Hey Guys, I am thinking about trading up to a 42' with twin HP 500 Carb Mercs with 400 hours (1996 - $100k+). I had a cylinder leakdown test performed today and the results showed some significant differences from Cylinder to Cylinder. The boat has sat idle with limited use for 12 Mos. Sea trial 2 weeks ago 1 hour not exceeding 4000 RPMs seemed to perform well during that period. Here are the results :

Starboard
#1: 10% | #2: 10%
#3: 25% | #4: 16%
#5: 20% | #6: 16%
#7: 8% | #8: 13%

Port
#1: 8% | #2: 8%
#3: 24% | #4: 20%
#5: 30% | #6: 30%
#7: 20% | #8: 18%

The dealer is giving me a positive spin on the results but I am a bit hesitant with such high numbers, even with the boat being idle. Any advice on how I should interpret these numbers? Thanks for your help. Take care.

Was the engines warmed up before they did the leak down?

Yes, they were run for about 15 minutes in warm weather.

Those numbers are high. I would be concerned. While the air was in the cylinder, did you try to take notice of where the sound of air leakage was coming from? Sometimes you can tell if the air leak is in the intake, exhuast or crank case.

Probably needs a valve job and head gaskets. The numbers are high, but probably not out of line with the amount the amount of hours.

An HP500 with 400 hrs. needs a valve job. It will probably run fine with no noticable power loss for many more hours though. My experience has shown that the valve seats tend to go away after 200-300 hours on the 502's. Then it's just a gradual deterioration after that until it gets bad enough that you notice something's wrong. Of course if there's any kind of water reversion going on the situation is worse.

I disagree. For a 400 hour engine, those are good numbers. My 500 hour engine had 60% from a burn valve (the other cylinders varied between 20 and 40%) and the boat had only slowed by 4mph.

One I have learned that the leakdown test is almost too good. It illustrates problems that really don't exist. Those motors will proably continue to run good for another 100 hours at which they will start to lose power. This shouldn't be a suprise to you though. After all, you are buying a used boat because it's price is attractive.

I try to shoot for under 10 on a new rebuild. Its not easy, takes careful work on the valve seats. I would go the extra step and listen for where its leaking and then oil the cylinders and redo. I figure valve job too, probably needs it. Oh, and springs.

cord,
You are right. Those would be normal #'s for a 400 hour motor. I just ment that those numbers are higher than you want. It indicates something is worn out. As it would be with that amount of running hours.

for a 10 year old boat with 400 hr probobly most of them hard thats not that bad. I think that a 100 k is a little high for that boat in that cond even if a fountain