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Old 01-09-2011, 20:08   #1
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Yanmar 3jh2 - Rebuild or Not ?

I have a Yanmar 3jh2 engine with a KBw10e gearbox, the gear box box needs to be rebuilt with new bearings and friction plates (slipping and overheating), the upper head was rebuilt at 7,000 hrs. The engine now has about 15,000 hours.

The real issue is the what level of rebuild is needed on the engine. The problems are related to an misalignment problem, the mounts failed, after new mounts installed and the prop "straightened" and aligned, I burned out two sets of plates and a bearing in 1 year. Turns out the aft end of the prop is not straight but out 25 th. I now have, again, a burned up gearbox, leaking rear engine seal (new in the last 100 hours) and a 15,000 hour engine.

Regardless of where the blame lies for this, my ignorance or professional incompetence, I need help solving the risk management issue. I have recieved two very divergent sets of opinions.

One, new engine replacement. Cost $10,000. solves issue completely.

The second , rebuild gear box, (new plates and bearing, $700, plus a couple hours labor. ) Replace drive plate (or friction plate or whatever you wish to call the thing with springs in it) Maybe $100, Replace rear seal which is leaking, $35 plus labor, ) and give it a go and see what happens!

The other option is to rip apart the engine and rebuild, estimates for new internal bearings, rings, and all the related stuff hit $6,000 maybe $7,000. This does not seem to be a viable option for a 15,000 hour engine verses a new engine at $10,000.

The key issue in the analysis (rebuild verse replace) seems to me to hinge on the main engine bearings, specifically the bearing by the rear seal which is leaking, ie, how worn is this bearing.

The engine expert I hired to look at the engine says there is a lot of play in the bearing, and by inserting a screw driver between the engine housing and the flywheel, he demonstarted that there was notecable movement up and down. He alleges that the bearing is near the end of its life,, crankshaft isues may be also a problem as he suggewsts that at 15,000 hours this engine is at the end of its useful life. Hence, instal a new engine. Proof that the bearings are going is confirmed, in his opinion, by my observation that while I have 60 plus psi under power, when I back off to idle when hot, I lose presure to around 25 and then it strabilizes at around 40.

The other school, non professional boatyard mechaincs but with a lot of mechanical savy, say, wait a minute, the screw driver test is BS, there will be discernable play regardless of the bearing condition, the key test is oil pressure. If you have in excess of 60 PSI when running under load, and 25 or so if you immediately backoff, your bearings still have lots of life. Why spend an extra $8,000 bucks when you may easily get severl more years of use out of this engine, it may burn a bit of oil, if the rings start to wear, but since it only smokes at idle and when cold, what is the issue? Just add oil when needed. Start saving $$ for when the engine goes, and be happy!
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The difference of course to me is $$$, one solution $1,500, vs $10,000. The new engine has a much less likely hood of failing over the next 5 years, that I understand; But what I would like to hear from my fellow forumites is how they view the risks of the "quick rebuild" and let it go option.

Please post only on the issue as presented, not on how I plan to crusie the boat. The cruising risks ( offshore passage to distant places, Carribena cruising, or jsut US coastal cruising) for me are about equal and well known to me, I can make thqat judgement! I just question my judgement about the predicted engine life.

Cheers to all


Tom
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Old 01-09-2011, 20:22   #2
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Re: Yanmar 3jh2 - Rebuild or Not ?

Have you done a compression test on engine?
Sealing the top end,doing the head,leads to blowing the bottom end out,piston rings, as i have seen.If comprseesion is good jack it up and put a new set of bering in it and see what happens.Do it yourself.You will learn and enjoy it.
Mark
PS.well,enjoy most of it.looks at scrapped nuckles..grins
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Old 01-09-2011, 20:37   #3
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Re: Yanmar 3jh2 - Rebuild or Not ?

Hi Mark

I have assumed compression is good; the engine fires easily. There is no prolonged cranking to get her going, if she turns over with any umph to the RPM she fires off,

Ha, when I do things like this myself, it usually costs way more than for me to hire a pro, but then I do spend lots of time watching, I have helped rebuild the transmission in the field in Madagascar, and did it on my own in Tobaggo, but never could get locking nut tight enough, so back to a pro!

What do you mean when you say jack it up and replace bearings? Can bearings be replaced without pulling the engine completely apart?

Cheers

Tom
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Old 01-09-2011, 21:29   #4
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Re: Yanmar 3jh2 - Rebuild or Not ?

If I were a diesel mechanic, I would rebuild a 15,000 hour diesel with the kind of uneven wear problems you've described.

I am not a diesel mechanic.

I bought a new Beta Marine 60 this year to replace a 23 year old Westerbeke W-52 in reasonable running order not because it had high hours, but because it had low hours, 1,100 to be precise. I plan to cruise for five years in two years' time; I wasn't about to just go as is with 20-odd unknown winterizations, a lack of easily obtained parts, and the wear pattern of infrequent usage without a rebuild.

The rebuild was quoted at $13,000, mainly for the extortionate parts prices. Even after I found out the W-52 is a Mazda S2 diesel as found in B2200s and '80s Ford Rangers, obtaining a reasonably priced rebuild kit was pricey. A new Beta, with a Kubota block, better fuel economy and easier access in most every sense, at $15,000, was not a hard decision for me, given that I plan to put maybe 1,000 hours a year on the thing, and it will need to be largely "field-repairable" by me.

A bonus is that I have now dual PTOs, eight more horses, a hydraulic gearbox and the whole thing weighs 120 lbs. less and I have more room in the bay as this engine is tall rather than broad. Again, you might want to consider fuel cost, access and weight savings as the icing on the new diesel cake, so to speak.

I would try to find a buyer for a situation where it can live another few thousand hours as a genset or running a sawmill somewhere, and would start saving for something shiny.
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Old 01-09-2011, 21:35   #5
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Re: Yanmar 3jh2 - Rebuild or Not ?

Tom, if the oil pressure recovers to 40 PSI at idle, then your bearings are fine. (as fine as can be on a 15,000 hr. engine) Wait on the engine replacement as long as you can, unless the rings are shot (excessive smoke).
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Old 01-09-2011, 22:01   #6
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Re: Yanmar 3jh2 - Rebuild or Not ?

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Originally Posted by Tumbleweed50 View Post
Tom, if the oil pressure recovers to 40 PSI at idle, then your bearings are fine. (as fine as can be on a 15,000 hr. engine) Wait on the engine replacement as long as you can, unless the rings are shot (excessive smoke).
I agree with tumbleweed...but then again Im cheap like that..if it aint broke(complete) dont fix it!
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Old 01-09-2011, 22:55   #7
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Re: Yanmar 3jh2 - Rebuild or Not ?

I had a very experienced marine mechanic tell me that the old slant 6 Ford diesel that came with Boracay was rebuildable and repairable.

$3,000 later and after spending a few months cleaning out the oil that the engine had spewed over the inside of the boat I concluded that he was wrong.

I now have a 4 year old John Deere that doesn't miss a beat. I think its dripped a couple of drops of oil over the last 4 years but I'm not sure.

I don't care what the mechanics say. I don't think worn out old engines are repairable or rebuildable. There has got to be a high probability that your current engine is cactus. You could spend $10k rebuilding it only to have it fail the next day.

You got 15,000 hours out of the old engine for a reason. It was used. A lot.
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Old 01-09-2011, 23:13   #8
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Re: Yanmar 3jh2 - Rebuild or Not ?

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Originally Posted by Tom Hildebrandt View Post
Hi Mark

I have assumed compression is good; the engine fires easily. There is no prolonged cranking to get her going, if she turns over with any umph to the RPM she fires off,

Ha, when I do things like this myself, it usually costs way more than for me to hire a pro, but then I do spend lots of time watching, I have helped rebuild the transmission in the field in Madagascar, and did it on my own in Tobaggo, but never could get locking nut tight enough, so back to a pro!

What do you mean when you say jack it up and replace bearings? Can bearings be replaced without pulling the engine completely apart?

Cheers

Tom
if it fires up easily and doesn't smoke them compression is probably still good.doing things yourself then asking a ro: to fix your screwups..laughng.thats how we all learn.T\Try this.Ask/pay the pro for advice first.A hours worth of his time for a talk and look will be well worth it.And most are happy to share there knowledge for a price.pay him again if you get stuck on something.The magic tool is woth it..grins.
CRANKSHAFT Bering's can be replaced without tearing the whole thing down.you need enough room under the engine to remove the oil pan.then is just a matter of spinning the old Bering's out.Lower will come out with the Bering cap.Upper you put a....makes special tool.i usually cut off a 10 penny nail to fit in the hole in the crank and turn it out.watch you turn the right way.there is a smooth side and a side with a 'only word i can think of is a flange..anyway they will only turn out one way.Get all Bering's out.Then leave the crank hanging loose on 2 caps and re-install new Bering's.A little molly grease and they should slip right in.Change support caps to do the others.Then put lower Bering's in caps with more molly.only on the crank side and tork the caps .you will need a tork wrench.should have one anyway if your going to do engine work.Buy a mid-priced one.think craftsmen.....
when ther torked mark them on the side with a sharpie and hit the starter or turn over by hand as fast as you can.look as sharpie mark to make sure you didn't do something back wards and spin a Bering.
clean old pan gasket/pan off and re-install.
Is not hard and Bering/pan gasket/seal set s are not to expensive.Worth a few days depending on what your time is worth.
Hope this helps.
Mark
PS,A 12x12 in mirror.can usually buy for a few bucks at home depot,helps.Buy a couple.dont ask me how i know that..grins.Also a good time to clean the oil pump ickup and replace the oil pump.
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Old 01-09-2011, 23:22   #9
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Re: Yanmar 3jh2 - Rebuild or Not ?

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Originally Posted by Boracay View Post
I had a very experienced marine mechanic tell me that the old slant 6 Ford diesel that came with Boracay was rebuildable and repairable.

$3,000 later and after spending a few months cleaning out the oil that the engine had spewed over the inside of the boat I concluded that he was wrong.

I now have a 4 year old John Deere that doesn't miss a beat. I think its dripped a couple of drops of oil over the last 4 years but I'm not sure.

I don't care what the mechanics say. I don't think worn out old engines are repairable or rebuildable. There has got to be a high probability that your current engine is cactus. You could spend $10k rebuilding it only to have it fail the next day.

You got 15,000 hours out of the old engine for a reason. It was used. A lot.
I disagree,
Old motors are as rebuildable as there are parts to suply them and enough metal to machine them to spects.Problem is getting someone with the knowlage to re-build/machine them.If your paying for a rebuild it should be warantied for leaks.Ask around and see if your mec keeps his word.
My Thoughs
Mark
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Old 02-09-2011, 00:23   #10
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Re: Yanmar 3jh2 - Rebuild or Not ?

The question is ?? you have play in the rear bearings doing the screwdriver test yes or not?

60 psi in cold and 25 to 40 in hot at idle seems to me a still healty engine, the point is the play with bearing, running the engine with play in the crankshaft destroy the whole thing in short time...

Asuming you rebuild the head, trany, and some other things, if you made a compresion test and looks ok and the bearing isue is solved i dont see a reason why this engine can made another 5000 or 8000 hours ...

Cheers...
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Old 02-09-2011, 02:02   #11
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Re: Yanmar 3jh2 - Rebuild or Not ?

If I read your post correctly, then your gearbox problems are from an external cause ie the shaft misalignment.
Regardless of what you replace, you are going to have continuing problems unless you address the shaft issue.
Have you thought of a flexible coupling?
Regards,
Richard.
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Old 02-09-2011, 02:37   #12
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Re: Yanmar 3jh2 - Rebuild or Not ?

Boden36.... Right you are, I have the shaft out being straightened as the engine end was out about 25ths, and will reallgn the whole bit when reassembling.

Tumbleweed50...The engine smokes a bit when starting, but it disappears when under load so I am thinking the rings have some more life.

I am thinking that the key issue here is whether this screwdriver test really does/does not show substantive wear in the bearing.

Given that this engine is already approaching the end of its useful life, I am thinking that the thing to do is rebuild the trans, replace the drive plate and rear seal, and see what happens. If with the new alignment, the rear seal stops the leak then I would be inclined to think the bearing wear is not too bad, and I may be able to squeeze another year or so out of this engine, all the while keeping a watchful eye on the oil pressure. In the meantime I can save money for a new engine.

If the rear seal starts leaking straight away, I would know that the wear is probably substantive, and then I can try to replace the bearings as Traveler37 suggested.

If that does not work, then I will just have to wait until some unknown relative decides to leave me $10,000!

Any other thoughts?
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Old 02-09-2011, 06:16   #13
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Re: Yanmar 3jh2 - Rebuild or Not ?

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If that does not work, then I will just have to wait until some unknown relative decides to leave me $10,000!

Any other thoughts?
I think your last comment says it all. You first need to save up for a new engine, so do whatever is needed tot the old engine to keep it running in the meantime unless catastrophic failure is encountered or imminent.
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Old 02-09-2011, 12:44   #14
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Re: Yanmar 3jh2 - Rebuild or Not ?

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I think your last comment says it all. You first need to save up for a new engine, so do whatever is needed tot the old engine to keep it running in the meantime unless catastrophic failure is encountered or imminent.

Ditto.
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Old 12-02-2012, 13:34   #15
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Re: Yanmar 3jh2 - Rebuild or Not ?

Thought I would post a follow up on this thread.

I purchased a used gear box, $500 bucks, a new engine mount $130 bucks ouch) as I found one that was sheared, and a new rear engine seal for about $10 bucks. Installed all the above and aligned shaft that had been straightened (about $60), installed a new cutlass bearing (about $30).


As part of this same job I replaced the raw water strainer, one of those plastic jobies for about $100 including hose and clamps.

It took a bit of coaxing for the engine to get going, lots of bleeding needed, but she is running fine. Engine vibration is significantly reduced ( a straight shaft, alignment and new cutlass bearing), there may be a bit of seepage around the rear seal but oil pressure is still in vicinity of 60PSI when cold and/or operating at temperature and 45PSI when hot and at idle. Still smokes on start up but this disappears when heated up and under load. Engine has now run over 100 hours on various family junkets in NC and whilst travelling south from Beaufort, NC to Savannah down the ICW.

So.. All is good so far. There is a very slight fuel leak from the injector pump below the injector connecting lines which is probably a result of getting the engine bled after it sat for 4 months. .I do not have the tools to tighten these properly so tomorrow I am going to have a mechanic check it out, hopefully a simple fix.

Cheers to all for their support and advice!

Tom
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