Compressor question, optimax 150, 2004

[Pecos23]

I was working on my motors and read European talk about checking your compressor by turning the top pulley three times clockwise, and if you get more than 3 turns before it gets hard to turn, then you have problems.
Well, I can keep turning the pulley more than three times and feel a little resistance but it doesn’t get that hard to turn. Definitely not has hard as was described in a couple posts.
I wiggled the pulley vertical and horizontally and no movement.

The motors are running well. But I have see my fuel economy drop slightly. It seems the WOT is less RPM, but I was loaded heavy last time out. Motors have 600 hours.
Should I be worried? I don’t want these things to blow and pump metal shavings into my engine.

I can not add a pic using the icon above the post, any suggestions?
Thanks

[SilverFox579]

You might have an air leak if the compressor doesn't build pressure by the 3rd revolution especially if there's no vertical or horizontal pulley movement. Fuel/air pressure test would be helpful.

[Pecos23]

How would I do an air compressor check?
i have been told my a Merc certified mechanic that there is a reed plate on these compressors that can leak and can be replaced. Do you know any additional information on this claim? Thanks

[SilverFox579]

If you don't have a dual glycerin filled gauge set to simultaneously check fuel and air pressure, you'll need to see the certified Merc tech. Leaky reed plate is a possibility as are several other things - the fuel/air pressure test is best place to start.

[Pecos23]

So, I am understanding that there is two sets of reeds in my motor. One set in the intake plentum for the engine, and one set in the compressor?
Do the compressor reeds go bad or or these a maintenance item?

[Pecos23]

Suggestions on a set of dual glycerin gauges?

[06 SB]

There was a bad batch of compressor reeds that Mercury sent out a TSB to dealers for replacement. Your dealer should have it.

[Pecos23]

Would the reeds be responsible for the building of pressure during the three revolution test sequence suggested by EuropeanAM? Also, does EuropeanAM still post here? His posts are incredible. Thanks.

[Pecos23]

Hi Don, any information you could provide would be appreciated. If I can get more than three turns on the compressor, which I can on both motors, does that mean that the compressor is getting weak, or does it mean it’s getting ready to fail?

[EuropeanAM]

David- the PISTON is responsible for generating the pressure as the compressor spins.

The REEDS are the intake and exhaust "sealing" valves in the compressor that control air coming in, and going out. Bent, broken, or damaged reeds can prevent proper operation of the compressor.

Of course, ANY air leak in the system would do the same. Simply plugging the output line (or covering it with your thumb while turning compressor by hand) will quickly determine if the compressor is producing air pressure.

Gauge sets are something you order from the manufacturer, or make up from a variety of hoses, gauges, and types. Neither are "cheap".

[Pecos23]

Don, thanks for the reply. I see a sketch for the gauges in my shop manual, I will go online this weekend and see if I can find the components to make my own oil gauge set. What do you know about a pinch test? I found a reference online, but was on able to post the Page to this thread

[EuropeanAM]

Before you go into that much effort- disconnect the air supply line, plug off with your thumb and attempt to spin compressor through with other hand. See if pressure builds by 3 turns.

[Pecos23]

I took my motors to the local merc shop and he put his air/fuel pressure gauges on my two motors. Here is the results.

Port Motor
80 PSI Fuel / 65 PSI Air
When the valve on the air side was depressed, some pressure was release an some water vapor escaped. Mechanic said might be condensation.
Fuel escaped under pressure when fuel valve was depressed, under pressure.
The pressure built quickly and stayed steady after the motors were shut down, but started to drop slowly over time.

Starboard Motor
80 PSI Fuel 65 PSI Air
No pressure escaped when we depressed the air valve, a little fuel from fuel side, very low pressure.
Pressure built quickly and motor ran well.
After shut down, both air and fuel pressure dropped quickly and steady.

Comments from mechanic:
Pressure is not as important as difference between air and fuel.
Pressure drop may point to fuel or air regulator valve, or tracker.
Suggested inspecting reed assembly for motor and compressor head.
Said his gauges might need calibrated, seemed odd that both motors had exact readings, but low.
Was not aware that it is suggested to clean rails and injectors with compressor failure. He is certified Merc.

Thanks, what do you guys think?

[SilverFox579]

I think you need a second opinion from a different Merc mechanic. Pressure does matter as does the differential. If those readings are accurate, and I doubt they are, your engines would not be, as you say, running well.

Fuel/air pressures should be 90/80 +/- 2psi.

[EuropeanAM]

Find someone that understands the system. There is a significant problem in the STB engine's air system (leakage).

And... any decent tech/shop should have a relatively accurate gauge set on hand. ALL pressures shown are incorrect.

[Pecos23]

As I suspected, and now 125 lighter in the wallet. he charged me an hour shop time to test pressure and then told me that his gauges might need calibrated. he's my only local merc certified guy, what's a guy to do?
How, were do I start looking for a leak in the starboard engine?
I'm looking for a set of gauges now. wanted to get out of there quickly as the clock was ticking and I knew something was amiss.

[SilverFox579]

A genuine Mercury set will hit your wallet hard, not passing judgement, just stating fact. I'm in process of building my own.

[Pecos23]

Yes, as am I. Found a decent set of oil filled gauges for about 50 bucks each at McMaster Carr industrial supply, https://www.mcmaster.com/#3795K13 Also found a pair of fuel injector gauges at tool source https://www.toolsource.com/fuel-inje...tkm560nen04bm6
for 26 bucks each. Going to replace the cheep gauges with the oil filled ones and have a set of gauges for about 150 bucks. A set of OEM mercury gauges are around 400 bucks.

[Pecos23]

OK, took my new gauge set and ran an air/fuel pressure check per don's recommendations.
Here are my results.

[SilverFox579]

You have an air leak on your starboard engine. Not sure what you mean by schrader valve insert, are you referring to the valve stem (core) or the valve itself? Also, which schrader valve has this problem - fuel or air? Your engines are a little older than mine which has both schrader valves on the port fuel rail and on mine the top one is fuel and one on side is air.