[333pg333]

What do you guys do re our cars propensity for spinning rod bearings? I gather that dry sumping is still the exception rather than the norm so what are we all doing to avoid engine rebuilds? I know that there are sump baffles, crank scrapers, crank mods, accusumps etc. Who is using what method and how many of us have had to rebuild the engine due to oil starvation? Also I believe that the 968 has oil piston squirters? Am I right? Why can't we have some sort of oil squirter at the crank or bearings so that on those long sweeping left turns when the oil is in the next suburb, we at least have some source of constant oil being sent to the affected areas?

Maybe it's a dumb question, but I feel dumb having to risk my engine every time I go out on the track. So dumb that I've bought a dry sump system but that won't get installed for a little while until we figure out where everything can be fitted on a road/track car while retaining p/s, a/c, and stock alternator. Need to come up with a bit of genius as to what sized and shaped oil tank and location too? Any ideas on this would be appreciated as well.

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[flash]

move the battery to the back of the car - that's what i did - it's in the right rear behind the wheel well - then you will have a really large area for a tank where the battery was

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[Jason Judd]

Patrick,



First, I would say that a dry sump would be the way to go.



I installed a larger capacity oil cooler...it runs the length of my radiator and stands about 3~4 inches tall. It gives me an add'l 1 qt capacity, plus I run cooler.



When we did the con rod bearings, we also put in the baffle kit.



I installed an Autometer oil temp gauge, so when I'm running at VIR this coming weekend I'll let you know what my temps are.



Jason

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[ether_joe]

I'm out of my depth here, but weren't people installing a second oil pickup to deal with the high-g oil starvation?

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[Eric_K]

What do you guys do re our cars propensity for spinning rod bearings?

Don't drive a 944. <img src="/forum/images/smilies/968/tongue.gif" class="smilie" alt="" /> joke. I don't have any direct proof but spinning bearings seems to be less common in the 968. Most of the 944 racers I know have gone thru multiple engines. I don't know if it is the fewer numbers, newer age, or Porsche fixed something. The oil pan baffling is different, oil squiters, etc. However, dry sumping is the ultimate solution.



I personally run a completely stock setup on the race car. I have refreshed the rod bearings as preventitive maintenance. I also run a thinner oil than most, but that is all I do differently. The engine has run flawlessly for 36 hours of endurance races & 3.5 race seasons so I'm not changing anything now.



Eric

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[Jason Judd]

Eric,



Do you do your rod bearings at the end of each season?



Jason

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[Eric_K]

Every other year. The last time the old ones looked perfect, so I'm not going to mess with it too often.

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[333pg333]

Ok lets see here:

Bob. our cars (R.H.D.) have the battery already in the rear due to the steering shaft dissecting that area which would be in front of your passenger. I have seen L.H.D. cars with the oil tank in that position and that would be great if we didn't need to steer the car, but alas. lol. We are actually thinking of on the opposite side but right down in the wheel well behind the left wheel. We are going to have to get a flap w hinge made on the outside of the car to get access to the tank. I'm pretty sure we can't have the tank come up into the engine bay as there is the master cylinder and other things up top.



JJ, yes the d/s will give me much more confidence. Running the extra oil cooler w lines etc should give you a definite cooling effect. Which oil pan baffle did you use? I'll be interested in your temps too. How are those big wheels and tyres going? Interestingly I saw where some Swedish racers were using the same sized tyres front to rear on their 951's and he was talking up to 305's! That's some big old front tyre there huh? We may get more understeer than you guys due to the turbo wanting to push wide, he was doing it for that reason.



EJoe, yes I did hear of the twin pickup method. Could be a good idea.



Eric, I didn't realize that you guys didn't suffer the same as we did? If that's the case I'd be interested why or what Porsche did differently down there on the 968's. I'll ask my mechanic, he'll know. That's an interesting theory using thinner oil? That's completely the converse of our thoughts. We are using a 20w60 this season. Porsche used straight 50w Shell for years but if it works for you hey keep going.

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[Renn68]

my 2c worth...........







On the second-hand replacement engine I replaced the big end and rod bearings and installed a Lindsey Racing oil pick-up collar and baffle and an oil temp channel to the MXL.



The RSBarn crankscraper/ windage tray arrive too late to make this build but will go in at the end of the season.



First fill after the running in oil was Mobil1 for its first track outing - this was replaced with the usual Redline 20/50 - pressure drop with temperature is significantly less with Redline.



On tight circuits like Taupo (NZ) oil temp will go over 130Cel - mid 120's at more open circuits like Pukekohe. A larger oil cooler is planned in the coming months - I'm machining the old oil plate to take AN fittings.



I'm trying to get some oil temp/ press data from the guys running accusumps at the same circuits to see if they get the same pressure variations - I really don't want to do another engine

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[Eric_K]

Very ugly. There is a big difference here though as that failure was caused by a cracked pickup tube, if I remember correctly from rennlist. This is different from the #2 bearing eating itself unassisted - although the results are identical. Cracked pickup tubes seem to be more of a problem than #2 bearing failures on 968s. The cracked pickup tube issue has been reported several times on this board.

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[Nine68]

<img src="/forum/images/smilies/968/rolleyes.gif" class="smilie" alt="" /> I agree - I think the oil pickup tube breaking is the big issue here, I had my oil pickup tube re-inforced, put in a crank scraper and windage tray, also I overfill the oil about 1/2 quart. My car has been on the track for 7 years and so far so good, I changed the rod bearings this year and they looked brand new.

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[Charles Geer]

[quote name='Eric_K' post='33339' date='Mar 27 2007, 08:47 AM']Don't drive a 944. <img src="/forum/images/smilies/968/tongue.gif" class="smilie" alt="" /> joke. I don't have any direct proof but spinning bearings seems to be less common in the 968. Most of the 944 racers I know have gone thru multiple engines. I don't know if it is the fewer numbers, newer age, or Porsche fixed something. The oil pan baffling is different, oil squiters, etc. However, dry sumping is the ultimate solution.



I personally run a completely stock setup on the race car. I have refreshed the rod bearings as preventitive maintenance. I also run a thinner oil than most, but that is all I do differently. The engine has run flawlessly for 36 hours of endurance races & 3.5 race seasons so I'm not changing anything now.



Eric[/quote]



I'm with Eric. Don't think the 968 needs it. We have checked the Rod bearings as an annual service and no wear reported. It may be the 968 baffle and oil squirters direct on the pistons. I think you will just be making your car unnecessarily heavier. Most PCA club race 968's are not running such as system.

Even though you would think the car needs it. It does not appear that there is any evidence that it does.

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[333pg333]

Hmm, that's interesting guys re the differences with the two siblings. From what I know you have the squirters but that is more for cooling the pistons than providing oil to the bearings. I may try and fit some squirters into my block. There's not much room but it can be done. Maybe more heat is generated with a turbocharged engine that increases the propensity of heat dissipating oils weight and decreasing the suspensive properties of the oil?

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[RS Barn]

I just had an interesting observation in a 951 vs 968 rod bearings.

I recommend track guys change rod bearing every other year just as preventive maintainence. Most customeres have a weeping/leaking pan gasket or bad motor mounts and I say let's look at rod bearings while we there. 968s tend to have wear on bottom of #2 and #3 and #1 and #4 look almost like new. This plays out the poor crank oiling theory.

I just did the same on a 951 with 66K and found #2 and #1 Upper bearing to be just worn into the Copper. This was about 3 Watking Glen laps away from "Blockendectomy"

My theory is the 951 wear more on top due to boost pressure on top of the piston transfering to top of rod vs 968's normal oiling wear.

I've also been playing with Crank Scraper/Windage trays and so far have seen much lower oil temps. The theory is oil is cleaned off the crank and from the air and drains to bottom of pan and gets picked up in a more fluid state with less airation and cavitation.

I also believe larger/dual oil coolers are the way to go-Possibly with lighter oil viscosity

Pete

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[333pg333]

[quote name='RS Barn' post='33443' date='Mar 28 2007, 07:26 PM']I just had an interesting observation in a 951 vs 968 rod bearings.

I recommend track guys change rod bearing every other year just as preventive maintainence. Most customeres have a weeping/leaking pan gasket or bad motor mounts and I say let's look at rod bearings while we there. 968s tend to have wear on bottom of #2 and #3 and #1 and #4 look almost like new. This plays out the poor crank oiling theory.

I just did the same on a 951 with 66K and found #2 and #1 Upper bearing to be just worn into the Copper. This was about 3 Watking Glen laps away from "Blockendectomy"

My theory is the 951 wear more on top due to boost pressure on top of the piston transfering to top of rod vs 968's normal oiling wear.

I've also been playing with Crank Scraper/Windage trays and so far have seen much lower oil temps. The theory is oil is cleaned off the crank and from the air and drains to bottom of pan and gets picked up in a more fluid state with less airation and cavitation.

I also believe larger/dual oil coolers are the way to go-Possibly with lighter oil viscosity

Pete[/quote]



Pete,

That's also very interesting and very topical. We have just been through a very quick engine assembly and meltdown of sorts which has some relevance to your points. My mechanic has just had his engine rebored and sleeved and went to the track after logging about 600kms on the motor for run in. He lasted 5 laps, came in and had an oil leak and coolant leak. They fixed these on the spot and then heard a knocking sound from within. That was enough to get towed home. (Great day out!) So in the ensuing days since he's stripped the motor to find all 4 brand new pistons absolutely %$%$%ED and the Darton sleeves are in pretty bad shape too. So he has been deliberating what could have caused this. From too high detonation, lubrication, tolerances too tight, bad pistons, heat from all of these, etc...Today he's decided it's from a couple of things. Firstly the brand of pistons are possibly questionable as they just forge for any car and are not specific to turbo cars, the tolerances that were specified were too small, and thirdly he had fitted a windage tray and this combined with not having piston squirters denied the lower part of the piston / cylinders from getting enough lubrication and cooling oil picked up and splashed by the crank.

Anyway it looks like he may be able to save some of the sleeves and have to buy a brand new set of pistons. Different brand huh? lol Also taking the windage tray off so he'll have one for sale very soon if anyone's interested? We also run a much higher weight oil than some of you guys are using. 25W60. We firmly believe that the purpose of the oil is not only to lubricate, but also to provide a form of buffering or suspension between all the expensive metal parts. The lower the viscosity and the hotter the car gets, especially racing, the thinner the oil becomes and doesn't provide much, if any protection in this manner. You may sacrifice a very small amount of power, but that's very minor compared to a spun bearing or the like. Anyway different strokes etc...

Patrick

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[flash]

i agree on the weight of oil - i'm sticking with the heaviest thing i can put in there - i know that formula 1 cars etc run a 5W oil, but they also run a new engine every race - we found in the datsuns and mgs that in order to spin the 8800 rpm the engines were capable of, we needed to stick with a heavier oil - the thinner oils would seperate, leaving the bearing dry - didn't take long to spin one like that (keep in mind that this was over 15 years ago and oils were different then too)



we also had to do some work on the oil passages, like removing small obstructions and things that would cause turbulence in the flow - any little bumps in there and there was a chance of an air gap



i understand the idea behind the lighter oil, less resistance and better heat transfer, but it presupposes that the oil is always there - i think some work would probably have to be done on the oil passages to insure that this happened before changing to a lighter oil - if you could do that, i suppose you could have the best of both worlds - i haven't looked at the oiling system in this engine to see how tough that would be though - anybody have any thoughts or experience on this?



as for the windage tray, did it block the squirters? typically these things really do work - what was the specific reasoning behind its removal?

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[Eric_K]

This is my take on running thinner oil. It could be completely wrong, but it hasn't failed me yet. There is a design deficiency in the oiling system. It seems to be mitigated in the 968 but I'm sure it is still there. Tracked 944's seem especially prone to spinning the #2 rod bearing and not just the turbos. I don't believe the problem is the oil being overwhelmed and breaking down (although it is a contributor) but it is a quantity problem. Just at the #2 and #3 rod bearings. The bearing is being starved of oil. You can go heavy and try to keep the oil that is there to hold up better or go light and try to get more oil on the bearing. A lighter oil will flow more volume at the same pressure. It is imperative to use a high quality oil and change it often. I use Mobil1 0W-30R. It is a racing blend that supposedly has a different additive package than their standard stuff. YMMV.

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[Renn68]

I thought oil pumps were postitive displacement pumps so volume was a function of rpm. The pump would still flow the same volume of the lower viscosity but at a lower pressure or are you talking about variations through the different oil paths - just thinking out loud.

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[Eric_K]

Yes, the oil pump can not change the volume it is pumping. That is rpm dependent. However, at high RPM either oil should be at max pressure as set by the oil pressure relief valve. So effectively the engine should see more oil since you are at the same pressure. How and where that oil flows could possibly be different too.

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[Renn68]

Not necessarily - oil pressure is a result of volume (flow) through the restriction between the pump and atmosphere and the viscosity of the oil. I wouldn't expect the prv is continually blowing off under normal operation - if it is it will be contributing to heat build and other nasties.



We ususally see a pressure drop for a given rpm as the oil heats up and its viscosity drops - volume remains the same - hence the question; hmmmm

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