I "vintage race" a 1957 MG, this is road racing, and we actually race pretty hard. The biggest problem with this engine is the oil pump drive gear -- they often fail, typically right after an engine rebuild.
This gear is a little crossed-helical gear, driven off a mating gear on the camshaft. They work fine in street cars, but often fail when run under racing conditions, i.e. 7000 RPM redline, with 70 psi oil pressure. The pump requires more power at this speed & pressure, putting more stress on the gears, and they sometimes fail. Normally, they either fail "right away" (within a few hours of start-up) or they last "forever" (until the next routine rebuild).
So the basic question is, what is the best oil to use to help prevent early failure of these gears?
No, I can't easily re-design the whole gear system. No, new ones aren't available -- so we have to re-use old ones. Yes, we have tried custom-made bronze gears (running against steel camshaft gear), they last about 3 race weekends. So I'd like to stick to the basic question here, WHAT OIL, rather than how to re-design the engine, thank you.
Some more background: if you're not familiar with crossed-helical gears -- they have a VERY small area of contact, so the contact stress is relatively high, and there is lots of sliding motion, so it is similar to the flat tappet/cam interface. The gear mesh is lubricated by engine oil, there is a small passageway drilled in the block, so some pressurized oil "kinda/sorta" squirts in the general direction of the mesh.
I have used Castrol GTX 20w-50 in my MG race engines for years, without problems. However, I just rebuilt a race engine and the oil pump drive gear failed after about 3 hours of run time -- first time it has happened to me. I followed the usual recommended break-in procedure for flat-tappet cams, i.e. I used Isky cam lube on lifters & lobes and also on the skew gears, ran 1 hour at 2000 - 2500 RPM in the driveway, etc etc. Always worked before. Haven't looked at the cam & tappets yet but I think they're OK. Thankfully I saw the low oil pressure and shut down before anything broke (I think).
Since this was the first time I've had a skew gear failure I am wondering what may have been different this time around (versus 4 or 5 previous engine rebuilds with no problems). Last time I rebuilt, was 1999 and everything went fine on that one. So:
1) Do you think zinc is the answer -- i.e. would an oil with zinc in the additive package, help to save my drive gears?
2) Anybody know when the API spec changed and they took the zinc out of most passenger-car oils? Was it after 1999? Maybe my Castrol 20w-50 isn't the same as it was in 1999?
3) Lots of guys recommend Rotella. I can't find a Rotella RACING oil, I can only find Rotella T multi-grades and Rotella T Synthetic, primarily intended for commercial/diesel use. Do they make a racing version of Rotella? If not, is the "regular" multi-grade still a good oil for racing? The answer man on the Shell site is evasive about racing questions.
4) Should I use an oil with zinc for break-in only? Or continue to use a zinc-rich oil long term for racing?
5) Is zinc the same as ZDDP? Or are they different?
6) Have read about GM EOS, I guess it has lots of zinc, why not just use a good quality passenger-car oil and add EOS to get the zinc content?
7) How do I find out the zinc percentage in various brands of oil? Shell won't tell me the zinc percentage in Rotella. Do I have to send all the candidates out for VOA to find out?
8) Valvoline Racing oil is readily available but I get the sense (from this Forum and others) that there are "better" oils out there. Is Valvo Racing out of date?
9) I'm not cheap but I don't like spending money on things I don't need ... so do I really need a synthetic? Typical oil temp peak is around 220-230 deg F. These old engines leak a LOT, and I change frequently, so I use a fair amount of oil in a year of racing. And of course the engine wasn't designed with synthetic in mind back in 1957. So I'm tempted to stick with dinosaur oil -- agree?
Any learned advice from you experts will be MUCH appreciated!
This gear is a little crossed-helical gear, driven off a mating gear on the camshaft. They work fine in street cars, but often fail when run under racing conditions, i.e. 7000 RPM redline, with 70 psi oil pressure. The pump requires more power at this speed & pressure, putting more stress on the gears, and they sometimes fail. Normally, they either fail "right away" (within a few hours of start-up) or they last "forever" (until the next routine rebuild).
So the basic question is, what is the best oil to use to help prevent early failure of these gears?
No, I can't easily re-design the whole gear system. No, new ones aren't available -- so we have to re-use old ones. Yes, we have tried custom-made bronze gears (running against steel camshaft gear), they last about 3 race weekends. So I'd like to stick to the basic question here, WHAT OIL, rather than how to re-design the engine, thank you.
Some more background: if you're not familiar with crossed-helical gears -- they have a VERY small area of contact, so the contact stress is relatively high, and there is lots of sliding motion, so it is similar to the flat tappet/cam interface. The gear mesh is lubricated by engine oil, there is a small passageway drilled in the block, so some pressurized oil "kinda/sorta" squirts in the general direction of the mesh.
I have used Castrol GTX 20w-50 in my MG race engines for years, without problems. However, I just rebuilt a race engine and the oil pump drive gear failed after about 3 hours of run time -- first time it has happened to me. I followed the usual recommended break-in procedure for flat-tappet cams, i.e. I used Isky cam lube on lifters & lobes and also on the skew gears, ran 1 hour at 2000 - 2500 RPM in the driveway, etc etc. Always worked before. Haven't looked at the cam & tappets yet but I think they're OK. Thankfully I saw the low oil pressure and shut down before anything broke (I think).
Since this was the first time I've had a skew gear failure I am wondering what may have been different this time around (versus 4 or 5 previous engine rebuilds with no problems). Last time I rebuilt, was 1999 and everything went fine on that one. So:
1) Do you think zinc is the answer -- i.e. would an oil with zinc in the additive package, help to save my drive gears?
2) Anybody know when the API spec changed and they took the zinc out of most passenger-car oils? Was it after 1999? Maybe my Castrol 20w-50 isn't the same as it was in 1999?
3) Lots of guys recommend Rotella. I can't find a Rotella RACING oil, I can only find Rotella T multi-grades and Rotella T Synthetic, primarily intended for commercial/diesel use. Do they make a racing version of Rotella? If not, is the "regular" multi-grade still a good oil for racing? The answer man on the Shell site is evasive about racing questions.
4) Should I use an oil with zinc for break-in only? Or continue to use a zinc-rich oil long term for racing?
5) Is zinc the same as ZDDP? Or are they different?
6) Have read about GM EOS, I guess it has lots of zinc, why not just use a good quality passenger-car oil and add EOS to get the zinc content?
7) How do I find out the zinc percentage in various brands of oil? Shell won't tell me the zinc percentage in Rotella. Do I have to send all the candidates out for VOA to find out?
8) Valvoline Racing oil is readily available but I get the sense (from this Forum and others) that there are "better" oils out there. Is Valvo Racing out of date?
9) I'm not cheap but I don't like spending money on things I don't need ... so do I really need a synthetic? Typical oil temp peak is around 220-230 deg F. These old engines leak a LOT, and I change frequently, so I use a fair amount of oil in a year of racing. And of course the engine wasn't designed with synthetic in mind back in 1957. So I'm tempted to stick with dinosaur oil -- agree?
Any learned advice from you experts will be MUCH appreciated!