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  #1  
Old 10-03-2008
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Who needs compression?

Boat 1984 Catalina 30’
Engine: M25XP
Engine behaviors that cause concern
  • Takes at least 2 often three tries to start with using the glow plug for about 15 sec each time.>>
  • Substantial white smoke for about 2 minutes after starting>>
  • Often need to increase throttle off idle to keep engine running until warmed up>>
  • Exhaust smell in cabin>>
  • Temp goes to 190 at full throttle in about 2 minutes>>
  • Engine shut down once at full throttle seconds after an alarm sounded>>
  • Temperature does not go down even at idle. The engine has to be turned off for the temperature to go down
  • Compression is 180, 200, 240
  • Smoke coming from crank case vent
Recent service: (some have no bearing on this question of course)
  • Someone tightened down the engine mounts without alignment
  • We replaced the exhaust piping and heat wrap
  • We fabricated a fiberglass coupling to glue (5200) to the muffler for the exhaust hose.
  • Fabricated an elbow with an injection pipe for the raw water
  • Replaced the raw water hose
  • Cleaned the contacts on the alternator (it wasn’t charging for a while)
  • Attempted to clean the bowl of the primary fuel filter, it is too damaged to clean.
  • We replaced the heat exchanger zinc it was completely used up.
  • Water pump is about a year old impeller OK
  • Alternator tested OK
>>
Since the compression is so low our mechanic wants to do a full rebuild.
As a stopgap measure we were thinking of replacing the heat exchanger: $650.
Replace filter: $315
Rebuild injectors: $285
>>
Do you think that we can get another season or two out of this engine?
Are any of the above items a complete waste of money if we are not planning on a re-power or rebuild?
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  #2  
Old 10-03-2008
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The low compression in itself should only cause trouble starting, and possibly the smoking as well. It really shouldn't have a bearing on the running temperature. (unless it's a head gasket problem and you're getting combustion gases into your water space... a possibility - it could also account for the white smoke at first.. burning antifreeze that may have leaked into a cylinder) Question: are you losing coolant?

The bad compression could result in some blow-by which will account for the smell in the boat. btw it may be due to valve guides rather than rings.. need just a head rebuild rather than a full rebuild..

The overheating could also be due to a clogged exchanger core, that is usually cleanable unless it's corroded or leaking. That would be the first place to start. Replacing the core may be premature.

The compression is low and your difficulty starting is a warning sign. A rebuild of some sort is in your future. If you do it now you have the security and peace of mind from now on. If you don't, you'll be nervous and uncomfortable, lacking confidence in your power and it will likely fail you completely at the worse possible time.... Tows home are ridiculously expensive these days.. money better put towards getting things right in the first place.

I'd fix it.. even with a reliable engine motoring for any extended period sometimes makes me nervous. (so bored with it I keep dreaming up things that can go wrong)
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Last edited by Faster; 10-03-2008 at 09:03 PM.
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Old 10-03-2008
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I wouldn't try it, heres why...
a head gasket is probably causing the white smoke (white=water, blue=oil, black=fuel)
*caveat, agree with at least cleaning the core, keeping in mind this would be stop gap at best.

Its quite possible that you might be able to get away with a ring job and "honing" & valves and guides.

If you wait, the carbon blow-by will probably have caused piston skirt scoring and cylinder wall damage.
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Last edited by cardiacpaul; 10-03-2008 at 09:39 PM.
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Old 10-03-2008
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What can I expect given that the core zinc was gone?
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Old 10-03-2008
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I asked the mechanic about head, valve issues. I asked about a wet compression test (spray in oil) but he said it was too dangerous, engine may start. Seemed pretty confident it was rings.

From a mechanics point of view I'm sure it dosn't make any sense to try stuff that may or may not work when the rebuild will work for sure.
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Old 10-03-2008
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Sounds like the exhaust is pluged.

Rick
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  #7  
Old 10-04-2008
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Quote:
Originally Posted by timebandit View Post
Sounds like the exhaust is pluged.

Rick
Why do you say that? The exhaust is brand new.
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Old 10-04-2008
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Here are my answers, I guess if I just add to your text the board won't recognize the new text and accept it.

Quote:
Originally Posted by davidpm View Post
Boat 1984 Catalina 30í
Engine: M25XP
Engine behaviors that cause concern
  • Takes at least 2 often three tries to start with using the glow plug for about 15 sec each time.>>
  • Air can't get out - air can't get in
  • Substantial white smoke for about 2 minutes after starting>>
  • Started rich- same as above
  • Often need to increase throttle off idle to keep engine running until warmed up>>
  • To fight back pressure
  • Exhaust smell in cabin>>
  • Back pressure
  • Temp goes to 190 at full throttle in about 2 minutes>>
  • When the exhaust can't get out it heats up everything
  • Engine shut down once at full throttle seconds after an alarm sounded>>
  • Over heat?
  • Temperature does not go down even at idle. The engine has to be turned off for the temperature to go down
  • See above
  • Compression is 180, 200, 240
  • When you look at compression figures you look for two things. the first is the defference between ajacent cylinders. 20 pounds is OK and 40 is on the weak side but not bad. Some a$$hole mechanics will not open the throttle wich will cause low readings. A plugged exhaust will cause the same. A head gasket leak will show up as either a low reading in to adjacent cylinders (compression flowing between them) or into the water jacket (to much pressure in the cooling system as noted by air bubbles or with a pressure gage.). Sometimes, on rare occasions you might get a leak to the out side of the engine the you can see. hear and smell.
  • Smoke coming from crank case vent
  • Back pressure escaping the cylinder at the bottom of the stroke past the rings into the crank case.
  • Personally I use water to seal the rings for a compression test. Without a wet test you are just guessing.
  • You could do an air test by bring the piston up to tdc on the compression and listen to see if any air is escaping out the intake or exhaust valves or into the crankcase you will need an air supply for this test though.
  • Rule #1--Last thing you mucked with is the first thing to mess up!
  • What was wrong with the exhaust?

Recent service: some have no bearing on this question of course)
  • Someone tightened down the engine mounts without alignment
  • We replaced the exhaust piping and heat wrap
  • We fabricated a fiberglass coupling to glue (5200) to the muffler for the exhaust hose.
  • Fabricated an elbow with an injection pipe for the raw water
  • Replaced the raw water hose
  • Cleaned the contacts on the alternator (it wasnít charging for a while)
  • Attempted to clean the bowl of the primary fuel filter, it is too damaged to clean.
  • We replaced the heat exchanger zinc it was completely used up.
  • Water pump is about a year old impeller OK
  • Alternator tested OK
>>
Since the compression is so low our mechanic wants to do a full rebuild.
As a stopgap measure we were thinking of replacing the heat exchanger: $650.
Replace filter: $315
Rebuild injectors: $285
>>
Do you think that we can get another season or two out of this engine?
Are any of the above items a complete waste of money if we are not planning on a re-power or rebuild?
Rick
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Old 10-04-2008
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Quote:
a head gasket is probably causing the white smoke (white=water, blue=oil, black=fuel)
In my experience, white smoke can also be caused by unburned fuel oil in the exhaust. That can be caused by a bad injector or no combustion.
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Old 10-04-2008
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Quote:
Originally Posted by davidpm View Post
(snip)
Compression is 180, 200, 240
The good news is your Universal is a marinized Kubota D950. Look at the dipstick for the Kubota numbers. With that you can buy Kubota parts at farm or lawn equipment dealers for about a third of what Westerbeke charges.

The compression spec on this engine is 448 psi new with an allowable lower limit of 337 psi and a variation of no more than 10% between cylinders. You're well below that.

Your white smoke is unburnt fuel from low compression. Hard starting and poor running when cold are other results.

White smoke can also be caused by coolant leaking into the engine. That can't be ruled out, but fixing the compression problem will fix any coolant leakage problem.

Quote:
Some a$$hole mechanics will not open the throttle wich will cause low readings.
A mechanic who compression tests a diesel with the throttle open has no idea what he's doing.

This engine is a diesel. It has no throttle valve in the intake. Throttle position will have no effect whatsoever on compression readings. Depending on the fuel pump arrangement, if there is no fuel shut off solenoid the throttle is used to shut off fuel to the engine. If the throttle isn't in the shut off position when a compression test is run, the engine will try to start. Since the compression gauge is most likely installed in a glow plug hole, if that cylinder fires the compression gauge will be blown up.

So if you see a "mechanic" try to compression test a diesel with the throttle open, fire him before he hurts himself on your boat.

From your description this engine has been badly neglected. Since the anode in the heat exchanger was gone, there's probably a bunch of corrosion plugging things up and causing the overheating. Sounds like your exhaust system is a bunch of mismatched pieces kludged together.

Quote:
Since the compression is so low our mechanic wants to do a full rebuild.
There is something called a cylinder leak down tester that's used to pinpoint where the compression is being lost.:

They're $30 at Harbor Freight, but you'll probably also need their $25 diesel compression gauge to get the fitting for the glow plug holes.

If you onlly need a valve job, just the head can be pulled and sent out. With the engine open you can decide if a full rebuild is necessary. If the rings are the problem, the engine has to come out and you might as well rebuild the whole thing then.

Quote:
As a stopgap measure we were thinking of replacing the heat exchanger: $650.
Do you know it's bad and can't be repaired? Better to pull it apart, clean it and see where you are before replacing it.

Quote:
Replace filter: $315
Absolutely replace the filter. But rather than a "marine" unit, I'd look at industrial models. For instance, Northern Tool sells Goldenrod Water-Block Fuel Filter for $37, with $12 replacement cartridges:



Quote:
Rebuild injectors: $285
Do you know something is wrong with them?

While you're replacing stuff, take the whole exhaust system apart, throw away anything that's bad, and rebuild it with good parts. Use double hose clamps and not glue for putting things together.

Quote:
Do you think that we can get another season or two out of this engine?
Once the problems are fixed, and provided it's maintained, it'll last decades.

Good luck,

Tim
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