replace or repair 4.108 perkins 1989

[c.K.]

my engine lacks compression turns over quite fast yet ran well for me the past 10 years
Oil analysis good no excessive oil use , no smoke, guess around 3500 hrs
Thinking new piston liners or replace
Just installed new prop shaft etc any suggestions are much appreciated
Thank you
CK

[marcjsmith]

3500 hours seems low for a rebuild. you say low compression, did you remove injectors and get a valid pressure?


if your intake is blocked this will cause the engine to spin very fast while starting as well



Causes of Low or No Compression

While it's good to know if you're experiencing low or poor compression, this is often just a symptom of a larger problem within your engine. There are quite a few things that can lead to compression issues, including:

• Leaking or Broken Valves:This allows the compression to escape the cylinder where the issue is located.
• Leaking or Worn Piston Rings: When these rings wear or fail, compression can leak from the cylinder.
• Broken Valve Spring: A broken valve spring allows the valve to stay open, which lets the compression leak out as well.
• Blown Head Gasket: This creates a poor sealing surface, which can allow compression to leak from one or more cylinders, depending on the extent of the damage.
• Worn or Broken Camshaft: Issues with your camshaft prevent the valves from opening the proper amount, which doesn't allow for air and gasses to enter and exit the cylinder.
• Broken Timing Belt or Chain: If this isn't working properly, then the camshaft isn't rotating at a proper speed, preventing compression from taking place as it should.
• Hole in Piston: A hole in the piston would again allow for compression to leak out.

Monitoring and Identifying Compression Issues

Low or no compression can affect one or all of the cylinders in your engine. Running a compression test can help you identify where you're having your issue, as well as helping to narrow down what specifically might be causing your problem. For example, a broken valve can be a reason for no compression in only one cylinder.
Low Compression in One Cylinder

Some common causes of low compression in only one of your cylinders include leaking valves, broken valve springs, camshaft wear, broken rings, or a bad head gasket.
Low Compression in All Cylinders

If your test results are showing low compression in all of your cylinders, it might be caused by engine flooding, worn piston rings, cylinder glazing, poor air filtration or dusting, or timing problems.
No Compression in One Cylinder

No compression isolated to one cylinder might indicate a dropped valve seat, broken valve spring, dropped valve, broken valve, or piston damage.
No Compression in All Cylinders

If you're experiencing no compression in all of your cylinders, it might be caused by a broken camshaft.
Again, a compression test can help you narrow down where your issue might be. Running a compression test helps you to know how your engine is performing year-to-year (or however long you go between compression checks), as well as how your cylinders are doing compared to each other. This allows you to isolate the problem, whether it is in one, two, or all cylinders.
A compression test can be run through the glow plug holes or the injector holes, depending on the engine specifications and the type of gauge you're using. Refer to manufacturer instructions for more information on your exact engine type.





FWIW when i was working on my perk 4108 beta rough quoted me a bit under 15k for a new engine.

[c.K.]

many thanks for this elaborate reply
some items on the list i have to eliminate like a hole in piston head gasket
This problem has been a gradual one, once running lots of power no smoke or oil use also the oil analysis was good I 'm thinking new piston liners and rings any other problems would show up during that repair
Like i mentioned just put in new shaft bearing prop another engine would compromise prop or shaft as well plus a haul out
what do you think

[marcjsmith]

hard to say, you gonna do the wok yourself and or farm it out. going to try to do in the boat or remove and send out...


Easy access or a lot of boat yoga?


in frame rebuild kit is 500 bucks I'm fairly mechanically inclined and I have good access so I'd try to do it myself over the winter. might have to do some light machine work..


still 3Khours seem very early for a rebuild..

[c.K.]

THANKS FOR THAT
no The repair I won't touch but installing a new engine I have done that think I'll start to take the engine out first

[skipperpete]

Consider adjusting the valve clearances and maybe observing cylinder blow by before diving into a rebuild.
A compression test is gives a good indication of cylinder pressure only...... and no clue to why the compression might be low so try a leakage test as well. You can use the same injector adapter as the compression test and will get a really positive indication of where the compression pressure is actually being lost.

[Stewie12]

No smoke or oil use suggests no wear and tear in my opinion. Have a compression test before you do anything.

[Greg Mason]

I am with Skipperpete and do a valve adjust. I had a blown head gasket on mine, and the only telltale was making black water in the reservoir. Do the easy things first.

[c.K.]

thanks I can work with that

[TreDeuce]

It is a diesel, so it might be a carbon buildup in the intake port which would/could cause the symptoms described. I had a similar problem with my Perkins and a Nissan diesel.

[MJH]

Originally Posted by c.K.

my engine lacks compression turns over quite fast yet ran well for me the past 10 years
Oil analysis good no excessive oil use , no smoke, guess around 3500 hrs
Thinking new piston liners or replace
Just installed new prop shaft etc any suggestions are much appreciated
Thank you CK

Replace or Repair? That's always a big question particularly when it comes to the engine. You first need an objective opinion as to what the problem(s) are, it could be more than one. If you are not capable of an accurate diagnosis then get an expert.

Are you the original owner of the engine? You "guess" at 3500 hours which isn't bad for 32 years or about 109 hours per year average for a sailboat. The model and serial number will tell you the manufacturing date, how did you "guess" at 3500 hours? I'm suspicious because of the lack of an hour meter reading.

You didn't mention Rebuild, an option that is only as good as the man (no offense ladies) doing the job. Once the rebuilder gets into it all sorts of additional options suddenly appear beyond the original intent and in the end you still have a 1989 engine. Choose carefully.

Good Luck.

~ ~ _/) ~ ~ MJH

[PaulvR]

Disclaimer: I am a Perkins man, on my boat, on my farm, and in my business: BUT, 3500 too few hours for this sort of thing. Great advice posted, use it.

Otherwise, a 4108 rebuild is a (one of very few) blue water yachting gold standard for the past many many decades on cruising boats. Do it if it makes you feel better, and then you know what you have, give it clean air, oil, water and fuel, and it should do more than 10000 hours!

[Lepke]

It's almost always cheaper to rebuild an existing engine than replace it with a new one. A properly rebuilt engine will last as long as a new engine. An engine designed with replaceable sleeves can be rebuilt as long as parts are available.
I have a 1972 4-108 on a generator and twin Detroits from 1947. All have many rebuilds left.

[cottonsail]

I went through the same dilemma. What I came up with is this: The 4-108 is ancient technology. It does not have a rear main seal, it has a packing. Like a 1955 Buick. The combustion technology is directly from Rudolph Diesel himself. 1897 technology. I chose to go with a Volvo Penta D2-50F new engine and transmission, alternator etc. a complete package. I now cruise at just under 7kts vs 6.2kts at the same 1 gallon per hour. When I do an oil change it takes about 10 hours of running before I see any oil discoloring. An oil change on the old Perkins the oil was totally black in 20 seconds. A lot is be said for newer technology's. The Volvo is a really sweet running engine but I do NOT recommend it because of trying to deal with Volvo Penta USA. Getting technical information from them is impossible. You cannot even get the installation manual from them and it does not come with the engine. I never saw it until a Volvo Penta tech came out to inspect and sea trial my installation. He downloaded it from a website only a Volvo tech can access. To do it all over again I would seek a new technology diesel but not Volvo.

[Niall leslie]

Applicable notes:
- If you cannot undertake the diagnostic work to a high standard then get in someone who can with the requisite experience and equipment. Any repairs required may / may not be minor.
- A rebuild is with all specifications returned to as new.
- For the factory Perkins rebuilds all that is used from the original engine are the head and block castings, manifolds and sump if OK. Cost is similar to new.
- All else is a repair.
- Very likely the best long term solution if major repair etc. is needed would be a new engine and gearbox etc.
- Most people concentrate just upon operating hours and forget the maintenance standards, lay up standards, environment etc.

Good luck,

Niall.