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Old 24-03-2020, 19:23   #1
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different motors

Hi ladies and gents

Looks like my 2 x detroit 8v71's are U/S as the mechanic who ripped me off for $15k has left them out in the weather and advice I have had says that all tin parts, plus cams, cranks etc, could be U/S!

Now need to source different motors but on a very limited budget. Money - 'It's all going out - with nothing coming in --!'

The detroits were NA's and specs vary from 305 to 325HP with high torque at low revs. Seems to be a lot of 250HP motors around but don't want to be coming into pen at 2000RPM's - or not enough torque to manoeuvre.

'Advice' says more modern motors will have different torque curves so am seeking some advice (wise) and possible guidance - not silly stuff (buy two new motors) as I don't expect to win lotto in the near future!

cheers

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Old 24-03-2020, 22:31   #2
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Re: different motors

Don't know what 'U/S' means, but sitting in the rain is not the end of the world for an engine.

Complete rebuild kits are for an 8v71n are about 1500.00 US, and are readily available. Cams and cranks are grindable if necessary; blowers, injectors, fuel, oil and water pumps are all rebuildable.

Costs to reconfigure for a repower are likely to be considerable.

Though it may seem scary, the most economical and efficient route will probably be to find a conscientious and competent mechanic and rebuild what you have,

Detroits are fairly simple; many have been rebuilt by complete novices. Perhaps blowers (tolerances are critical) and injectors (for testing and calibration) need to be sent out, and the crank evaluated and measured if bearings are worn or if rust is bad, but most everything else is 'user servicable'...
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Old 25-03-2020, 01:56   #3
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Re: different motors

Docking with lower HP motors shouldn't be an issue. Usually don't even leave idle speed. Very rare to use much more than 10% of the rated power.

If there is an issue dropping to lower HP it will be getting onto plane.
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Old 25-03-2020, 04:04   #4
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Re: different motors

Quote:
Originally Posted by jimbunyard View Post
Don't know what 'U/S' means, but sitting in the rain is not the end of the world for an engine.

Complete rebuild kits are for an 8v71n are about 1500.00 US, and are readily available. Cams and cranks are grindable if necessary; blowers, injectors, fuel, oil and water pumps are all rebuildable.

Costs to reconfigure for a repower are likely to be considerable.

Though it may seem scary, the most economical and efficient route will probably be to find a conscientious and competent mechanic and rebuild what you have,

Detroits are fairly simple; many have been rebuilt by complete novices. Perhaps blowers (tolerances are critical) and injectors (for testing and calibration) need to be sent out, and the crank evaluated and measured if bearings are worn or if rust is bad, but most everything else is 'user servicable'...

What he said.



By far cheapest way forward is to rebuild what you've got. I would spend a bit on a good machine shop -- let them inspect, magnflux, and probably grind cranks and camshafts, check blocks and heads for flatness and mill if necessary, and I'd probably let them do the valves -- you can do valves yourself, but what a faff without the tools. Hone and measure the liners; check the pistons, replace as necessary. Check the flywheels for runout. Send the blowers off to a specialized shop for that, and the injectors to a specialized shop for that. If tin parts are ruined, get replacements from a junkyard -- there must be a million of those old Detroits lying around.



At the end of the day it will be some work, but what you have will be better than new and you won't spend all that much.



Some inspiration: https://www.technomadia.com/2013/08/...diesel-engine/


What beasts those engines are!
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Old 25-03-2020, 04:57   #5
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Re: different motors

DD’s are rebuildable forever, almost.
U/S means unserviceable.

Believe it or not but even if I gave you free motors, you may still spend more fitting them then you would overhauling your DD’s, especially since they are NA. Everything changes from the exhaust to the transmissions, wiring harness, instrument panels and motor mounts and especially the mount beds.
But from a torque curve etc, that’s not a problem, the transmission ratios even that out, higher revving motors just turn faster RPM to turn the prop at the same speed.
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Old 25-03-2020, 06:58   #6
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Re: different motors

DD 8V71 do not become scrap by being left out in the rain!

First pull the dip stick and see if there is any water in the oil pan .

Next bar the engine over to be sure a cylinder is not full of water from an open exhaust.

Next pull all the valve covers and move the throttle , watch the rack and be sure none of the injectors are stuck.They all should slide together.

Hook on a battery and crank the engine for 5 or 10 seconds .

If it spins with no problem sticking , great

Find an outboard tank , fill it with diesel fuel , and use the rubber primer bulb to load the fuel system.

Now crank the engine in 20-30 second shots , it should start.

This test will decide if the engine is useful.


Adjust the valves and injectors , and stick it in the boat.
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Old 25-03-2020, 15:35   #7
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Re: different motors

Arenít these in some of the old trucks Iíve seen on YouTube where itís been in a field for 20 years and then get then running?
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Old 25-03-2020, 17:43   #8
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Re: different motors

I with the rest of the posters here.

Get your old engines back under your care and control.

They will be repairable and probably relatively cheaply. They might not be as new but they will be good.

I don't know how mechanically savvy you are but now might be the time to become so.
Even if you aren't doing the hands on work, you can be doing the inspection and the managing of the work.

It always easier to refit the existing engines back into the boat than trying to adapt different engines into the existing ancillary equipment.
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Old 25-03-2020, 22:13   #9
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Re: different motors

Thanks all for your 'sensible' replies and now - I tend to agree with you.

I am in Perth Australia and there isn't many GM Detroit motors about, as they switched to Volvo, Cummings etc, 20 years ago

However, need to tell you all that these motors were in the boat when she sunk. I removed all the injectors and had motors rotating but told to stop by insurance assessor. 9 months later, the insurance company wouldn't pay out and I had two seized motors.

They have now been stripped, well pistons were still in sleeves when I last saw it, with one crank being pitted and one cam, when motors went under, 32v went to weakest point to earth and that was a cam bearing - which has now fused onto the block.

That is the last I saw of the motors ( 6 months ago) and now knowing that the mechanic is a right prick, imagine he has just left them out in the weather - so everything exposed.

Gearboxes were stripped and needed minor work.

Cheers

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Old 25-03-2020, 23:06   #10
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Re: different motors

GBMacca
Not sure what your budget is but these motors looked good for the price. Slightly lower horse power but maybe you can google other 55’ Chris Craft and see if any one else has different motors. I surveyed a similar size American boat in Bundy that had lower hp motors. I will find the survey and let you know.
https://www.gumtree.com.au/s-ad/rans...nes/1234769353
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Old 26-03-2020, 00:35   #11
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Re: different motors

GBMacca I just found the file and it was a 58 foot Haterras that had the screaming Jimmy's replaced with two 250hp John Deere diesels. If I remember rightly the owner was happy with the conversion. The engine room looked huge with the smaller motors in it.
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Old 26-03-2020, 04:06   #12
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Re: different motors

Quote:
Originally Posted by gbmacca View Post
Thanks all for your 'sensible' replies and now - I tend to agree with you.

I am in Perth Australia and there isn't many GM Detroit motors about, as they switched to Volvo, Cummings etc, 20 years ago

However, need to tell you all that these motors were in the boat when she sunk. I removed all the injectors and had motors rotating but told to stop by insurance assessor. 9 months later, the insurance company wouldn't pay out and I had two seized motors.

They have now been stripped, well pistons were still in sleeves when I last saw it, with one crank being pitted and one cam, when motors went under, 32v went to weakest point to earth and that was a cam bearing - which has now fused onto the block.

That is the last I saw of the motors ( 6 months ago) and now knowing that the mechanic is a right prick, imagine he has just left them out in the weather - so everything exposed.

Gearboxes were stripped and needed minor work.

Cheers

Gbmacca



That's still not fatal. If you've got bad pistons or sleeves, I've seen new piston & sleeve kits on Fleabay for as little as $100 USD; you can buy them here for $178: https://dieselpro.com/detroit-diesel...nder-kits.html. Here's an entire overhaul kit with all new pistons and sleeves and all the bearings and gaskets for $1671 USD: https://dieselpro.com/detroit-diesel...e-rebuild.html. You can get camshafts out of a junkyard if you need to (or buy reman ones for $700 -- $800), and any good machine shop can bore out bad bearings and put in an insert. The crankshafts are unkillable -- in the worst case they grind them for oversize bearings.



It's just not that big a deal -- these beasts are pretty much impossible to kill. As others have said -- being left out in the weather is not really a problem for those massive old lumps of iron. Archeologists 10,000 years from now will probably be digging up those Screaming Jimmies and startin them up.


It will be much cheaper to rebuild your engines, than to try to repower, especially if you are repowering with different engines.


Of course if you just DON'T LIKE THEM -- and DD's are a matter of taste -- that's a different matter, and this would be a good time to put in something you like better. But prepare a big bucket of cash.
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Old 26-03-2020, 04:33   #13
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Re: different motors

My 4-53 Detroit sat out for ten years berfore installation and twelve before use. All that was bad was some dried up gaskets, two on the engine and two in the tranny. Asenior mechanic showed me how, as a rank amateur, to deal with the complex part, which is the head and everything attached to it like injectors and valves. Oh, one injector needed flushing.

I'll bet that there is nothing wrong with your engines. Just test them as soon as possible. Fast Fred had a good algorithm above.
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Old 26-03-2020, 04:37   #14
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Re: different motors

Quote:
Originally Posted by Dockhead View Post
That's still not fatal. If you've got bad pistons or sleeves, I've seen new piston & sleeve kits on Fleabay for as little as $100 USD; you can buy them here for $178: https://dieselpro.com/detroit-diesel...nder-kits.html. Here's an entire overhaul kit with all new pistons and sleeves and all the bearings and gaskets for $1671 USD: https://dieselpro.com/detroit-diesel...e-rebuild.html. You can get camshafts out of a junkyard if you need to (or buy reman ones for $700 -- $800), and any good machine shop can bore out bad bearings and put in an insert. The crankshafts are unkillable -- in the worst case they grind them for oversize bearings.



It's just not that big a deal -- these beasts are pretty much impossible to kill. As others have said -- being left out in the weather is not really a problem for those massive old lumps of iron. Archeologists 10,000 years from now will probably be digging up those Screaming Jimmies and startin them up.


It will be much cheaper to rebuild your engines, than to try to repower, especially if you are repowering with different engines.
Totally agree with Dockhead.

Get hold on your old engines, pull them apart, hunt down the parts, find a good machine shop in Perth (there were several really good ones around that I knew of a decade ago) and get cracking!
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Old 26-03-2020, 04:42   #15
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Re: different motors

IF the engine has been stripped of all useful parts and the tranny its time to look elsewhere .


A running takeout pair might suit .Call some of the local engine sellers and ask if someone is upgrading.


Put an add in Craigs list if it exists there.


IF you have the trannys and there OK look at less popular diesels in skool buses etc,


In the USA the international DT 466 is a great engine and dirt cheap , usually found in skool buses.
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