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4108 rebuild

nimbusgb

New member
"the 4-108 in my 1987 boat has

"the 4-108 in my 1987 boat has some 6000 hours plus on it. After running up to temperature coming back to idle causes the oil pressure light to come on. setting the throttle to arouns 1200 rpm keeps the light out until things have cooled down a few degrees and after a while normal idle can be tried without the oil pressure switch kicking in.

I have a few problems. 1/ the boat is 2000 miles away so I cant get to it to test things and may not be able to for another 6 weeks or so. 2/ I had no oil pressure sensor installed at the time so I cant verify actual pressure.

So - With 6000 9 not pampered 0 hours or more on the clock it is likely that the engine needs some attention anyway.
I have been offered a complete engine for a good price. Similar spec with all the ancilliaries and a somewhat 'questionable' service record since its rebuild about 500 hours ago.

My idea is as follows.

Aquire the replacement engine and depending on its condition either do a limited, partial or complete rebuild.

Ship engine to boat and get it replaced at the yard.

Questions are :

Wisdom of replacing a 4108 with another 4108 ( 0 to 500 hour engine ) It could well last another 20 odd years ( by which time all the diesel may have run out anyway ) or should I look at re-engining now?

How does one tell the condition of the engine without a teardown? Could be run 'on a bench' but no way to load it significantly. Compression tests and oil pressure tests obviously but what else?

Anything to 'look out for' when approaching this project?

Thanks"
 
"G; Day Ian,
6000hr


"G; Day Ian,
6000hrs is pretty good innings for a 4
108 a couple of things you can do that may help
#1 check lube oil cooler clean +water flow.
#2. change to heavier grade oil say 20/50.
#3 change at 100hr intervals inc filter.
#4.check pressure with manual gauge.
To find out condition of a engine with out a hot test as you would be aware is difficult they have all been JUST been reco'd with paint job.
In no particular order.
#1 oil+fuel leaks.
#2 check for condensation/ rust under rocker cap-cover.
#3 oil- coolant condition.
#4 check water pump + alternator bearings
#5 rock grank pulley back & forth should be smooth no clunks.
#6 remove injectors look for water stains, they should a very dark grey colour
#7 remove starter look for rust, condition of ring gear +pinion gear &oil leaks.
#8 check fuel filter for h2o+ grit
#9 check lift pump filter screen for dirt.
#10 remove sump check be's & mains piston btms ect. Hot test.
#1 comp test.
#2 lube oil press test
#3 fumes at dip stick &rocker cover - back pressure.
#4 unload & load each injector in turn, listen for sharp mettalic knock.
# 5 check coolant for oil and bubbles.
#6 check exhaust colour & beat.
#7 take engine to at least 3,000rpm..listen.
# 8 ease of starting 108s can slow with out help.
#9 check the head ect for hot spots.
Hope this helps, Shakey."
 
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