Resurrecting a 6-71

[cycle61]

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!

[PNW_Steve]

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.

https://www.youtube.com/watch?v=vbiNndfNNKI

[somewhereinusa]

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.

[Lamacose]

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

[PNW_Steve]

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.

[Ronnie]

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.

[Mekanic]

Originally Posted by PNW_Steve

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.

[PNW_Steve]

Originally Posted by Ronnie

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.

[PNW_Steve]

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 Diesel® by clicking this link DDC Oil

[BlackJohn]

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

[cycle61]

Thanks for all the suggestions, everybody! I've heard the oil thing, planning to roll down with all my heavy tools, ten gallons of Delo 100, weight depends on season, CO2 extinguisher, a pair of new group 31 batteries, and two each new filters for oil and fuel.

The guy I'm buying it from has a lot of industrial equipment, and we're planning to lift it with some 20 ton bottle jacks, pull the wheels and clean the brake drums, install an EEZ TPMS, probably replace the front tires, and then power up the electrical and see what works as far as lights and auxiliary circuits. The hoses don't feel hardened, but I'm expecting a few air and coolant leaks when we get it up to pressure. Pulling the valve cover and checking the rack for free movement sounds like a very good idea.

Anybody have a PDF copy of a Detroit manual?

[Ronnie]

Originally Posted by PNW_Steve

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 Diesel® by clicking this link DDC Oil

I would like to see that publication, if possible.

I have not seen carbon build up, or scuffing of the liners in my engines. One if them the last rebuild was in 1954. Built in 1942 and in daily service through the mid 70's . It is used every weekend now and has been for 20 years now.

[PNW_Steve]

Google is your friend...

Detroit Diesel 2 Cycle 2 Stroke Engine operating Oil Tips

Tejas Coach Works Factory DDC Oil Information Data Page

[Iceni John]

Guys, it's very simple: just use the correct oil that Detroit requires. If it's not CF2-rated straight 40-weight (or 50-weight in very hot conditions), don't use it. In addition to Delo 100 that still has the lowest sulfated ash content, there are several others to choose from - Mobil Delvac 1240, Citgo (assuming anything's being exported from Venezuela these days), Shell Rotella T-1 (but not the other Rotellas), and what I use now, Conoco/Phillips 76 T5X. Any good lube oil distributor can get these for you, and if you live near the coast or the oilfields they'll be readily available.

Do NOT use S-rated straight 40-weight for gasoline engines: it doesn't have the right additive package for HD diesels, god knows what the sulfated ash content is, and it has high sodium and potassium levels that will screw up your next oil sample analysis. (You do get your oil sampled regularly, I hope?)

See, I told you it was simple. It ain't rocket surgery.

[Ronnie]

Here is what my DD service manuel says, about multi weight oils,


-15W-40 Multigrade Lube Oil-

Detroit Diesel Allison now approves and recommends the use of the new generation 15-40 lubricating oils, providing the following ash limits, zinc requirements, oil performance levels, and conditions are met.

1.The sulfated ash (ASTM D-874) content of the lubricant shall not excede 1.000% by weight, except lubricants that contain only barium detergent-dispersal salts where 1.5 by weight is allowed.

2. The lubricant shall meet the performance requirements shown in API Service Classifications CD/SE.

3. The zinc content (zinc diorganodithiophosphate) [yes, I spelled it right!] of all the lubricants recommened for use in Detroit Diesel engines shall be a miinimum of 0.07% by weight. However the zinc requirement is waived where EDM lubricants are used.

[Iceni John]

Originally Posted by Ronnie

Here is what my DD service manuel says, about multi weight oils,


-15W-40 Multigrade Lube Oil-

Detroit Diesel Allison now approves and recommends the use of the new generation 15-40 lubricating oils, providing the following ash limits, zinc requirements, oil performance levels, and conditions are met.

1.The sulfated ash (ASTM D-874) content of the lubricant shall not excede 1.000% by weight, except lubricants that contain only barium detergent-dispersal salts where 1.5 by weight is allowed.

2. The lubricant shall meet the performance requirements shown in API Service Classifications CD/SE.

3. The zinc content (zinc diorganodithiophosphate) [yes, I spelled it right!] of all the lubricants recommened for use in Detroit Diesel engines shall be a miinimum of 0.07% by weight. However the zinc requirement is waived where EDM lubricants are used.

For which specific engines? What is the Detroit publication number and date?

John

[yeggs]

Hey There! I had a real messed up 6-71 turbo in my Crown and ended up getting wayyyy deeper into it then I thought I was going to have to. In the end it was a pretty cool project and I learned a lot about these really neat old mechanical two strokes. They are really fun, in a big dirty clockwork sense, and are designed to be field-serviceable in a way that more modern engines aren't. Except for the starter, they don't need any electrical at all! It's all gears and springs and weights. Neat! You sound like you've got it, and there's already been some solid tips posted covering most of this, but for the sake of having multiple sources, here's what I'd do:


* Drain the old diesel, replace with new, and replace both fuel filters -- If any water got in the diesel, even from condensation from the seasons passing, it'll damage the injectors real quick, and that'll ruin your day.


* Oil Change. Straight 40 weight, no question. Mine takes most of a 5 gallon bucket.



* Replace or clean the air filter.


* Understand the shutdown mechanism, make sure it moves. Some (most??) have a mechanical flap actuated by a cable that smothers the air intake (should be right above the blower), some have a mechanical linkage that moves the fuel rack to "no fuel," mine has a pneumatic shut down solenoid that uses the same air as the air brakes, so it won't shut down with the key until there's some air built up, unless you get in there and push it yourself. Freaky, if you're not expecting it.


* Make sure the airbox breather (aka "the dribble tube") is open. Some (most?) have a check valve, some have some sort of way to close it when stored. It's on the side without the blower, just below the 6 bore inspection ports, right in the center of the block. Should be a 1/4" copper or steel tube pointed down.



If it's a 2-valve, it might (or probably??) has the old-style fuel rack (the linkage that connects governor to the injectors), which means that it could get stuck open (ie, in "full fuel" position) if any one of the 6 injectors sticks, and cause a run away. I'd guess you could feel that if you move the fuel/accelerator lever on the outside of the governor manually with the engine off, but it might be hard to tell without some practice. You could pop the valve cover off and make sure the rack moves freely back and forth (ie, from "no fuel" to "full fuel" and returns to idle fuel when released) if you want to be thorough.



You have to take the rocker arm assembly off to pull the injectors, and then you'd have to run the rack with a timing tool you probably don't have to get it back together, so I would hold off on that.


Be REAL careful manually turning it over with a bar, you can start it like that! Fuel rack MUST be in "no fuel" if you're manually turning it.


TL;DR: change the diesel & oil and their filters, move the engine shut-down in and out a couple times, have a plan B, and then fire the sucker up!


Plan B? A CO2 extinguisher if you're fancy, a plywood board if you're cheap -- just something to completely block the air intake if all hell breaks loose. It'll probably be fine.

[yeggs]

I've got some random pictures of the insides of my 6-71TA in my album here:


School Bus Conversion Resources - yeggs's Album: Crown


I should really update that thing...

[Crown_Guy]

What John said.

Don't screw around trying to re-invent the wheel. Just get Delo 100 straight 40 wt and use that. NOT Delo 400!!! You may have to work a little to get it, and maybe even have to order it and wait for it to come in, but that's what you should use.

Any further arguments regarding the usability of any other type of oil is merely your refusal to accept that the correct answer is what's already been stated so precisely by John. Your wishing to find another oil, and changing the facts won't work, facts are stubborn things. I hear this a lot myself and am tired of the back and forth of it all. The 2-strokes are unique animals with very specific requirements, and anyone using one should accept that they are special and bow to the inevitable. It's only become a source of confusion and never ending questions with the decline in their numbers, and the lack of everybody just knowing what to get, and using it without question, since that was what was correct for them. The fact that that oil is correct for them has not changed at all, only that there are fewer of us around who know, remember, and understand those old and established facts of life in the operation of any DD 2-stroke engine series. Delo 100 was available everywhere, due to the vast numbers of engines around using it. That's no longer true, so it's not stocked much anymore and needs to be special ordered. You will play hell trying to find it in stores today. But that's just one of the prices you pay when playing with such a fine old example of the engine designers engineering art. I'm pretty sure there will be lots of running 2-stroke engines, long after all the computers have burned out, and impossible to find or replace with most of the newer engine designs.

You may also have missed Johns comment about what exact DD engine that tech bulletin was referring to. Detroit Diesel today is fully invested in 4-stroke engines Series 60's etc. which are like the Cummins, Cats, etc. They are not putting out new bulletins regarding the old, and to them obsolete 2-stroke engines. Today most people only know Detroit Diesels as Series 60 type engines. NOT 2-stroke -53, -71, -92 etc which ruled the roads only a few short years ago. Their recommending the use of 15-40 multi-grade oils is intended only for the current engines they are selling, Series 60 4-strokes and NOT for older 2-strokes. Multi-grade oils are exactly right for the current 4-stroke engines, only.

Just go get some Delo 100 40wt and be sure to carry with you several gallons as you drive because you won't find it easily, if at all, on the road when you need it, as it always needs to be added. It is a DD 2-stroke after all, and if it's not leaking a little, or burning it, there may be something wrong with it........only a little joke. But another fact of life in the operations of a DD 2-stroke.

[Ronnie]

Sorry but the facts are DD does recommend the 15w40 in 2 strokes according to my service manual dated 1979. this is for 71 series engines. Now my older manual dated 1972 says straight 40 w. Oil technology changes and DD clearly says as I quoted that as of 1979 that the then new generation of 15w40 oils are good, as long as they meet the specs given. I know Amsoil 15w40 marine oil meets specs, the older rotella meets specs. Have not checked the latest version of rotella, as I do not use that.

Lets not stay in the dark ages fellows, things change, DD has in it's own service manual acknowledged this. If those who want to use straight 40 go for it. but lets not insist everyone must follow this, as it is clearly out dated info.