diesel mechanics

[Corey Mason]

I've never dabbled with diesel engines once in my life. And I planned to just throw outboards on my b25 (whenever I can grab a good project). Just curious though...how different are diesel engines compared to regular gassers?

I've pretty much written diesels off due to cost of a new one...and even used ones are expensive. But I figured if I could find an old one...or a busted one that can be salvaged...perhaps its worth it to learn the differences and rebuild it.

I've completely torn down and rebuilt several other engines (gassers) before...and it actually came pretty easy for me. Now I'm curious if the diesels are even similar or comparing apples to oranges.

Also, if I run diesel engines...don't they need transmissions? (You can tell I've NVR even thought about inboards ha). That would also be an additional cost to consider right?

[Bruce]

Basics.
Unlike gasoline which uses fuel, air and spark to ignite the cylinder charge, diesel uses fuel and air. The diesel charge is compressed at at much higher rate 20:1(varies diesel) vs 8:1(varies gasoline) and that creates heat that leads to combustion.

On carb engines the gas mixes with air in the throat of the carb and if adjusted right atomizes into a very fine mist which is needed for proper combustion.

On injection both gas and diesel the air is regulated and at the proper time an injector (either mechanical or electrical) fires and releases the fuel under pressure and coming out of the tiny holes in the end of the injector it also should vaporize to help with proper combustion.

Diesel blocks are for the most part designed to be more robust and can have replaceable cylinder sleeves or standard bored cylinders like a gas engine.

Cam timing for opening the valves and in the case of some injection systems are the same between gas and diesel for timing.

Newer diesels can be a common rail systems which is where a common rail is pressurized with fuel and then when the injector is fired, the fuel enters the cylinder at the correct time.

Older and still some diesels use an injection pump where you have as many fuel tubes coming off the injector pump as cylinders. The injector pump is timed to the engine thru gears and rotates its own internal cam which pushes small pistons up and down to push fuel thru the tubes and out the injector at the correct time.

That's pretty much the basics. Diesels are not hard and in fact easier to diagnose in many cases.

Much of the new engines both gas and diesel that have been computer controlled need a laptop to read computer faults. Much like an OBDC tool for a car. But the basics still apply. Many always look to the much more complications of the computer when the basics combustion process is the key.

Whether you run inboard gas or diesel you will need gears(transmissions).
The basics of rebuilding are the same, pistons, bearings, rods, crank, flywheel, head, valves, timing, etc.

[Corey Mason]

Thanks...I didn't know diesels combusted in that manner.

I guess I should have phrased my Tranny question different. In an outboard the transmission is already there....you just buy an outboard and slap it on.

If I buy a used Cummins (or whatever) is it expected that the trans will be with it? Or are they like cars where if I say I'm buying a new v8...I'm only getting the long block v8 and will have to pair it with the right trans.

[CaptPatrick]

Corey,

All inboard engines will require a transmission...

[Carl]

...transmission sold separately.

[Corey Mason]

Man, its a shame I used my real name to register. Makes asking dumb questions that much harder ;)

Where does one go about looking for some diesel engines/transmission? More specifically on the used side as I'll never be able to afford new.

I've checked out Adhuntr.com, but not exactly sure what the search for to get the best results. Is there a site/place you guys go to for browsing?

[Bruce]

Corey,
Never a dumb question. Ever.

Boats and harbors publication is a good source.

[IRGuy]

Corey...

Re: Your "dumb" questions comment one thing you will find in this forum is help.. lots of valuable help. When I started playing in this sandbox I asked a lot of neophyte questions too.. and guys like Captain Patrick and Bruce (to name two of many) all responded in the same manner.. The only dumb question is the one you didn't ask. We all started somewhere.. so don't ever be afraid to ask anything that you are serious about. I don't think I have ever, in the 8 or so years I have been here, seen even one sarcastic or condescending answer to any serious question.

One thing I might mention is that diesel shops occasionally repower boats, and on occasion they salvage an old engine and rebuild it to resell.. I know my local diesel guy does on occasion. You won't need a big engine for a B25.. maybe smaller than most diesel shops usually deal in, but it certainly doesn't hurt to ask. Just beware of an "aerosol overhaul".. ie: a used engine that has been repainted but not been rebuilt. From what I have read, mostly on The Hull Truth website.. there are quite a few shady engine rebuilders, gas, diesel and outboard, out there.

[Rocket]

Unless you are planning to run ALOT of fuel through that motor or are very concerned about the expolsiveness of gasoline, you might want to ask the question why diesel? The B25 are not that heavy and don't need the torque and massive props, shafts, struts and gears that go with them, not to mention fuel tanks, gauges, motor mounts and all the other ancillary gear that needs to be changed. Gas motors have become more economical and reliable, diesel (through the adoption of electronic controls and environmental compliance) less so. The difference in capital cost is huge. I own a fleet of trucks, all diesel, so I am actually a big fan of diesel motors, but for recreational boating the cost/benefit of the diesel versus gas in sub 30' boats just doesn't stack up for me.

[Navatech]

I'm originally a Marine engineer (a.k.a. grease monkey) and, as such, specialized in diesel engines... I also like their longevity and the fact that the fuel isn't explosive... Having said that, practically anything under 30' can use a gas engine more economically then a diesel...

The one exception would be if you plan to run your boat commercially... If you're anything like the common recreational boater (i.e. 100-200 hours/year) you're better off with a gas engine money wise then a diesel...

I do NOT agree with all the reasoning of this well known marine surveyor but it's a good read and he does raise valid points:

Part one: http://www.yachtsurvey.com/GasDiesel.htm

Part two: http://www.yachtsurvey.com/GasNdiesel.htm

FWIW, one of the biggest beefs I have with him his reference of the move in the US to diesel engines in the 70's in order to claim that diesels aren't that good an engine... It was a half hearted move where they basically redesigned gas engines into diesel engines... The breakdowns were only to be expected!... A diesel engine is a very different animal!... Just look at the compression ratios: around 1/9 for a gas engine and easily double that for a diesel... If you want to look for excellent automotive diesels there's no need to look further then any of the European car manufacturers... The likes of Mercedes, VW, Renault, Fiat and Citroën all make great automotive diesels starting at about 2 liter 4 bangers... One of the most dependable cars I ever had was a VW Polo Classic with a 2L diesel...

[Pete Fallon]

Corey Mason,
After reading your posts I have a few questions for you. #1 Have you already purchased a 25' Bertram? If so what kind of power does it have. #2 If your thinking of repowering with diesels be prepared for sticker shock on the pricing of small diesels, either straight inboards with transmissions or Inboard outboard models. #3 If your looking for outboards the longevity is not really there yet, plus they cost a bundle and you have to have some type of bracket which can also be very expensive and require a lot of fairing to get rid of the old built-in outer transom profile. Some will argue that they are reliable but I feel that a 25 Bertram should be powered with either straight gas or diesel inboards, another though is that I/O lower units are nothing but headaches if left in saltwater for any length of time.
The newer I/O's from Volvo Penta have a composite out drive outer casing but are very expensive to buy or repair. The old twin engine 25's had either I/o's or inboards and most were V drive transmission set ups. The straight inboards in my opinion are the way to power a 25 Bertram. Some of the foreign engine companies like VW, Issisu(spelling) and Volvo have a very good engine set up for a 25.
As a marine surveyor I feel that the resale value is better with straight inboard and conventional 1:5:1 ratio trannies, either gas fuel injected or diesels, I would not waste my money on outboards, a pair of 225 hp outboards will set you back nearly $45,000 by the time your finished with all the accessories, ie: outboard bracket, controls, gages, props etc.
Welcome to the sand box, at least your starting to work with a decent platform in a 25' Bertram.
Pete Fallon

[jspiezio]

Thanks...I didn't know diesels combusted in that manner.

I guess I should have phrased my Tranny question different. In an outboard the transmission is already there....you just buy an outboard and slap it on.

If I buy a used Cummins (or whatever) is it expected that the trans will be with it? Or are they like cars where if I say I'm buying a new v8...I'm only getting the long block v8 and will have to pair it with the right trans.

Corey- to give you a little lingo, engines without a transmission are usually referred to as "bobtails". You might (or might not) see this in some of the ads.

[Joseph Fikentscher]

A friend repowered his 25 with diesels.

[Corey Mason]

I currently do not have a b25 project yet. I almost bought one a few months ago from NYC (I live in fl) but to get everything lined up was too much. Now after Xmas we are a Lil lower on our savings and will probably be waiting til summer or the end of this year before buying a project. ...long story short, wife gave me $700 in Jan to flip cars/engines to pay for the boat (with some savings). So far I'm up to $3000 and that's after my reg job. I continue looking everyday to see what's out there though.

And honestly Pete, I had about 2% chance I would actually repower with diesel...I just wanted more knowledge to simply make sure I covered my bases in decision making.

I will be using the boat heavily when I do get it. I'm an avid fisherman and my wife and I both work in the school system meaning we have 3 months off for boating...I mean summer.

Basically the boat will be made for fishing, but used for simply being on the water. I don't plan to simply load the rods, haul ass to the honeyhole, then haul ass back in. It will be used more as enjoyment of being on the water, nice and slow...some trolling to the honey hole, and cruising back in on the sunset. ...also some overnight trips for shark fishing (catch and release).

Point being...I don't need a go fast boat with 700hp.

I have been very set on a bracket with an outboard (single for now til more financially stable).
Reasoning for this is...
1) I hate the gigantic motor housing that gets in the way.
2) I like the simplicity of outboards. Since I'll be doing all the work myself, I prefer simplicity. I know I can install/rig up an outboard with minimum research/work than installing any inboard.
3) I hear only negative about I/O.
4) around here (Pensacola/destin area) I can grab a very nice used outboard with 5-800 hours on it for $5k.
5) from 2+ years of searching and drooling, this has been my dream boat...and one I want to restore, keep, and pass down to my kids. So, resale value hold little to no consideration.

I've figured on just throwing a 225 (could vary slightly) on a bracket and calling it a day. Would be very economical to simply troll with (so I hear) and yet would still have enough power/speed to hopefully get me away from storms.

The biggest downside I think is obvious...it is a single engine, and compared to other powering options...I would say most unreliable (even though they are getting much better). This would be the first thing to change( add a second outboard) whenever the time/money comes. Until then, I wouldn't go anywhere without a membership with seatow.

[Rocket]

perhabs Captbone will chime in with about 300 pictures of outboard conversions on 25' Bertrams. He has a fine collection of them. I know of a few that did not even use a bracket, but merely notched the transom. If the notch was wide enough, one could go to twins in the future.

I don't know why the I/Os get such a bad rap. From a price/effectiveness/longevity perspective I have received great value from I/Os over the years. Never a bellows problem, maintenance has been pretty simple and cost effective, fuel economy very good, reliability excellent.

[Corey Mason]

Actually I talked with captbone about buying his boat when it was for sale, I just wasn't quite ready to buy. I loved his boat; except I prefer a bracket of notched transom

[Carl]

Two motors are nice...adds a bit of backup reassurance if one should go down.

Down side...
-if your running off a common tank fuel issues would effect both engines.
-if you hit something with one motor...good chance you'll hit the second too.

Tune ups and maintenance are twice as bad.


How true this is is a matter of choice...
When all that fits the budget is a single motor, I can rationalize a single motor being better without much issue. Besides a yearly subscription to Boat US or Sea-Toe is much less costly then a second motor.

Budget says two motors...I can give you a list of why two are better then one too.


I had two single motor boats...always made it back to dock under my own power.

My advice...do whatever you need to do to just get out on the water in a safe boat and one that fits your budget...sucks when you can't use it cause filling the tank or repairs keep you at the dock....or worse, have it sitting at home on the trailer.

[Craig Mac]

Joseph,

Your friend's 25 looks interesting, can you post some more info and pics?

[Corey Mason]

Exactly my thinking Carl. I read that info from David pascoe. I don't really care for the guy but he did have some points.

Well after your inputs I think I was right in the way of going with gassers. I just wanted to make sure I covered that area of decision making. I appreciate the input guys!!

And yes that b25 with twin yanmars looks awesome....I'm sure it cost 2/3 of my house though ha.

[Kevin]

When I think outboards I think the opposite of simple. That is unless you are running something like a Yamaha OX66. Depending on the make there are lots of expensive parts that are disposable. Injectors both fuel and air, air compressors, fuel pumps, superchargers, plugs, coil packs, lower units for that matter and the list goes on. Not to mention the computers, especially if they are salt water cooled like one brand of engine that has not been able to get it right for over 15 years now. There is another batch of motors that have bad mid-section exhaust housings that fail and lead to salt water intrusion in the cylinders. Of course that is just based on what I have seen. There are some expensive parts on diesels but for the most part you change the oil and the impellers. Throw some additive in the fuel and they are good to go unless you get a hand grenade model.
I only average 100 engine hours a year but do not regret going diesel one bit. All my trips local and long hall would have been unthinkable with gas, at least in my boat and its only 28 feet.
Don't rule anything out until you have done your homework. In the end go with your gut instinct. It will be your boat and your imagination as to how it works.
My biggest piece of advice would be get something you can use and run it for a while. After you run it you will better understand what needs to be done based on experience and not a dream.
I did some things twice and even three times because I thought I knew what I needed. Lots of money down the shitter.
My boat is exactly how I want it now......but it took the better part of 7 years.

[Pete Fallon]

Kevin,
The Yamaha OX engines are simple but you have to carry a blow torch with you to burn off all the carbon build up on the oxygen sensor at 50 or so hours. I was thinking of you the other night when the blizzard hit they showed the breach in the sea wall in Situate and Marshfield, the weather is awful up here I picked the wrong year to move back but the medical is so much better up here. Both of us have had surgery since moving back in August. Keep the floaters out of the waterways down there they slow down boat traffic.
Pete Fallon