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Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 14181
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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Looking marine mechanic familiar with Yanmar 3 G eng

Customer Question

Looking for a marine mechanic familiar with Yanmar 3 G engines
Submitted: 6 months ago.
Category: Boat
Expert:  Jason replied 6 months ago.
Hi Sid, my name is ***** ***** of questions do you have?
Customer: replied 6 months ago.
Are you familiar with Yanmar 3 G engines?
Expert:  Jason replied 6 months ago.
Customer: replied 6 months ago.
See following details:Currently trying to identify a almost impossible to start 3GMF with very loud knocking and engine movement. As understood 1100 hours once on salt water now in fresh. No previous indication of hard starting loss of power or unusual noises.Sid it would probably be best if you describe both the initial failure and oil change...Specifically previous engine operation, any sounds or power loss during failure. Also try to capture AJ's service as best you can. Note any presence of water in fuel or other contaminants and start attempts and when the knock became apparent.Mechanic # ***** called to assist mechanic #1 with complaint that engine would not turn over. Arrived and so spun fully decompressed with no problem. Close thru hull and check oil and no apparent water. Subsequently the engine would spin compressed but the starter seems to struggle and so assume either a marginal starter or low batteries. Very loud knocking and exhaust is black indicating un-burnt fuel but no start. Although she would not start she seemed very very close. As the HP pump bleed screw was badly corroded followed up the next day and sprayed with PB for overnight soak and let batteries recover.Mechanic #2 Attempt day 2
Removed water pump belt. Bleed fuel system from secondary to injectors. After many attempts engine started again very rough and loud knocking sound. Managed to crack each injector with noticeable reduction in RPM on each cylinder. Also conferred with Doug at Yanmar Mastry service for advise.Mechanic # ***** ??????? Sid you will have to fill in if at allMechanic #2 day 3
Again remove water pump belt and per advice check intake,remove exhaust elbow. Low start battery precluded another starting attempt so moved forward and pulled all injectors and bleed ( mechanic #3 opened the fuel system) and spray test each injector and pump fwd mid and aft. All injectors pop and the spray pattern looks OKCompression test Factory recommendations < 10% deviationDry Wet Rotella 30 weight
Fwd 320 440
Mid 340 440
Aft 280 380Cannot probe for piston clearance as insulator and pre combustion chambers are stuck in head.Mechanic #2 Day 4
Retested aft compression and shows 320 but probably was still wet as fwd was also previous above the previous dry value and showed 400. Again consult with Mastry.Additional commentsThe knocking is very loud and not normal and follows engine revs. With all cylinder decompressed there is no knocking or additional vibration. The knocking is low with only the aft cylinder compressed #2 compressed is louder and when #3 is compressed is the loudest. Again this is with the engine fueled (ie injector in place and properly bled) or not fueled (ie. all injectors removed and test plug in compressed cylinder.)Further mounts appear fine although without a running engine is difficult to evaluate but doubt that there was a catastrophic failure here.Understand we are in an area starving for marine diesel mechanics and as I am working outside of the normal issues I usually address. Both Sid and I wish to move forward with as much information as possible to effect a repair correctly. Obviously the knocking with no apparent cause is troublesome.At present we are looking at 1 action item and 3 optionsAction item - As elbow is in an awkward position remove from boat and thoroughly inspect and clean.1) Continue to assume a fueling problem. Send injectors for pop test and service reassemble and attempt to start.2) Remove head and check to check is we have a short con rod. Check valves, rods, gudes, springs, pre-combustion chambers. Replace injector copper seals and heat shields etc.3) Although probably not at issue the HP pump could be removed and serviced.Or any combination, please advise
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Expert:  Jason replied 6 months ago.
Okay, I read all that. What are your questions?
Customer: replied 6 months ago.
Any suggestions on how to proceed--how to get the engine to fire up?
Wondering if the next move should be to remove the head and check the pistons and rods.
What would be your suggestions?
Customer: replied 6 months ago.
Did you receive my last?
Expert:  Jason replied 6 months ago.
Sorry for the delay, I was on the phone with another client. The compression numbers listed, 320, 340, and especially 280 are all to low to support diesel combustion. The engine is either worn out, or has sticking piston rings. You can try seeing if it will run on WD40. WD40 acts like starting fluid for a diesel. So try running it on the WD40 for a minute or two and see if the rings free up. But if the numbers do not come up, the engine will need new rings and liners. Does that make sense?
Expert:  Jason replied 6 months ago.
Do you have any other questions on the issue?
Expert:  Jason replied 6 months ago.
The specification in the Yanmar factory service manual for compression when the engine was new is 3.43 MPA. When you convert MPA to PSI you get 497 PSI. The specification for the service limit on the engine (Service limit is what Yanmar would consider worn out) is 2.75 MPA, when that is converted to PSI you get 398 psi. What that means is Yanmar will make no guarantees of how the engine will run, or if it will run at all, below 398 psi. Your pressure of 320, 340, and especially that 280 are all below manufactures specifications by quite a bit. If all of the cylinders were reading in the say 360 to 380 ballpark the engine would run, but it would lack power and blow a lot of black smoke due to incomplete combustion. But when the highest cylinder is 340 and the lowest is 280, that is simply not enough pressure to get diesel fuel to combust. Does that make sense? I do realize this probably isn't what you wanted to hear. But numbers are numbers, and the specs in the books do not lie. Your shop that you are dealing should have all of this, and honestly I don't know why they are continuing to work on it when compression is clearly below spec. I don't know how you want to leave this but I do want to make sure you are happy with my service before you go. If you had a further question on the issue by all means feel free to ask. If not, Just in case you do not understand the way the website works (and some folks do not). You do have to put forth a positive rating in order for it to credit me for helping you. When ratings are not done, the website simply keeps your deposit and they will not credit me. The ratings box is located at the top of the screen. To rate, you must select the star you wish and also confirm it. Please let me know if you run into any problems or errors when trying to do it. If you do have a problem, or if you can not see the ratings box which is at the top of the screen. Please reply back "I rate Jason's service _______" and fill in the blank.Questions do not close out, so if you have to come back later on with follow up questions to the issue you still can even after doing a rating.Thank youJason
Expert:  Jason replied 6 months ago.
Expert:  Jason replied 6 months ago.
It looks like you read my reply without putting through a rating for me. Please keep in mind the website does charge you to speak with me, but they will hold your money and not credit me for helping you out if no rating is put through. If you have a problem with the ratings box or can not see it please let me know.ThanksJason
Expert:  Jason replied 6 months ago.
Hi Sid. Just checking in. Did you have any further questions on the issue?Thanks,Jason

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