4-108 injection pump

[CSY Man]

Hmm, some of the 4-108s are goverened @ 4000 RPM, including mine.
That would be the non-commercial version.

Perhaps the Navy Launch was considered "commerical"?

It the real/max RPM under no-load is only 1325, you are probably getting only 15 HP instead of 50.
Yeah, no harm done but there is more goodies to be had..

[CaptG]

CSY MAN......If the info I have is correct the navy rates it @ 25hp @ 2400 RPM underload full load. That would be 22 souls aboard and displacement of 8,800. I got that from the navy manual. That's why I'm starting to question the tach acuracy. It seems like it's showing half speed.

Aloha......Gerry

[SkiprJohn]

Aloha Gerry,
Wish I was on Oahu to give you a hand on this. I have an electronic digital tach and it works really good.
Just a haunting thought but your prop sounds a bit large. Is that the prop that the Navy used?
Did you do a search on proper prop size here on the forum?
Lots of questions but a good thing is that the engine is not overheating.
JohnL

[Alan Wheeler]

If it is the old mechanical tack, it is highly likely that it is reading incorrectly. If it is electronic, then you may need adjustment.

[CaptG]

Aloha John & Alan,
Prop size,gear reduction, etc came right off the navy spec sheet & operator's manual. I figured after several hundred years the navy ought to know how to set up a boat. At least I hope they do.
I took her out in the bay today & ran her at full throttle. Made 7.5 kts @ 1400 rpm & held fast at 180 degrees. BUT......she was blowing so much black smoke it looked like the sea water discharge was dark gray. I backed off to 1200rpm & all cleared up. Prior to IP rebuild top rpm was 1300 & no smoke. Could this smoking be the symptoms of retarded IP timing ?
Thanks for the help..........Gerry

[Alan Wheeler]

No the black smoke is poorly burn't fuel due to either not enough air, or overloading. Did you check RPM in neutral?? Open her up and see what she revs to with out iot in gear.

[CaptG]

Alan......I ran her up to full throttle out of gear as you suggested. 1900 rpm (according to my tach )& no smoke or soot. I also tried in gear tied to the dock & made 1100 rpm @ full throttle and lots of sooty looking stuff on top of the water but not a lot of smoke. I then pulled back to the highest rpm I could reach dockside before IP was rebuild which was 1000 rpm and no smoke & no soot on water. There is no air filter, just a screen which is clean.
I'm thinking that in the sea trial in my previous post it wasn't smoke but soot she was blowing. It looked the same coming out of the pipe as it does dockside but because I was making 7.5 kts I didn't notice it floating on the water.

Aloha.........Gerry
PS. revving full throttle out of gear sure sounds like more then 1900 rpm.

[SkiprJohn]

Aloha Again Gerry,
The handheld digital tach that I have was about $35 including shipping. You might get them cheaper at the local electronic stores on Oahu. Very handy tool for checking alternator speeds, engine speeds, etc..
JohnL

[CaptG]

Aloha John........You must have bought your hand held a long time ago. I just check at NAPA and they are $140. Where did you get yours?

[SkiprJohn]

Nope. Got it two years ago. I'll see if I can find the receipt. It was from an on-line catalog. I'll let you know.
JohnL

[SkiprJohn]

Oops, prices are up. Try Circuit Specialists, Inc in Arizona. Catalog number DT-2234B Digital Photo Tachometer. $39. I'd try Best Buy or Circuit City or some of those other big box outlets we don't have over here.
JohnL

[CaptG]

Aloha John......went to their website & the tach is on sale for $29. Of course the shipping is $39 more. I'll check the big box stores here first.

Lucky we live Hawaii............Gerry

[Alan Wheeler]

Mate!! I need you to send me one my way. I borrow one from a friend. It cost $600. I don't use one often enough to warrant the expense.
Anyway's, yep I think the next step is to varify the actual RPM. Those motors are capable of 4K RPM. But even if it has been govern'd to only rev to say 2K RPM, then 1100 is a long way away from there. Even the 1900 you are seeing for that matter. Before going any further however, get the digital tacho and check. The mechanical ones can be higly inaccurate in their old age. We need to know a few actualls before going further.

[Maddog]

Time for me to jump in. I have a 4-107. It is almost the same as the 4-108 with minor exceptions, (Head bolt size and others). I know that I am slightly over proped. I cruise at 1600 rmp at just under hull speed with no smoke. I can rev up to 1800 rpm then I get the black smoke showing that it is overloaded. Yes I am getting a new prop. The power curves for this engine show max torque and rpms converge at 2200 rmp. This is what I am going to shoot for. I got to say that the perkins engines seem to do well at lower rpms compared to other diesels. My engine is 35 years old and has had one overhaul and seems to be fine. It just keeps going. It does leak oil, why? Beacause that is how the British like it.

[Alan Wheeler]

It's when it stops leaking oil, is when you have to worry:-)