Upgrade to Perkins 4-236 from 4-154

To the Forum,
A update on the engine change in “Slo~Belle”. The Perkins f-154 was pulled in one afternoon. The replacement “Runner” Perkins 4-236 fit the foot print of the 154 with slight modifications to the mounts, no big deal. The engine was floor tested by the installing shop and deemed a very good deal. As hours were unknown this was a good result.

We had raised the salon floor 1 1/2 inch using one inch foam and 1/2 inch plywood in anticipation. The 3:1 gear was replaced with a 2:1 gear both being velvet drive units. We retained the 22x16 dimension wheel but had to exchange the left hand for a right hand wheel.

Results? More than we had hoped. Yes we are over wheeled. The engine is rated at 2500 RPM. we achieve 2000 RPM WOT. Hull speed (6.9 knts) is achieved at 1400 RPM leaving 600 spare RPM and there is no indication of strain on the engine, in fact it just runs sounding relaxed and does so till 1800 RPM where it begins to stress in sound (Heavy breathing) but the gain is nil. near 8 knts WOT, big water mess, squat stern. ( am convinced that this is a FD hull not SD) There then is no need to exceed 1400/1450 RPM.

The fuel burn is 1.4 gph @1400 RPM, engine temp is holding at 160 degrees which is still low. We have not done a exhaust temp test. We didn’t change the exhaust diameter. The Perkins 4=246 calls for 3 inch and the Perkins 4-154 called for 2”. The builder had installed 2 3/4 inch so it must have been for compromise such as this instance. There is no indication of exhaust back pressure. Oil pressure is 60# steady.

So- for a Craig list $1000,00 complete running engine with no missing parts, and a Craig list reduction gear purchase of $500.00 the end result is a happy outcome. Shop time was near $6500.00 which included modifying the electrical system and upgrading the fuel system.

Thanks to all of the contributors to the comments during the initial conversations. All was digested and the best used. This forum rocks!


Al

Thanks for the update Al. Those 4.236 Perkins are some great engines.


1983 Present 42 Sundeck
Twin Lehman 135's

Agreed!!! That is Perkins best engine!!!

You might consider this. I too have an overwheeled boat. However several years ago I had an inch of pitch taken out . It is still overwheeled but no where near as badly.
Of course to maintain the same boat speed I had to bump the revs up but the kicker is I realized the engine ran better. Not by sound but by watching the exhaust.

I have a dry stack so I can see very directly any changes.

People we travel with confirm my observations. Once up to temp they cannot see an exhaust trail.

It was cleaner. There was far less sooting. The engine was using the same amount of fuel but at the higher revs it was using LESS fuel per firing and pulling in more air for a cleaner burn.

I know all the arguements [well most of them] the other way and for years I went by them.

No I'm not going to repitch again as it is now close enough but the proof to me that the engine liked the new pitch was the cleaner exhaust.

It is an 7-8 knot boat so reaching full rated on plane is not a consideration.

You don't need to repitch all the way to rated but it sounds like you have limited the engine too much and not left much or any margin. If you have a wet exhaust you may not see the results untill you push too far at which point it will black smoke.

Reconsider the pitch and think about allowing the engine to breathe better. Just give it a bit more margin.

Your choice of course.

C Lectric- This forum is really a total enjoyment! Thanks for your observations. I agree with those in terms of clues to potential problems. The engine is not showing any smoke, Normally Perkins puke out blue smoke on startup and then after warming up, it dissipates, We are not noticing even that factor with the exhaust.
Our black smoke begins around 1800 RPM during the test run following the engine swap.
I recall stating that the engine is very comfortable at 1400/1450 giving us our hull speed (6.9) plus, actually seeing more 7 knot average. the engine is burning 1.4 gph. Our temp is holding at 160 degree which is still low.
With 500 RPM to spare and no need to exceed the 1450 point we are content.

Yes, the option to take some pitch out at some point or may be the opportunity to obtain a spare used wheel with a less pitch will become a goal,
Here is a good source:
http://stores.ebay.com/donsmarine-2...d=808379809&_trksid=p4634.c0.m14.l1513&_pgn=1

Cheers,
Al

C-lectric and forum,

Another thought and remembrance comes to mind.
In reading the shop manual for the 4-236 it was noted that there is three levels of RPM the engine is rated. The first is pleasure boat light duty 2500 RPM, the second is commercial heavy duty where the rating RPM is 2300 RPM and the last is continuous duty where the RPM is 2200 RPM. I may be off a bit on these term other than the pleasure boat. Given that the RPM is reduced with each more demanding use, it makes me comfortable that our maximum RPM of 2000 is a bit closer to the continuous rating in term of over propping.
Just wanted to add this to the conversation.
Al

Al,
For the Perkins 4-107-108 it's rated for 50hp at 4000rpm, 40hp at 3600rpm and 36hp at 3000rpm. All the Willardites use the 3000rpm rating. The 50hp rating is for English taxi cabs. From somebody that knows these engines and their ratings a WOT rpm should emerge.
The 2200rpm rating you posted may well be based on an engine w a WOT rpm of 2500 running backed off to 2200. That would be a lot different than running 2200rpm w an engine that ran 2200rpm at WOT.

These Perkins ratings are a bit strange to me (just that I don't understand them I'm sure) and I hope someone can clear this up. Al, I suspect that your engine is rated at 2500rpm at WOT and 2200rpm on a typical propeller load for maximum continuous duty. But the 2200rpm rating may or probably has nothing to do w propeller curves???

The WOT RPM may be marked on the fuel pump. My 4.236 says 2650.

Al that sounds totally weird.

Propeller curves are all computer guesstimates and have almost no real world application.

For real info one requires a fuel map or BMEP graph.

manyboats said:

Al that sounds totally weird.

Click to expand...

I agree. By that logic the more overloaded the better????

FF,
Propeller curves is what most people use .. including industry. There is a good reason I'm sure. The prop curve gets one in the ballpark. Then there's the really high tech business (PI) of looking up rated rpm, opening the throttle wide and observing the rpm. Not rocket stuff but that's all there is to getting the prop loading right.

Bayview,
Overpropping ..Didn't you go to school?
WOT rpm? Who in the world would look on the fuel pump for general engine specs? Al must be joking.

Indeed. Why allow the facts confuse the issue.

FF-
For the "Spot run, see Spot run" crowd, I being a member, could you define:"For real info one requires a fuel map or BMEP graph." a bit? Asked from actual amateur process of filling the fuel tank full, running at set RPM (1400) for X number of hours on an admitted over propped wheel obtaining a 6.8-7.3 knot average refilling the tank and realize a 1.3 gallon fuel burn.
Operating temp 160 degrees, no smoke and quite operation, with 500 RPM reserve.

I remain confused at to the "What might be, what could be, what should be"line of reason.
What is missing to conclude that the described components and factors are in alignment harmony?
Are computer models in conflict with actual operation?

Al--- In my opinion if the prop(s) diameter and pitch is such that the engine is operating within it's parameters, fuel consumption is what you think it should be and the boat's performance is what you want then everything is fine.

Prop configuration is like anchors--- it can be discussed ad infinitum with everyone having their own opinions and theories about what pitch, what diameter, how many blades, and so on. And there are formulas and calculations to figure all this out if one want to take it to that level.

There are certainly good reasons for all of these data points, but with regard to our little recreational boats whatever calculations needed to be made were made by the manufacturer and as long as one is in the immediate neighborhood of what they designed the boat and its powertrain to have then all will be well.

If we were talking about ship propulsion, as in tankers or bulk carriers, or if we were talking about high-performance vessels like Navy frigates and submarines and stuff, then the discussion takes on a different tone altogether.

But between the manufacturer and a good prop shop it's pretty easy to get the right setup for boats like ours. Tweaking things to reduce fuel consumption at cruise by 0.0025 gph or whatever just isn't worth the hassle and expense in my opinion if you and your engine(s) are happy with your current setup.

The "See Spot Run" version of my opinion is this: If what you have is working just fine, don't sweat the small stuff. Just keep using it. You'll be out on the water having fun while the other folks are agonizing and arguing over formulas and calculations and haranguing the prop shop guys.

"For real info one requires a fuel map or BMEP graph." a bit? Asked from actual amateur process of filling the fuel tank full, running at set RPM (1400) for X number of hours on an admitted over propped wheel obtaining a 6.8-7.3 knot average refilling the tank and realize a 1.3 gallon fuel burn."

Sounds like your "overprop " solution is working perfectly for your boat.And your boat is happy with perhaps 20 HP.

The hassle is the engine folks ask the engine to be able to pull max rated RPM , and if you read a prop graph you will see the 2100RPM or 2400RPMprop is not capable of putting much power in the water at say 1400 -1600.

This forces operators to operate at higher RPM to get the power required in the water.

With a larger "overprop" as yours the power which the engine can easily provide at low RPM can be used.

Works great , although on many boats the engine can never reach the Mfg WOT RPM

No harm is done , the fuel burn is low and the engine life is extended , and the noise level is reduced , all great!

A fuel map helps find the lowest RPM that is the most efficient for the HP needed to push the vessel. Sounds like you found a sweet spot with out the tool.

So little to gain and so much to loose ...............

If you don't know ALL about it. All you have is EGT to indicate (not precisely) when you throttle into engine damage zone. And I suspect most all overpropped boats don't have an EGT. And the red line is different for all of them. And it's so easy to do it right.

"So little to gain and so much to loose ..............."

ONLY with a guess .,

Using the engine MFG fuel map or BMEP graph is his observed power produced and fuel burn , and recommended loading at the various RPM.