| Author |
Message |
    
John Vogel
Visitor
| | Posted on Wednesday, January 18, 2012 - 09:50 am: | 
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It seems to me that ther is excessive oil comming out the exhaust stack. The moror is NOT burning oil. The oil is oozing out the stack. Please help as I do not know much about this oldmarine engine. |
jimmys
Member
Username: jimmys
Post Number: 14
Registered: 01-2011
| | Posted on Wednesday, January 18, 2012 - 11:32 am: |
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John,..
Your 6-71 is Idling to much, or not working hard enough and the Combination of unburned Fuel and Carbon is creasoting your exhaust system. You need to get your 6-71 up to 1800 RPM's, in gear underway, for at least 10 Minutes, or more to burn out all the deposits,..these two stroke engines are injecting fuel every stroke, so you are not getting the fire deck up hot enough to burn all the fuel. If you have a steel dock close buy,..go up to it and run your engine in gear hard!! You just need to burn out all the excess fuel and clean out your exhasut system and
you are probly having to use Eyther to start your engine now. You are going to be spitting out allot of fuel and Carbon, so don't do it close to other vessels. Stop idling and trolling to long,..there is a trolling valve available on the Twin Disc Marine Gears |
larry_from_md
Advanced Member
Username: larry_from_md
Post Number: 31
Registered: 06-2010
| | Posted on Wednesday, January 18, 2012 - 12:30 pm: |
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Could allso be a bad injector letting fuel into the cylinder.I worked on one that was running on one cylinder and oil like stuff comeing out. After trying to ajust the injectors i got it to run on 2, then i pulled them and found one with the tip broken off. |
jimmys
Member
Username: jimmys
Post Number: 15
Registered: 01-2011
| | Posted on Wednesday, January 18, 2012 - 09:40 pm: |
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Yes,..You could have a Injector with a blown tip,..very possible. If any water got through your Fuel Filters,..the injectors Tips Do Not like Water and blow out!! Is your 6-71 missing a little? You can take off your Valve Cover, run engine at a idle and take a Large Screw Diver to Stop each Injector, stopping or holding Down the Injector spring loaded plunger and you will notice a drop in RPM's, due to that one firing Okay,..finding the bad Injector, or blown tip one, where the RPM's don't drop. The blown tip one is just filling the cylinder and Air Box with raw fuel, out the Air Box drin tubes and the Exhaust. |
John Vogel
Visitor
| | Posted on Thursday, January 19, 2012 - 07:57 am: |
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Well let me first start by saying thanks for the prompt respones. It is true that I do run the boat at lower than normal RPM's. I'm worried about running the old engine to hard. I'm pulling 3 38inch crab dredges. I got the boat with the 671 in it, they were going to scrap the thing. There is no tack on the boat. Where is the RPM send on the motor. Do i need a special tack or can I use something else. She starts right up with no problem and I do not use Eyther. I do not notice a miss, she seems to me that she is running smooth. If I take the valve cover off will I have to buy a new gasket,use the old one or is there no gasket? I'm new to this DD671 Grey Marine. Thanks again for helping me with this. |
jimmys
Member
Username: jimmys
Post Number: 16
Registered: 01-2011
| | Posted on Thursday, January 19, 2012 - 12:54 pm: |
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It sounds like your 6-71 does not have a blown tip or excess fuel problem,..running smooth and all,..so it is just the idling to much and don't worry about just running up the engine RPM higher, when you are going too and from the fishing/crabing grounds.
Ther are three different locations for running a Tach off of your engine and I have the parts to get the location available on your engine, to mount the Tach Drive,..recomending the Electronic Tach,.(Best to get to you Bridge Instrument Panel,..do you have a Engine Instrument Panel now?
I have a Instrument Panel, with a Mechanical Tach and Temp Gauge on eBay right now,..Listing # 380400691202 and a Duel Tach Drive, w/Drive Shaft for a 6-71 on eBay also,..Listing # 380399202068,.. |
johnoxley
Advanced Member
Username: johnoxley
Post Number: 49
Registered: 04-2010
| | Posted on Thursday, January 19, 2012 - 04:49 pm: |
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25 years ago I was new to GMs. I had 12V92 that would not start. Injector stuck shut, but when the DD mechanic got the engine started, I saw him touch each exhaust stub just next to head to see if all injectors were warming the exhaust equally. I do this now when checking over a "new" engine. Easy to do on the 71's. A cold exhaust stub = bad injector.
What is the nature of the oil discharge? Grey smoke, black smoke, white smoke or oil spots? Injector dribble will still burn and sort of work, but drops of fuel pass through unburnt and sooty drippy discharge results. Raw fuel might also be contaminating the sump oil which could hide oil burning. If discharge is from sump oil, DD book shows piston ring check by opening air box covers and exmining each piston in turn for springiness of piston rings - small blunt tool OK - do not use a scriber. Broken ring will not be springy. Stuck ring will be stuck. |
John Vogel
Visitor
| | Posted on Friday, January 20, 2012 - 10:24 am: |
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Jimmies, i made an offer on the gauge and I won the drive. I will need instructions on mounting. The nature of the oil comming out the exhaust is a wet exhaust stack with a coating of oil on the inside and then the outside of the pipe. She blows white at start up but then stops after warm up. I know these motors are oily but I don't think this is normal. |
jt_vogel
Member
Username: jt_vogel
Post Number: 7
Registered: 11-2011
| | Posted on Wednesday, January 25, 2012 - 12:13 pm: |
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Thanks guys! I took her out last night and ran her hard. Today the exhaust stack is just black with carbon and no wet oil.I guess ideling her at the dock wasn't the best idea but I needed to make shure she was running every day. I hope the the old girl will take the beating she is about to get. I am crab dredging the Barnegat Bay here in NJ. I got the boat and motor for free (they were gonna junk her). Well here goes. Now I'm a Crab Drager. |
johnoxley
Advanced Member
Username: johnoxley
Post Number: 50
Registered: 04-2010
| | Posted on Thursday, January 26, 2012 - 01:15 am: |
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Hi - a DD techo told me to treat my 12V92s hard - it does no good to be nice to them. If you have to idle, switch off. Give them real work to do or nothing. Run the single grade locomotive oils designed for them.
We have twin tugs each with twin screw handed 6-71s. We took them over and found that all four engines ran hot. Replaced sw pump impellers and ran a little cooler, but did some exploration and found all 4 heat exchangers were partially blocked with at old zinc anode remnants and the sw pump discharges were all practically blocked with salt. Motto - do not rely on reactive maintenance. Suugest you pull the anode plugs and look inside the pumps and heat exchangers. |
jt_vogel
Member
Username: jt_vogel
Post Number: 8
Registered: 11-2011
| | Posted on Thursday, January 26, 2012 - 11:49 am: |
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I need a manual for this 6 71. I have little knowledge about this motor. I just want her to last as long as possible. If anyone can help with getting me a manual it would really help. Thanks. |
jimmys
Member
Username: jimmys
Post Number: 17
Registered: 01-2011
| | Posted on Friday, January 27, 2012 - 05:08 pm: |
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I saw a Service Manual for Your 6-71 on eBay,.. |
anthony ruiz
Visitor
| | Posted on Sunday, December 16, 2012 - 12:57 am: |
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Trolling cover gasket on my twin disk is blowing out anthony |
Charles Wayne Purdy
Visitor
| | Posted on Sunday, December 16, 2012 - 07:50 am: |
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Look just don't forget the type of oil in the engine.
Old guy told me one time that GM's need ruffage.
In other words if your using the best multigrade oil you can find to be good to the engine perhaps that is the problem.
I have seen it a number of times.
Good luck! |
