Mixing elbow leads to manifold problems

[garylinger]

I was finally able to take the old mixing elbow assembly apart and put the new and old parts back together, with a lot of sweat and creative thinking. When I attached it to the exhaust manifold one of the 4 bolts broke in the manifold. After trying to drill to use an ex out I decided my luck would ruin the manifold so I took it off and took it to a machine shop. Voila! - it is now ready to put back on (when the new gaskets are delivered). Upon looking at the other bolts, they were ready to break also. The machinest noted their condition and was perplexed until I told him the ground wire was attached to the manifold stud closest to the elbow flange. He thinks the electric current was causing the bolts to deteriorate where the copper gasket was in contact with the bolts. Has anyone else experienced this type of problem? Where should the ground attach (this is a Yanmar 2QM15)? Can any other 2QM15 owners tell me where their ground wires attach? This is the heavy duty battery ground.

 

[BobM]

Hi Gary...I'm going to the boat Wednesday and will have a look. I REALLY hope your boat proves the exception.

 

[Steve Dion]

Gary:

While it is not a cure all, you should be sure that you use "never-sieze" on the threads. I cannot imagine that this will take care of your problem for the next 20 years it is a prudent thing to do.

 

[kloudie1]

On my 3 GMF, the big ground is on a lug on the clutch/flywheel housing.. I think I'd move your ground to something like a motor mount bolt ..?? where the motor mount bolts to the engine block. and yes, anti-sieze on all of the new bolts threads going in..

 

[BobM]

I checked and the ground wasn't attached to the manifold. I didn't figure out exactly where it was attached. I'd definitely move it closer to the transmission, as the grounding is actually occuring through the drive shaft into the water. Therefore the closer the ground connection is to the shaft, the better.

Another point...if you have one of those rubber disks to reduce vibration in your drive train, make sure that it has a means of ensuring that it isn't isolating your ground from the shaft....that would be BIG trouble.

By the way...the cap on the end of my manifold and the bolts are looking pretty rusty...but the exhaust elbow looks fairly new. I'll have to hit them with PB blaster in preparation for future removal. I kind of planned to replace the elbow at some point, just so I'd know that it isn't a problem, or at least clean it out. I hope you took some photos to help a brother out!

 

[garylinger]

I didn't take any photos (the sketches from the service manual and the parts manual pretty much tell the story - it is simple but takes MUSCLE). You confused me about the ground - does the ground (negative cable from the batteries) need to be in electrical contact with the prop shaft???

If/when you decide to do it I will give you as much advice as I can.

 

[Paul F]

Ground Attachment

On my 2QM15 the battery ground and other grounds are off a bolt on the block near the transmission housing. I am not at the boat but I believe it is the bolt shown in red on the diagram below. It is either this bolt or the one next to it.

 

[BobM]

Thanks Gary. I'll take you up on that.

Sorry for confusing you. It is my understanding that, unless a boat specifically has a grounding bar mounted to the hull, for lightning protection or for a SSB radio, then the ground is essentially down the shaft to the water. Therefore, the closer the ground is to the shaft, the better, as less of a potential will exist across other engine components. Perhaps the manifold was chosen because it contains raw water, again something that will ground the boat and potentially more efficiently than through the drive train. However, from the sounds of things a lot of damage was done by the current. Here is some info on corrosion. By the way...did you check your engine zincs?

http://www.boatus.com/boattech/MarineCorrosion.htm

 

[garylinger]

That was a very good article on corrosion and electrolysis. I have a good basic understanding of 'electricity' but I guess what I am confused about is the difference between grounding of the d.c. (battery) circuit and the bonding of other non-electric metallic portions of the boat. My d.c. circuit ground was/is the manifold stud. I will by looking to move it to another location.

As for my engine zincs, I replaced both of them during the winter. The old ones were very deteriorated and crumbled when I removed them.

 

[filthy liberal scum]

re ground strap

mine is attached to one of the bolts that attach the bell housing to the engine block. definitely use anti seize on the manifold bolts. be very careful not to damage the exhaust manifold, or your engine will be a candidate for a mooring anchor. YANMAR NO LONGER MAKES THIS PART, SO THE ONLY OTHER OPTIONS WOULD BE TO FIND ANOTHER ENGINE THAT HAS ONE OR HAVE ONE CUSTOM MADE !!!!!!!