Perkins 4.108 - which variant?

[Cheechako]

Originally Posted by oldcal46skipper

Source: Perkins Engines Workshop Manual,
Publication No. 601 SER 05821088 Publish date 1982
Workshop Manual for 4.108 & 4.107 & 4.99 Marine Engines


Page B.2 Technical Data Rating Details
4.108

Pleasure Craft (high speed) 47 shp @ 4,000 RPMs
Pleasure Craft 45shp @ 3,600 RPMs
Commercial Craft 37shp @ 3,000 RPMs

Note: Maximum rev/min is dependent on hull design as the correct engine rating should be matched to the duty of the boat.

That what Mr. Perkins says...
Having rebuilt over 200 Perkins 4.108's, spin them on up there and call me for a rebuilt Long Block

That's what I've been saying on this forum for years. Many engines are rated at different rpms for different uses. Yet, people still insist you have to run an engine at near max rpms...
Buy your engine with the HP you want at the RPM you want. Or run your engine at an rpm that develops enough HP for your boat. You dont have to run it higher.

[kenbo]

Originally Posted by Cheechako

That's what I've been saying on this forum for years. Many engines are rated at different rpms for different uses. Yet, people still insist you have to run an engine at near max rpms...
Buy your engine with the HP you want at the RPM you want. Or run your engine at an rpm that develops enough HP for your boat. You dont have to run it higher.

I've always felt, maybe wrongly, that most folks equate rpm to load. And in the case of a propeller that relationship is not linear or reliable. People hear/read you have to rune the engine at 75-80% load and they simply due the math of 75% of max rpm and think that their done.

A good example of staying in the sweet spot of load or fuel map is a variable pitch propeller being used in conjunction with an exhaust gas pyrometer. Set rpm wherever you like, and then vary pitch (load) until you get to the sweet spot on exhaust gas temp. Most if not all diesel manufacturers will tell you the range of temps for the fuel map sweet spot if you ask.

People could do the same with a fixed blade. You can safely overprop
IF you also use an exhaust gas pyrometer. Save a lot of money on fuel and run at low rpm. Whats the commercial fisherman saying..."fuel in the tank is money in the bank".

[kenbo]

Originally Posted by Wainui

Some good information above.
Have you ever had a 4108 rev at 4000?
I had heard that the exhaust system choked it down, but I maybe mistaken.
My engine was early 60’s.
I had to get a larger HE to stop overheating.
Regards

Unless you need 47 hp why would you? If you mean can a 4.108 reach 4000 rpm, then yes, if the fuel delivery system and exhaust system is correct. But I wouldn't run it there for very long.

[CSY Man]

. Have you ever had a 4108 rev at 4000?

Yes, had to run @4000 for 2 sea-trials: When I bought the boat and when I sold it 14 years later: It delivered 4000 both times, no problem.

Sure you can over-prop with a pyro gauge to make sure the engine is not overloaded, or just prop it so as to reach the rated RPM.

[Midnight Son]

Most engine OEMs used to, before electronics took over our engines, derated power first, with a lower fuel stop, then with smaller capacity injectors At some point they would use the next smaller engine in the lineup, at it's highest STABLE rating.

[NNBill]

When talking "variants" of the old 4-108 workhorse, the only two major different ones where the 4-108, and the 4-108NA. The major differences where the 4-108 has a Hurth / ZF transmission and a Bowman heat exchanger. This is identifiable by the heat exchanger being integral with the exhaust manifold, and having two black rubber end caps holding the core into the housing. These engines also had, I believe Lucas electrical components. The 4-108NA (North America) engines had Borg Warner Velvet drive transmissions, Sendure type heat exchanger mounted over the bell housing and Delco electrical components.

[CF32907]

Originally Posted by rbk

That is burnt fuel, white is unburnt fuel.

You do have some idiots respond giving info they know nothing about. I was a marine engineer and surveyor for 20 years. White smoke means your burning water, best find out where it's coming from. Rich black smoke is unburned fuel, you have one of these problems. Your over propped or have a fouled prop. Your injectors are carboned up or spray patterns are fouled and injectors need to be cleaned and spray patterns set. A 4108 should have a WOT set to around 34-3600 rpm. That don't mean to run it there. A good cruise rpm is the top of the torque curve, that's about 24-2600 rpm. That will be the most economical for that engine for the cruise speed durived. I've seen 4108 go to 6-8000 hr's before needing rings and valves ground. These are just bullet proof engines. To finish off on exhaust, if you have gray smoke, that is oil burning, and it will be either bad valve guides or rings.
Most people think over propping will make them go faster on lesser amount of fuel, this will not happen. When you over prop, unburned diesel will was down cylinder walls, stripping the oil film and greatly reduce time for worn rings.
The 4108 is used in pumps, gensets, hydraulic mules, etc. They are designed for some applications up to 4000 rpm. Parts are available world wide.
Boats are normally set for 3500rpm WOT, so if your turning up 3800 you are under propped and not utilizing HP for the amount of fuel burned. If your top RPM is 2800-3000rpm your over propped and wasting fuel while wearing out your engine prematurely. These rpm are the same if your a light displacement or a barge, makes no difference in what there pushing.
Happy Sailing All,
Capt. Vince Rakstis, Ret. St. Petersburg, Fl.

[CF32907]

CaptVR here again, I forgot to mention one other item. On starting a cold engine, all of the small Pekins and most other smaller displacement diesels, especially if there turboed will smoke on start up. You will normally always have a bit of blue black smoke on start up. After about 5-10 minutes and fast idle 900-1000k and worm up, you should not be getting that smoke. But some smoke is normal on start up. Also applying power relatively fast, you may get a little smoke, no real concern.
Again, happy sailing all. CaptVR

[rbk]

Originally Posted by CF32907

You do have some idiots respond giving info they know nothing about. I was a marine engineer and surveyor for 20 years. White smoke means your burning water, best find out where it's coming from. Rich black smoke is unburned fuel, you have one of these problems. Your over propped or have a fouled prop. Your injectors are carboned up or spray patterns are fouled and injectors need to be cleaned and spray patterns set. A 4108 should have a WOT set to around 34-3600 rpm. That don't mean to run it there. A good cruise rpm is the top of the torque curve, that's about 24-2600 rpm. That will be the most economical for that engine for the cruise speed durived. I've seen 4108 go to 6-8000 hr's before needing rings and valves ground. These are just bullet proof engines. To finish off on exhaust, if you have gray smoke, that is oil burning, and it will be either bad valve guides or rings.
Most people think over propping will make them go faster on lesser amount of fuel, this will not happen. When you over prop, unburned diesel will was down cylinder walls, stripping the oil film and greatly reduce time for worn rings.
The 4108 is used in pumps, gensets, hydraulic mules, etc. They are designed for some applications up to 4000 rpm. Parts are available world wide.
Boats are normally set for 3500rpm WOT, so if your turning up 3800 you are under propped and not utilizing HP for the amount of fuel burned. If your top RPM is 2800-3000rpm your over propped and wasting fuel while wearing out your engine prematurely. These rpm are the same if your a light displacement or a barge, makes no difference in what there pushing.
Happy Sailing All,
Capt. Vince Rakstis, Ret. St. Petersburg, Fl.

I can produce hundreds of more articles like this from reputable companies from four by fouring, marine, tractors, tractor trailers and on and on and on:
https://www.capitalremanexchange.com...moke-by-color/

[rbk]

Originally Posted by CF32907

You do have some idiots respond giving info they know nothing about. I was a marine engineer and surveyor for 20 years. White smoke means your burning water, best find out where it's coming from. Rich black smoke is unburned fuel, you have one of these problems. Your over propped or have a fouled prop. Your injectors are carboned up or spray patterns are fouled and injectors need to be cleaned and spray patterns set. A 4108 should have a WOT set to around 34-3600 rpm. That don't mean to run it there. A good cruise rpm is the top of the torque curve, that's about 24-2600 rpm. That will be the most economical for that engine for the cruise speed durived. I've seen 4108 go to 6-8000 hr's before needing rings and valves ground. These are just bullet proof engines. To finish off on exhaust, if you have gray smoke, that is oil burning, and it will be either bad valve guides or rings.
Most people think over propping will make them go faster on lesser amount of fuel, this will not happen. When you over prop, unburned diesel will was down cylinder walls, stripping the oil film and greatly reduce time for worn rings.
The 4108 is used in pumps, gensets, hydraulic mules, etc. They are designed for some applications up to 4000 rpm. Parts are available world wide.
Boats are normally set for 3500rpm WOT, so if your turning up 3800 you are under propped and not utilizing HP for the amount of fuel burned. If your top RPM is 2800-3000rpm your over propped and wasting fuel while wearing out your engine prematurely. These rpm are the same if your a light displacement or a barge, makes no difference in what there pushing.
Happy Sailing All,
Capt. Vince Rakstis, Ret. St. Petersburg, Fl.

Here's a few more for ya to read up on. Too bad thinking about all the customers you probably overcharged or misdiagnosed over the years...Yes excessive continuous white smoke can indicate a cracked head, but to jump to that right off the bat is fear mongering and a money grab form shady mechanics looking for a big job when in reality its probably just a fouled injector.

https://www.berrimadiesel.com/diesel.../smoke-signals

https://www.bestpackers.org/what-die...g-to-tell-you/

https://www.cbac.com/concord/media-c...lained-by-our/

https://nwfuel.ca/types-diesel-exhaust-smoke/

https://www.boats.com/how-to/diesel-...lack-or-white/

https://www.agriculture.com/machiner...ls_198-ar15040

https://www.injectorsdirect.com/does...ctor-problems/

https://www.cruisingworld.com/how/re...smoke-signals/

Excessive Smoke | Texas Outlaws Diesel & Auto Repair

https://www.rpmdiesel.com/marine-die...-smoke-colors/

[kenbo]

Originally Posted by CF32907

You do have some idiots respond giving info they know nothing about. I was a marine engineer and surveyor for 20 years. White smoke means your burning water, best find out where it's coming from. Rich black smoke is unburned fuel, you have one of these problems. Your over propped or have a fouled prop. Your injectors are carboned up or spray patterns are fouled and injectors need to be cleaned and spray patterns set. A 4108 should have a WOT set to around 34-3600 rpm. That don't mean to run it there. A good cruise rpm is the top of the torque curve, that's about 24-2600 rpm. That will be the most economical for that engine for the cruise speed durived. I've seen 4108 go to 6-8000 hr's before needing rings and valves ground. These are just bullet proof engines. To finish off on exhaust, if you have gray smoke, that is oil burning, and it will be either bad valve guides or rings.
Most people think over propping will make them go faster on lesser amount of fuel, this will not happen. When you over prop, unburned diesel will was down cylinder walls, stripping the oil film and greatly reduce time for worn rings.
The 4108 is used in pumps, gensets, hydraulic mules, etc. They are designed for some applications up to 4000 rpm. Parts are available world wide.
Boats are normally set for 3500rpm WOT, so if your turning up 3800 you are under propped and not utilizing HP for the amount of fuel burned. If your top RPM is 2800-3000rpm your over propped and wasting fuel while wearing out your engine prematurely. These rpm are the same if your a light displacement or a barge, makes no difference in what there pushing.
Happy Sailing All,
Capt. Vince Rakstis, Ret. St. Petersburg, Fl.

I have a few questions Capt. When you say WOT of 3400-3600 do you mean loaded or unloaded? Most 4.108's that I've been around have the fuel rack stopped at 4000. So if your recommendation is WOT 3400-3600 loaded your overpropped. If you mean reset the fuel rack stop to 34-3600 and prop to that number then I agree. I think the 4.108 is rated for continuous duty at 3000 rpm delivering around 40 hp.

Black smoke indicates incomplete combustion of the fuel, not necessarily "unburnt" fuel meaning it's still in the liquid phase.

[Capt Billy]

Originally Posted by lancelot9898

The max rating is 4000 rpm and the max continuous is 3600. I cruise at 2500 rpm doing 6 plus knots.

According to the tech manual the 4.107 and the 4.108 the maximum rated output is 3000 rev/min

[kenbo]

Originally Posted by Capt Billy

According to the tech manual the 4.107 and the 4.108 the maximum rated output is 3000 rev/min

From my Perkins shop manual:

Maximum continuous is 3000 (37 hp) meaning 24/7/365

Maximum intermittent is 3600 (46 hp) meaning 1 hour limit at this rpm

But this is all pedantic if you don't set your fuel rack stop accordingly or operate with an exhaust gas pyrometer.

[mabowers]

I get 3600 max, *with a clean prop*, 2700 max with 3 months of barnacles

[exMaggieDrum]

I had a circa 1972 4108. I had black smoke since I bought the boat. Every shop mechanic and people I know who really know engines said it was from unburnt fuel. Which could be due to injector issues or too much load from a fouled or too large or overpitched prop.


In my case it was an overpitched prop. I was in the process of moving to a smaller pitch but sold the boat first. I told the new owners about it.


At the slip, in neutral I could get 3400rpm or so. In gear, only about 2600 max. And my manual (original) said I should get 3600 max but should avoid going over 3000 unless for emergency or short times.



I really need those extra rpms at the prop and was not getting the fuel economy I should have. I was going to put on a MaxProp or a FlexFold and they both told me I needed the same diameter prop with a smaller pitch. I had a 17" prop with 14 pitch. I was told I should have a 10 or may be 11 pitch max. My experience with MaxProp is that they really know what they are talking about in recommending prop specs.