928GT Fantastic Lack of Camshaft Wear

[Buchanan Automotive]

At work at the moment we have a 1989 year model 928GT with the usual kms for a 33+ year old road going Porsche ( meaning more than 160,000kms ) and we had the engine apart for the usual engine reseal ,rotting head gaskets ,minor exhaust valve guides / deteriorate valve stem seals / carbon ed up piston ring lands ( the pistons and bore are fantastic ) , timing chains and nylon chain guides and a cosmetic improvement of the engine and engine bay ( make it look better ), new 12v engine harness and fuel injection harness major repairs etc , but that's not the reason for this post , it was the condition of the 33+ year old GT camshafts ( 4 of them ) .    This GT  has NO & I mean NO camshaft lobe wear , not even a tiny spec of pitting  , same goes or the timing chain sprockets ( these are cast with the cams and love to wear on the wrong oil ) the cam chain sprockets were like new , the cam lobes look like new & naturally the corresponding hardened metal faces of the hydraulic lifters look like new as well

The reason why this 928GT has no cam wear along with the other lucky" few " 928S4 / GT / GTS that had always been on correct viscosity / high oil film strength engine oil from new escaped the carnage  ( unlike all the other 928S4 / GT / GTS ) Porsche's had to run the gauntlet in the very late 1990's and into the early to mid 2000's of people changing the engine oil ( regular servicing ) and installing incorrect low viscosity and naturally low Oil Film Strength engine oil/s , like a 10w-40 or worst still a 5w-40 so called synthetic engine oil , even some of the 15w-50 engine oils ( in the earl;y 2000,s) were terrible in oil film strength as these had very low ZDDP ( AW ) but high in other experimental AW additives which didn't work in a spectacular fashion ( glad I was not using that brand of 15w-50 when that was happening ) , so I do not even trust a 15w-50 because of that episode , but its a mute point as 15w-50 engine oils are being phased out by a lot of oil companies   

Note ) The 928GT ( and 1988 Club sport / same cams ) according to Porsche folklore is meant to a little bit more prone to camshaft lobe/s wear ( yes the pointy bit of the lobes ) because it is by comparison to the same era 928S4 , the GT / CS cams have a different cam timing but more importantly the GT / CS cams ( 4 of them ) have an extra 1 mm extra lift which means the wiping loads are increased a little bit ( or a big bit ? ) & this is were oil film strength even more vital & most ( if not all ) late last century & this century low viscosity so called synthetic engine oils are terrible at this particular job in relation to " High Loaded Flat Tappet Design " last century engines engines & the 944 ( single cam per bank or twin cam ) or the 928 ( single cam per bank or twin cam ) are very high loaded flat tappet design engines , basically what that means is , you have strong twin valve springs per valve holding the valve closed , the very classic last century euro designed aggressively pointy cam lobe /s is the very thing that is going to use brute rotational force acting on the hydraulic lifter face ( rotating at high speed ) , its metal to metal brute combat with the tiny amount of oil ( splash only ) trying its best to keep the two metal surfaces apart and to make them last ( preferably ) more than 10 minutes let alone decades 

When you get the time , calculate a 4 stroke engine at say 6,000 RPM ( could be a 928 ) , the cam shaft/s is rotating at 3,000 RPM ( Revs Per Minute ) divide that into seconds and see how many times the individual intake and exhaust valves are operated per second , its mind boggling & that's just 6,000 RPM ( the poor cam lobes )

Note 2 ) There is NO oil pressure supplied to lubricate the cam lobes to lifter face contact area = its just splash feed ( oozing out of the cam bearing journals sideways ) & that means the actual bearing surface between these two hard metal surfaces is only the Oil Film Strength & we have seen way too many 928S4 cams or other GT cams or other GTS cams that are pitted to a small degree or to a large degree ( meaning stuffed ) from a low viscosity ( so called synthetic engine oil ) that unfortunately the oil film barrier was broken through and the result is metal to metal grinding   & even though the 928GT / Club Sport were not made in large numbers , Porsche some years ago sold out of one of the cams needed ( meaning if you need 4 new GT cams , you can only buy from Porsche 3 of them these days ) , why did they run out ? , because there were wearing out ( unnecessarily as it turns out ) and they just kept selling new GT cams until you can no longer buy a new set of 4 

Note 3 )  Interestingly but not surprisingly its one of the two Exhaust GT / CS cams that are NLA ( No Longer Available ) from Porsche & why would that be ? 

Answer } Its because exhaust cams get hotter than inlet cams in twin cam heads & as the exhaust cam gets hotter ( this is quite normal ) , the lower viscosity oil on the said cam lobes ( splash only ) just gets thinner and thinner with the added disadvantage of lower ZDDP of the so called synthetic engine oils have ( low oil film strength ) you will see more cam lobe wear on exhaust cams , meaning you might see a little cam lobe wear on inlet cams , but on the same engine the exhaust cam lobe wear is always more , so over the decades people would buy from Porsche the bare minimum and the bare minimum might be two exhaust cams or even just one exhaust cam , but ONLY enough to get it running to sell the said car ( that's what humans do ) 

So here we have living proof ( for want of a better expression ) in this case of a 928GT ( 33 + years old ) with its original GT cams ( 4 of them ) ,and naturally this 928 engine has been  "started cold " thousands and thousands of times in the last 33 + years & the cams are like new ( literally ) and always on a high quality 20w-50 ,  

Note 4 } We have only ever seen cam lobe wear / ( twin cam ) timing chain sprocket wear etc on the Porsche 944 ( all versions ) and the 928 ( all versions , be it single cam or twin cam ) and on the air cooled 911 series ( all versions ) with cam wear / rocker and rocker shafts wear & timing chain sprockets wear when the said engines have been on a this century low viscosity so called synthetic engine oil & the clue is the above engines are all from deep last century and were designed to be on a good quality last century engine oil viscosity with good levels of ZDDP & only the 20w-50 ( as mention in the Porsche owners manual ) for these last century Porsche cars stand out  

The above is in relation to the climate in Australia ( from minus 10 deg cel to unlimited high ambient temperatures )  & Last Century Porsche cars ONLY , but I know it applies to just about every other last century makes as well  

Note 5 )  With mild cam lobe wear etc we have seen( over the decades) where switching back to a good quality ( high oil film strength ) 20w-50  engine oil from a low viscosity / lower oil film strength / so called synthetic engine oil will in most cases stabilize the wear , but it "Can Not " reverse the wear and put the metal back on , the metal is gone for good & by the way ,when using the wrong oil , where do you think the metal particles from the cams and lifter faces & the cam chain sprockets goes as its washed down into the engine sump with the returning oil ?  & do not say ( oh ) it goes into the oil filter , yes some will as some is sucked up by the oil pick up screen/tube via the oil pump and these hardened metal particles are now damaging the oil pump on the way to the oil filter , but the other particles that have not been picked up yet by the oil pick up  are thrown up and under the alloy pistons & alloy bores and makes a really good grinding paste for those pistons and cylinders  

Regards

Bruce Buchanan

Buchanan Automotive

[tomo]

Great read, But are you saying that synth oils are no good for today, Or only referring to when they were used on the the early engines when they should not have been? 

[Buchanan Automotive]

The below is what I mentioned in the post  3/4 of the way down }

The above is in relation to the climate in Australia ( from minus 10 deg cel to unlimited high ambient temperatures )  & Last Century Porsche cars ONLY , but I know it applies to just about every other last century makes as well  

Regards

Bruce B

[3legs]

Thanks Bruce. That is one of the best explanations of why you should be using the correct oil I have seen in a while.

I think I will check my receipts from my last oil change to see what they have used.

[Carrot01]

this is good advice that I will take on board.

My motor has only done 5kms (sleeved rebuild) but its probably still on stock cams etc (131,000 documented kms).

Been told to change the oil after 500kms so will go straight to 20w/50

Thanks Bruce.