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Alex
Le Mans
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Joined: 06 Mar 2014
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2000 Porsche 996 Carrera 4

PostPosted: Mon Aug 05, 2019 9:29 am    Post subject: Reply with quote

What do you mean by shaft play?
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cvega
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PostPosted: Mon Aug 05, 2019 11:20 am    Post subject: Reply with quote

when holding the bearing by the housing one hand and shaft with the other, you can feel detectable movement of the shaft inside the bearing itself. Whether it's within specs, I don't know. While we were there replacing clutch and leaking IMS, was worth replacing, I think...
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Alex
Le Mans
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2000 Porsche 996 Carrera 4

PostPosted: Mon Aug 05, 2019 11:31 am    Post subject: Reply with quote

Ah, so you mean there was play in the bearing. Thumb
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cvega
Monza


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PostPosted: Mon Aug 05, 2019 11:32 am    Post subject: Reply with quote

Yes - sorry if I didn't describe it well. It didn't look bad but it made sense to replace it while car was in bits.
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Dammit
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PostPosted: Mon Aug 05, 2019 2:06 pm    Post subject: Reply with quote

Sorry- bit of a hijack, what's the opinion on the approach to the IMSB of making a small hole in the end of the IMS itself, and then replacing the standard oil pump drive shaft with one that has a groove in it to send pressurised oil to the IMSB?
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Alex
Le Mans
Le Mans


Joined: 06 Mar 2014
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Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Mon Aug 05, 2019 2:17 pm    Post subject: Reply with quote

For me the concept is a good idea but how this works in reality with regards to the (less) oil flow to the other engine components leaves it in a higher risk area potentially. Maybe this could be overcome with a better pump? Dont know
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Dammit
Watkins Glen


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PostPosted: Mon Aug 05, 2019 2:26 pm    Post subject: Reply with quote

It's a good question, I wonder how we'd answer it?

FWIW the (anecdotal) stuff I've been reading suggests that the pressure pump is pretty good, the problem with the oiling system is not to be found there, but rather with gravity uncovering the oil pickup, interrupting the supply to the pump.

But as I say, that's anecdotal.

I'm tempted to remove the seals from the large/final IMSB in the new engine and modify the IMS (AKA, put 2mm hole in the non-flywheel end), and machine a groove into the IMS-Pressure pump drive gear shaft.
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Alex
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PostPosted: Mon Aug 05, 2019 2:32 pm    Post subject: Reply with quote

If the engines in bits I'd just fit the later larger bearing and remove the seals. There's plenty of oil round that area to keep a frictionless bearing happy.
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Dammit
Watkins Glen


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PostPosted: Mon Aug 05, 2019 5:52 pm    Post subject: Reply with quote

I’m sure you are right, I just quite like the belt and braces approach of having pressurised oil going to the bearing.

However- unless we move the oil filter to a different place in the circuit that would mean supplying pressurised but unfiltered oil to the IMS.

Now this sounds bad, but bear in mind that the oil pump bearings are also fed the same oil.
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Alex
Le Mans
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PostPosted: Mon Aug 05, 2019 5:58 pm    Post subject: Reply with quote

Only solid bearings need pressurised oil. Frictionless bearings only need a light amount of lubricant.
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MisterCorn
Dijon


Joined: 08 Jan 2011
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2004 Porsche 996 Turbo

PostPosted: Mon Aug 05, 2019 6:04 pm    Post subject: Reply with quote

Dammit wrote:
. Unless we move the oil filter to a different place in the circuit that would mean supplying pressurised but unfiltered oil to the IMS.

Now this sounds bad, but bear in mind that the oil pump bearings are also fed the same oil.


Hmm, I hadn't thought about the filtering. Feeding the most delicate and vulnerable bearing with unfiltered oil doesn't sound good.

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deMort
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Joined: 21 Mar 2015
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PostPosted: Mon Aug 05, 2019 6:04 pm    Post subject: Reply with quote

If the shaft is continuously under the oil lvl so that it will never drain out then in theory it would be possible...

You would be increasing the weight of the shaft and therefore the load on the bearings though .. i think that would be counterproductive to what you are trying to achieve .

If it isn't fully submerged then you would have a shaft half filled with oil at times .. that would cause an imbalance in rotation .

There is a very sizable amount of space inside the ims shaft to keep filled with oil .
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Alex
Le Mans
Le Mans


Joined: 06 Mar 2014
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Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Mon Aug 05, 2019 6:10 pm    Post subject: Reply with quote

I can't remember the exact application but I remember at work once having a problem with a roller bearing that was pressure fed with oil - think it slowed the machine down of something like that. The whole concept of roller bearings is to get away from pressurised oil feeds.
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Dammit
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PostPosted: Mon Aug 05, 2019 6:22 pm    Post subject: Reply with quote

Ok, I’m convinced- lets park that idea.
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deMort
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PostPosted: Mon Aug 05, 2019 6:29 pm    Post subject: Reply with quote

Alex wrote:
I can't remember the exact application but I remember at work once having a problem with a roller bearing that was pressure fed with oil - think it slowed the machine down of something like that. The whole concept of roller bearings is to get away from pressurised oil feeds.


Can i just say .. even thought the idea is shelved ..

Alex .. worship

Oil as a lubrication is one thing but too much would act as a restriction .. it would need to be pushed out of the way by the ball bearings .. heat and a restriction would cause shaft rotational stress .

Spot on Thumb

Damn its always a learning day on this forum .
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infrasilver
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Joined: 04 Oct 2010
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2001 Porsche 996 Targa

PostPosted: Mon Aug 05, 2019 6:30 pm    Post subject: Reply with quote

The oil pump shaft has been known to snap so for me removing metal from it doesn't sit right with me (I fitted a billet drive shaft in mine) and I would want both the seals removed from the IMSB to let the oil flow through the bearing if I was to consider a modified shaft.
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Last edited by infrasilver on Tue Aug 06, 2019 12:04 pm; edited 1 time in total
 
  
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Alex
Le Mans
Le Mans


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Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Tue Aug 06, 2019 8:52 am    Post subject: Reply with quote

Point 4 taken from here: http://www.petronomics.com/bear_mistakes.htm

With a circulating oil system, oil is pumped from a separate reservoir, where it cools down and lubricates simultaneously. The heated oil is then returned to the reservoir, where it cools down again. Filters in the system remove contaminants from the oil as it circulates. A circulating oil system can often greatly increase bearing life expectancy.

Circulating oil, however, should not be used in high-speed applications, such as machines tool spindles, because of unacceptable friction losses as the lubricant moves through the bearing. In these applications, only a small amount of oil is needed, and a spray-mist system is generally preferred.

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Dammit
Watkins Glen


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PostPosted: Tue Aug 06, 2019 9:39 am    Post subject: Reply with quote

Thanks Alex. Only question I have is what counts as high speed?

The IMS rotates at half engine speed IIRC, which would mean it would see ~4,200 rpm maximum in our engines, and a great deal less than that for 99.999% of the time.

What speed does a machine tool spindle rotate at?
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Alex
Le Mans
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2000 Porsche 996 Carrera 4

PostPosted: Tue Aug 06, 2019 10:16 am    Post subject: Reply with quote

My milling machine does 3k rpm, lathe 1.8k rpm and surface grinder 3k rpm on their spindles.
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Hertsdriver
Monza


Joined: 12 Nov 2018
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2004 Porsche 997 Carrera 2

PostPosted: Tue Aug 06, 2019 10:41 am    Post subject: Reply with quote

Although I completely agree that an oil feed is unnecessary in this application, surely a car engine propelled IMS shaft isn't going to suffer from frictional losses if oil fed to a detrimental effect like an electric motor on a lathe (thats already geared up/down) where I could see drag becoming a problem on such a small powered motor to cause an issue in slow down. An internal combusion engine has a significant increase in power/torque to make that not an issue, or am I barking up the wrong tree?
 
  
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