Lehman 120 Turbo Delete

[Taras]

Hi All,
I'm looking at a boat with Ford Lehman 120's that came with Turbo's and were rated at 225hp (660 hours, 1985 vintage). The current owner says the Aftercoolers are plugged up and need to be replaced. He was quoted $5k for the parts so he decided to "bypass" the Turbo and Aftercooler. Says the motors run just fine with them bypassed, just at a lower horsepower. I haven't surveyed the boat yet but of course will get a really good hull and mechanical survey (if it gets to that point).
My question is, is this fix of "bypassing" the turbo an OK fix? Any issues with doing this? I'm ok with running the boat with just 120 hp. Its a 50' trawler and doesn't need 225 hp. 120 hp should be fine for running at displacement speeds.
I've never owned a boat with Lehmans, but I'm a fan of them for their efficiency and simplicity.
Any input here would be appreciated!
Taras

 

[rslifkin]

I'm pretty sure you can keep the turbos, bypass the aftercoolers, and end up what they offered for a ~180hp rating. I'm not sure if a fueling adjustment is needed or not.

 

[alfamike]

By bpassing after cooler

Well the fuel injection pump is calibrated for both the turbos & after coolers,.

So the engines will run rich and if throttled up much past low mid throttle & will make a lot of black smoke which will deposit on your transom, not to mention throwing away fuel at todays prices.

So be careful as you may be getting some one's expensive problem as there are 2 engines in this 50 footer. You can or the PO may have already over heat the pistons & cause serious issues, so maybe go look at some other boats out there.

You Need a BIG discount, I mean big - not some paltry $ 5 K.

Good Luck.

Alfa Mike

 

[Comodave]

No, the injection pump is the same whether it has the aftercooler bypassed or not. If you bypass the aftercooler then you have a 180 HP engine not 120. In our last boat we had the SP225s. I knew that the aftercoolers were made of unobtanium so I contacted Brian at AD and asked him if it was ok to bypass the aftercooler so it would still be good for a future owner. He said absolutely yes. I asked about changing the injection pump, he said no changes that both the 180 and the 225 had the same setup. So I bypassed them and had no issues. The buyer of the boat wanted them hooked up so I did that. Call Brian if you still have any concerns. 804-435-3107

 

[Lepke]

Turbos increase the air pressure to the engine and in the process raise the air temp several hundred degrees. The higher temp can damage the engine, that's why an aftercooler is added to higher hp engines. By cooling the air it condenses and puts more air into the cylinder.
The aftercooler can be plugged either on the air or water side, maybe both. If you bypass the aftercooler the engine could be damaged if you run at higher rpm for long periods. Also you have to explain the problem to the next new owner in the middle of a sale.
If they were my engines, I'd remove the aftercoolers, clean them, and pressure test. They may be usable. I've run into many engines where the owner put off cleaning the aftercoolers or flushing the water side and with the maintenance done, come back to life. Also an aftercooler is less complicated than a water to water heat exchanger. A company that makes custom heat exchangers or replacements could build new ones for a lot less than the discount in selling price.
The injector pump has an internal governor. The governor will increase or decrease fuel until it matches the rpm requested by the throttle lever. W/o the intercooler the upper hp and upper rpm is no longer available. However if the throttle is at full, the air entering the cylinder will be extremely hot because the governor will try to increase fuel to meet the upper rpm. In combustion the exhaust gas temps (EGT) will be even higher and could damage cylinder components.

 

[Taras]

All excellent comments. I am enlightened.
Thanks to the Lehman experts out there for your advice!
Much appreciated!
Taras

 

[BruceK]

Found this Spec Sheet while checking the cubic capacity of the SP225. It may help.
https://everythingaboutboats.org/lehman-s-sp225/

 

[DDW]

The injector pump has an internal governor. The governor will increase or decrease fuel until it matches the rpm requested by the throttle lever. W/o the intercooler the upper hp and upper rpm is no longer available. However if the throttle is at full, the air entering the cylinder will be extremely hot because the governor will try to increase fuel to meet the upper rpm. In combustion the exhaust gas temps (EGT) will be even higher and could damage cylinder components.

^^ This. However, since it is a boat, the diesel torque load is almost entirely predicted by the prop, and a maximum only at full speed. If you reduce the prop pitch (or diameter) so that the engines can reach their maximum governed speed, there is little danger of overfueling. If it was a truck and the driver had a heavy foot, easy to overload. A boat can only be overloaded with too much prop, not too much throttle (disregarding some very unusual conditions).