454 compression test question
 

The question is for a 38 foot Bertram motor yacht I put a deposit on.... its no performance boat but would like opinion from the engine gurus.

The boat was repowered in 1997 and the 454 330hp mercruisers have roughly 900 hours on them.

The boat is in heated indoor storage so the compression test was done on cold motor.

All cylinders are 125psi except cylinders #5 and #6 which are 95psi.....both port and starboard motors have identical readings.... all 125 except the #5 and #6 cylinders. The motors do sit on a slight angle due to them being inboard and straight shaft drives. Are the 5 and 6 cylinders the richest running ones resulting in more rings wash from more gas? The boat is pending a sea trial and the owners says boat runs great. The owner is a friend the family so he is credible.

Would like opinions.

just my guess, but i would think they would compress closer to 145-150.
so all 125 is simply because they are not new obviously, the other 2 lower, either less new, or a bit tired, but might also be just ''carbonized''. maybe a magic cleaner in bottle could help, might be too dirty on a valve to close properly... Should do a leak down test to see where the leak goes, or add some oil in cylinder to see if the ring would seal more. if so, ring is the problem, if not, ... head gasket? valve? or...

might work like that for years cruising around a slow speed !

At 900 hrs, their in need of work even if they run fine, as been said, all the compression is down but two are worse than the others.

I would try another compression gauge first to make sure it isn't a gauge issue. I had a gauge that would read a good 20 psi less than others. Damn Matco junk.

Wish I had that kind of luck. There is something to be said though about those 454/330's. regardless time for a rebuild. probably running on borrowed time. Does seem rather odd both engines are exactly the same. Your not having problems getting the compression tester in all the way on those those cyl are you?

As mentioned above leak down would help but I seriously think it's time to pull em.

150 pds is normal I believe.

before you get all worked up and pulling stuff apart ,Why don't you service motors and run the boat..JMO
Went back and saw it was subject to sea trail ..Although 900 hours is a pretty good bit as has been said ,if you just cruise they could go for years

I was just in ft Meyers on a pairasail boat. The motor had a 454 bravo 3. It lasted 3000 hours.

did you have the throttle wide open? if not you will get a bit lower numbers

Budget for a repower, but you have two engines, so run it until one breaks. You might get ten years of free money, lol. At least you know they run. No guarantee with new motors.

I was going to post same thing.