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Compass790 · 27-03-2018, 11:05

Our Yanmar YSM 8 has the oil pump rotor shaft spinning in a hole in the aluminium case. This hole was worn oval & the oil pump would occasionally fail to prime. I drilled out the hole to 8.7mm from the original about 8mm & made a new shaft to suit. I made this out of bronze ( LG2 ) as I didn't want the case to wear any more, I'd rather the shaft wore out as I can machine another. Cant drill the case out anymore as the surrounding aluminium will be getting too thin. Any metallurgical types out there who can comment on this? I can machine another steel shaft if using bronze is a very bad idea.I'd need reasons as to why it's a bad idea. Dont want to buy a new case from Yanmar which is their solution to the problem. Would like to post a pic but I cant seem to. Tried googling idea, cant find any objections but???
thanks if anyone can shed some light on this

jimbunyard · 27-03-2018, 18:56

Make a light press fit bronze bushing for the aluminum pump housing.
If the bushing seems too thin, make a new shaft from steel and 'shoulder' the bushing end to allow enough thickness to press the bushing into the housing.

I would be a little leery of using bronze for the drive shaft, especially if it has a flat key drive and you reduced the case end for bushing clearance, because of potential strength issues and the importance of the oil pump to the engine...

Compass790 · 27-03-2018, 19:53

Quote:

Originally Posted by jimbunyard

Make a light press fit bronze bushing for the aluminum pump housing.
If the bushing seems too thin, make a new shaft from steel and 'shoulder' the bushing end to allow enough thickness to press the bushing into the housing.

I would be a little leery of using bronze for the drive shaft, especially if it has a flat key drive and you reduced the case end for bushing clearance, because of potential strength issues and the importance of the oil pump to the engine...

Thanks Jim I thought of doing the bush way but hadnt thought of the shoulder part, good idea but I dont have a mill to do the case & I'm restricted to DIY. Yes it has a flat key drive. I will still try it unless a metallurgist says a definite no. I have a steel spare & the engine oil alarm is very reliable so will stop it immediately if it sounds. Will look at it after a number of hours & see how it's going. I suspect it should be strong enough as they make prop shafts out of bronze but I dont know. Glad for your input to the problem & will nut out a way to use your suggestion if I have to bush it.

**Wotname** · 27-03-2018, 22:02

OK, I'm not the expert you are seeking (

) but I would have thought there would not be a great load on the oil pump shaft, thus the bronze might be strong enough.

**Wotname** · 27-03-2018, 22:04

OK, these are not photos of the OP's pump but they are very very similar similar. I posting them so others can see what the OP is talking about.

Compass790 · 27-03-2018, 22:25

Thanks for posting pics Wotname, wish I could do that, site doesn't seen to recognize my phones format.It'll be operator error for sure, LOL but I try. Only difference between Wotnames' unit & mine is length of rotor assembly. Hope it helps for anyone to comment. Probably should be trying on a machinists forum but there must be a few on here.
Cheers cobber

jhulmer · 29-03-2018, 13:42

Quote:

Originally Posted by jimbunyard

Make a light press fit bronze bushing for the aluminum pump housing.
If the bushing seems too thin, make a new shaft from steel and 'shoulder' the bushing end to allow enough thickness to press the bushing into the housing.

I would be a little leery of using bronze for the drive shaft, especially if it has a flat key drive and you reduced the case end for bushing clearance, because of potential strength issues and the importance of the oil pump to the engine...

this is the correct answer! I've been in the machining business most of my life and this is what needs to be done and should have been done by Yanmar. IMHO!

Compass790 · 29-03-2018, 14:46

Quote:

Originally Posted by jhulmer

this is the correct answer! I've been in the machining business most of my life and this is what needs to be done and should have been done by Yanmar. IMHO!

Thanks, thats what another life long machinist told me as well. He also said it's common engineering practice to make the rotating part out of the hard material & what I thought was a cunning plan was wrong. I'm still going to trial it as it's easy enough to check how it's lasting ( undo 3 bolts on cover plate) as I'm not confident in my ability to machine a good thin bush. I can make another hard shaft though. The engine dates from 1980 & what chewed out the shaft hole was a bit of big-end bearing shell so the steel on aluminium did last a fair amount of time altho I agree with what you say, better if it had a bronze bush.
Appreciate your input

Pauls · 29-03-2018, 15:02

Bronze is an entire class of materials. Bronzes vary in strength almost as much as steels do. The standard approach, as many have said, is to make a new shaft out of steel. That is the way I would do it. That said, there is nothing wrong with a bronze shaft if the bronze chosen is strong enough.

Regards making and inserting your bronze or brass bushing in the aluminum housing:
1. You said you drilled out the housing. A drill will create a low quality hole with poor surface finish and poor dimensional control. It will be far better to finish the hole with either a reamer or with a boring tool.
2. Because your bushing is going to be fairly thin walled the installation will be more long term robust if you install the bushing with a high strength cylindrical retaining compound from Loctite.
3. Make sure that you maintain the alignment of the new bushing with the rest of the pump bearings/seals/etc.

Compass790 · 29-03-2018, 15:16

Quote:

Originally Posted by Pauls

Bronze is an entire class of materials. Bronzes vary in strength almost as much as steels do. The standard approach, as many have said, is to make a new shaft out of steel. That is the way I would do it. That said, there is nothing wrong with a bronze shaft if the bronze chosen is strong enough.

Regards making and inserting your bronze or brass bushing in the aluminum housing:
1. You said you drilled out the housing. A drill will create a low quality hole with poor surface finish and poor dimensional control. It will be far better to finish the hole with either a reamer or with a boring tool.
2. Because your bushing is going to be fairly thin walled the installation will be more long term robust if you install the bushing with a high strength cylindrical retaining compound from Loctite.
3. Make sure that you maintain the alignment of the new bushing with the rest of the pump bearings/seals/etc.

Well Pauls the bronze is LG2, about 1/2 the tensile strength of steel ( mild) AFAIK. Shaft is bigger than the steel one as in O.P. Yes agree totally about reamer but a drill press was all I had. If it proves to be a problem I can lap it with diamond paste which I should have done anyway. If I'm forced to attempt to make the bush I'll certainly install it using 609 loctite. Will use the rotor to centralise it till glue goes off. Only seal is an o-ring on the cover, you can see the groove on Wotnames' pics.
Thanks for yr help

jhulmer · 29-03-2018, 19:57

Compass
I recently rebuilt a 4JH2E and the oil pump is cast iron which is a different animal all together from cast aluminum in regards to wear in an oil bath. Cast iron is porous and self lubricating and will last as long as the engine. At rebuild I would install a new pump because steel on cast iron would be better then bronze in an oil bath.
Steel on Aluminum is a crime in my opinion. It’s done regularly however, designed obsolescence.

As pointed out above the need for precision on boring the hole is important to maintain center to prevent premature failure after repair. If you are confident that the drill tracked the center of the hole then a reamer will work for the repair in a pinch with the risk of premature failure down the road. However, I would advised taking the housing to a machine shop to have it properly bored and a bushing pressed into the bore and the shaft checked for fit. This setup, I expect, will outlast the original as sintered bronze is porous and self lubricating. Especially in an oil bath.

Compass790 · 29-03-2018, 20:52

Quote:

Originally Posted by jhulmer

Compass
I recently rebuilt a 4JH2E and the oil pump is cast iron which is a different animal all together from cast aluminum in regards to wear in an oil bath. Cast iron is porous and self lubricating and will last as long as the engine. At rebuild I would install a new pump because steel on cast iron would be better then bronze in an oil bath.
Steel on Aluminum is a crime in my opinion. It’s done regularly however, designed obsolescence.

As pointed out above the need for precision on boring the hole is important to maintain center to prevent premature failure after repair. If you are confident that the drill tracked the center of the hole then a reamer will work for the repair in a pinch with the risk of premature failure down the road. However, I would advised taking the housing to a machine shop to have it properly bored and a bushing pressed into the bore and the shaft checked for fit. This setup, I expect, will outlast the original as sintered bronze is porous and self lubricating. Especially in an oil bath.

JHulmer, no arguments with the best way as you described but I'm a DIY guy who uses what I have. May spring for a reamer tho as I can get one from China for $15 if I have to bush it. Many Jap cars have steel cams spinning in aluminium & they do 200,000 miles easy pulling more revs than our Yammer. . I got the drill reasonably central using the rotor shaft in the drill chuck on a drill press, but yes the bore finish is bound to be bad so I'll expect some scoring. The bronze I used is not sintered as the oil pump obviously has constant oil supply except for start-up. I know sintered is better but LG2 works fine with oil feed .I shall report back as to how the bronze shaft looks after it's done some hours but I'm prepared to have to make a steel shaft & bush case if necessary.
Thanks for your input

**Wotname** · 29-03-2018, 23:18

Quote:

Originally Posted by Compass790

...... Many Jap cars have steel cams spinning in aluminium & they do 200,000 miles easy pulling more revs than our Yammer. . .......

FWIW to others not familiar with this oil pump, it is driven by the camshaft so operates at half the engine RPM; thus the OP is probably running the oil pump somewhere between 1,000 and 1,500 RPM.

jimbunyard · 30-03-2018, 03:13

That the rotor shaft has the 'tang' rather than the 'slot' alleviates to some extent my concern with the strength of the bronze; if the situation were reversed, I would have expected the 'slot ears' to fail at some point...

The clearances in a trochoidal gear pump are critical for it's efficient operation, hence the concern with centering of the drive shaft hole; if the hole is too far off center in any direction, but especially in the 6 or 12 o'clock positions (in regards to maximum and minimum clearance between the drive and driven rotor), flow may be reduced or the pump may lock up.

If, when assembled, the pump spins freely with oil in it, I would err on the side of caution and not worry about any further 'finishing' of the hole.

Both of the materials are soft enough to not worry particularly about galling, especially when run in an oil bath; any minor imperfections in the hole now will polish themselves out in very short order, provided that the pump is adequately lubed on startup.

When I install oil pumps, I squirt all the moving parts with oil, then fill them with engine assembly lube. If possible, (though I don't think it is in your case), after the engine is assembled I fill it with oil and prime the engine with a long drive pin and an electric drill. There is a surprising amount of torque required to turn a primed oil pump, and I'm sure that it is multiplied commensurately when the oil is very cold...