Perkins 4-108 Nightmare

[jimisbell]

Thanks. I am glad you agree with what experience has taught me. 70 years of experience is a nice database to draw on.

Thanks again for the compliment.

[cburger]

Originally Posted by Tom967

If you want to save a few bucks..Take a look at the Kabota...The guy who runs Boat US here in Key West told me just
yesterday..that's what he repowered with..rather than with a Yanmar...paid 7000

Tom,

The price I got from the Ct. Beta Marine rep for a 37hp Beta including 2:1 reduction gear is $9236.00. Would you be willing to speak with your friend regarding maybe another source for this powerplant as he seems to have paid less.

Thanks,

Chris

[CaptKarl]

Okay I Jumped onto this forum but I’m on a parallel track. I bought my boat seven years ago and it had sat for 25 years with 500 hours on the 4-108. I have been totally amazed at its performance with the 1,500 hours I put on it sine I bought the boat. I did have to re-pitch the prop to get upto 3,000 rpm, but it has taken me and the 13,000 pound boat close to 10,000 nautical miles . My two complaints are it is hard to stop the oil leaks which it goes through about 1 qt per 100 hrs, and it is noisy, mostly because it is under the pilot house floor and hard to sound dampen. This engine runs great but will be up for sale within the year if someone wants to wait it out.

I plan to do more off shore cursing and wanted the nose issue resolved. I just picked up a slightly used Yanmar 4JHE (Last generation) for a very good price. They are supposed to be much quieter. It is a little rough from corrosion on the outside but from what the inside looks like it has less than 500 hours on it. The first issue I see is that the gear is 2.17 to 1 and my Perkins was ~3 to 1. My calculations show I would have to change my prop pitch from 9 to 6 to get the Yanmar up to 3,100 RPM in the power curve.

I have two sets of questions; is it bad to have such a shallow pitch and higher rpm on the prop shaft, or should I get new gears for the transmission? What about drag during sailing with a shallow pitch prop?

The second is, someone mentioned it might fit right on my old engine bed. My rough measurements don’t agree but I don’t have the real dimensions of the Perkins. Does anyone have installation measurements for the 4-108? Will it fit?

[Benny]

Karl - I have a 108 and I'm sorry I don't have the dimension - not in my repair manual that came with the boat - I do have a question that you seem to be able to answer - how did you determine the correct prop for your displacement - is there a formula somwewhere I could use as I think mine is undersized for my 22,000 displacement.

Thanks for any info, Randy

[KC7CC]

Originally Posted by never monday

His estimate and current costs don't seem unreasonable.

--------------------------------------


If he can't learn engines , then he will
pay the price .
Thats good "reasoning" ...
-------------
But i know engines , i dont pay that price.

Its easy to lose reputation , if you once
err ...
1200cc VW was a 80K motor...JUNK .

But the 2nd generation Diesel , was a
250K motor .

The PathFinder is VW with a backwards cam.
It has 17 HP , at max economy .


The problem is , ppl see it is capable
of more HP , and use it .

17 HP is the most econo' HP ,
so why not just size it thusly .
It is not a heavy block , parts are more
common than any D' ever .
It should be turbo' for even more econ' .
Turbo does not reduce life .
It has 4 cyl and thus much smoother and
easier to crank . D' are started on Propane
and a comp' release . They warm , then
switch to D' oil .
Some prefer to install a bigger battery
and replace starters frequently .

This is an old engine , using low pressure
injection , as ussual ( just enough to combust).

New D' use 10 times higher injection pressure,
but you need a bank loan to repair it .
More econ' , much cleaner running ,
? injectors cleaner longer ?
A M.B. 5 cyl is in millions of Vans
in USA . Built in Italy .

Some D' spray oil under piston , to cool it .
Isuzu puts a chamber in piston , to make
it run hotter ! JUNK !
Pistons are like Space shuttle tiles , they
need to hold off heat .


MB is far ahead of all D' and will NEVER
be challenged .


KC7CC .need to crew a cruiser in TX .
62 Y.O. , W.M. , non-Liberal ,
165lbs , good nite vision , E.E. , engine mech' ,
inventor , Ham , No drink/smoke. Smoked for 30 years
it dont bother me . werty swissinfo org

[CaptKarl]

Originally Posted by Benny

Karl - I have a 108 and I'm sorry I don't have the dimension - not in my repair manual that came with the boat - I do have a question that you seem to be able to answer - how did you determine the correct prop for your displacement - is there a formula somwewhere I could use as I think mine is undersized for my 22,000 displacement.

Thanks for any info, Randy

Benny; Originally my prop was 11x17 but I could only get to 2,600 RMP. My surveyor suggested I get it re-pitched. The prop guy just got the Max HP of the engine and the gear ratio and re-pitched it to 9” for $80. Then I could get to 3,000 which is top cruising recommendation for the engine; I actually cruse at 2,300 to 2,500 in heavy seas. I also lengthened my shaft by 3” because it was too close to the hull. The result was higher RPM and no cavitation at high RPM and way less cavitation when backing down.

My calculations were to compare my new engine shaft RPM to Pitch ratio to the old. In Excel I divided my pitch x Shaft RPM by the inches in a mile where the engine is in it’s cruising speed, shaft rpm was determined by Engine RPM x gear ratio. I took that speed and applied the reverse logic to my new engine and adjusted the pitch in the spreadsheet until I was in the new engines power band. In the end I had my old engine gear ratio off and the two Shaft RPM’s are close so I don’t necessarily need to re-pitch. When I get the new engine installed I will run tests to see if I need to tweak the pitch.

After all my calculations I found several sites on line that will calculate the prop size and pitch you need. The formula thy use is similar to what I did but they include a slip factor. I also called a prop shop they can calculate it for you easily.

In the end every boat is different and until you actually test it you won’t know for sure, the formulas will just get you close. The proper pitch will allow you rev the engine up close to red line but not over rev the engine. If you run tests and see how fast you can rev it up the prop guy can tweak it into perfect pitch. It is very important to be able to run the engine at the proper speed, if you are over propped it is hard on your engine. There are a lot of over propped sailboats, the owners like sound of the low RPM.

Hope this helps

[Benny]

Thanks Karl - The blades on my prop are quite small without much twist to them. The reading on the prop is 18 LH 13 but it takes a few revs to start the boat moving from stopped in calm waters and when I stop her by going in reverse, she takes a bit to slow down - I've owned many inboards and she just seem to respond too slowly. I guess I'll have to just take her out in different conditions and see how she performs. The pitch might be right as the calculations on the sites work out to the 13 pitch but the blades may not be big enough or shaped properly to attain full efficiency

[Benny]

Was surfing through propeller sites and found out that I have a 3 blade sailboat prop which has smaller blades that create less drag - better for sailing but not better for powering through big waves or emergency stops.

Can anyone advize me or relate their own experiences as to whether it might be better to get a regular 3 blade prop or can this one handle those situations I mentioned

Thanks, Randy

[Benny]

Sorry - didn't mean to kidnap this thread - the posts on propellers should probably now be moved to the propulsion/propellers catagory - could a mod tell me how to move my posts or do it for me?

Thanks, Randy

[delan]

I recently discovered a 30 yr old sailboat inside a machine shop in Miami that had never been completed or launched. I purchased it, and now have about 80 hrs on it. It runs very well and pushes the 10 ton sailboat to 7knots at 3000rpm or 6kts at 2200, which I generally run at.
I'm told I should avoid synthetic oils, does anyone know why?

Sorry if I'm a little off topic, but after reading this fascinating thread for the last hour, thought I'd chime in.

Best Regards, Joe, Miami Beach.

[cburger]

Joe, the people at Foley Engines in Worchester Mass. , even though the owner is "a little off the ranch" have great experience with the 4.108.
they reccomend a mix of synthetic with traditional oil. You can find their site on Google very easily.

[ssullivan]

I also can say that Foley Engines in Worcester (prounounced "wister", or "wiiiisssstaaah" if you're a real MA person) was a great resource for everything for that engine.

Also, isn't there a museum somewhere that needs a brand new 4-108?? That's a very cool find!

[delan]

Thanks for the tip, that site's a great resource.

[John Galt]

Keeping in mind that this route leaves you with no recourse when and if it fails in terms of warranty, this is a regular listing on E-bay.
eBay Motors: Perkins Diesel Engine 4.108 Remanufactured LOW SHIPPING (item 190218347748 end time May-08-08 08:44:23 PDT)


Having said that, I have a 4-108 that will need replaced before I go cruising. Pat NM will repower with Yanmar. I like the idea of a reputable dealer backed with a factory warranty for one of the most vital parts of my boat.
Rick

[speedoo]

My 4-108 has been terrific. Definitely worth a rebuild if it's really that much less expensive than a repower, IMHO.