Yanmar exhaust problem - weak bolt holes

[Tacomasailor]

Yanmar 4JH2E exhaust problem on a sailboat but I figured you guys would know way more about diesel engine techy stuff.

Our Yanmar 4JH2E is 20-years old and has 2,900 hours on it. The engine has worked flawlessly except for needing a coolant pump. We have owned the boat and engine since new.

I replaced the heat exchanger bundle as a warranty item in 1997 because Yanmar assembled a bunch of them incorrectly. No other work has been done on the exhaust system.

Last week we noticed a minor exhaust leak was putting exhaust in the engine room and later in the main cabin. Went back to the dock.

We then could see that there was a ¼” gap on one corner of the mating surface between the heat exchanger and the mixing elbow. Exhaust was leaking out of three of the four sides.

With more close examination, after removing three raw water hoses that blocked the view, we discovered that the bolts holding the mixing elbow / heat exchanger together had serious problems.

- One bolt was completely missing
- One bolt was backed out ½ way
- One bolt was finger loose
- One bolt was still locked tight at 40 foot pounds

The Yanmar Factory Rebuild Manual (purchased in 1995) and the online Yanmar parts manual show that there should be four studs threaded into the heat exchanger. There should then be NUTS holding the mixing elbow flange to the flat face on the heater exchanger exhaust outlet.

Our engine had four (actually three because one is missing and I can not find in in the pan under the engine) BOLTS, which were very damaged. The 12mm head on one bolt was rusted and almost round. The other two bolt heads were clean and clearly marked with a number 7 but no other grade or class markings. The threads on all three bolts were almost completely filled with “material” and my thread cleaners and gauges were of no use picking the material out of the threads.

I was able to thread a new 8mm .125 pitch nut onto one bolt and it did clean some of the threads but the material was in effect, welded to the threads.

The local Yanmar dealer sold me four new 8mmx20mm bolts that were marked 8.8 and JH. They had a 13mm head rather than the 12mm on the original.

I have to lie on top of the Yanmar and look over the back of the engine to see and work on the bolt holes. There is not quite enough room for me to get two really good hands onto the bolts and holes.

I tried to thread the new bolts into the old holes but they did not turn easily and seemed likely to cross thread. I carefully cleaned the holes with a new 8mm .125 tap. I have tapped a lot of holes and have a pretty good feel for the work.

The tap took a lot of in-and-out work and gentle encouragement but eventually I was able to get a clean hole down to 35mm depth. The new bolts threaded in neatly and smoothly and spun down to the bottom as they would in a new hole.

When I mounted the mixing elbow to the heat exchanger I was able to easily turn all four bolts down to where they begin to compress the split washer. Two of the bolts, (the one that was missing the bolt and the one that was backed ½ way out), turned down tightly and “bit” as I would expect.

The bottom two bolts turned down with a socket to about 5 foot pounds but then just slowly turn, as if in thick mush, and never really bite or take a set. The lowest setting on my torque wrench is 10 foot-pounds and neither bolt will make the wrench break or click.

I repeated the process with a 30 mm and 35 mm bolt to see if I could get the bolts into deeper and better material. The longer bolts will not set either.

I believe the heat exchanger is aluminum but am not sure.

There is plenty of material around the two weak holes to drill a bigger hole and use a threaded insert of some kind (Full-Torque or timeset ?) but I am not sure if that is the right thing to do. My big concern is that I have no way to ensure I drill a perfectly straight hold for the insert.

I cannot find anything about the torque that should be applied to good new bolts. The one bolt that was still set when I removed the originals was about 40-foot pounds.

There is no load on the flange – just the exhaust pressure and the heating/cooling due to the exhaust gas.

I know the right thing to do is remove the heat exchanger and take the heat exchanger to a machine shop and have them put in slightly larger holes and threads.

Are there any easier or less drastic possible solutions?

With no real shear or pull on the bolts would epoxy work?

 

[RT Firefly]

Greetings,
Mr. T. Quite a conundrum to be sure. My only comment would be that the area the bolts thread into may be too hot for epoxy. I quickly searched for and found this stuff BUT it notes it's only good up to 400F. THAT is my concern.
HighHeat | Temperature Resistant Epoxy Putty

 

[BryanF]

I would take it off. Have it drilled out and inserts put in. If I was miles off shore or at the corner of no and where epoxy would be worth a try to get me home. My thoughts.
YMMV and all that. And it could well get too hot for epoxy as RTF pointed out.

 

[RT Firefly]

Greetings,
Mr. T. did some more searching and... High Temperature Adhesives and Epoxies, Ceramics, Insulation, Epoxies and Epoxy
Mentions some products good for 4000F. Now, whether or not any of them would work for your particular application is an entirely different matter.
I'm tending to concur with Mr. BF. Fix it right the first time. The stuff I linked may be good for a quick fix but it will be a band-aid at best.

 

[CPseudonym]

4 flute core drill bits are great for opening up holes and follow the existing hole well. If you can get a drill into the area to work, it and a quality tap will allow you to DIY(if you have the confidence to try it). We all have different confidence levels and I'm not there to see your conditions, sailboats are notoriously tight.

Otherwise I would either remove it and DIY or at that point just take it to a local machinist and let him do it. Below is an example of what a 4 flute core drill looks like.

http://www.amazon.com/gp/aw/d/B000LEDX4K?pc_redir=1414062593&robot_redir=1

 

[LarryM]

Tacomasailor,

I have made that exact repair on a Yanmar before and I think your best option is to remove the heat exchanger and have Keenserts, Timeserts or Helicoils professionally installed.

A standard M8 x 1.25 Class 8.8 fastener has a dry torque specification of 25.4 ft/lb per ISO 898. Threading into aluminum requires that you reduce that to about 75%. It sounds like the failure was due to the use of bolts instead of the studs and nuts originally installed by Yanmar.

If it were mine, I would have my local machine shop install their preferred inserts, the ones they have the tools and expertise to work with. While they are at it, have them check the flange mating surface on the HE to make sure it is flat and true. Then, I would use the factory Yanmar studs, nuts and washers. Install the studs with a good thread locker and be sure to use a new stamped steel exhaust gasket. Finally torque the nuts to about 20 ft/lb and you should be good to go for the life of the engine, or at least the HE.

If you try a lesser repair, you risk recurring leakage and HE damage. The exhaust is really hot at the flange before it is cooled in the mixing elbow, and there is a lot of expansion and contraction in the joint.

Finally, that HE is EXPEN$$$$IVE so a proper repair will save you money in the long run.

Best of luck. . .

 

[Shoalwaters]

Larry is spot on: Helicoils and studs, not bolts. Any lesser fix will niggle at you abd spoil every trip you make.

 

[healhustler]

I concur with Larry. I've got an HE also, and fudging the exhaust arrangement with anything but a standard Yanmar level fix would be nothing but worry….always on the mind. This is a doubt you don't need to have. I feel your pain.

 

[Tacomasailor]

A simple solution

I want to thank all of you who replied and helped me understand that I had to do the right thing. And that right thing turned out to be quite easy!

After hearing from all the knowledgeable folks here - I decided to remove the heat exchanger ( HE ) and do a proper repair job.

It took less than 90-minutes to remove the alternator, all the raw water hoses, and mounting bolts or studs. Then discovered that the heat exchanger was too wide to slide off the two studs because it hit the port side of the engine room. It actually hit the two 00 cables that run from the battery switch to the starter and Link 2000 resistor that measures current. I removed the cables and was then able to remove the HE.

Took it to the dock and cleaned it and then tried to remove the bolts that hold the caps on the exchanger bundle. One of the bolts came loose easily the other not so easy. I used Liquid Wrench and a good impact wrench but no luck.

About then Chris, my professional boat mechanic and bicycle buddy, wandered by to talk and have a beer. He had just finished working on a similar HE and said we should take it to his shop.

Propane torch to loosen the stuck bolt
Drilled out the four holes with a 8.5mm (21/64) drill
Tapped new 10mm .150 threads
Put in 10mm studs that reduce to 8 mm 0.125 on the the outside (automotive exhaust studs)
Mounted mixing elbow on studs and tightened the 8mm bolts

Now the remaining problems:
- heat exchanger bundle is corroded into the exchanger housing (Chris says muriatic acid will free it up)
- HE housing around the forward bundle where the O-ring seats into a groove in the housing is badly corroded away. So much material is missing that the O-ring was protruding from the side of the cap (Chris knows a welder that builds up these exchangers all the time)
- need to bead or abrasive blast the HE and repaint it because the paint is blistered and bubbling all over
- Starter and solenoid are a rusty mess (Chris says a shop on Shelter Island sells re-built Yanmar starters for $136 + my old one)
- port lower section of Yanmar block is a rusty mess and I am not sure what to do
- need to replace three more raw water hoses and a 25" long raw water copper tube
- alternator is also a little corroded and it may need some attention

The good news is that the interior of the heat exchanger was almost perfect (except at the flange where there was some erosion) and the mixing elbow was very clean and free of any deposits. The mixing elbow and HE mating faces were clean and true.

Maybe another week will find the Yanmar running again

ONE last question - we used automotive exhaust studs - will they be a problem in dealing with the diesel exhaust heat?

 

[LarryM]

I want to thank all of you who replied and helped me understand that I had to do the right thing. And that right thing turned out to be quite easy!

ONE last question - we used automotive exhaust studs - will they be a problem in dealing with the diesel exhaust heat?

Those will be perfect! Sounds like you have saved the HE and it will now be completely functional.

As for the rust, I have used POR-15 on marine engines in the past. It works well and I'm pretty sure the factory Yanmar spray engine paint could be applied as a top coat after using the system for the first coat(s). You might give them a call.

It is important to keep an eye on the end caps, exhaust flanges and fittings in the cooling system. At the first signs of any seepage, repair immediately and you will likely find a simple and inexpensive repair. If you ignore it very long, you can find some nasty $urpri$e$ waiting for you!

 

[Tacomasailor]

"As for the rust, I have used POR-15 on marine engines in the past."

I've also used POR-15 on several marine projects and after five or six years am very happy and somewhat astounded how well it stopped the corrosion and has painted the beautiful paint finish I put over it.

My HE did not look quite that bad