Jgray

Motor is a 99 HP500 Carb with 150 hours. I have no noticable loss of power but I do have a greyish black film on the transom (all of the transom) and am using 1Qt. of oil per 5-7 hours. I think some of my rings are smoked, what do you guys think?
Here are the Comp test readings
#1. 180
#2. 190
#3. 170
#4. 195
#5. 195
#6. 210
#7. 190
#8. 185
Thanks for any insite on my situation.
Jamie

offthefront

compression looks fine ... what do the plugs look like ? One Quart in 7 hours is not too bad ...how hard you run it ? The HP 500's need top end checked about 200 hours ...but that is usually valve spring issues ....m

BadDog

Get a fresh charge on the battery, using a syringe shoot about 1/4 ounce of oil into each hole just prior to testing said hole. Roll over several times and then check compression. Be sure to cover the hole with a towel or something. Do this with all spark plugs out. I usually run the carb dry prior to compression testing to avoid fuel wash during the test. In my case I disconnect the fuel pump 12vdc and idle till it starts to quit.

Jgray

OTF. Plugs all look the same, slightly brown on porcelian. I usually cruise about 3.5 - 4k, with the ocasional wot. I just bought the boat, former owner put a set of canfield heads(mild port job) with the comp springs and a different cam in it around 75 hours.

Baddog, would this be a "wet compression test"? I will try this tomorrow, if I don't take it out. Should this give me different readings?

Thanks for the help.

BadDog

Someone correct me if I am wrong. If the compression raises significantly then the oil caused the rings to seal better and your rings are a little tired. If it does not go up much at all the rings are in pretty good shape. With those numbers though I don't think you have anything to worry about. What you are really looking to do is establish a baseline for when you test later. Keep all variables the same so when you test later you can spot a trend.

Lmarth

Just a couple of observations based on the information you provided. First, the compression numbers aren't out of line with the possible exception of cylinder #3. The oil consumption also isn't atypical depending on how hard it was run. Oil consumption on a BBC isn't necessarily ring related. The valve guides in the heads often contribute to this. You don't indicate what the guide material is, the stem clearance , what oil seals are being used, etc. Soot all over the transom could be the result of an over rich induction system. You've gotten some good advice here. I'd squirt a little oil in #3 and see what it does. Then I'd do a simple leakdown test. If the numbers are low or are inconsistent, I'd leak it again after removing the valve covers and exhaust manifolds. Doing the leakdown test with a mechanics stethoscope will tell you what's happening.You can listen in the exhaust ports, drop the scope down below the cam to the crankcase to hear what's going past the rings and down the carb into the intake plenum to listen to the intakes. One step at a time, first things first. Your dilema is that you don't know exactly what was done to the motor and how it was done before you bought it. If nothing more, you'll have a good Baseline for the future.I hope this helps.

Jgray

Guys, great advice thanks alot, this gives me some great direction as to how to proceed. I am going to do a wet compression test tonight and pull a valve cover off to see what valve seals were used. Also I am going to hunt around today and get my hands on a leakdown tester.
Thanks again Jamie