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engine life

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I'm looking at SC's at the moment and I see a lot that have covered about 120,000 miles advertised. Many of these say they have had a top end rebuild. My worry is that if a car needs a top end rebuild the bottom end can't be far behind.

What kind of mileage should you expect from a well maintained 911 before the engine needs a complete overhaul?

Thanks
 
Hi Chris longevity is one of the best qualities of an SC engine a properly used and maintained SC bottom end should see over 200,000 miles with ease. Not all these top end rebuilds are necessary in my opinioin. These cars are often driven with kid gloves and hence engines display all the characteristics of worn rings and worn valve guides when some spirited driving might be the first option worth trying, this obviously doesn't apply to cars that smoke like steam engines and with broken studs etal.
 
ORIGINAL: bones

Hi Chris longevity is one of the best qualities of an SC engine a properly used and maintained SC bottom end should see over 200,000 miles with ease. Not all these top end rebuilds are necessary in my opinioin. These cars are often driven with kid gloves and hence engines display all the characteristics of worn rings and worn valve guides when some spirited driving might be the first option worth trying
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Amen, they will go on for ever if looked after properly and given a good caning every once and a while, stretching those rods is a good thing!
 
Chris

One of the reasons for top end work is that head studs can snap when the car is over-revved. This will usually only occur if the clutch gets dropped during enthusiastic (i.e. track) driving and the momentum going through the gearbox is taken up in the engine. In normal driving the rev. limiter should prevent the problem.

The gist of this is to say that top end work isn't necessarily a sign of an intrinsically poor design so much as the engine being worked beyond its limits.

My SC has not had an top end work as far as I can see. It's got 75500 on the clock. I've done three track days this year since buying the car and the engine is without doubt the best performing part of the whole package. Unlike the 915 box...
 
1. 1st won't engage when moving, which I gather is not unusual. However, I've heard conflicting advice as to whether these boxes left the factory with a first gear synchro or not. Any idea?

2. 3rd engages with a crunch if you're pushing on unless you hold the level in neutral for half a second on the way through. Not impossible to live with, but has been frustrating during track use.

3. 4th to 2nd changes are very unpopular! Again not critical, but...

4. Change up into 2nd is very notchy (although seems fine as far as the box itself is concerned). From reading other posts, I wonder if this is a bushes/linkage issue?

Thanks Peter
 
Martin, my 'box has been rebuilt and it goes in and out of all gears on the move so that thing with first not an issue with a box in good nick IMO - does double-declutching make any difference?

I would say that whatever a rebuild costs it's worth it, these 915 boxes are brilliant once sorted, would definitely have another one, though next car more likely to be an early 930.
 
Agree with everything John said especially double de-clutching - though if you track it you probabaly do that - but becauase your problem seems to be with all gears I would suggest rebushing all the gear linkage and readjusting the gate just in case a PO or mechanic didn't get it right. This is work you can do yourself and will improve the shift whether you need to repair the box or not. Check the clutch adjustment too, if the box is getting worn all these things add up to make matters worse.
Try Swepco 201 gear oil or Castrol Magnatec gear oil. These measures may at least delay an expensive rebuild. 1st gear has a synchro. When you change the oil look at the magnetic drain plug for teeth and excessive swarf.
 
Regarding the 'box;I have found it best to make sure that the clutch adjustment is absolutely spot on,not just within limits.This is the only thing that the Haynes manual is good for!!!.Synthetic oil does make a difference especially from cold,when compared with mineral oil.
Finally,the 915 box has Porsche designed Baulk Ring synchromesh.It is not meant to go in gear unless the speeds are nearly synchronised-a hang over from the VW Beetle days for people who had never owned a car before.G50 and later boxes have Borg-Warner synchromesh on which you can ram the lever into gear at any speed and blow the engine!
I find that after driving an ordinary car it takes several miles of driving to raise your driving standards to operate the 911 precision machinery[:D][:D]
 
Finally,the 915 box has Porsche designed Baulk Ring synchromesh
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Quite correct - a system that even Ferrari used, which they licensed from Porsche.
This was designed for racing in mind (as all Porkers used to be), when engine revs/road speed would more normally be matched (the old hard on the throttle/brake idea).

Not quite so good for normal road use - hence the G50.

I must admit, I never go from 4th to 2nd - never got used to the idea, mainly because my 915 box in the SC didn't let me. Down through the box, me. Easier.
 
Thanks all. Looks like we've hijacked Chris's post though!

I had the clutch replaced recently. This didn't in itself do anything for the gearbox issues, although it did make the clutch operation much easier and more progresive.

My double declutching technique needs some work - I will persevere.
 
ORIGINAL: Martin Perry

Thanks all. Looks like we've hijacked Chris's post though!
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Not a problem! Gearbox foibles are as useful to know as engine ones. My dog leg type 69 912 box after 205,000 miles is still going strong, can engage 1st on the move and moves up through all gears well. The only difficult area is changing down from 3rd to 2nd. You have to give it plenty of time and be spot on with the position of the gearstick or it will crunch.
 
Bones's remarks about the llife of the SC engine are spot on, it has a great reputation, probally one of the more reliable engines in a SC.
I had my own SC's top end rebuilt for a couple of reasons (@ 100k), firstly the oil return tubes where leaking badly, secondly I found a broken inner valve spring and thirdly the gear box was coming out (and therefore the engine as well) for first and third worn dog teeth gears (a common problem on the 915 gearbox) so instead of fitting collaspable tubes I decided to have the heads removed and overhauled, replacing the spring and any worn valves/guides. If anybody claims the engine has had a top end rebuild ask for the detailed invioce which should show what was replaced and that it was a true overhaul not just a gasket replacement.

My own experiance is that all the tuning books, magazines etc give the SC bottom end a bullet proof reputation due to it being based on the turbo 930 engine which obviously develops more power. How long before it will need rebuilding depends on frequency of oil changes in the past, how its been treated on start up and has it been driven as a Porsche should be, often and for a reasonable distance i.e throughly warmed up.

Rats

Bones, I assume you are talking metaphorically about the steam
 
Hi Martin,

I'm certainly no expert and John mentioned to me that a flawless box will take a shift into 1st on the move no probs, but my SC has a good box except for change into 1st on the move. I too have heard/read of this a lot so it must be common regardless.

This double-declutching lark doesn't seem to make a difference but maybe i'm doing it wrong. I was under impression it was: clutch in, into neutral, clutch out, clutch in, change to first (ie from second, slowing right down) CRUNCH!
 
My SC used to be like that - and stayed that way for the 6 years that I owned it.

I suppose that I got used to it - the rest of the car was great.
 
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