compression test

[Xplicitlnck]

Well sunday I am going out to do a compression test on hopefully my new searay. It has twin 7.4 310 hp mercs. I have a couple questions. First I will be removing the belt so I dont disturb the winterized engines. Good or no good? Second I will disconnect ignition coil to stop spark and open throttle body completely for air flow. Third remove all plugs and connect comp tester. What is the recommended amount of strokes per cylinder to get an accurate reading and what numbers should I expect for this motor with around 800 hours? Or atleast what is exceptable. Ohh yea almost forgot what is the best way to shut down fuel pump safely so I dont load up fumes and fuel in the bildge. Thats an important one.
Does that process sounds good? Ive done plenty of car engines but never a boat.
Now for the genny. Same procedure and what numbers should I expect from a westerbeke with 52 hours?
While im on the topic of going over engines what else should I look for that would show excessive wear?
Im not sure what transmission it has I think its the bg velvet 5000. Any known problems with them?
Any and all info is welcome
Thanks

 

[fwebster]

The one thing you are forgetting is that the engines need to be at operating temperature before you do a compression check. I don't think you can get an accurate reading on a bore as big as a 7.4 while the engine is cold soaked. To be low, the compression will need to meet minimum factory specs and show more than 10% differential between cylinders. That isn't much of a margin for error given the different rates of expansion for pistons, rings and cylinder walls.

 

[skylark]

definitely, a stone cold motor will not produce accurate comp numbers

 

[Xplicitlnck]

C that was my original thoughts but I looked up mercs procedures and they stated tjat you should do it at room temp.I know that doesnt mean 35 dergrees but they stated it doesnt have to be at operating temps. Im having him throw a bildge heater in the bildge the night before to bring the temp up to around 60. Or should I wait till the day before the survey when we fire up the engines. Or should I just bring 6 gallons of pink and poor them into the strainer when im done. My main purpose of this is to avoid setting up a survey and haul out and then the day before calling everything off because of bad numbers. Thats not fair to the marina or surveyor. And the owner of the boat has already agreed to put the survey off until I return from vaca late feb so its also not fair to him to put the survey off to a later date then march 3rd. Any ideas. I never winterized a half fresh half raw water cooled engine. If its as simple as closing seacock and pooring pink into the strainer until it comes out the exhaust im fine with that but if theres more involved then well.....

 

[my3sons]

You should do the compression test after sea trial, when the motor has run and is warm.
A cold motor's numbers won't mean much, as stated above, and depending on how they were winterized, the cylinders will be dry, or they may have fogging oil in them. or a combination of both.
I don't know the story behind your possible purchase, are you friends with the seller? I ask this because I wouldn't want the exposure to risk of playing with someone elses engines, and if I were the seller, I wouldn't want someone other than an accredited surveyor or marine tech doing the tests. Nothing meant against you, I'm just throwing it out there, ignore me if I'm off base, and
good luck with your purchase.

 

[Xplicitlnck]

Nope not off base and I understand were you are coming from and completely agree. Ok maybe I will just wait till after sea trial and pay a mechanic to release all liabilities on my end. Thanks again.

 

[HUMPH]

Have a good marine mechanic do the engine survey. Don't try to save money on the most expensive part of your potential boat.

 

[Alex F]

Jonathan,

I understand the intention on doing necessary inspection before start laying out money based on relationship you've established with the seller, but I have to agree that this is crossing the line in regards to liability. There are several scenarios where you can end up in very bad situation, so for this reason alone I'd suggest to hire a professional (with proper insurance). If you have time before vacation and your idea is to spend only couple hundred before paying for a full survey, then consider running the engines and generator and then re-winterize them.

As you said earlier, it's not a big deal to re-winterize the engines and the genny. All you need is apporx. 15 gallons (6 for each engine and 2-3 for genny) of pink, container and hose with couple of fittings. Run the engines til they're reached to normal temp, close the seacock and pour the pink in the seastrainer. Make couple of calls and get pricing for this to be done my a professional mechanic. If it's too much, then it might be worthwhile waiting for your return and do all at once to save couple hundred.

 

[Xplicitlnck]

I called the owner last night. We agreed to wait for the survey to go any furher. Thr surveyor will do the comp check after seatrial on the same day. I guess I got a little excited and didn't think about the liabilities. I usually am better than that. But hey thats what I got you smart guys for. Thanks again

 

[dicor]

Jon I remember reading that when taking a moisture reading the hull should be at a temp below freezing for at least a week to insure the moisture is not frozen. As I understand it the moisture reader cannot read frozen water. So waiting for warmer weather to have it done is probably a good idea. Don

I also found this article some time ago when I was buying my boat. It's pretty lengthy but very detailed I found it very helpful when choosing a surveyor, I almost sounded as if I knew what I was talking about when talking to these guys.

What A Pro Looks For In a Boat Survey ~ by Henry Mustin

Every prospective buyer should have a detailed professional survey before signing on the dotted line. This pro explains how you can and should inspect regularly your vessel’s primary structure and critical components for deterioration or flaws

Surveys are performed in two parts: the out-of-the water portion and the in-water (or sea-trial) portion. Before starting the out-of-the water inspection, the bottom surfaces, rudder, propeller and shaft should be clean. The surveyor should have on hand a good-quality, all purpose scraper, a good light such as a painter’s lamp, a sharp probe or a jackknife, plus a paint scraper for removing small sections of antifouling coatings.

Take a quick walk around the hull and deck, noting any very obvious flaws, such as grounding damage below the waterline, cracks in the hull, keel problems, rudder problems, unusual stress on deck, deflection of deck surface, or cracked ports. During the first look at the hull, you can get a “feel” for the general condition and maintenance of the vessel. Note any hard spots showing on the hull laminates, alignment of the keel and rudder, any pitting or scale corrosion of the shaft and prop, and the condition of the shaft cutless bearing (the rubber bearing sleeved in the strut).

The two primary hull-laminate tests used today are the percussion test and the moisture test. Neither of these should be performed by a novice. Percussion tests are done with a phenolic (plastic-headed) hammer, or below the waterline with a six-ounce peening hammer. The point of this test is to locate previous repairs or glass separations and voids in the laminates, which are found by listening for hollow or soft returns. In good laminations a very sharp return is heard. Because there are many, many different sounds in any hull, caused by internal tanks, hull reinforcing stringers, bulkheads, water in the bilge, engine beds or partially cored sections, it would be too confusing for a novice. A professional surveyor taps the entire hull, topsides and bottom, and makes a note of any unusual sounds on a sketch pad. Later, during the interior inspection he notes what may have caused that return. Percussion will normally ferret out any repairs where filler was used in the repair and, with the scraper, these areas can be inspected visually.

After completing the percussion test, I use either a Sovereign or a Protimeter moisture-testing device to assess the relative moisture content of the hull laminates. These meters are not accurate enough to give EXACT percentages of moisture and should under no circumstances be used to this end. The meters unfortunately have both an exact scale and a smaller relative scale, and are often used improperly. The instrument works on a principle of radio frequency emission, which locates moisture in a hull and is calibrated to record the amounts on a scaled meter. It is best used to confirm what is already suspected to be a problem. By using the instrument over the entire bottom surface, a general level of moisture content can be ascertained. The question is: What is excessive and what is normal?

Obviously, the moisture content on a 25-year-old boat should be greater than that of a two-year-old boat. In making a correct evaluation the age and the construction materials involved must be considered. If the meter reads “saturated” over the entire hull or deck, then this is a pretty good indication that all is not well! In a case such as this, the percussion test would have been a very negative one, like tapping rotten fruit — dead, no resonance.

The difficult call is where the moisture is at the mid-to-high level, but not yet near saturation. On the Sovereign meter, this area is in the “actual” scale at about 15 to 18 percent (a normal “healthy” reading is between four and 10 percent). Rarely do readings on a boat hauled over the winter show less than four percent, and when it’s been in the water for a season, the readings are going to be in the eight- to 12-percent level.

Let’s say we have a boat that shows a reading of 15 percent. The percussion tests were acceptable, there is no evidence of unusual stress on the hull, and the boat shows good maintenance by the owner. No osmosis is present. While you do not see anything structurally deficient in the boat, the elevated moisture could indicate that the hull may develop osmosis-related problems at some later date. That date is impossible to predict. I have seen hulls showing 18- to 20-percent moisture with nary a blister, and I have seen blisters on boats showing eight percent. The meter is one tool of many, and it cannot accurately forecast when blisters may occur.

Rudders and skegs are tested by the same methods of percussion and moisture, although finding high levels of moisture in foam-cored rudders is nearly an everyday proposition. The spade rudder is now made to tear away if the lower third of it sustains a hard enough hit. Examine the fairness of the blade surface to note if moisture has been active enough to cause any swelling that would cause the blade to separate. Normally, a rudder with fair surfaces and clean join lines, which is well secured around the post entry, is going to be all right. Tapping rudders involves differentiating between the foam-core sections and the rigid steel reinforcements inside the blade. A solid laminate rudder is inspected in the same manner, but the resonance is more apt to be like that of a hull. The weak side of all rudders is the join line of the two halves, and it is not unusual to find splits and water leaking from these, especially after a cold winter when any moisture has frozen and expanded between the blade surfaces.

Seacock And Shaft Considerations: An average-size cruising boat may have anywhere from four to 10 sea inlet and discharge valves, commonly called seacocks. Because they are below the waterline, the importance of them cannot be minimized; one failure will sink your boat. Valves are of three types, the gate valve, the ball valve, and the tapered barrel type. Gate valves are uncommon, usually having been fit by owners and backyard mechanics, and almost never by manufacturers. They are specifically prohibited by the American Boat and Yacht Council (ABYC). Ball valves, on the other hand, have only gained real popularity in the last five years. They are not serviceable and the handles could be made of mild steel (and rust prone). The traditional seacock has been, and still is, the tapered barrel type. These have been around for 50 years, they’re easily disassembled and lubricated. Marelon (a plastic of sorts) has also become popular in the last five years. They’re corrosion proof, but not as strong or as heavy as bronze.

The first part of a valve inspection is the exterior one, in which the coating of anti-fouling or fairing material is removed so that the exterior flange can be viewed. Look for hairline cracks, corrosion, deterioration, pitting and scaling or any green or pink tinge. Green could indicate an electrochemical reaction, pink might indicate a loss of zinc in the casting, causing brittleness. A sharp rap with a peening hammer on the flange should indicate whether it is brittle enough to crack. Old-style flanges protrude from the hull; with a knife blade you can see how much tolerance there is between the hull and the flange base and whether the bedding material has begun to wear away. When this bedding fails, water slowly is absorbed by the hull laminate where there is no protective gel coat. This can cause a softening of the laminate just around the valve stem. To check for this, apply pressure with the head of a hammer at the area two inches surrounding the seacock to see if it will flex under a load, and use a probe judiciously as well. If the bedding is poor or there is any weeping inside the vessel at the valve itself, remove the valve and inspect the laminate. If all is well, rebed the seacock. This is a serious matter, and I recommend that boats older than 10 years have all the seacocks pulled, inspected and rebedded or replaced. A similar inspection is made on the inside of the boat, with good light and a magnifying glass to help spot hairline cracks in the castings. Hoses connected to seacocks should not be clear plastic or garden variety, but high-quality flexible hose, double clamped at the valve connection. Existing hose showing stiffness, cracking, checking or collapsing should be replaced promptly. Pull all hoses from the hose barbs on the seacocks. Check the ends of the hose barbs for discoloration, thinning, or even chipping.

Shafts and propellers: Auxiliary production sailboats use marine-grade stainless steel or bronze for shafts. Shafts need to be straight and free of corrosion. Visual inspection will reveal corrosion. The shaft bearing should be inspected for any signs of wear or slack. Check also the key pin that prevents slippage of the prop around the shaft. Lastly, inspect the two nuts that secure the prop and the cotter pin on the shaft tail. Sailboats wear out cutless (shaft) bearings about every three to four years on average and this can be accelerated by the use of folding propellers. The condition of a bearing can be judged by grasping the end of the shaft firmly, and applying pressure vertically and then laterally. Preferably, the bearing will be tight around the shaft, without any play, though a very small amount of slack is acceptable. Check the rubber in the bearing (this is a water-lubricated type) for signs of cracking, and inspect the set screws that hold the bearing secure in the strut.

On full-keel boats with attached rudders, a no-strut bearing or P-bracket is used. The bearing is lagged or bolted through the hull, but the basic inspection is the same.

Shaft alignment is an important consideration for the surveyor. Alignments are better evaluated in the water than out, but if you cannot have a sea trial, then close visual inspection of the shaft while rotating the propeller, perhaps with the aid of a jig, will allow you to note any extreme irregularities.

Rudder inspection: One consideration in a survey is the amount of play allowable between the rudderpost and the tube that supports it inside the boat. When too much play is present, either the rudderpost will rattle in the tube under way, or friction will develop and it will be more difficult to steer. The movement of the post also puts added stress on steering gear cables and can stretch them, causing slack steering.

By grasping the lower section on the blade and forcing it both fore and aft, and then laterally, you can ascertain play. In a tiller system, more play can be tolerated, as there is no wire-and-quadrant system attached to it, but any “slap” or wobble will be annoying and lead to more rapid wear and fatigue failures. To minimize play, you may need to add grease to the tube, replace a fitted nylon bushing in the tube, or replace or install actual bearings in the tube.

The rub rail should have some interior backing or reinforcement, as the rail is designed to absorb loading (landing) stresses. This can be done with a partial core in the topsides, or a piece of hardwood on the inside of the hull, to which the strake is thru-bolted. It’s desirable to have this piece of wood glassed to the hull interior. The strake ought to be a thru-bolted rather than a screwed type, but the latter is common on smaller craft.

The toe rail (or cap rail) is the piece covering the hull and deck joint on most sailing vessels. As such, it has to be as watertight a covering as possible, and this depends on the closeness of the fit and the type of bedding or sealant used. Normally, the surveyor can inspect the condition of the sealant by going inside the vessel and making an inspection of the exposed underside, checking for hardening or shrinkage of the sealant and, importantly, for readily apparent signs of leakage. Older vessels using teak toe rails almost always need theirs removed, cleaned and rebedded after 12 to 15 years.

Rails, stanchions, lifelines, ports, hatches and cleats must suit the intended use of the vessel, but all the deck hardware should be well-reinforced under the deck. Both coastal and offshore boats need enough deck stanchions, rather than a token one or two per side, and lifelines should be doubled and made of heavy stranded wire. The portlights should be relatively small and elliptical if possible. Hatches ought to have some reinforcements under the Lexan. A few other arrangements fall into this category of inspection, including the size of the cockpit scuppers (ability to drain out a large volume of water quickly), the ability to dog securely the anchor locker if it’s accessible from the deck, and the ability to dog hatches from the deck and the interior of the vessel.

Structural bulkheads and stiffeners: When inspection of the exterior hull and deck, and the percussion and moisture evaluations are complete, the next step is the visual inspection of interior structures. This includes all forms of hull stiffeners, which provide support to the wide panels of unsupported fiberglass (or wood, or steel). Into the hull are fabricated fore-and-aft stiffeners called longitudinals, athwartship supports such as bulkheads and frames called transverse stiffeners, and the floors, which help support the ballast in an external keel. These supports prevent unwanted hull twisting or flexing.

These stiffeners are attached to the hull during or shortly after the laminate layup, and are generally preformed, hollow or foam-cored. Inspect them for cracking and/or separation from the fiberglass layers securing them, and for cracks at any other joints, which would obviously indicate a presence of excess stress. You will need to take up all interior crib sole and berth covers to get a good look at them. If a full pan liner is fitted inside the boat, then take a good light and shine it up under the bilge access boards to either side.

Usually there are five sets of bulkheads: one at the chain locker, one aft of the forward cabin, one aft of the main cabin, half or partial bulkheads that form the galley and nav station partitions, and, lastly, the lazarette bulkhead. In modern designs without a transom overhang, the lazarette bulkhead has all but disappeared.

A good bulkhead installation should have the following characteristics: First, it should be attached all around, rather than just the sides and bottom. Second, there needs to be a “cushion” that spreads loads between the sharp edge of the bulkhead and the hull shell, otherwise you may develop a hard spot and have exterior gel coat cracking problems. These cushions can be in the form of foam or fillets that increase the width of the edge. Lastly, as the bulkheads are secured in place generally by fiberglass cloth called tape, the bond to the wood surface has to be good and it should be fairly wide. Good builders “etch” the bulkhead surface for better contact with the tape. The bonding surface should be fairly wide at the 90-degree angles, I think about four to five inches on a 35- to 45-foot vessel. Some builders also thru-bolt the tabs and the bulkheads, which I think is a good practice.

One of the recurring problems I have observed in bulkheads on racing boats stems from the flat, shallow bilges, where water is in constant contact with the bottom tabbing. If the tabbing loosens, the water sits in the void and eventually begins to rot the bottom of the bulkhead, which then becomes a structural consideration rather than a cosmetic one.

Many interior liners will not give a boat the support that stringers and bulkheads are designed to provide. Too often, liners are nothing more than cosmetic, covering an unreinforced hull shell. When you see a liner badly cracked or twisted, it is generally an indication of this problem.

When bulkhead problems exist, they are fairly easily detected. For one, you can’t open the doors properly if the bulkhead has shifted. If there are broken tabbing connections, any movement or separation can generally be plainly seen and any unfairness of the large surface of the bulkhead might indicate pressure being exerted. You also will see any hard spots from the bulkheads during the exterior inspection of the hull. It is a good idea to use an awl to probe judiciously at the corners of all the tabbing connections, but especially at the bottom edge where it comes into contact with water. Check for soft wood.

Ballast: Now we come to the join of the keel ballast to the hull on an externally ballasted vessel. I have said my preference is for a heavy fiberglass stub molded into the hull to which the keel bolts can be bolted, but some boats have full-length keels bolted flush to a much smaller stub, or none at all. Now you have this large lateral plane surface and only a relatively small surface to bolt to. This is going to generate plenty of stress even without being subjected to a grounding.

There are two principal methods of attaching keels mechanically. One is to place the keel bolts in line and generally make them pretty hefty. The other is to place them side by side in pairs using slightly smaller diameter bolts. In order to further strengthen the keel-to-hull join, it is common to install vertical bilge floors, very similar to those in a wood boat, and to take the bolts up through the floors before attaching the nuts. This has the effect of distributing the ballast load to a greater surface area and reduces bending loads on the bolts.

The keel area is critical for a proper inspection and good care needs to be taken by the surveyor in ascertaining the centerline strength of all boats. Cracks in the stub, broken or cracked floors, poor fiberglass connections to the floors, elongation of the keel bolt holes resulting in leaks through them, and any corrosion of the bolts themselves are all common problems. Quite often I find steel washers placed under the stainless nuts in the bilge; after some years these deteriorate and bolt slack develops. This causes a separation between the lead and the stub or the hull itself, leading to increased torsional stress and leaks.

Steering gear failures account for a large percentage of accidents in sailboats and not a few very hairy moments of total lunacy when the gear lets go suddenly. I think this is caused by the fact that steering compartments are often difficult to access and not well understood, so they get little or no maintenance. They require adjustments at least every year and sometimes adjustment during the season.

Determine what type of system you have. By far the most common is the radial drive, wire-to-quadrant style, which account for about 90 percent of wheel-steered boats. Next, determine if the system uses a packing gland (stuffing box) on the rudderpost as it enters the hull. This also applies to some tiller models as well. Inspect the packing gland in the following way: Check the hoses, clamps and casting for wear, rust and so on. If the fitting is leaking, back off the lock nut, then tighten the packing nut down slightly while holding off the shaft with a wrench so that it does not turn, then, when the flow stops, snug up the lock nut. If you cannot stop the flow of water, the flax packing has worn away and will have to be replaced. This is more easily done out of the water if you are squeamish about large amounts of water entering the hull. Newer designs, however, rarely have packing glands.

The mechanically fastened parts of the steering gear are as follows: The quadrant or radial disc is bolted to the rudderpost and should have aircraft nuts (self-locking) if possible; you don’t want these nuts slipping off. There has to be a locking collar around the rudderpost, normally under the quadrant, which prevents the rudderpost from slipping lower and binding the quadrant. Make sure this is securely in place.

In some systems, where the post is led through the fiberglass tubing, there may be a grease fitting. Make sure this is kept full and turned down every month or so during the season.

Now we come to the wire sections of the gear. The steering is accomplished by way of a sprocket in the binnacle housing, over which a chain is fitted. This is mated to 7x19 flexible stranded stainless wire that exits the bottom of the binnacle at the adjustable idler plate, then leads aft to the quadrant where it dead ends to two eye bolts, threaded so that the system can be adjusted for slack.

Inspect the wire for any burrs or breaks. None are acceptable. If any strands are broken, replace the wire. If it’s slack, tension the wire at the eye bolt threads. How much? About an inch of deflection along the horizontal runs of the wire is acceptable, but do not tighten wire too much or the stranded wire may chafe on the sheaves. If sheaves show excessive scoring, especially on the shoulders, they may have to be realigned. The entire unit should be clean and well greased.

As for the one- to two-percent of steering systems that are geared or pinion, these fail mostly due to universal joints, tooth failure (on the rack and pinion gears), or wear (on the worm gears). There are quite a few mechanical fastenings on the systems, mainly machine bolts, nuts, sometimes lags, that require normal maintenance and lots of grease.

 

[Xplicitlnck]

Good reading thank you.

 

[AKBASSKING]

Agree great read.

X smart move on letting the surveyor do the compression check. To add, I agree the check needs to be done at normal operating temp. Wiring the throttle wide open, disconnecting the coild wire, removing all the plugs are all correct. You crank the engine over until the needle on the compression gage stops moving up. The one thing folks forget is the compression check is a double check. The first round is done "dry" then the second check is done after you squirt a little oil in the cylinder "wet" and compare that reading to the dry reading. If it jumps more than 10psi then you have a piston ring issue.

 

[Xplicitlnck]

Gotcha. :smt009

 

[semperfido]

We did oil analysis when we did our survey. It really helped with my purchase. Blackstone labs got them back to me in like 3 days. Just an idea.