diabolical1

Hi All ~



I just wanted to ask anyone experienced with cutting teardrops on the oil passages of the eccentric shaft. I particularly want to know how to determine the size and what bits to use because the e-shaft is really hard to cut and shape. Also, do I polish the teardrop or do I leave it with some texture?



Thanks,

1

Kim

Why do you want to do this?

diabolical1

if i understand the concept correctly, it's supposed to aid oil flow between the shaft and bearings.

Old Splatterhand

you mean, since the journal spins in the rotor(bearing) you want to shape the oil passage somehow to improve the flow, right?

is this common somewhere? in the V8-scene or something? i'm just curious

diabolical1

yes, exactly.

well, i had never heard of it on rotaries until relatively recently. however, i did hear about it on piston engines before. i never gave it much thought until i saw it here: http://www.rx7club.com/showthread.php?t=489429



i've since spoken to this gentleman, and he made a compelling case. it took me weeks of on and off thinking about it to understand what i think i now do. add that to the fact that i have a couple of long-term engine projects that i want to get started now that i have the time, albeit sans funding, so i figured i'd throw it out there on this forum and try to gather more insights.

Lynn E. Hanover

I do it. I copied it off of VW cranks, that came that way from the factory. I cannot say if it helps, hinders, or has no affect at all. It seems like it would help. It is fun to do, and looks cool. Extensive cleaning is required when done.



When in a hurry, I have dropped in a new crank with no mods at all and had the same performance. So that works fine too. Just keep the oil pressure above 100 PSI.



There were some folks who kept killing rotor bearings running stock oil pressure, The built a cooaxial sleeve to fit over the front pulley and measuered oil pressure in the crank, with 75 PSI showing on the gage.



They got 7 PSI. When you scream the engine the column of oil leading into the crank is exposed to a centrifugal load that cancels most of the oil pressure. So, even though you should (in theory) get that all back when the oil leaves the centerline and starts down the run to the rotor bearing, it just falls a bit short.



And therefore, the romance with high oil pressures in a rotary.



On racing cranks in piston engines there is a common practice of addng a slight depression around the oil outlet to the rod journal. This is to allow high pressure oil to be exposed to a larger area on the bearing.

So, at least this part of it works, as nearly all people use it.



Then you look at a Cosworth 4 cylinder crank ( cut from a forged slug ) and it looks like a stock Pinto crank at the oil holes. The rest of the crank looks like a work of art, and not at all like a pinto crank.



So do it, or don't do it. But if you are on the engine a lot, run 100 PSI and there will be few problems.



Lynn E. Hanover

diabolical1

that's just downright frightening!



thanks for the response, Lynn.



yes, i'm planning to run 100 PSI. i'll be using the FC rear regulator. what i was NOT planning to do was shim the front, but i guess now i will.



so ... could you give me some tips on what bits to use to make them? what surface to leave? (i'm thinking polished should be better.) also, how do you decide on what size to make them?

Lynn E. Hanover

Well,



The VW shapes were very generous, and way wider than the grooves in the bearings. I just try to stay closer to about three times the width of the groove in the bearing. Leading on the main bearing holes and trailing on the rotor bearing holes. Small flame shaped stones work the best. The stone gives a "good enough" finish.



If it is an all out engine, oil the front main bearing with an additional exterior (at least a dash 10) hose.



If it is going to spend a lot of time above 9,000 RPM, an external oil pump (even with a wet sump) is fine.

For constant use above 9,500 RPM then the external dry sump system is a must. Keep oil pressure above 100 PSI for NA engines and many recomend 110 to 115 for turbo engines.



In this picture I have placed a steel tube through the front oiling port to show it's location. The stock plug is drilled out. A hole for a dash 10 boss fitting is tapped. A boss fitting uses a copper "O" ring to seal.

A tapered pipe thread will work, but if over tightened, will crack open the port and ruin the iron.



Lynn E. Hanover

diabolical1

wheew ... i'm so glad to hear you say that because after i made my last post last night i went out to the garage and spent a few hours toying with a shaft. yes, the stone worked the best when a carbide bit barely touched it. once i learned the rhythm of how to get the desired shapes, i ended up with some pretty large teardrops, not quite 3 times the width of the groove, but large enough for me to start thinking, "oh **** ... maybe i'm in over my head." i ended up sanding the finish down with some 220 grit. i was planning to try something finer today, but if you said the stone was good enough, then i'll probably just leave it as is.



okay Lynn, i don't want to wear out my welcome ... or your patience because , but i have another question. for the ones that oil the main bearings, is it better the bevel the larger edge of the teardrop or should i leave the edge sharp?



PS

just out of curiosity, those VW cranks that you mentioned coming from the factory wth teardrops on the cranks, were they air-cooled engines or water-cooled?



thank you so much for your time and insights.

diabolical1

by the way, that's supposed to be "FD" rear regulator ...