[928uk] High Mileage Nervousness - Cam Chains

[Simon Crowe via 928uk]

When new it was the biggest 4 cylinder engine on a road car, which would have presented the engineers with some interesting balance and harmonics issues, but they certainly did a good job. 

I do wonder how much of the 928 chain concern comes from association with the 4 pot. I'm working on the principle that if it was worn the I would hear it first.

> On 18 Oct 2015, at 09:25, marton hasenberg <marton at sunrise.ch> wrote:
> 
> I read a theory somewhere that the 4 pot motor cylinders are at a different angle than the 928 ones so the oiling pattern is different hence leading to this cam chain problem?
> I believe the 4 pots were derived from the 8 and the design change required some compromises like, for example, the balance shaft.
> 
> Mit freundlichen Grüssen/ with best wishes
> 
> Marton Hasenberg
> Rheinstrasse 2
> 8193 Eglisau
> Switzerland
> 
> 076 514 84 08
>> On 18/10/2015 00:59, Simon Crowe wrote:
>> Hi Guys,
>> 
>> The cam chains are an issue on the 944 S2 and 968, who's 4 cylinder engines borrow the head and cam gear from the 928 32v V8's. No idea why the four pots suffer this and the 928's generally do not. The chains don't break but stretch, and then cause the cam shaft sprocket to wear unevenly. Because the sprocket is part of the camshafts, the final fix is to replace the two camshafts.
>> 
>> Lots of advice on the net to routinely overhaul the tensioner             pads on these 4 pot engines, but I've not seen the same advice for the 928 on a wholesale basis. Personally I've never replaced on either of my cars. I like Rogers comment that suggest that the original chains are better that replacements anyway.
>> 
>> You will see that the uk sourced tensioner pads have 944 part numbers. 
>> 
>> On a tangent, I read somewhere that a guy in the US managed to install the 968 Variocam system onto his 928 engine.  
>> 
>> Simon.
>> 
>> 
>> 
>> 
>> 
>> 
>> On 17 Oct 2015, at 22:36, Paul via 928uk <928uk at lists.928.org.uk> wrote:
>> 
>>> Nice one Marton
>>> 
>>> Fortunately that only shows that I was aware of the issue some time ago, but didn't think my car would last so long that I'd have to be concerned about it...
>>> 
>>> Paul
>>> 
>>> 
>>>> On 17 October 2015 at 22:32, marton hasenberg via 928uk <928uk at lists.928.org.uk> wrote:
>>>> Hi Paul
>>>> 
>>>> Did a search and found this from 2009 - from someone named Paul - not sure it helps  :)
>>>> 
>>>> `
>>>> Oh dear God!
>>>> 
>>>> For what it's worth I use Penrite HPR15, and this is my reasoning:
>>>>  
>>>> There was an informed debate on the Landshark list sometime last year about Oil. This basically seems to have concluded: 
>>>> Flat face hydraulic tappets (used in the 928 but not more modern cars) require levels of Zinc (ZDDP) that were present in oil until the mid 90s for protection 
>>>> Modern Cats are poisoned by ZDDP, thus newer                       oils have lower ZDDP, older Cats such as those on the 928 are more robust
>>>> Newer oils also have generally lower viscosity to enable them to meet fuel efficiency requirements
>>>> 928 bearing failures are associated with low viscosity oils and hot environments
>>>> Following this I have decided to stop using generic 10W-40 semi-synth, and switch to Penrite HPR15 (15W-60) which is approx £30 per 5ltrs.
>>>>  
>>>> I hope others who were ignorant of the ZDDP issue will reseach this for themselves and reach their own conclusions.
>>>>  
>>>>  
>>>> The chain sprockets on the cam shafts can lose teeth, this happens when the cam chains stretch. The standard advice is to replace cam chains if there has ever been piston valve contact, but I'm not sure whether there is a fixed replacement interval. I expect people tend to replace the chains when replacing the nylon tensioner pads.
>>>>  
>>>> Paul
>>>> 87 S4 Manual
>>>> 
>>>> 
>>>> Mit freundlichen Grüssen/ with best wishes
>>>> 
>>>> Marton Hasenberg
>>>> 
>>>> 
>>>> 
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