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Old 09-21-2018, 04:42 PM   #1
Skoolie
 
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Resurrecting a 6-71

Bus I'm looking at has a Detroit 6-71, non turbo two valve and a manual transmission. I'm friends with the owner, and I trust his mechanical aptitude enough to seriously consider this machine. It's been sitting for about ten years, and according to my friend was run once a year or so until five years back.

I've looked at it in person, and don't see anything abjectly frightening. Coolant and oil are still full, the oil doesn't look contaminated, and I'm assuming I will need to drain and replace the fuel. Other than that, what would you look at before starting one of these up after a long slumber for an 800 mile drive?

Thanks!
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Old 09-21-2018, 05:16 PM   #2
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I have seen a number of DD 2 strokes that have sat without running for many years start and run fine.

I have also seen blower seals fail on startup and dump engine oil into the intake resulting in a runaway.

Make CERTAIN that you have a functioning emergency shutdown.

If it were me, I would try to drain the diesel tank, fill with fresh diesel, add an algaecide and replace the fuel filters.

I have heard of folks pulling the injectors and putting a small amount of light machine oil in the cylinders. I have never seen it done.

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Old 09-21-2018, 05:18 PM   #3
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Pull the valve cover and make sure the injector rack moves freely and returns to idle position. Make sure shut off works. Other than that most I have seen start quite easily.
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Old 09-21-2018, 05:23 PM   #4
Mini-Skoolie
 
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Granted it has been a while since I worked on a 6-71, but I think I would do the following at a minimum before trying to start it & then drive it any distance.
1) Roll the engine over by hand to ensure it is free to turn. Open the air box covers and look for moisture, stuck rings, or signs of damage in the cylinders. Clean the air box drains.
2) Remove all six injectors and have them bench tested or just replace with rebuilt units. A stuck injector could lead to blowing a tip and catastrophic cylinder failure.
3) Flush the fuel system & replace all filters. Drain the fuel tank and refill with fresh fuel. Carefully inspect the fuel lines (supply & return) replace as necessary
4) Drain and replace engine oil and replace the filter(s).
5) Drain the cooling system and replace the coolant, replace the thermostat. I would strongly recommend replacing all hoses in the system. Clean the radiator fins for debris. Consider having the radiator flushed.
6) Replace all fan belts.
7) Check tranny & re-end oil levels.
Lubricate all throttle linkages and ensure proper movement.
9) Replace the air filter cartridge or clean the oil bath (if equipped)
10) Check the blower screen for debris or deterioration.

Once the engine has been started and is deemed to be running ok, drive it and get it to operating temps for 25-50 miles and change the oil and filters again. I would consider changing those oils once they are up to operating temperatures. This would help get any moisture out.

My biggest concern would be accumulated moisture and any damage that it may have cause. I'd plan on a lot of new leaks due to gaskets drying out. (not that a 6-71 ever leaks, LOL)

Keep up posted on how it goes.

Andy
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Old 09-21-2018, 05:58 PM   #5
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One thing to keep in mind regarding the DD 2 strokes. They are VERY particular as to what oil you feed them.

You need a diesel engine oil specifically for a two-stroke diesel. These oils have the API Service Category CF-II. Yes, 40 wt. is correct, but SAE 40 CF-II.

Delo 100 40wt is the "standby" for DD 2 strokes. NO Delo 400, Rotella or multigrade oils.
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Old 09-21-2018, 07:56 PM   #6
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I have been running a number of 6-71's and 4-71's for many years on 15w40 rotella without any issues. Even do oil analysis, and that shows no issues.
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Old 09-21-2018, 09:00 PM   #7
Mini-Skoolie
 
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Quote:
Originally Posted by PNW_Steve View Post
I have seen a number of DD 2 strokes that have sat without running for many years start and run fine.

I have also seen blower seals fail on startup and dump engine oil into the intake resulting in a runaway.

Make CERTAIN that you have a functioning emergency shutdown.

If it were me, I would try to drain the diesel tank, fill with fresh diesel, add an algaecide and replace the fuel filters.

I have heard of folks pulling the injectors and putting a small amount of light machine oil in the cylinders. I have never seen it done.

....
A CO2 fire extinguisher is your friend in this situation. AND they will have no clean up and do NO harm to the engine.
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Old 09-22-2018, 01:25 PM   #8
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Quote:
Originally Posted by Ronnie View Post
I have been running a number of 6-71's and 4-71's for many years on 15w40 rotella without any issues. Even do oil analysis, and that shows no issues.
OP: PLEASE do your due diligence regarding what oil you run in your DD 2 stroke before you decide. It really is a big deal. Oil analysis will not tell you about carbon build up on the rings among other things.
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Old 09-22-2018, 01:29 PM   #9
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From Tejascoach. Com:

I used to think that 40 Wt was only for hot months and that we should cut back to 30 Wt during the cold months. I have a good friend who retired from the R&D department at Detroit who set me straight on that logic. He sent me a Detroit Diesel publication that had photographic evidence showing the damage done to the 2 cycle engine when anything other than STRAIGHT 40 wt. oil is used. When either using 30 wt. or a multiple viscosity oil such as 15w 40 the cylinder liner shows unacceptable scuffing and wear during a 100 hour accelerated test whereas using the straight 40 wt. oil a photo with the same 100 hour accelerated test still looks new with the factory's hone marks without any wear. Read the entire Detroit Dieselģ by clicking this link DDC Oil
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Old 09-22-2018, 01:45 PM   #10
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That sure sounds like one interesting project you are considering. Good luck with it, will be an awesome learning experience waking that baby up.
Enjoy the ride!


John
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