Perkins 4-108 hard to start

[Seman]

Hello Cruisers & Engineers

I have had my Passport 42' for the past 14 years in a tropical climate.
It takes about 6-7 revolutions before it will start when cold. Same for the past 14 years.
Somebody suggested that the return lines from the injectors are too small, sucking in air overnight.???
Can anybody help?

[Alan Wheeler]

Ummm that's an interesting ;-) suggestion. Besides, if air was in the lines, it would most likely not start at all. I think the guy maybe thinking and getting confused with another similar fault due to return lines sizes. It is not air that causes the issue however.
But firstly,
You should expect some delay. Just how long depends on many factors. The essential things to check are,
Engine start battery in good condition and charge??
Startermotor in good condition, turning over at full speed???
These are the First most common causes. It could easily be that the engine is simply not turning over fast enough due to either of these possible faults. Just because it turns over, does not mean it is turning over fast enough.

Injectors in good condition with a proper spray pattern??
This is the second most common cause to poor cold starting.

Compression good??
Fuel in good condition??

All the above are important question to try and check over. A Diesel has to create a lot of heat during the compression of the air, so as the fuel will ignite. Too slow at turning over, not enough compression, mositure, cold metal etc all have an impact on the engine not getting the air hot enough to ignite the fuel. The poor injector spray pattern will allow fuel to squirt instead of spray. A squirt will not ignite as easily as a spray.

[seman_]

Hello Alan, Thank you for your speedy reply.
Have replaced the injector pump recently, also Injectors were serviced.
The Voltage on the starter motor is down to around 10V with fully charged batteries when turning over.
Thought that was acceptable.?
Speed of the starter motor is hard to check.? It sounds OK to me, but I suppose after 14 years I wouldn't know the difference.
Thanks again, Walter

[Alan Wheeler]

Intitially I would say that the voltage of 10V at the starter was too low. But that is a difficult one to measure. You need to do two test points. One at the battery and one at the starter. If the batteries are dropping to 10V, then that could be the source of one problem. If the batteries are staying closer to the 12V, then the problem could be too small diameter leads, poor electrical connections. Or....the starter is drawing too much current. This can be caused by worn bearings and the Perkins starter is prone to that. It slows the starter dramaticly. The engine will sound like it is turning over OK, but a healthy starter will make it fly.

[Ex-Calif]

Since this post went up I have been thinking this so I'll just say it.

Is 6-7 revolutions bad? It's been this way for 14 years and you don't say it's getting worse.

In 14 years you must have changed the battery bank. When the new batts went in was it the same?

As Alan eluded to there are a few variables but basically if you have fuel and air in the right mix and compression she'll start. If you really wanted to check it out I'd do a cold and warm compression check and see if there is any excessive leak down.

Oil helps seal the rings and if an older engine it could take 7 revs to get a nice film on the cylinder walls to help the rings seal.

[SkiprJohn]

Aloha Seman,
The key to starting your diesel, no matter what make, is revolutions per minute. If the starter motor is not giving you what you need, have it rebuilt. First check your batteries. 4-107s start afte a lot of encouragment at very low rpms but they start so much better and quickers when the batteries are up and the starter motor is working right.
Do you have glow plugs?
Don't use ether!!
Kind Regards,
JohnL

[Boracay]

Could you tell us how old your engine is, how many hours it has done and it's general state of repair.

The other aspect is: What are you intending to use the engine for?

An engine that is sluggish to start is not going to be a problem when it is near a large city.

In the middle of nowhere it could be a right royal pain in the neck.

[Alan Wheeler]

I have a Friend with a boat fitted with twin 450Hp Volvo engines. He has a special cut in timer fitted. When you start the engines, they turn over without starting for a few seconds so as the oil pressure comes up on them, then the timer cuts in and allows the engine to start.

[MikeNZ]

Do you have the Perkins start aid hooked up - sort of miniature flame thrower that uses diesel and an electric element!? Mine has never been connected but I think in cold weather every bit of extra warmth you can add to the fuel intake would help. Does anyone with a 4-108 use this sucessfully?

[Alan Wheeler]

It wouldn't get cold enough over your way would it Mike?? :-)

[MikeNZ]

Ha...cold is relative term!

Anyway are you North of us? I know Nelson is pretty much same lat as us.

[seman_]

Thanks for your interest & help.
I'm in the tropics, temperature should not be a problem.
The engine might have done around 10 000 hrs and I'm spending a lot of time offshore.
Will check the starter motor out.
If I can't fix it, I can live with it.

[GordMay]

Originally Posted by Alan Wheeler

Intitially I would say that the voltage of 10V at the starter was too low. But that is a difficult one to measure. You need to do two test points. One at the battery and one at the starter. If the batteries are dropping to 10V, then that could be the source of one problem. If the batteries are staying closer to the 12V, then the problem could be too small diameter leads, poor electrical connections. Or....the starter is drawing too much current. This can be caused by worn bearings and the Perkins starter is prone to that. It slows the starter dramaticly. The engine will sound like it is turning over OK, but a healthy starter will make it fly.

Fully Charged Battery Test:
No Load Open Circuit Voltage should be about 13.5 -14.2 Volts
Static Voltage Drop (not cranking) should be less than 0.3 - 0.5 Volts.
Loaded battery voltage (when cranking) should be over 10.0 - 10.5 Volts.

[Alan Wheeler]

If the batteries are staying closer to the 12V, then the problem

I was meaning(though poorly stated) that the voltage measured at the battery terminals while the starter is being cranked over, should read no less than 12V. But from Gords comment, maybe I am being a little optimistic expecting to see 12V. However, the difference measured between the battery terminals and the starter terminals will tell you how much voltage drop you are getting across the cables.
For instance, say the battery terminel does in fact give a reading of 12V. And the starter terminal gives a reading of only 10V. That means that 400W (which = lots of heat) of power is being wasted in the cable/connections, instead of making it to the starter.

[GordMay]

Wheels raises some good points (I should never post whilst also engaged in a teleconference).

The cranking voltage drop at the battery terminals depends upon the starter current - with larger starters often dropping batteries to near 9 Volts, and very small starters to 12V.

I suggested 10.0 - 10.5 Vd, based upon the smaller starters found on small diesels (< 40-50 HP max.), in typical starting circuits.

Assuming:
- a fully charged battery, with an Open Circuit Voltage (OCV) of 12.6V, and an Internal Resistance of 0.01 Ohms
- a 150Amp (1,875W, or 2.5 H.P.) Starter Motor
- 8 Starter Circuit Components (connections, switches, Solenoids, etc)* - Total Vd ≈ 0.6V

By Ohm’s Law: Volts = Amps x Resistance (V = I x R)
Vd = 150A x 0.01 Ohm = 1.5
Battery Voltage = 12.6 (OCV) - 1.2 (Vd) = 11.4
BUT
* There are up to 8 other components in the starter circuit, each contributing between 0.03 V (switch) & 0.10 V (Ground connection, or Solenoid) drop. These addition Voltage Drops can be individually measured (or calculated); but I generally use a rough total figure of 0.6 V.
Hence:
Total expected Voltage Drop = 1.5 + 0.6 = 2.1 Vd
Cranking Battery Voltage = 12.6 - 2.1 = 10.5 Volts

Larger Starter Motors, additional Components, and/or High-Resistance* Wire, Connections, and or Components will increase the Voltage Drop (decreasing the battery voltage).
These High-Resistance elements are the cause of slow crank, failure to start, and starter failures.