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Old 01-14-2013, 12:55 AM   #1
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FL120 replacement raw water pump

In some other thread I was asked about the Johnson replacement pump for the FL120s original Lehman drive coupler/Jabsco impeller raw water pump setup. As I learned a long time ago from Bob Smith at American Diesel, who designed the drive coupler when he was at Lehman in New Jersey, the drive coupler will eventually break. It's just a matter of when. New ones are no longer available and a weld fix will not last long.

The solution, as recommended by Bob and any diesel shop with experience with these engines, is to install a new Johnson pump in place of the orignal setup.

I took this photo at the boat today. Unfortunately we do not have the pump part number on the boat anywhere obvious. But American Diesel can tell you and your diesel shop should be able to as well.

We have the 1" pump on our engines. This is actually the pump required for the FL135. The pump normally put on an FL120 is the 3/4" pump, which looks the same. But the 1" pump provides more flow and this can be advantageous with regards to cooling the transmission. It definitely is with ours.

The clearance between the fuel injection pump drain plug and the upper raw water outflow elbow is greater than it appears in the photo, but not much greater. This makes it a bit more tricky to change the oil in the injection pump every 50 hours. But I came up with a split water hose funnel sort of thing that makes the job actually quite easy despite the tight clearance.
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Old 01-14-2013, 05:47 AM   #2
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The clearance between the fuel injection pump drain plug and the upper raw water outflow elbow is greater than it appears in the photo, but not much greater.

Since that is a flange mounted pump, it can very easily be rotated a few degrees and might provide more clearance for that drain plug. Maybe even enough to install a drain fitting and a hose.

Or does something else interfere?
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Old 01-14-2013, 10:35 AM   #3
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The pump can be rotated but not much. Whichever way you go an elbow comes in contact with the block pretty quickly. But some people do rotate them to move the upper elbow closer to the block by a bit and this apparently does help improve the access to the drain plug to a degree.

While perhaps not evident in the photo the drain plug is not centered over the upper elbow on the raw water pump but is actually a bit inboard of it. So rotating the pump counterclockwise will not put the plug as much in the clear as one might think from the photo.

I've found that the system I came up wth to drain the injection pump works fine with no need to rotate the pump. Getting a wrench and fingers on the plug to remove and replace it is not the challenge, it's getting something underneath the hole to catch the oil that's the issue.

But regardless if the pump is rotated or not I'm told there is not enough clearance to mount any sort of drain fitting. People on the GB owners forum have tried and to my knowledge nothing has worked.
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Old 01-14-2013, 11:08 AM   #4
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Greetings,
Apologies in advance for potential thread creep but could I use my Reverso oil pump to drain the injection pump from the fill or overflow holes?
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Old 01-14-2013, 11:58 AM   #5
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While perhaps not evident in the photo the drain plug is not centered over the upper elbow on the raw water pump but is actually a bit inboard of it. So rotating the pump counterclockwise will not put the plug as much in the clear as one might think from the photo.


But regardless if the pump is rotated or not I'm told there is not enough clearance to mount any sort of drain fitting. People on the GB owners forum have tried and to my knowledge nothing has worked.

It looks like the drain is inboard of the upper elbow though it is impossible to see by how much. It must be a plug diameter if you can remove it so loosening that nut visible just to the right of the pump body will let you rotate it clockwise a few degrees. Since there is enough vertical clearancd to remove the plug now there should be enough to use a "banjo" fitting to provide a drain point.

Then something like a Reverso pump could suck out the oil but it seems like overkill for such a small amount. The setup and breakdown would take 5 times longer than the job. I would rather just put the drain hose in a jug and do something else for a while.
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Old 01-14-2013, 12:22 PM   #6
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Since that is a flange mounted pump, it can very easily be rotated a few degrees and might provide more clearance for that drain plug. Maybe even enough to install a drain fitting and a hose.

Or does something else interfere?
Yes I have rotated mine and it provides adequate clearance for the oil change.
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Old 01-14-2013, 01:40 PM   #7
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Cost of the Johnson pump?
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Old 01-14-2013, 02:25 PM   #8
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Cost of the Johnson pump?
We did our two engines a number of years ago. At that time I believe the 1" pump was between $400 and $450. The 3/4" pump was about $40 less, IIRC.

There is sufficient clearance to remove and replace the injection pump oil drain plug above the Johnson pump even with the Johnson pump mounted as ours are. That's not a problem at all. The issue is catching the oil.

The system I came up with works great for that with nary a drop spilled so I have not had any reason to cant the Johnson pump. But doing so will provide a bit more room if you think you need it.

A number of people on the GB owners forum have tried all manner of ways to make it easier to change the injection pump oil with the Johnson pump below it. Different fittings and so forth. To date nobody has been able to come up with a system that works given the lack of clearance even with the pump canted.

Also the metal the injection pump body is made of is very soft. So it is extremely easy to strip the threads in the drain hole. For that reason it is very important to always use a new soft washer when installing the drain plug and to be pretty conservative when tightening it. We have a stock of soft aluminum washers we get from our diesel shop for this purpose.

It's not that big of a deal actually. Some people even simply let the lube oil come down onto the pump body and catch it underneath and then wipe the pump down with a rag.

Regardless, the slight inconvenience to changing the injection pump oil is more than made up for by the elimination of the failure-prone Lehman drive coupler.

I should add that there is no issue with the Jabsco impeller pump itself that is used on the original FL 120's raw water system. They are easily overhauled and brand new ones are still available, or they were last time I checked. It's the Lehman drive coupler that powers the Jabsco pump that you want to get rid of.
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Old 01-14-2013, 04:47 PM   #9
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Since there is such great risk of buggering up the aluminium threads on that drain plug and since it has to be removed and replaced so often, I would have a look at a (probably) 3/4-16 banjo bolt and fitting to replace it once and never touch it again.

The odds of screwing one up are high, especially if it is on a twin ... horror of horrors!
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Old 01-14-2013, 05:00 PM   #10
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Greetings,
OK gang. I sense thread creep. Starting a new topic on L120 injection pump. Carry on with the raw water pump comments.
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Old 01-14-2013, 05:16 PM   #11
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Since there is such great risk of buggering up the aluminium threads on that drain plug and since it has to be removed and replaced so often, I would have a look at a (probably) 3/4-16 banjo bolt and fitting to replace it once and never touch it again.
If it would fit it would have been done years ago.. The Johnson conversion is not new. We first heard of it shortly after buying the boat in 1998 .
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Old 01-14-2013, 05:34 PM   #12
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Do we have an approximate number of hours before the Lehman drive coupler becomes suspect?
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Old 01-14-2013, 05:55 PM   #13
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I think Rick is on to something...but me...I catch what I can and don't worry about the rest that gets away....

I let it drip into the drain pan and when I'm done in a few minutes of draining and adding...I wipe the pump off and replace the oil diaper in the drip pan under the engine...

Rigging too much to catch the pint or so takes longer than wiping off the pump and a little oil smeared around never hurts anything.

The banjo bolt and petcock would be the ticket...but just more stuff to possible give issues down the road and my bolt and copper washer is fine for reuse as the tightening torque is very low (can't find the number right now). But like oil pan drain plugs....just bit beyond hand tight is good.
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Old 01-14-2013, 06:58 PM   #14
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Do we have an approximate number of hours before the Lehman drive coupler becomes suspect?
Not that I know of. I think it's a totally random thing. When it was discovered that one of our drive couplers was failing I'm guessing there were about 1,800 to 2,000 hours on the engines. But the drive coupler on the other engine was just fine, and in fact we've kept it and the Jabsco pump bolted to it as a spare raw water pump.

All I know is that in talking to Bob Smith about it he told me what I've already described earlier and said that eventually, every coupler will fail in this way. How long "eventually" is is anyone's guess.
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Old 01-14-2013, 07:05 PM   #15
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Could you use an 'O' ring on the drain instead of the copper washer?
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Old 01-14-2013, 07:23 PM   #16
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I sure wouldn't. It would probably guarantee the plug would fall out from vibration in fairly short order and I doubt it would seal up very well. The manual calls for a soft metal washer and that is what's been recommended by our diesel shop, Bob and Brian Smith at American Diesel, and the engine gurus on the GB owners forums.

With a new soft metal washer at every pump oil change and "intelligent" fastening torque, we have 40-year old threads in perfect shape and the pumps have never leaked a drop from the drain plugs.

Our diesel shop (Tri-County Diesel in Bellingham) originally supplied us with copper washers for this purpose but a number of years ago they switched to even softer aluminum washers so that's what we use now. They should not be re-used.
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