With all the nice weather we've been having I've gotten an early start on boat projects this year. All winter I've know that I faced a few more than normal projects this spring because by the end of last season the exhaust manifolds were leaking fumes and water fairly bad and making lots of extra noise, it was getting almost impossible to shift the 3 stage Kodiak jet into reverse without killing the motor and the main jet thrust bearing/seal was leaking.
So, so far I've pulled the drive shaft (this is motor forward boat), the exhaust manifolds, taken the jet apart and removed the main shaft, pulled up a big part of the floor boards and gotten the shift cable out to the boat. While I was at it I thought I might as well do the throttle cable, so I pulled it too.
With the exhaust manifolds removed the spark plugs are really easy to get at so I figured I might as well run a compression check. The motor was cold and hadn't been run since last year but I figured I would try it anyway. Using the standard cylinder numbering looking at the front of the motor, #1 is on the right, #2 is on the left, #3 is on the right, #4 is on the left, etc. With all the plugs out these were the readings.
#1 = 130, #2 = 87, #3 = 110, #4 = 112, #5 = 65, #6 = 112, #7 = 65 and #8 = 120
Oh, that seemed terrible, way to low and to much variability. This is a 1993, 454/7.4L Gen V 320 hp motor that should have something like 120 to 140 PSI from the factory. So I figured I would put a little oil in each cylinder and run the compression check again. This time it came up with this
#1 = 180, #2 = 120, #3 = 128, #4 = 140, #5 = 120, #6 = 135, #7 = 127 and #8 = 140
Really wild numbers, so what is going on I wonder. So I do some more research, talk to my son-in-law who is a pro diesel mechanic and gas guy and decided I have to warm up the engine some, then open the throttle all the way and run another compression check with all the spark plugs out.
So I got the fire extinguisher out and my ear protection and hit the key. I have to say the firing up that engine with no exhaust manifolds and fresh oil in the cylinders was pretty exciting, especially with the gas tanks on either side of the engine, smoke and flame and lots of noise. It fired right up like it usually does and, once the smoke cleared, settled down and run out smooth. There was still a lot more flame coming out of the exhaust than I expected, especially #3 and #5 and #4 and #6, the middle cylinders on each side.
Anyway, I let it run for about 6 or 7 minutes, shut it down, pulled the spark plugs and ran another compression check and got these numbers.
#1 = 125, #2 = 130, #3 = 118, #4 = 122, #5 = 95, #6 = 115, #7 = 110 and #8 = 120
I actually ran at least two checks on each cylinder and cranked it long enough that the needle quite moving completely so I think these are pretty accurate numbers, but they are still kinda low and more variable than I would like to see.
... I know, this is getting long but if I don't include all the info I'll just have to put it all in later.
Over the last couple of years I've noticed a slight drop in RPM on the engine at WOT. When I first got the boat it would run to 4200 RPM with no trouble, but lately its been only hitting 4100. 100 RPM don't seem like much but speed wise that is 3 or 4 mph on the top end. On top of that the impellers have been getting looser with 826 hours and no rebuild so I would have expected the engine RPM to actually have gone up a little, not down.
So now I don't know what to do. I hate to have to think about re-powering this spring. I was planning on spending a couple thousand on the boat not $10,000.... or more.
Just thinking, a few years back the engine started backfiring pretty bad through the carb under heavy load. At the time I found what seemed to be some bad spark plug wires, so I replaced the wires, put in new spark plugs, a rotor cap and rotor. The problem kinda went away and it certainly ran better, but I could still hear a slight popping through the carb when I took off at WOT. I finally called a mobile marine mechanic here in the valley and as soon he heard it he said that I had some bent push rods and intake valves that weren't closing all the way. He also said that this was something he had run into a lot on this type of 454 and was caused by backfiring. Hey, I was willing to try anything and sure enough, he pulled that valve covers and popped some of the push rods out and they were bent, they wouldn't roll on a flat surface. I think we replaced 4 total and I've probable put 400 hours on the boat since then.
Maybe I'll check the push rods again. Any other suggestions? Did I include enough info? Questions? I could sure use some help.
Those 300 hp FMJ diesels are sure nice but can a guy ever save enough fuel to pay back a $25,000 engine upgrade or is there anyway to even justify c-bolts LS2?