Marine starters, alternators, etc. are no spark electric motors. In a car, tractor, etc. no spark is a non-issue as any type of fuel vapor exits the vehicle easily and safely. In a marine applicant the starter is in the bilge where vapors can not exit easily. Although not a serious potential issue with a diesel engine, if there is a propane line anywhere inside the boat and it happens to leak the vapors settle in the bilge where a spark from any type of electric motor can cause a real problem (kaboom!). So yes, there is a very distinct difference between a marine starter and a tractor/truck/car starter.
I wondered if you were thinking about ignition protection. The key isse isn't that a boat tends to have an enclosed engine room. It's whether the engine uses a fuel that is explosive at STP (Standard temp & pressure). Gasoline is, diesel isn't.
In a gas engine boat, all the equipment needs to be ignition protected. I grew up with gas engine I/O boats and had an atomic 4 in a Catalina 27 many years ago. I can't tell you the number of people that were angry at me at a fuel dock because I wouldn't leave immediately to make space for them. I just refused to start the engine until my nose (my #1 gas vapor sensor), sniffing at the engine room ventilation outlet, confirmed the absence of gas fumes. After the Cat 27, I graduated to diesel boats and I've been much less stressed over fueling ever since.
When one complicates the scenario, and adds in a LPG leak (adding in an explosive fuel source), you could create a problem. However, that source problem is the LPG leak, not the starter motor. For that scenario, there better not be any pieces of equipment in an engine compartment (with a leaky LPG line), that could cause a spark.
AFAIK an ignition protected starter motor is not a requirement for a diesel engine. Diesel engines are designed assuming their use in a diesel (non-explosive) fuel environment.
I don't have specs handy to check against, but I think a L135 starter is not ignition protected as shipped from the factory. As the doc shows, the starter is used on many tractors. That's evidence that Lehman used the starter motor that Ford supplied. Design Economics would make me doubt Ford sourced/made a special "marine / ignition protected" starter for the L135 block that would have been used for boats after marinization by Lehman.
If I'm wrong, I'd really appreciate a reference.
