oil pump versions NX650 XR600 XR650L

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scrambler
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oil pump versions NX650 XR600 XR650L

Beitrag von scrambler » Mo Mär 10, 2014 7:28 am

Hi there,
Since I was frequently asked by English native speakers about NX650 issues I decided to open a NX650 sub-forum to answer all questions, no matter English or German ;-)
So the first issue is the question about the right oil pump, which is very easy to answer at this time, since only two oil pumps are available - all other versions are out of stock and outdated (for reasons I will explain in a later article) anyway.
One of the oil pumps still available is OEM 15100-MY6-670 – it was used in NX650 1993-1995, XR600 1991-2000 and all XR650L. Earlier versions of these models can also use this pump with the short dowel pins 8x24.
The other pump is OEM 1500-MAN-690 for NX650 96-99 and all SLR/FX/FMX. This pump is, in my opinion, no improvement (which I also will explain later).
Cheers, Michael

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scrambler
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wet sumping of RFVC engines

Beitrag von scrambler » Mi Jul 02, 2014 8:59 am

When the NX650 Dominator was introduced end of 1987, Honda claimed that its engine was a huge improvement over the past XR/XL 500/600 versions. However, the engine was taken almost unchanged from the first RFVC version, the 1983 XR500. The oil pump was still the same – and some parts (e.g. check valve) never changed during NX650 production. However, already the 600er versions got problems with the lubrication system – excessively high oil consumption (up to 2l /1000km) and ruined rockers/camshafts were common (e.g. http://www.xl600.de/cms/uploads/media/f ... ertest.pdf).

In retrospect it’s obvious, that an oil pump, which was designed for a 500cc, 34 hp engine, might be still sufficient for 600cc, but with 650cc, 45 hp it´s simply overwhelmed.

Knowing this, it’s not surprising that Honda several times changed the design of the NX650 oil pump. The first change occured 1988, already a few months after the introduction of the NX650, during the running production (something Honda usually avoids at all costs). The oil pump got seals at the pump shaft to minimize leaking. Before that, the so-called wet sumping was common – after killing the hot engine, the oil-level in the frame reservoir dropped due to leaks of the oil pump. It was often claimed that this kind of standing engine wet sumping is not critical, and actually the RFVC engine can survive with it for a long time.

The problem however is that (without an oil-sight tube http://up.picr.de/16668645wv.jpg?rand=1426349036) no one can tell it apart from the more dangerous wet sumping that occurs when the engine is running. According to theory, an intact oil pump should always keep a high oil level in the frame reservoir, otherwise the oil accumulates in the crankcase, turning the dry sump into an wet sump. The engine is getting rid of the excess oil by blowing it out of the crankcase blower (the oil is sucked in by the carb and burned), thus causing excessive high oil consumption. Exactly this happened to me a few years before Langer’s experiments (see below). While going at a fast pace and engine oil 4000km in use I suddenly had an oil consumption of more than 1,5l/1000km. After the next oil change and at a more moderate speed the consumption was back to normal (about 0,3l/1000km). And I was lucky; rockers/camshafts were still ok.

Wet sumping was already well known by drivers of brit bikes http://www.britbike.com/forums/ubbthrea ... ber=116070

That the running engine wet sumping could also possibly be an issue with Hondas was not known until a few years ago. A guy from our German Dominator forum with the nick Langer, a (“Langer” means “the long one”) was sucked up by the oil-checking procedure and developed an oil sight tube to check it on sight (http://www.technologyplace.de/nx650/), even during driving (not recommended ;-)).

With that gadget, he noticed that the oil in the frame reservoir sometimes vanished during driving. As an engineer he was challenged and started to do some experiments with the dismantled oil pump. He discovered that the oil-pump (depending on oil temperature and oil wear) may show temporarily internal (along the pump shaft) and external leaks (between the body parts of the pump). For instance, the leaking was stronger with higher oil temperatures and with oil that was already 5000km in use, whereas with new oil, there was almost no leaking (which would explain the short changing intervals of 3000km given by Honda) as long as he did not exceed a certain temperature.

The mean thing is that after disassembling, the wear of the pump was still within the limits of the factory manual. So no chance at all to recognize a bad pump by simply measuring the wear. All of a sudden, we had the explanation, why so many RFVC engines died with cylinder head damage - leaking oil pumps and/or drivers, which overrun the oil changing intervals and overheat the engine. So wet sumping that occurs even with fresh oil is dangerous and a clear indication that the oil pump is not working properly and one should consider changing the oil pump. That wetsumping could be an issue must have been known by Honda - an indication is the oil check plug at the clutch cover.

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But back to the question, which oil pump to choose. In 1993, the next evolutionary step was the introduction of reinforcements (likely to minimize leaking) of the oil pump body parts. This pump with the oem number 15100-MY6-670 was stock in 1993-1995 NX650 and all XR650L.

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Finally, the last version 15100-MAN-690 was introduced in 1996 and used in all following RD08, SLR650 and FMX650. The rotor of the frame pump was strengthened by 50% (to counteract the wet sumping), but at the same time, Honda eschewed the oil seals. Why remains unclear; a reason may be that without seals, the oil pump is able to vent itself after running dry. With oil seals, it may occur (IMHO only when mounting a new, dry oil pump) that the pump may not get rid of the internal air and subsequently does not deliver. A hint for that theory is this service bulletin from September 1988 when Honda described how to vent a pump with oil seals.

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I got only one experience with the last version of that sealless oil pump. For my red scrambler (http://up.picr.de/16320537nd.jpg) I used an almost new FMX650 engine with only 18.000km – and I noticed that even with that low mileage, the engine already showed signs of (standing engine) wet sumping. I haven’t tried what would happen at higher mileage, but from experiment I know it will get worse. Not surprisingly, there are many reports of FMX650 with high oil consumption and ruined rockers/camshafts.

Bottom-line: the pump of choice for all NX650 up to 1995 is OEM 15100-MY6-670 because of its oil seal wet sumping is reduced to a minimum (as long as it’s not worn out, of course ;) ).

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