compression on BBC
 

just had the compression checked on my motors.
1979 454 400hp 980 hrs never had any internal work done
what should the normal comp. be for these motors?
here are the results.

port motor stbd motor
#1- 190 #1- 140
#2- 150 #2- 125
#3- 130 #3- 130
#4- 125 #4- 150
#5- 135 #5- 130
#6- 50 #6- 110
#7- 150 #7- 125
#8- 185 #8- 140

Brad

Re: compression on BBC
 

I beleive it should be around 150 normally. Looks like you have a few that are way off. Looks like time to rebuild.

Re: compression on BBC
 

never seen a 190 or a 50, but that can't be good. stbd motor not that bad, but it's also ready for a rebuild. (you can't complain about the cost if you've run a motor 25 years without going inside!)

Re: compression on BBC
 

the weird thing is that the boat still runs okay. still spins the same rpm as it always has, runs fine with no missing. but the port motor is much quieter than the stbd one

cant complain though they have had a good life

Re: compression on BBC
 

I agree with ichornet, the top two readings seem to be out of line. If your boat is running fine, don't worry about it. 980 hours is time for a rebuild. Question is whether you run till something breaks or rebuild now.

Re: compression on BBC
 

My port engine (1996 454) had the following results (600hrs running time):

2. 142
4. 110
6. 130
8. 140

1. 132
3. 140
5. 118
7. 142

I'm doing a valve job this spring to bring cyls 4 & 5 back up. I had a noticable rpm drop last season, though the engine ran well otherwise.
I've heard the stock 454 lower end, with good maintenance, will go 1500+ hrs without problems, but its normal to expect a valve job (or 2) along the way. Sitting in storage 6+ months a year is tough on valves, seats, etc. Good luck!

Re: compression on BBC
 

the exhaust is much quieter than the stbd motor. engine noises still the same . checked the compression on the port cylinders twice.
I was just thinking about this, last year I blew the port trs outdrive. I was running about 4800rpm and launched off another boats wake and noticed the outdrive after I slowed down. I also noticed the motor being much quieter after that
I wonder if I free reved the motor (never hit rev limiter though, set at 5200 rpm) and bent a valve or push rod or a few of them? I think I am still going to pull them out though and at least go through the heads. if it doesnt need anything else

Re: compression on BBC
 

That chould be why you have the 190 psi in one cylinder. I'd pull the lower end apart too.

Re: compression on BBC
 

Not sure in your case, but more exhaust noise on one motor means less water in exhaust, like corroded exhaust or damaged impeller

Re: compression on BBC
 

high vompression numbers like 190 are often cuased by water in the clyinder :( whatever the case is though with a clyinder at 50 it needs to come apart.