Devil_Inside
Petty Officer 3rd Class
- Joined
- Jun 17, 2007
- Messages
- 76
I have a 1995 Mercruiser 5.7 TBI/EFI with a Bravo 3 outdrive, approximately 800 hours on both. I am getting a slight vibration in the engine with the drive removed, usually around 1000RPM. With the drive installed, I get the same slight vibration in Neutral, around the same RPM. Once I put the drive in F or R, with the boat in the water, I get really bad vibration between 900RPM and 1200RPM. If I exceed 1300RPM everything smooths out.
The drive has had somewhat of a history of failing input shaft seals. The seal failed at the end of 2016 season and was replaced by a Merc dealer, along with the input shaft yolk.
The same seal failed again almost exactly a year later, at the end of the 2017 season, and it was once again replaced by a different Merc dealer. According the the second dealer, the first service was performed incorrectly and that's why the seal failed again. The same dealer also checked the engine alignment and prop shafts for run-out and end play - all within spec.
Furthermore, in the Spring, I decided to replace my power steering hoses because they were badly corroded. I filled the system with ATF and I followed the bleeding procedure (engine off, lock to lock 15-20 times). I thought all the air was out, but when I started the engine and turned the steering wheel quickly to port, the drive started shaking violently side to side. It did that a couple of times and I am worried that this may have damaged something, such as the rear motor mounts. I then repeated the bleeding procedure, but I am still not confident that all the air is completely out. All of this was done while the boat was still sitting on a trailer. Once I splashed it the steering seemed normal.
I removed the power steering belt in an attempt to eliminate the power steering system as a possible contributor to the problem, but that did not seem to make a difference.
Here are some additional troubleshooting steps I have taken:
- I did a compression test on all cylinders - two if them were a hair over 150, four were about 165, and two were almost at 175. Not sure why two of them were so high, but I don't think it is very concerning.
- I replaced all spark plugs with new NGK BR6FS gapped to .040. Five of the old plugs were nice chocolate brown, three were slightly more white, but not enough to cause a concern (I think)
- I replaced the distributor cap and rotor, which unfortunately turned into a huge job because one of the cap bolts broke off. I had to pull the distributor to drill the bolt out and I ended up re-setting the timing. I followed Merc's procedure - since I have a Delco distributor I had to do the paper clip trick to disable the spark advance to set the base timing to 8*BTDC. While I was there I also quadruple-checked the firing order.
- I used a borescope to inspect the rear motor mounts since they are impossible to see otherwise. The front mounts are solid, the rears have some movement, but I can't tell it is excessive or not. Keep in mind that once I am in that RPM range of 900 to 1200 (in gear), everything shakes so I can't tell if the mounts are causing the problem or doing their job. It is really, really hard to see.
I also tried to inspect the coupler, but in reality I couldn't see much at all; there's a lot of corrosion on it, but that's all I could see.
Next I am planning on hauling the boat out so that I can remove the drive once again and re-check the engine alignment. If one of the mounts is bad, I am hoping that the alignment will be off, but I suspect it will be fine once again.
I am really at a loss. It sounds like the engine needs to come out, but I was hoping to get some kind of definite answer before I tackle that job. I am almost tempted to run the thing as-is until it blows up since I don't want to waste half of my season, but that's not usually how I do things, and I am afraid that I might damage something else. It is hard to keep the engine out of that RPM range because I have a 30 minute ride to open water and the 900-1200RPM is more or less my "no wake" speed.
Do you have any thoughts or suggestions?
The drive has had somewhat of a history of failing input shaft seals. The seal failed at the end of 2016 season and was replaced by a Merc dealer, along with the input shaft yolk.
The same seal failed again almost exactly a year later, at the end of the 2017 season, and it was once again replaced by a different Merc dealer. According the the second dealer, the first service was performed incorrectly and that's why the seal failed again. The same dealer also checked the engine alignment and prop shafts for run-out and end play - all within spec.
Furthermore, in the Spring, I decided to replace my power steering hoses because they were badly corroded. I filled the system with ATF and I followed the bleeding procedure (engine off, lock to lock 15-20 times). I thought all the air was out, but when I started the engine and turned the steering wheel quickly to port, the drive started shaking violently side to side. It did that a couple of times and I am worried that this may have damaged something, such as the rear motor mounts. I then repeated the bleeding procedure, but I am still not confident that all the air is completely out. All of this was done while the boat was still sitting on a trailer. Once I splashed it the steering seemed normal.
I removed the power steering belt in an attempt to eliminate the power steering system as a possible contributor to the problem, but that did not seem to make a difference.
Here are some additional troubleshooting steps I have taken:
- I did a compression test on all cylinders - two if them were a hair over 150, four were about 165, and two were almost at 175. Not sure why two of them were so high, but I don't think it is very concerning.
- I replaced all spark plugs with new NGK BR6FS gapped to .040. Five of the old plugs were nice chocolate brown, three were slightly more white, but not enough to cause a concern (I think)
- I replaced the distributor cap and rotor, which unfortunately turned into a huge job because one of the cap bolts broke off. I had to pull the distributor to drill the bolt out and I ended up re-setting the timing. I followed Merc's procedure - since I have a Delco distributor I had to do the paper clip trick to disable the spark advance to set the base timing to 8*BTDC. While I was there I also quadruple-checked the firing order.
- I used a borescope to inspect the rear motor mounts since they are impossible to see otherwise. The front mounts are solid, the rears have some movement, but I can't tell it is excessive or not. Keep in mind that once I am in that RPM range of 900 to 1200 (in gear), everything shakes so I can't tell if the mounts are causing the problem or doing their job. It is really, really hard to see.
I also tried to inspect the coupler, but in reality I couldn't see much at all; there's a lot of corrosion on it, but that's all I could see.
Next I am planning on hauling the boat out so that I can remove the drive once again and re-check the engine alignment. If one of the mounts is bad, I am hoping that the alignment will be off, but I suspect it will be fine once again.
I am really at a loss. It sounds like the engine needs to come out, but I was hoping to get some kind of definite answer before I tackle that job. I am almost tempted to run the thing as-is until it blows up since I don't want to waste half of my season, but that's not usually how I do things, and I am afraid that I might damage something else. It is hard to keep the engine out of that RPM range because I have a 30 minute ride to open water and the 900-1200RPM is more or less my "no wake" speed.
Do you have any thoughts or suggestions?
