Weston

Oil, oil, oil. Rod bearing failure is usually the result of metal-to-metal contact, and oil is what keeps that from happening. First and foremost, you want oil that has a good amount of ZDDP (aka Zinc) in it. I've seen 944-Spec engines survive amazing amounts of abuse when running a high-ZDDP oil, while other 944 racers on regular oils are spinning bearings and throwing rods from far less. Valvoline VR1 and Shell Rotella T synthetic are both readily available, reasonably priced, and good for plenty of ZDDP.

I ran Valvoline VR1 20w50 on the track for a few years and it always did a great job of holding oil pressure when hot. I had tried Castrol 20w50 early on and saw about 1 bar less oil pressure, so I stuck with Valvoline VR1 and my engine has held up great. A lot of guys have blown motors, but I'm one of the first 4 guys who started racing 944-Spec in this region a few years ago, and I still haven't had a bearing problem. I swapped in new rod bearings as a precaution in late 2007, but the original bearings from 1984 were still in great shape.

At my last race weekend, I tried Rotella T synthetic 5w40. I was worried about the thinner weight, but it is a good formulated oil and other racers are running it with good results and reliability. It was a very hot weekend (100F with Colorado's thin dry air, my coolant was overheating the whole race, but at least the oil has a 951 cooler), and I did see about 1 bar less oil pressure when hot, as well as my oil light flickering when I came off the track and let the RPM's drop, but I didn't blow anything up. I still need to drain the oil and decide if I want to keep running this, or go back to VR1, but early indications appear to be good. I've badly fried oil on the track in other cars before, but I'm not seeing those symptoms here yet. I also want to swap in another set of rod bearings as a precaution before NASA Nationals, so I'll get a good look at actual wear when I do that...

joonas

Weston, at what rpm you shft to higher gear and what is the oli pressure at that moment?
Do you have oil temperature gauge? How often you change oil?
Do you have some kind of baffle or other modifications done to the car?
Oil that I am using should be as good as it gets
http://www.rallysport.ca/lubricants/...258%20(GB).pdf
Rod bearing spins when it touches the crank, so how can zddp prevent that?

AlpharettaRK

I replace rod bearings every 100 hours on the hour gauge (that's probably 50 hours of track time) change the oil (Mobil1 15W50) every 20 hours and have never (knock on wood) had rod bearing problems. I think if you have multiple failures you either have a tolerance issue (I think the factory tolerances are fine - too tight is as bad as too loose) with the bearings or an oiling problem.
You didn't ask me, but I shift right at the rev limiter every time. When my engine is hot I see 3.5-4 bar at high rpm on the factory gauge and occaisionaly see oil temps of 120 but usually 90-110 (I've added an oil temp guage in the sump), even in the Georgia (USA) heat. I have added an external oil cooler, and kept the original oil-water cooler.
Good Luck
Cheers
Randy

JET951

Hi Joonas, can you recall the kms and viscosity of the oil on the first (original failure)?.
Now to oil viscosity , if you open the owners manual( printed by Porsche) that came with the car when it was new and go to the page that shows the oil viscosity's to use depending on ambient temps you will see that the first cab off the rank in the" look at me shaded centre section" for the ambient temp ranges of minus 10 deg Celsius to unlimited high ambient temp is either a 15w-50 or a 20w-50 oil viscosity .
Now an oil viscosity of say a 5w-40 should only be used for a fuel economy runs ,meaning no big revs and driving in a manner to achieve max fuel economy ,if we just stay here for a moment in my opinion I would only use a 5w-40 oil viscosity in a Porsche from last century if the max ambient temp never rose above +10 deg celsius meaning the average ambient temp will be around zero deg cel or less for normal road conditions .
Now if we start talking about motor sport (club) events then one must up the viscosity a bit , because the oil temp will always be hotter and that means the oil pressure will drop, now why is this important particularly in a 944 or a 928 , because on a 944 the no 2 big end bearing is the first to starve of oil pressure at or near max revs , and its no 2 and 6 on a 928 , now how do we reduce this tendency without big mods , simple we just look at the owners manual and the answer is a 20w-50 or a bit higher .
(remember these engines were designed back in the early 1970's for oils that are readily available , lower viscosity so called synthetic oils were a product of another two decades later and Porsche's in this century are designed for these lower vis oils) .
We only use on our own 951 and customers 951's , 944S2's , 944's, 968's on the track Valvoline racing 25w-60 and nothing else with no failures and many Porsche club class and championship wins .But to achieve this we will not let a customers 944 out on to the track for the first time without a new set of standard big end bearing shells (we do it in the car / sump off etc), we have caught a few 944S2's that we removed the sump for the first time (19 year old car ) and finding no 2 big end bearing shells only worn but shells for 1,3,4 all ok , and in every case the service history has shown that from around the turn of this century these same cars had been on a diet of a much thinner so called synthetic engine oil .
Note :
A) if you see the oil pressure warning light on at idle , it is trying to tell the driver something , low pressure at idle will always give you lower pressure at high revs as well , it has no choice .

B) the 944 and the 928 series should of had an oil pressure gauge(in car) like the 924 , because the 924 goes from 1 bar to 10 bar , where as the 944 and 928 is an insufficient 1 bar to 5 bar , why is it insufficient ? because max oil pressure is around 8 bar(the the relief valve opens) and when oil temp is 115 deg cel or more all engine oils thin out and the pressure for the same revs drops and with a 5 bar gauge it gives the impression that you are near max oil pressure when in fact with a 5w-40 oil hot on the track you will be lucky to get 4 bar at the oil pressure sender let alone the poor old no 2 big end journal .
Now to crankshafts for the 944 , I never get them machined , we always buy good second hand ones , for two reasons
A) second hand ones are still plentiful and cheap
B) I have had some bad experiences with machined Porsche crankshafts years ago
Why have we changed some ? because every now and then we see one with just a slight wear pattern on just one journal (usually 2) and I will not take the chance , and its paid off ,
OH by the way , we do not run scrapers or special baffles or even different oil coolers , but this may change in the future but for now no need .
Regards
BB

jwade944

I have had two failures while racing. Both times, the block was too damaged to repair. The first engine had 96k miles and over 5 years of track service. After it failed, I replaced the engine (with new rod bearings) and added an Accusump. The second engine failed in the 10th race weekend. I replaced the engine, removed the Accusump and added a Lindsay Racing baffle. I replace the rod bearings every two years (12 race weekends), but have not found any problems since I added the baffle.

joonas

Sean, thank you for reply!
I have written about my two #2 failures here https://rennlist.com/forums/924-931-...2-failure.html
Clarks link has the description of both failures.
First failure was with engine with no history 10W60 Valvoline VR1 Racing.
Second failure, rebuilt engine had a failure after 8000 km 5W50 Valvoline VR1Racing. When car lost power during acceleration I looked oil pressure that was 3 bar and coolant was up to 100C.
I drive my car to open track events where I drive 5 to 10 laps in the row. Usually 5.

I did not know 10 PSI per 1000 rpm rule then so I thought if I had oil pressure like 3 bar I would be ok.
Right now my experience with my 88 944S is that without external cooler oil temps rise fast and go up to 120C pretty quickly. Oil temp is not tied together with coolant temperature. Oil temp goes higher with rpms.

I have 1 to 10 bar aftermarket oil pressure gauge. Oil is Motul 20W60.
It shows 4,5 to 4,8 after startup and cold idle. If I rev engine to 2000 rpm oil pressure goes to 5,5 bar or something.

Do you know for sure that 944 OPRV should open at 8 bar? I searched for that info https://rennlist.com/forums/924-931-...-pressure.html

When at track I get more than 4 bar at idle until oil comes up to 80C. At first I get 4,5 bar at high rpm, then if oil goes over 110C I get 4 bar max and at 120C I get 3,8 max.

Right now I shift at 6000 rpm or lower if pressure goes down.

I cannot get 5 bar oil pressure at high rpm when oil is 80C or higher is that normal or OPRV is opening too soon? It also takes some time cranking when the oil pressure goes up, around 10 seconds.( I have DME relay connected to switch so I can get the pressure up before engine starts).

I did not install OPRV myself so I cannot tell how it was installed.

joonas

Randy, thank you for your comments!

If we look 10 PSI (0,7 bar) for 1000 rpm rule we find out that if you have 3,5 bar oil pressure you could rev the engine to 5000 rpm max.
I have read that 10 PSI for 1000 rpm rule is general rule and might not apply if engine tolerances are changed and it is built as racing engine.

As far as my engine failures one thing that might be the biggest problem could be oil temp. If coolant goes up to 100C then I dont know how hot the oil might be. I did not have the oil temp gauge before.

joonas

Can you tell us what kind of oil are you using? What is your oil pressure and temp at high rpm at the track? At what rpm you shift?

JET951

Hi Joonas , I made a typo, the 928 oil pressure relief valve opens around 8 bar , the 944 series 1987 onwards opens around 7 bar .
Regards .BB.

joonas

Was it somewhere in the manual or how you know when it opens?
What kind of pressure you see at cold idle with 25W60 oil?

Eric_Oz_S2

I don't have an oil temp gauge, but on my S2, oil pressure is always 4-5 bar with higher revs on the track. The S2 has an external oil cooler though.

JET951

Hi Joonas, we have taken loads of notes on oil pressures at work over the years on 944's , 951's and other Porsche's in preparation for club track work using workshop oil pressure gauges , don't get too confused too much as to the idle oil pressures hot or cold , except of course the oil pressure warning on at idle hot( to low pressure warning),remember the name of the game is to do one thing that overrides all else and that one thing is to get just enough pressure at the big end journals (particularly no 2) at high revs when the oil temp is well into 110- 120deg cel range , and as a basic starting point for us was the owners manual and the simple 20w-50 main reference .
We very quickly settled on the Valvoline racing 25w-60 .

Note 1 ; an oil that has the viscosity on the label of say a 5w-50 will not give you the same oil pressure as say a 25w-50 at say 120 deg cel even though both numbers end with a 50, its almost as if the 5w-50 ( usually more vii's in it ) is acting like a 7w-45 if you know what I mean.

Note 2 ; we often find that your average 19 year old oil pressure gauge (the one in the instrument cluster) is not giving the exact same indicated pressure as the more accurate workshop oil pressure test gauge , so in other words the gauge in the dash may not always reflect whats happening exactly , however we find the the backup oil warning light is usually pretty good .

Note 3 ; oil pressure hot , in this I mean real hot 120 + oil temp , even with a 25w-60 oil we will naturally see less oil pressure all through the rev range (idle to max revs) as opposed to the same oil with an oil temp of say 85 or 90 deg cel .

Note 4; I know this sounds a bit basic , but we usually change the oil after every event (one full day at the track)

Note 5 ; the oil pressure relief valve opening pressure (around 7 bar) is normally only reached when the engine is cold and the engine rpm is above 2,500 , and when hot will drop away proportional to the hotter the oil gets and naturally the thinner the oil viscosity to start with the more pressure is lost as it heats up . So with the oil that we use , the average high rpm pressure range(110-120 deg cel) is never below 5 bar and usually not much more than 5.5 to 6 .But remember oil temp plays havoc in this regard .

Note 7 We usually change the big end bearing shells every couple of seasons , sometimes more often , just depends on the number of events per season.

Regards
BB.

joonas

I use 20W60 oil and cannot get 5 bar oil pressure eaven with 100 C oil. I think I need to shim the OPRV to see if that makes a difference.