502 Mag Rebuild or New 502 ???
10-27-2010, 02:05 AM
#21
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A leak down test is similar to a compression test. On a leak down, you use a compressor and pump air into the cylinder with the piston at TDC. The air leaks out and you can hear where its going. The gauges on the leak down tester tell you the % of leakdown. A well set up, fresh, broken in engine should be 5-10% or so leakdown.
10-27-2010, 06:34 PM
#22
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The two peice rear main seal does indicate a Gen 4 block. Look on the side of the block around the freeze plugs and see if there is an embossed Bow Tie symbol cast in the block. The fact that it has been identified as a Gen 4 block means the HP500 cylinder heads will not work on your block. You will likely be best off machining the existing heads or you could upgrade to aluminum heads and sell your existing parts. The bow tie emblem is simply a bonus, any four bolt main block will be fine for your purposes. Since the engine will be out of the boat I would inspect #1 and 2 rod bearing and number 1 main bearing for some insight of the rotating assembly condition. With those hours re-ringing the engine will probably not gain you much, the cylinders are likely egg shaped from wear. You could replace the bearings if the crankshaft surface and existing bearings look fairly good. Definately replacve the oil pump and weld the pick-up.
03-18-2011, 11:35 PM
#23
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502 rebuild
Hello, First I would like to say you guys have helped out so much on this site. I have learn so much from reading the post on here. My question are this. I picked up a 1992 Baja 260 last year this time. It is powered by a 1992 Gen IV 502 Mag carb with 670 hours on it with out any overhaul done on it. The boat is in great shape. Looks like it just came off the show room floor. I picked up the boat at a Baja dealer in my area. I spent 14000.00 on it. The motor seems to me to run strong. I burned about a 1 QT of oil in 14 hours of running it this summer. I started looking into rebuilding it because of the hours it has. I had allot of guys telling me to just leave it alone because it sounds and runs great. I do about 55 mph with a B3 and a rev4 21p prop at about 4600 rpm. I don't really hold it there long because of the age and hours. I took it to a marina close to my home to have a compression and leak down test just to see how healthy the motor is just the other day. Well the number don't look good.
HOT MOTOR TEST
#8 140
#6 90
#4 110
#2 125
#7 130
#5 140
#3 110
#1 150
leak down test showed #6 60-75% leakage and #1 10% leakage. leaking from intake.
COSTS
Rebuild cost from a very good Marine engine builder cost is 6000.00 2 year warranty.
A new Gen VI 502 mag 7200.00 1 year warranty.
or just do a Valve train for 2000.00
Question is what should I do? I love the boat it looks new. Really it shocks people when they see it. Oil PSI is good. I have had some tell me not to just do valve train and some say it is okay to just do the top. I have some tell me the Gen IV motor is much better then the newer Gen VI motors. Thanks for all the help.
HOT MOTOR TEST
#8 140
#6 90
#4 110
#2 125
#7 130
#5 140
#3 110
#1 150
leak down test showed #6 60-75% leakage and #1 10% leakage. leaking from intake.
COSTS
Rebuild cost from a very good Marine engine builder cost is 6000.00 2 year warranty.
A new Gen VI 502 mag 7200.00 1 year warranty.
or just do a Valve train for 2000.00
Question is what should I do? I love the boat it looks new. Really it shocks people when they see it. Oil PSI is good. I have had some tell me not to just do valve train and some say it is okay to just do the top. I have some tell me the Gen IV motor is much better then the newer Gen VI motors. Thanks for all the help.
