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Old 12-01-2022, 06:24 PM   #1
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Post DIY rebuilding of diesel engine Yanmar 6LY

By popular request (whooping 2! people expressed some interest) I will document the rebuild process of my Yanmar 6LYA-STP engine for my own records and in case it will help someone in a similar situation.

After many hours of deep research (thanks, YouTube) i learned some tips and tricks to make this rebuild successful and enjoyable.

Disclaimer: I'm not a professional mechanic, and this is my first rebuild, so use this information at your own risk.
A professional mechanic will suggest you send the engine for rebuild to a good machine shop. It will take months and cost you more than a good used engine, but mechanics have to eat too.

Quotes I was getting for a rebuild started from $25k which is around the cost of a used engine like that. And there are not that many used 6LYA engines available (pretty much 0 at this time). And, a "lightly-used" engine is a very loose definition and you can end up with having to do 2 rebuilds.

Why this rebuild was started:

The engine was seized when i got this boat (2002 Mainship 430). It could not be rotated or slightly moved by a 3' breaker bar on the crankshaft nut. Applying more force would probably break something.

To get this over with, someone will probably ask, "why on earth did I buy a boat with a seized engine?"
- i was bored. as simple as that

From what I found so far, the water got into the cylinders from the poorly designed exhaust via turbo and air inlets (see photos). The engine was left with the water inside for a long time, so the pistons and valves rusted to the block.

Removing the injectors (and later removing the head) and soaking the cylinders with Mystery oil for 3 months did not free them up.

After taking the engine apart to the bare block, I did not find any damage to the pistons or rods, so it looks like the engine was not started with the water inside, which would cause it to hydrolock and do some physical damage.

any questions - ask
any comments - post

if you notice I'm doing something wrong, let me know - i appreciate all the help and would not be able to do this without you.

Until the next post ...
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PXL_20220927_130937987.jpg   PXL_20220927_130621685.jpg   PXL_20220925_232726453.jpg   PXL_20220925_230119185.jpg   PXL_20220903_113524749.jpg  

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Old 12-01-2022, 06:53 PM   #2
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Ok, have you removed the block from your boat?
I would do more than just use a drill motor and a hone to remove the rust.
Does that engine have removable liners? Did the crank and cam sit in water?
A competent machine shop is your friend in this situation.

The head and block can be made as good as new so avoid shortcuts.
The turbo internals may be toast but the housing may be reusable.

Have the rods measured professionally to be sure they're not bent.
Hydrolocking can compress them almost invisibly.

The pistons may be reusable if the block/liner doesn't need boring.
The injectors obviously will need rebuilding.
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Old 12-01-2022, 06:59 PM   #3
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Post Documentation used

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Old 12-01-2022, 07:16 PM   #4
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Originally Posted by KnotYet View Post
Ok, have you removed the block from your boat?
I would do more than just use a drill motor and a hone to remove the rust.
Does that engine have removable liners? Did the crank and cam sit in water?
This engine has sleeves/liners. I already got old ones out. After i clean them up some more and see if the damage is more than the surface rust i may be replacing them with new sleeves.

Shafts were not sitting in water and seem ok with some surface rust only on crankshaft and no damage or any wear on the bearings. i did not fully clean and measure them yet. this is still an outgoing project.

Quote:
Originally Posted by KnotYet View Post
A competent machine shop is your friend in this situation.
the few shops with good reviews I called so far are not interested in doing small work and want to do a full rebuild only with a very long lead time. i did not call the shops with bad reviews. I asked Yanmar tech support for recommendations, they sent me to a local rep here in Ontario, Canada who said he can suggest only the shops who does a full rebuild
i'll keep looking but i may be on my own here.
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Old 12-01-2022, 07:37 PM   #5
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Fortunately this is not rocket science. I hope you can find a 1- or 2- man
shop that will measure those rods and advise you along the way. I've been
spoiled by living in an area that is well supplied with competent machine shops.

You're going to need to clean up and hot tank the head and get the valves
done. You'll need a shop for that anyway.

I would price a set of replacement liners. Any visible pitting is too much.
Don't assume you can use new rings right out of the box. They must be fitted.
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Old 12-01-2022, 07:37 PM   #6
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For rust on iron parts, investigate Evaporust. It does a remarkable job of removing rust without harming anything else. The only safety warning it has is don't let your your kid fall in the bucket and drown. You can apparently drink it, wash your eyes out with it, or remove rust with it. The only thing I've found to be careful of is make sure you fully immerse a part. If it sits partly in for awhile, it will develop a waterline at the top of liquid.
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Old 12-01-2022, 07:46 PM   #7
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What is the expected budget?
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Old 12-01-2022, 08:23 PM   #8
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A decent machine shop should be able to inspect the head for you, you may luck out a bit on the head based on it's height relative to the water ingress. I would have the crank inspected, replace the liners myself and proceed based on the crank condition.
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Old 12-01-2022, 08:51 PM   #9
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As an owner of two of these engines, I will be watching your progress. Good luck!
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Old 12-01-2022, 08:58 PM   #10
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Quote:
Originally Posted by KnotYet View Post
Fortunately this is not rocket science. I hope you can find a 1- or 2- man
shop that will measure those rods and advise you along the way. I've been
spoiled by living in an area that is well supplied with competent machine shops.

You're going to need to clean up and hot tank the head and get the valves
done. You'll need a shop for that anyway.

I would price a set of replacement liners. Any visible pitting is too much.
Don't assume you can use new rings right out of the box. They must be fitted.
Can you elaborate what you mean by the rings must be fitted?
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Old 12-01-2022, 09:25 PM   #11
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I assume there are oversized pistons available? If so, just get the liners bored oversized once you get the new pistons by a good machine shop. Send the head along too and have them service the valves. Check all bearings with Plastigage and if worn, replace after having the crank inspected, otherwise reuse the original bearings. Be meticulously clean and put it all back together with a new turbo and redo the exhaust routing.
This isn't rocket science.
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Old 12-01-2022, 09:26 PM   #12
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I think he means the rings gap must be measured and adjusted to fit
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Old 12-01-2022, 09:33 PM   #13
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Quote:
Originally Posted by DDW View Post
For rust on iron parts, investigate Evaporust.
good old Evaporust I'm on the 3rd gallon of it now.
i use it in my new shiny ultrasound cleaner to "super clean" everything i take off the engine. great thing.

i start with 20 min of ultrasound cleaning with 1 to 3 parts of simple green and distilled water and after that 20 min in Evaporust both at 40C temperature.
so far, all the parts come out looking like new without any physical cleaning. I'll post some photos when i get to this part.
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Old 12-01-2022, 09:37 PM   #14
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Quote:
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Can you elaborate what you mean by the rings must be fitted?
Referring to new replacement rings, there is a specification for the end gap,
i.e, the gap when the ring is fitted perpendicular to the bore. New rings will
often be supplied a few thousandths long to accommodate variation in bore diameter.

lwarden: 'I assume there are oversized pistons available? If so, just get the liners bored oversized once you get the new pistons by a good machine shop.'
Waterant may be able to re-use his pistons if they are in decent shape.
I would go whichever way has the fewest headaches and least cost.
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Old 12-01-2022, 09:47 PM   #15
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Quote:
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What is the expected budget?
So far, I have spent around $1k on building the gantry crane in the boat saloon to raise the engine, reinforce the floors, build a platform to move the engine to the deck, and rent a trailer for a week to get it home.
This expense I would have even if I used a shop for a full rebuild.

$1.5k on the engine shop craine, so i can take it on and off the trailer and move heavy things around in the garage, engine stand so i can rotate it to work on it, 20L ultrasound cleaner, and some tools i did not have.

I'm getting quotes from part suppliers for the parts I will be replacing. So far, it looks like the total for parts will be around $4000, which includes all the gaskets, new bearings, new liners ($1200), rings, a new V-pulley, which i butchered while trying to remove from the shaft, a new starter, and a rebuild kit for the turbo, and shipping this all from Japan.
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Old 12-01-2022, 09:51 PM   #16
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I assume there are oversized pistons available? If so, just get the liners bored oversized once you get the new pistons by a good machine shop. Send the head along too and have them service the valves. Check all bearings with Plastigage and if worn, replace after having the crank inspected, otherwise reuse the original bearings. Be meticulously clean and put it all back together with a new turbo and redo the exhaust routing.
This isn't rocket science.
Right. Easy peasy.
The engine had only 280 hours so there is no wear, just rust damage.
The pistons are in "like new" condition after cleaning and i plan to keep them and replace the liners and rings. seems to be an easier and probably less expensive way to go considering i did not find any shops around i would trust with boring the existing liners and trying to find larger pistons that will fit properly.
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Old 12-01-2022, 09:59 PM   #17
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A decent machine shop should be able to inspect the head for you, you may luck out a bit on the head based on it's height relative to the water ingress. I would have the crank inspected, replace the liners myself and proceed based on the crank condition.
The ocean came into the engine through some of the exhaust valves.
There is no likelihood the internal passages and valve seats, etc. are ok.
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Old 12-01-2022, 10:20 PM   #18
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Right. Easy peasy.
The engine had only 280 hours so there is no wear, just rust damage.
The pistons are in "like new" condition after cleaning and i plan to keep them and replace the liners and rings. seems to be an easier and probably less expensive way to go considering i did not find any shops around i would trust with boring the existing liners and trying to find larger pistons that will fit properly.
Measure each piston.
It is not unheard of for pistons and liners to be matched.
Hopefully Yanmar's will be interchangeable. My only Yanmar was a 12hp single!
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Old 12-01-2022, 11:17 PM   #19
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Post Engine removal

So far, removing the engine from the boat was the most challenging part of the project, which took several days in preparation and two days for execution.

The major challenge was a small door we had from the cabin to the aft deck. The engine fits in this door with 1" clearance on each side and only 4" of vertical clearance, which is not enough for a boom crane to get inside and get the engine. And the engine is not in the middle of that door.

It may be different for your boat, and if you are lucky, you have a huge hatch in the aft deck so the engine can be picked up by a crane from the shore or wide and high saloon doors to use a boom truck to get inside, raise the engine and take it out.

But nothing is easy on the boat, and our process can help you to find a way for your boat configuration.

The whole engine removal process was done in several stages:
  1. Reinforce the cabin floor by adding horizontal members and vertical supports between them and stringers on the bottom of the hull. Total of 8 with 4 vertical supports per engine side.
  2. Build the gantry crane in the cabin with two 5' bases of out 2x6" (left and right), two 4x4x73" vertical support posts (height of those posts should've as high as possible with clearance to the sealing just enough to fit the I-Beam which is 7" high), steel I-Beam between them, 2 diagonal supports between I-Beam and posts, 4 diagonal supports between posts and the bases, 2 trolley carts, 2 chain hoists on each cart.
  3. Rise the engine to the cabin floor using an extra-long chain hoist. The normal hoist was too short to lower down enough from the top of the i-beam to the chain attached to the head brackets on the engine.
  4. Move the engine to the side of the cabin so you have enough space to build the platform which leads out of the cabin to the deck
  5. Put the engine on the base, which is strong enough to support it, with hoists attached to the sides of the base.
  6. Build a platform that will be used to slide the engine on its base out of the cabin to the deck
  7. Raise the engine on the base with 2 hoists attached to the left and right side - this was required in our boat to fit into the vertical clearance of the aft cabin door, move it over the platform and lower to the platform.
    - to fit into the aft door vertically, we had to remove the head. It's possible to keep the head, but the inclination angle of the platform has to be pretty steep.
  8. Use one of the chain hoists to pull the engine and base on top of the platform from the cabin to the desk
  9. Take it from the deck to the trailer or truck with any heavy equipment your marina has.

The cost was around $1k.
The major components were:
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Reinforced saloon floor.jpg   Gantry crane in the saloon.jpg   Engine raised to the saloon floor level.jpg   Engine moved to the side and put on the platform.jpg   Platform with engine raised by two pulley to get it up to the i-beam.jpg  

Platform with engine is moved above the ramp.jpg   Engine is moved out of the saloon.jpg   Engine is on aft desk.jpg   Picked up from aft deck.jpg   Engine is secured in the trailer.jpg  

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Old 12-01-2022, 11:52 PM   #20
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Seems to me you did the hard part already. If liners and rings are less expensive than pistons and boring and the pistons are good, by all means go that route. Seems you are off to a good start and imagine all you will learn from this project. That is a low hours engine so hopefully there won't be many more surprises.

Carry on...
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