Engine re-build - Detroit - Desicion made - Start 03 Nov 2011

Divemaster1 said:
I'll look at this and see what can be found ...
Click to expand...
I see your point, but I for one would be really surprised to find those bits in the sump.
Just thinking of the basic air flows inside the engine while running, imho there's only one way they could reasonably go, and it's through the exhaust.
I would expect a careful examination of the turbo blades borders to show at least some (albeit hopefully not critical) marks.
Best of luck anyway, looking forward to read about the next steps!
 
Divemaster1 said:
During operation, there will be water vapour from the air charge ... and some oil/fuel vapour fumes etc., whch will settle at the bottom of the air box. This condensation is removed by the airbox pressure through drain outlets in the side of the block...
Click to expand...

I'm intrigued. I may be being thick though. During operation, there is a flow of air from the atmosphere, through the roots blower/turbocompressor, and into the cylinder through those ports halfway down the cylinder liner. Then out thru the exhaust valves. At cruise that's quite a wind on the intake side- 1500x12 litres of slightly compressed air per minute, give or take. surely that wind will remove any moisture and fumes? Also the entire block is say ~80deg when running, so how is any moisture in atmospheric air going to condense? I don't get it

Also, given that the airbox is pressurised by the turbo compressor and/or roots blower, admittedly only to maybe 1 bar or so, wouldn't you get an air leak/bleed out of these drains? Into the sump? Does that not matter? Maybe not. Maybe the drains are very small bore. In which case your missing metal could be stuck anywhere in the labrinth work of this drain system, and not necessarily in the sump

Sorry for all the questions. you've got us hooked on this project with this thread! We all want to know every last detail about DD71s!
 
Last edited:
sarabande said:
Alf - no sarcasm. I am just happy that everything seems to be going well- if slowly - and wish I had your skills and knowledge. It is a seriously good post, and will encourage someone else to have a go at a simpler repair perhaps, and that will make them a better sailor.


The pics in particular are excellent but a bit daunting for someone who just normally deals with Landrovers :)
Click to expand...

OK .. thanks .. sorry for reading something into it which wasn't there... :D
 
jfm said:
I'm intrigued. ..........During operation, there is a flow of air from the atmosphere, through the roots blower/turbocompressor, and into the cylinder through those ports halfway down the cylinder liner. Then out thru the exhaust valves. ...... surely that wind will remove any moisture and fumes? Also the entire block is say ~80deg when running, so how is any moisture in atmospheric air going to condense? I don't get it

Also, given that the airbox is pressurised by the turbo compressor and/or roots blower, admittedly only to maybe 1 bar or so, wouldn't you get an air leak/bleed out of these drains? Into the sump? Does that not matter? Maybe not. Maybe the drains are very small bore. In which case your missing metal could be stuck anywhere in the labrinth work of this drain system, and not necessarily in the sump

Sorry for all the questions. you've got us hooked on this project with this thread! We all want to know every last detail about DD71s!
Click to expand...

Keep on asking and I'll have more to investigate... :)

Agree that when running not much will gather ... however, six cylinders, two stroke means that when stopped @~80 deg at least one piston will be low in the cylinder with flow from atmosphere throught he scavenging ports, with exhaust valves open .... cold air from outside, hot cylinder/block will generate moisture... which will have to be drained out somehow to avoid ingestion into cylinder again upon startup and running.... that is done through small bore drainholes with valves which only is open at low/no pressure.

I need to investigate more into this, but does not hold up hope to find the pieces .... but still want to try .... as well as visually checking turbine blades....

Glad that the thread is engaging... :)
 
Divemaster1 said:
with valves which only is open at low/no pressure.
Click to expand...

Ah, that could be the secret Alf. The drains are open when engine is stopped, but close when the air intake system is lightly pressurised by the roots blower/turbocompressors. Neat trick.

I hadn't appreciated what a nice engine these DDs are till I saw this thread (and I've since read some more on them via google)
 
jfm said:
....... I hadn't appreciated what a nice engine these DDs are till I saw this thread (and I've since read some more on them via google)
Click to expand...

Nice to hear that others see some of the good sides of these iron lumps...... got bad rep in leisure boating for being heavy, thirsty and noizy ....... and usual problem is builders / owners overloading engines by over sized props and poor installation. They don't like that .... but love to work.... and sounding good doing so (noizy without right water traps though )..
 
I am a great lover of these engines, like any engine they need installing correctly and setting up with well matched components. I have even re-engined with DD's and never had a problem.

Having worked on them in industrial applications where they are absolutely hammered i appreciated them, easy to work on, durable, and with some nice design touches. These are the sort of engines the average individual can work on with confidence as they are not overly complicated.
 
ccscott49 said:
......... If you could have got at the airbox, you can see the piston rings as they pass the induction ports. Just as an aside, you can judge the wear (on military engines anyway) by inspecting the rings through the airbox, they have a groove etched in them, that when it disappears, the rings need changing. Clever eh!
Click to expand...

Still groves etched in the compression rings.... and access to the inspection ports are easy from the outside... will get a photo next time I'm up.... as that may be the place where I'll find the broken pieces ...
 
Divemaster1 said:
Changed my mind I think .... DD recommended full cylinder kit (Liner, Piston crown & skirt, Rod, Clamshell bearings etc.) as "best practice" ...so asked for price + new seals etc.......
Click to expand...
Yet another change of plans ..... looked at the fragility of piston rings last night (and broke one .... on the old piston).... , made some calls etc., and decided to hand in the removed assembly (Liner, Piston, rod etc.) to local DD. They will check rod for damage, and do the piston assembly, including inserting the piston into the liner for me... so the liner and new piston is ready to go into the cylinder block. Saves me damaging the rings etc., with the wrong tools.
 
Latestarter1 said:
Steel articulated pistons came out in early 90's.

Liner and piston crown both expand at the same rate enabling very tight tolerances.

You can get juce the brains out of the jug with no risk of burning the crown.

Alloy skirt contains cocktail shaker arrangement to keep cooling lube oil up in the crown area.

Downside, greater reciprocating mass, cost, and a bit of a biggie, if you drop a valve, all ends in tears. Steel piston, steel valve no room for everybody, so if they get half a chance they exit to atmosphere..........Out the side of the block.

Concept gradually being replaced with iron pistons.
Click to expand...

The leyland (rolls designed) L60 opposed piston engine used in Chieftains, up to Mk3, had oil cooled seperate piston crowns, made of bronze, a slip ring on the little end fed oil to it. Not articulated, but bolted on, that was back in 1970.
 
ccscott49 said:
The leyland (rolls designed) L60 opposed piston engine used in Chieftains, up to Mk3, had oil cooled seperate piston crowns, made of bronze, a slip ring on the little end fed oil to it. Not articulated, but bolted on, that was back in 1970.
Click to expand...

Well that accounts for it!

Rolls Royce never had a clue about how to design diesel engines.

Served on a ship with Rolls CV8 gennies, over complex, noisy horror boxes. And as for Rolls Eagle truck engines a plumbers nightmare, incapable of containing it's vital fluids.

Story comes full circle, when we were replacing Jaguar gasoline engine in the Scorpion FV101 light tank. On a visit to Bovingdon one of the retired brass who never actually retire showed me a Chieftan tank tucked away in one of the workshops. At the time of its introduction Chieftan had the best gun and best armour and huge export potential exept it had hopeless engine. The tank I was shown was a bit different, Leyland L60 had been replaced with Detroit 12V71, built by Vickers prove the concept in field trials. Caused red faces in Whitehall, wiped the floor with L60 powered version.
 
Latestarter1 said:
Well that accounts for it!

Rolls Royce never had a clue about how to design diesel engines.

Served on a ship with Rolls CV8 gennies, over complex, noisy horror boxes. And as for Rolls Eagle truck engines a plumbers nightmare, incapable of containing it's vital fluids.

Story comes full circle, when we were replacing Jaguar gasoline engine in the Scorpion FV101 light tank. On a visit to Bovingdon one of the retired brass who never actually retire showed me a Chieftan tank tucked away in one of the workshops. At the time of its introduction Chieftan had the best gun and best armour and huge export potential exept it had hopeless engine. The tank I was shown was a bit different, Leyland L60 had been replaced with Detroit 12V71, built by Vickers prove the concept in field trials. Caused red faces in Whitehall, wiped the floor with L60 powered version.
Click to expand...

That's cos they had a thing about making rear crank seals out of wood!
 
tinkicker0 said:
simple, experienced diesel guys dont get paid enough to buy a diesel boat.
Click to expand...
I've just seen this, which made me thinking.
And you know what, that's not too bad, you still have a petrol boat after all.
It would be ok, if it weren't that your skills can literally keep the economy moving, whilst there are other foks around whose skills are questionable at best, and criminal at worst, who are paid enough to buy boats which they would not even be able to move from the dock, if someone else didn't on their behalf.
Sad world, innit? :(
 
removing the flybridge

hi all
sorry to get involved but i had to comment on this thread re removing the flybridge/saloon,it has been done before and actually is common on "traders" the big ones of course !
A very good friend and a fantastic shipwright told me a story of how they did it when he was an apprentice ?
Just thought you ought to know it is an option.
good luck with your engines
 
You must log in or register to reply here.

Other threads that may be of interest

N
Volvo Penta Alarm Module/Alternator Issues
Replies
1
Views
171
superheat6k
superheat6k

Share this page

Top