the flywheel by the battery?

I mean that you overheated the pistons and rings and probably scuffed the cylinders. Using the battery to check is no good as the pistons move too fast to let much if any blow by when you just have your finger in the hole.
With no plugs, the flywheel should turn fairly easily by hand and allow you to feel and hear if there is blowby. It should be obvious whether or not you have leakage while turning slowly by hand. If 70lbs is correct, then while turning slowly by hand you should not be able to develop much if any pressure.
Pulling the heads is a last resort and will take more time and cost some money
in head gaskets.

 

[lookingforluck]

Re: 70 lb compression on mariner 150???

About how much do rings and head gaskets cost? Anyone know?

 

[redjmp]

Re: 70 lb compression on mariner 150???

Around a couple hundred.
Problem is that alone wont fix your problem if indeed you have only 70.
Did you try my down and dirty test?
If it doesn't hold pressure then you will most likely need a rebore and new pistons if your cylinders are badly scuffed.
50-100 each for new pistons and a few hundred more on top for machining.
You can only get away with new rings only if the old ones were simply wearing out from age. Even then, you would need to get the cylinders deglazed/honed.
Since at this point, you have the motor totaly disassembled, you might as well check and replace the bearings, reeds, etc if needed.
Could easily top $1000 and that might be cheap.

 

[lookingforluck]

Re: 70 lb compression on mariner 150???

How do you know if the oil pump gave up?

 

[redjmp]

Re: 70 lb compression on mariner 150???

Well most gas is clear and oil is blue so if you see blue gas at the carbs then there is some oil.
Most people don't trust the oil pump as it will eventually fail and take your motor with it.
Most people just premix the oil and gas and bypass the pump.
The only way to tell if indeed it is pumping correctly is to use premix in case the pump is not working properly, you will still get proper lubrication, and fill up the resevoir and burn a tank of gas and then see how much oil you have to add to top the resevoir.

 

[studlymandingo]

Re: 70 lb compression on mariner 150???

Have you done any further testing on this motor?​

 

[lookingforluck]

Re: 70 lb compression on mariner 150???

No, I haven't done any more testing other than a decarb and gained about 5lbs per cylinder so I am at 75# now

 

[lookingforluck]

Re: 70 lb compression on mariner 150???

Should this thing be starting and running good with such low compression??

 

[studlymandingo]

Re: 70 lb compression on mariner 150???

Probably would be hard to start with such low compression. This is why everyone has recommended trying a different compression tester. Wouldn't hurt to pick one up at the auto parts store, I think you can rent one for very little.​