pj_florida
New Member
I'm looking at buying 1996 Sundancer w/Bravo II, 7.4L. Boat has 854 hrs. Had a comression test that showed 105-110 PSI each. Is that good or should I be concerned? Thanks!
Help! Is the compression good?
- Thread starter pj_florida
- Start date
Well merc says above 100psi and each cylinder whithin 10% of each other is good...so I say yes if it runs strong. Would like to see it a bit higher. My '92 454 with 765hrs is 125 to 135psi. Did you test it warm with all plugs pulled and throttle plate held open?
I agree - I'd like to se the numbers higher. But, as Quint mentioned, at least they are all similar.
When was the last time the engine was run - or how long was it run before doing the compression?
When was the last time the engine was run - or how long was it run before doing the compression?
- Nov 12, 2006
- 5,334
- Boat Info
- 1999 Sea Ray 330DA
Twin 7.4 MPI (310 propshaft HP) V-drives
- Engines
- Twin Mercury Marine marinized 7.4L L-29 V8s
Cast iron block w 4-bolt mains
Was that with a warm engine or a cold one? Was the throttle at WOT? Did they pull all the plugs then test? Did they turn the engine multiple times to get the peak reading or just one compression stroke?
My 7.4s have compression in the 180 to 185 range, so while 100 is OK, it's barely OK. Boat better be pretty darned inexpensive because I would doubt that engine has much more life left in it.
Best regards,
Frank
My 7.4s have compression in the 180 to 185 range, so while 100 is OK, it's barely OK. Boat better be pretty darned inexpensive because I would doubt that engine has much more life left in it.
Best regards,
Frank
AKBASSKING
Active Member
- Apr 13, 2008
- 4,649
- Boat Info
- 1988 Yacht Fisher
- Engines
- Twin 375hp Cat 3208 T/A
Warm engine, all plugs pulled, throttle wired WO. I am assuming this is what was done, but this is only HALF of a compression test (dry).
Then you need to go back, squirt a little oil in each spark plug hole, (right before screwing the compression gage in the hole) and redo the entire test.
This will tell you if you have any piston ring issues. If the compression jumps significantly, then you may have a problem.
Then you need to go back, squirt a little oil in each spark plug hole, (right before screwing the compression gage in the hole) and redo the entire test.
This will tell you if you have any piston ring issues. If the compression jumps significantly, then you may have a problem.
The W.A.V.E.
New Member
I agree with Fc3. My engines range from 165 to 170 and even though 100 is acceptable, it wouldnt be acceptable to me. 850 hours isnt too many hours unless they have 850 hours with very little maintenance. You may never know for sure so look for the signs of early fatigue in the engines and judge for yourself.
Good Luck
Good Luck
