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Robertb
Dijon


Joined: 01 Sep 2003
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2002 Porsche 996 Carrera 4S

PostPosted: Tue Jan 21, 2020 2:22 pm    Post subject: Oversized crank bearings... Reply with quote

I read the in a 911&Porsche World mag from a few weeks ago some comments in an interview with Westwood. They said they offer oversized crank bearings specifically so the crank can be reground and reused where it previously could not (presumably assumes there is not some crank bearing-related catastrophic failure which damages the crank beyond repair). This sounds like a good thing, unless I am misunderstanding.

Any thoughts?
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Paynewright
Monza


Joined: 17 Apr 2018
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PostPosted: Tue Jan 21, 2020 7:29 pm    Post subject: Reply with quote

I posed this very topic a while ago and Hartec replied. Regrinding is the easy bit. Re nitrocarbonising (hardening) the new surface can alter the journal dimensions and its a bit hit/miss.

I think thats what Baz said.

Ian
 
  
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kurlykris
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Joined: 30 Jun 2014
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PostPosted: Tue Jan 21, 2020 7:38 pm    Post subject: Reply with quote

I was thinking about this very thing last night while watching Abom79 Metal Spraying shafts on Youtube, I was wondering if it was possible to induction harden the sprayed metal and then regrind the journals back to factory dimensions. I couldn`t find a definitive answer as to whether the newly sprayed metal can actually be hardened Question
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Paynewright
Monza


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Location: Nr Lutterworth Leics


PostPosted: Tue Jan 21, 2020 8:43 pm    Post subject: Reply with quote

Previous....

http://911uk.com/viewtopic.php?t=134784&highlight=regrind
 
  
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Robertb
Dijon


Joined: 01 Sep 2003
Posts: 7559
Location: South Oxfordshire

2002 Porsche 996 Carrera 4S

PostPosted: Tue Jan 21, 2020 9:00 pm    Post subject: Reply with quote

Thanks... exactly the article I’d seen.

It would be interesting to get Westwood’s view too.
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Westwood10
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Joined: 28 Nov 2013
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PostPosted: Wed Jan 22, 2020 10:45 am    Post subject: Reply with quote

We started to sell these undersize bearings early last year. We took over the sales of the bearings from a company in Germany that had been doing them for many years. We spoke to a number of Porsche engine rebuilders who all agreed that with the sizes we were providing, the cranks did not need to be re-hardened. Of course, if you wanted to do this, it would not be a problem.

They are not a fast mover for us, but they compliment the other Porsche parts we sell.

Hope this helps.

Duncan
 
  
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Westwood10
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PostPosted: Wed Jan 22, 2020 10:45 am    Post subject: Reply with quote

We started to sell these undersize bearings early last year. We took over the sales of the bearings from a company in Germany that had been doing them for many years. We spoke to a number of Porsche engine rebuilders who all agreed that with the sizes we were providing, the cranks did not need to be re-hardened. Of course, if you wanted to do this, it would not be a problem.

They are not a fast mover for us, but they compliment the other Porsche parts we sell.

Hope this helps.

Duncan
 
  
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Robertb
Dijon


Joined: 01 Sep 2003
Posts: 7559
Location: South Oxfordshire

2002 Porsche 996 Carrera 4S

PostPosted: Wed Jan 22, 2020 11:41 am    Post subject: Reply with quote

Thanks Duncan, that's useful to know.

BTW its always good to see the Westwood Cayman at Shelsley! Thumb
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Westwood10
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PostPosted: Wed Jan 22, 2020 3:56 pm    Post subject: Reply with quote

Thank you. Not sure if we are doing Shelsley this year!!! Porsche Hill climb Championship are not going there, and i don't enjoy competing there, so will be at other venues. We will certainly be doing the Porsche Prescott event in June, because that was superb last year.
 
  
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Robertb
Dijon


Joined: 01 Sep 2003
Posts: 7559
Location: South Oxfordshire

2002 Porsche 996 Carrera 4S

PostPosted: Wed Jan 22, 2020 4:57 pm    Post subject: Reply with quote

That's a shame... not realised that PCGB weren't attending in 2020. I've been spectating at Shelsley for years, but I had noticed that the field does seem a little thinner recently... are you able to share why don't you enjoy competing there? (apart from the rather binary outcome to any slight errors on the hill!). Feel free to go via PM if you want.

I'll try to get along to the Prescott meet in June.
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Westwood10
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PostPosted: Thu Jan 23, 2020 11:46 am    Post subject: Reply with quote

Nothing to Hide about shelsley, just don't like the paddock, and the general way the club works. The club don't care about competitors, we are just a form of revenue!!
 
  
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sportsandclassic
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Joined: 21 Apr 2008
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PostPosted: Sat Jan 25, 2020 5:37 pm    Post subject: Reply with quote

Grinding high performance engine crankshafts is always a risky process,

First off you should ideally know how deep the crankshaft has been hardened to. It is normally only just below the surface of the crank pin journal. If you grind to first undersized bearing assuming 0.010” then that’s probably already gone through any hardening. If you are re-hardening then it can add thickness and slight distortion to the finish and would need re-sizing.

I have made enquires to have this type of work done and been advised by the companies of to bother due to inconsistency in the final product.

Does anyone know for certain what depth the 996/997 crankshafts are hardened to?

Personally I would advise against this on this particular crankshaft.

Mike
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MisterCorn
Dijon


Joined: 08 Jan 2011
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Location: Nottingham, England

2004 Porsche 996 Turbo

PostPosted: Sat Jan 25, 2020 6:34 pm    Post subject: Reply with quote

So I guess we need somebody with a hardness testing machine who can take a standard crank and test it at various undersizes to see how deep it is.

MC
 
  
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bazhart
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Joined: 20 May 2009
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PostPosted: Sun Jan 26, 2020 11:27 am    Post subject: Reply with quote

For what its worth - we already did this about 10 years ago and the result was very shallow and from memory I think about 3 or 4 thou of full hardness (I will try and find the records from back then to confirm) but anyway not enough to regrind 0.25mm undersize and retain full hardness. We know of some that tried and they didn't last too long on track!

We found some oversized shells from other models that we modified in a jig and had some of our cranks re-hardened allowing a few tenths for the white layer (that grows during nitriding). We had to guess the resulting thickness of the white layer and found the right allowance which then had to be polished off.

The cranks are still running today but it is a bit hit and miss how thick the white layer turns out and at the time we found enough used cranks to continue without re-hardening.

Also several cranks would pick up a 4 thou bend during their life requiring all journals to be re-ground which runs out almost as expensive as a god used crank with a full set of new undersized shells.

Later Porsche moved the tag on the shells to the other side of the con-rods (previous early ones had a tag groove in both sides) so the non Porsche shells we had modified to use were no longer useful and we just continued to use good used or new cranks.

Now it is difficult to find a catalogue to find suitable shells from other models to seek out one you could modify to use and as with all our new computer technology you just input the model first to find its relevant shell and measurement details are often no longer available so it would take for ever.

We do presently happen to have some new racing special shells in production (for our own rebuilds) in standard size but if supply of cranks runs out we could order a quantity of undersized versions and consider setting up a service for others to suit but the quantities needed to make it viable are high, we would have to collect together a lot of cranks to make it all worthwhile and we would not accept the liability to pay for replacement cranks and a full engine rebuild that someone else undertook if it still failed..

It might be that a softer journal might last reasonably long in a road engine that is not driven too aggressively but as engine builders we have no control over how our customers drive their cars or look after them and would never take such a chance - anyway who pays for the new crank and second rebuild if such a process failed. We feel the risk is too great but others may not agree and that's up to them!


Baz
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bazhart
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PostPosted: Mon Jan 27, 2020 9:43 am    Post subject: Reply with quote

For background - decades ago cranks were 1st made with journals too big, then hardened for a long time in ovens, then quenched (which distorted them), then ground back to size - but could therefore be re-ground.

Once manufacturers have decided that rebuilding engines is generally unlikely these days (fashion replacing practicality), they didn't need the re-grind option - so (like Porsche) didn't make oversized shells as an option and then didn't need to harden the cranks any deeper than a thin surface depth (because if they did wear down that far they were scrap anyway).

Then they could Nitride harden the surfaces (which doesn't require quenching so didn't distort the crank) and then the more shallow the depth - the less growth in the white layer so there was a disadvantage in nitriding for any longer than needed for enough depth to stop wear and they would only need slight polishing to finish = quicker turnaround manufacturing time, a very much cheaper process, less time in ovens, less machining operations and the benefit is a lower price to us the consumer.

With pressure on manufacturers of sports cars to show willing in reducing emissions and increasing MPG - they all started reducing the width of big end shells (to minutely reduce drag and MPG) and Porsche were no exception. This cut down on crankshaft weight and often reduced the size of the engine but limited the life a little (which fitted in with the new philosophy of non rebuildable engines).

I have a picture I will try and post showing the difference between a 944 and 996 crank that makes this more obvious.

So nothing wrong with the whole plan to make a version of a 911 more affordable in the modern World - but creating a problem if the engines do eventually need or benefit from rebuilds and cranks wear!

Baz
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944 v 996 crank.png
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944 v 996 crank.png


  
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Robertb
Dijon


Joined: 01 Sep 2003
Posts: 7559
Location: South Oxfordshire

2002 Porsche 996 Carrera 4S

PostPosted: Mon Jan 27, 2020 12:26 pm    Post subject: Reply with quote

Thanks Baz, very interesting engineering insight as always. The pic is certainly an eye opener to see the actual difference.

Its annoying the bearings cannot be accessed from underneath like the BMW V8 M engine, rather than requiring a full removal/strip.
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maldren
Suzuka


Joined: 07 Oct 2016
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PostPosted: Tue Jan 28, 2020 8:47 am    Post subject: Reply with quote

I'm sure Baz is right with his comments on reducing bearing sizes but a comparison of air cooled vs water cooled bearing sizes would be better example.

The 944 was 4 cylinder so inherently less well balanced (even with a balance shaft) and would therefore need bigger bearings.
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bazhart
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PostPosted: Tue Jan 28, 2020 9:39 am    Post subject: Reply with quote

But there is a different oil pump system between air and liquid cooled engines and you can see from the overhang of the 996 crank compared to the 944 (which is basically similar in overhang to the air cooled 911) that more flexure in the crank would result. furthermore the later engines produce much more torque at lower revs (due to their camshaft variable timing systems) which increases the load on the shells and are generally larger capacity and with heavier pistons as well.

The air cooled cranks were also hardened more deeply and this does influence their life expectancy.

Baz
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bazhart
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PostPosted: Wed Jan 29, 2020 12:26 pm    Post subject: Reply with quote

The 944 had larger mains but there is no reason for the big ends to be bigger as they see out of balance forces all the time anyway and maximum at TDC and BDC regardless. The 944 big end while the same dia as pre 1977 911's (@52mm) was nearly 40% wider while the crankshaft webs were more than twice as wide (to stiffen the crank from flexing).

While that year of air cooled 911 changed through to the 1995 versions from 57 to 60 mm dia mains, the 996 to 997 (and Cayman S) went from 60 to 63mm.

The air cooled big ends varied from 52 to 53mm (55 for the later air cooled turbo).

The big ends for the 996, 997 and Cayman S however remained the same @53mm but with the shells only 15.5mm wide despite the extra torque and bhp (don't stock air cooled parts so not sure how wide those big end shells were - perhaps someone could enlighten us).

Overall very skimpy big ends for the output and no simple way to re-grind cranks if needed - a great shame for everyone.

Baz
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fot0
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Joined: 03 Apr 2018
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Location: Thames Valley


PostPosted: Thu Jan 30, 2020 8:20 am    Post subject: Reply with quote

bazhart wrote:
The 944 had larger mains but there is no reason for the big ends to be bigger as they see out of balance forces all the time anyway and maximum at TDC and BDC regardless. The 944 big end while the same dia as pre 1977 911's (@52mm) was nearly 40% wider while the crankshaft webs were more than twice as wide (to stiffen the crank from flexing).

While that year of air cooled 911 changed through to the 1995 versions from 57 to 60 mm dia mains, the 996 to 997 (and Cayman S) went from 60 to 63mm.

The air cooled big ends varied from 52 to 53mm (55 for the later air cooled turbo).

The big ends for the 996, 997 and Cayman S however remained the same @53mm but with the shells only 15.5mm wide despite the extra torque and bhp (don't stock air cooled parts so not sure how wide those big end shells were - perhaps someone could enlighten us).

Overall very skimpy big ends for the output and no simple way to re-grind cranks if needed - a great shame for everyone.

Baz


@Baz
What is the bottom line here before rumours proliferate around the web (and we can't have that said about the m96)? With what you have explained here in great detail and your article in a recent magazine is the crank in most cases reaches end-of-life. So simply replacing standard shells (if the crank is within spec) will not cut it long term? Not talking about race engines here.

Many years ago, I rebuilt another problematic engine on a Dolomite Sprint. I had the crank regound, tufftrided and balanced. Along with a bunch of other upgrades it was reliable producing much more power than standard. I am not a metallurgist by any means, so excuse my naivety, but re-hardening a crank will introduce all sorts of other issues such as warp and is not an option due to previous hardening?
 
  
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