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GARY S
Monza


Joined: 06 Aug 2016
Posts: 175



PostPosted: Sat Apr 27, 2019 9:04 am    Post subject: Reply with quote

"a couple of taps with a light hammer"!!! As Alex has already commented, what stresses/damage is this doing to the sensitive items attached or linked to the IMS? In 2012 I spoke with Hartech about whether it was possible for them to check & if necessary replace the IMS bearing on my (November 2004 registered) 997.1 with one of the common aftermarket items. They explained they only upgrade the bearing to the post 2006 larger bearing as part of an engine strip down as they have found replacing an early bearing in situ if fraught with potential problems. In their experience bearings hardly ever come out smoothly even with the "removal tool" shown being used on the internet & putting the new one in subjects sensitive internal components to unnecessary stresses.
 
  
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rigsby99
Monza


Joined: 22 Oct 2015
Posts: 204
Location: South Cheshire


PostPosted: Sat Apr 27, 2019 9:18 am    Post subject: Reply with quote

GARY S wrote:
"a couple of taps with a light hammer"!!! As Alex has already commented, what stresses/damage is this doing to the sensitive items attached or linked to the IMS? In 2012 I spoke with Hartech about whether it was possible for them to check & if necessary replace the IMS bearing on my (November 2004 registered) 997.1 with one of the common aftermarket items. They explained they only upgrade the bearing to the post 2006 larger bearing as part of an engine strip down as they have found replacing an early bearing in situ if fraught with potential problems. In their experience bearings hardly ever come out smoothly even with the "removal tool" shown being used on the internet & putting the new one in subjects sensitive internal components to unnecessary stresses.


Indeed, I wouldn't expect Hartech to fit any after market device, they have their reputation and warranty to consider and will only do things properly. But that doesn't mean that the in situ fixes don't work, they are perhaps risky but have been done by individuals and Indys with obvious success in the thousands. You pays your money and take your chances....

I would very much like Baz's views on bushes as opposed to bearings!
 
  
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Griffter
Spa-Francorchamps


Joined: 22 May 2016
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PostPosted: Sat Apr 27, 2019 9:34 am    Post subject: Reply with quote

rigsby99 wrote:
Alex wrote:
So do you think that by fitting a pipe in the side of the oil filter that allows oil to be pumped to the other end of the shaft have zero effect on pressure at (for example) the crank bearings or cam shafts?


No it wouldn't as long as the bearing, oil cooler, gauge etc didn't leak or, in the case of a bearing was tight enough to maintain the pressure. Worn main bearings will show a drop in oil pressure assuming that the pressure control system cannot compensate.


There’s pressure and there’s flow. A gauge requires pressure but not flow, so it will not affect the flow of oil (or therefore the available pressure) to other components.
An oil-fed bearing, however, requires a flow of oil and incurs a pressure drop across it, so it would potentially affect the flow of oil (and available pressure) to other components.
Of course you would expect the capacity of the oil pump and the pressure regulator to be such that the minor effect of an oil fed bearing would be inconsequential to the oil flow and pressure to other components, but it will depend to some extent on where the tapping is and what the flow characteristics of the oil fed bearing are. Given the M96 is known to be prone to surge in hard cornering I’m not sure I’d risk it.
 
  
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Alex
Le Mans
Le Mans


Joined: 06 Mar 2014
Posts: 17137
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Sat Apr 27, 2019 9:37 am    Post subject: Reply with quote

Taken from another thread:


bazhart wrote:
Ball bearings do not require oil under pressure - just a small amount of splash oil is perfect for them.

Oil pumps deliver oil pressure and flow that increases with revs until the maximum oil pressure designed is reached when a blow off or bye pass valve opens to prevent over pressuring the system.

These engines have increased oil supply points due to the inclusion of 24 hydraulic tappets, three hydraulic tensioners (unsealed so a leak path) and variable camshaft solenoid actuation.

The galleries that deliver the oil to the cylinder head area are not sealed (just alloy to alloy face closures) so also have small leak paths.

As a result the leakage potential at low revs is relatively high.

The pump is a crude double gear pump that drops both pressure and delivery volumes considerably at low revs and as the gear shafts wear the diametral clearance increases reducing low speed pump efficiency further.

The Gen 2 engines have a much more sophisticated oil pump (much more expensive).

If the engine is being stripped the larger splash oil fed ball bearing is the best solution available (and we can supply the Porsche IMS with the larger bearing for later cars or - we re-manufacture a shaft that incorporates the larger bearing in both Hivo (later engines) and roller chain (earlier engine) variants (only available during a Hartech rebuild at the moment) and it costs less than the Porsche version with the larger bearing.

Since the weaknesses in the design (bore ovality, cracking and/or scoring) may lead to an increasing number of engines needing a rebuild - and bearing in mind the small number of IMS bearing failures so far anyway - it may be better to wait and have a larger ball bearing version fitted during a rebuild.

If a rebuild is not going to be considered (or afforded) than replacing the bearing with a 6204 single row ball bearing with a stronger spindle and splash oil feed should last several years (although if the engine has suffered an IMS bearing failure it is best to strip and rebuild the engine as in our experience debris goes everywhere and can cause more serious damage and a more expensive rebuild eventually).

There can be resulting problems unless the people retrofitting the bearing kit "in the car" without stripping have special tools and take great care - so there can be a small risk in doing that and probably no less than leaving it alone anyway.

There is nothing wrong theoretically with a pressure fed plain bearing kit - it should provide a reliable system but it will inevitably have some affect on the oil pressure and delivery volumes on hot tickover. I would consider adding the new oil pump and the associated casting if oil pressure was not high on hot tickover before the change.

I don't think anyone will have enough time or money to test hundreds of cars for enough years to establish conclusively whether this additional oil supply need will result in any deterioration in average engine life but crankshafts are not hardened very deeply and shells are relatively thin - so most engines we rebuild (over say 30K) require new shells anyway and in view of all the uncertainty and relative rarity of IMS bearing failure anyway - combined with the eventual higher probability of requiring an engine rebuild - and the relatively expensive "upgrades" available - we suggest it might be better on average to wait until then and fit a larger ball bearing version.

If you can easily afford this pressurised solid bearing kit and are happy to accept the slight risk - and want the peace of mind and have no plans or expectations to have an engine rebuild anytime soon then I feel sure it will work better than an IMS small bearing replacement.

We have had a few ceramic bearing failures in (but have also had most other types to) but they are insignificant in numbers compared to other failures like bore scoring, cracked cylinders, crankshaft bearing failure and valve seats falling out or valve heads breaking.

The loads imparted to the shaft from the chain slap are very much higher than most people would imagine (hence the under-spec of the original bearings) both linear and lateral loads can be very high and not helped by the relatively crude hydraulic tensioners (compared to most of the air cooled 911 range with hydraulic tensioners) and they wear quite quickly and have a reduced effectiveness with time and mileage.

A good watch is the "rollring" tensioner shown in a video on the Internet youtube to see how bad chain snatch can be at relatively low revs.


Baz

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spongebob squarepants
Long Beach


Joined: 20 Dec 2009
Posts: 6039
Location: Manchester and Iraq


PostPosted: Sat Apr 27, 2019 9:53 am    Post subject: Reply with quote

Not sure how you can compare car SOS with Wheeler dealers. One show just does a pis s poor bodge job, the other a proper full restoration, I suspect Fuzz Townsend has forgotten more than Ed and Ant ever knew, particularly Ant!
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rigsby99
Monza


Joined: 22 Oct 2015
Posts: 204
Location: South Cheshire


PostPosted: Sat Apr 27, 2019 10:09 am    Post subject: Reply with quote

Griffter wrote:
rigsby99 wrote:
Alex wrote:
So do you think that by fitting a pipe in the side of the oil filter that allows oil to be pumped to the other end of the shaft have zero effect on pressure at (for example) the crank bearings or cam shafts?


No it wouldn't as long as the bearing, oil cooler, gauge etc didn't leak or, in the case of a bearing was tight enough to maintain the pressure. Worn main bearings will show a drop in oil pressure assuming that the pressure control system cannot compensate.


There’s pressure and there’s flow. A gauge requires pressure but not flow, so it will not affect the flow of oil (or therefore the available pressure) to other components.
An oil-fed bearing, however, requires a flow of oil and incurs a pressure drop across it, so it would potentially affect the flow of oil (and available pressure

to other components.
Of course you would expect the capacity of the oil pump and the pressure regulator to be such that the minor effect of an oil fed bearing would be inconsequential to the oil flow and pressure to other components, but it will depend to some extent on where the tapping is and what the flow characteristics of the oil fed bearing are. Given the M96 is known to be prone to surge in hard cornering I’m not sure I’d risk it.


Hartech, in your later submission do not rule out a pressure fed bearing modification, they only state that oil pressure may be affected on hot
tickover, if that is the case you've got bigger problems then a single small new and presumably tight bearing being fitted. There are lots of plain pressure fed bearings in the engine one more is not going to make any difference on a healthy engine. Especially as it is being independently fed. Surge is irrelevant. especially as you don't get to much of it on hot tickover!
 
  
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Alex
Le Mans
Le Mans


Joined: 06 Mar 2014
Posts: 17137
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Sat Apr 27, 2019 10:52 am    Post subject: Reply with quote

Out of interest what are your views on what they fitted in WD?
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rigsby99
Monza


Joined: 22 Oct 2015
Posts: 204
Location: South Cheshire


PostPosted: Sat Apr 27, 2019 11:09 am    Post subject: Reply with quote

I don't know as this is the first time I've seen a bush being used as opposed to a plain bearing which is why I would be interested in Baz's observations.
 
  
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Alex
Le Mans
Le Mans


Joined: 06 Mar 2014
Posts: 17137
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Sat Apr 27, 2019 11:15 am    Post subject: Reply with quote

rigsby99 wrote:
I don't know as this is the first time I've seen a bush being used as opposed to a plain bearing which is why I would be interested in Baz's observations.


It is a plain bearing that's used in the program. Ant just calls it a bush (which is just another name for a plain bearing).


https://en.wikipedia.org/wiki/Plain_bearing

A bushing, also known as a bush, is an independent plain bearing that is inserted into a housing to provide a bearing surface for rotary applications; this is the most common form of a plain bearing
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rigsby99
Monza


Joined: 22 Oct 2015
Posts: 204
Location: South Cheshire


PostPosted: Sat Apr 27, 2019 11:23 am    Post subject: Reply with quote

Yes but the prog was maybe a bit light on detail as to the construction of said bush. They are generally found in suspensions not in the rotating parts of engines.
 
  
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Alex
Le Mans
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Posts: 17137
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Sat Apr 27, 2019 11:51 am    Post subject: Reply with quote

So what's your view on the solid bearing/bush (same thing) used in the program?
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rigsby99
Monza


Joined: 22 Oct 2015
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Location: South Cheshire


PostPosted: Sat Apr 27, 2019 12:01 pm    Post subject: Reply with quote

Crank shaft, cam shaft bearings are generally referred to as plain but they have white metal liners. Looking at the WD video again the bush rotates within the new bearing holder and has a lubricating hole and ring to give continuous lubrication. It looks as if the bearing holder is maybe ceramic to avoid metal to metal contact in the absence of white metal shells? It obviously works. The oil feed is not exposed, seems to sit behind the cross member.
 
  
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Alex
Le Mans
Le Mans


Joined: 06 Mar 2014
Posts: 17137
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Sat Apr 27, 2019 12:04 pm    Post subject: Reply with quote

I wondered why you thought it didn't seem like a good idea at all.
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kas750
Shanghai


Joined: 31 Mar 2013
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Location: Chorley lancashire

2006 Porsche 911

PostPosted: Sat Apr 27, 2019 6:24 pm    Post subject: Reply with quote

rigsby99 wrote:
Yes but the prog was maybe a bit light on detail as to the construction of said bush. They are generally found in suspensions not in the rotating parts of engines.

Solid bushing are found as small end bearings in lots of applications and as main bearings in vintage vehicles..
 
  
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kas750
Shanghai


Joined: 31 Mar 2013
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Location: Chorley lancashire

2006 Porsche 911

PostPosted: Sat Apr 27, 2019 6:25 pm    Post subject: Reply with quote

rigsby99 wrote:
Yes but the prog was maybe a bit light on detail as to the construction of said bush. They are generally found in suspensions not in the rotating parts of engines.

Solid bushing are found as small end bearings in lots of applications and as main bearings in vintage vehicles..
 
  
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Griffter
Spa-Francorchamps


Joined: 22 May 2016
Posts: 368



PostPosted: Sun Apr 28, 2019 8:44 am    Post subject: Reply with quote

I think the term “bush” is what’s unhelpful here. A bush and a bearing both connect two components and allow relative rotation between them. Comparison of a suspension bush with a journal bearing is the kind of confusion that can arise when the terms are used interchangeably. The only example I can think of where a bush really is a bearing (well, strictly one half of a bearing) is a bronze sintered bush, or possibly a polymer bush which might be used as a cheaper alternative to a roller bearing.
Anyway I don’t think anyone’s saying an oil fed journal bearing on the IMS shouldn’t work; the marvel is that Porsche didn’t do it that way in the first place!
Concerns re oil pressure may or may not be well placed. Of course surge is irrelevant at hot idle, but it’s not irrelevant if the oil feed to your journal bearing is interrupted mid corner. A splash lubricated IMS bearing would survive surge temporarily interrupting oil pressure to other components, but that’s avoiding the problem of low oil pressure rather than solving it!
 
  
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Alex
Le Mans
Le Mans


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Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Sun Apr 28, 2019 9:21 am    Post subject: Reply with quote

People's understanding of the word bush. It's simple - it's a Layman's term for a cylindrical shape with a hole through it. People then think specific parts are named that word and only those parts.

It's like calling a wheel a circle then saying a dial isn't a circle.
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