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Old 06-07-2019, 09:41 PM   #1
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Old Detroit 671 Ti

Hello Everyone, prepping to start my twin 1984 671 TI after sitting for 6 years. Pretty nervous, appreciate any tips.
Thanks
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Old 06-07-2019, 09:58 PM   #2
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Take rocker cover off and make sure injector racks are free to move. Bar over engine with a wrench on crank pulley and make sure there are no hard spots, should turn with modest effort. If you can't turn engine a turn or two, there is a problem, sort it out before hitting the starter.

Check fluid levels. if it turns ok and inj are free, try a start.
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Old 06-08-2019, 08:36 AM   #3
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Starting old 671's

Thanks Ski, already removed covers, checked racks, seemed to move smoothly.
I am going to change oil also, any special advice or special attention? I thought about some way to distribute oil when refilling.
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Old 06-08-2019, 09:20 AM   #4
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have a way to disconnect the starter quickly incase the through out solenoid sticks. Mine did and I had a hammer close by and wacked it a few times and disengaged.
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Old 06-08-2019, 09:44 AM   #5
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Quote:
Originally Posted by Krattski View Post
Thanks Ski, already removed covers, checked racks, seemed to move smoothly.
I am going to change oil also, any special advice or special attention? I thought about some way to distribute oil when refilling.
Bar engine over a couple of times.
Remove rocker arm cover. Pour oil over rockers/push rods etc while starting.
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Old 06-08-2019, 11:27 AM   #6
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Yep, pour oil over rockers, some will go in cam pocket. Make sure air dampers on blower are free to operate, test it a couple times before start. And be in a position to trip it if engine runs away. Some also put vise grips on rack tube to make a handle to go no fuel if needed. Won't work if inj tube is solid vs spring type and an injector sticks, then you count on air damper.

Watch oil pressure right after start, should start building in 5sec, if not, shut it down.

Can prime oil system through gallery, some do this, some don't, never heard of bottom end suffering.

If oil looks good and smells good, I would not bother changing til after it has run a bit.
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Old 06-08-2019, 04:01 PM   #7
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My current boat had 671 engines that sat for 6 years without any storage prep. After checking the rack, they started fine. In 60 years of using Detroits, I've never seen a stuck injector or a stuck piston (unless they were submerged). I wouldn't change the oil until after it's started and warmed up, maybe even after a sea trial.
With the linkage between the rack and governor removed, you can move the rack it's full range by hand while you look for the individual injector movement.

Older Detroits came with a jacking bar that fits the front pulley, usually found somewhere near the engines. I found my current one in the bilge.
Check the impellers and engine zincs.





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Old 06-09-2019, 06:08 AM   #8
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Starting old 671's

Thanks for the info, that's the plan I am going with.
I am on dry land in my shop yard, i would like to run them for some time to get the bugs out, do you know the best place to connect water for cooling during testing? The exhausting water can just follow it's normal path exiting the rear exhaust ports correct?
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Old 06-10-2019, 03:21 AM   #9
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If your engines are heat exchanger cooled, I'd connect the raw water pump intake to a 55gl drum of water and return it there. It takes awhile at idle to heat 55 gallons. Depending on your temporary exhaust, I'd return the raw water from the point on the exhaust manifold where it normally goes back into the exhaust elbow.

If water use is no problem, you can not use the raw water pump and just connect a garden hose to the heat exchanger and drain out the other side.

If they're keel cooled engines then connect a 55gl water drum where the keel cooler connects.

I'd have a plan to close off air (to stop the engine) in case you don't get the rack/governor set right.



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Old 06-10-2019, 01:13 PM   #10
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These are all good suggestions. You can drop a low pressure 'sump pump' into a 55 gallon drum that is positioned to accept the water from the exhaust and pump it back via garden hose into the thru hull with a plunger adapter. This will provide water to the raw water pump as well. If you are doing any of the direct cooling methods like going to the heat exchanger directly, you'll want to disconnect the raw water pump drive so that you don't toast the impeller which you've likely replaced in prep for this startup.

As mentioned before, there should be a flapper valve to shut off air going into the engine, this will be what you use to shut down if the throttle gets stuck. The governor adjusts the rack full fuel for start and if one injector sticks full, it can hold all of them open, so stopping the air will stop the engine. Your 1984 models may have springs on the rack that allow the rack to return even if one injector sticks. You can see that with the valve cover off, there will be two screws for the old style, and one screw for the new style on each actuator that goes to the injectors on the rack.
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