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blw -> RE: The Complete Saito Notes by Bill Robison (5/12/2007 3:53:17 AM)
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Cam box gasket
I have checked several new gaskets, for both the old and new pattern cam boxes. They have all measured within a few tenths of 0.0075” thick.
General engine lubrication
Saito, in common with most other model four stroke engines, depends on luck as much as engineering to oil the cam and its bearings.
On the engineering side, the piston ring has a much larger gap than would be expected, this is to allow more leakage, blowing the unburned oil from the combustion chamber through the ring gap into the lower part of the crankcase where it accumulates. After the engine has been running this accumulated oil gets to be more than needed, the excess is blown out the case vent.
Where the luck comes in, with the older style rear vent nipple, is getting the oil to the cam. As the engine runs the oil is whipped into a vapor, this works its way through the rear bearing into the cam area, also oiling the front bearing. The rocker gear depends on the little oil that goes up front, and then leaking past the tappets to get to the overhead. When the engine is mounted inverted enough oil puddles in the cam box to get plenty into the valve gear through this leakage, but an upright mounting usually needs to have the rocker covers pulled for oiling often.
The newer engines have the vent nipple on the forward part of the case, opposite the cam box. This forces the oil through the rear bearing and does a much better job of lubing the cam and tappets.
Now. The oil itself. Since only a small part of the oil goes through the rear bearing (With the rear vent) it’s important to have a good oil. And since all the oil has to leak past the piston ring, and synthetic tends to burn in the combustion chamber leaving very little to leak past the ring, you should see this is another argument in favor of castor oil which does not burn in normal engine operation.
OK, so you say the oil leaks past the ring on the compression stroke, before the synthetic has a chance to burn. Some does, but the majority blows past the ring on the power stroke, the cylinder pressure is much higher then than on compression. The synthetic has burned by then, the castor survives and goes into the crankcase.
Valve and rocker lubrication
As stated, so long as the valve gear is oiled any good oil will do. Personally, it's ATF Dexron.
A note on "Moly" grease. The chassis lube has a very small amount, but if you want a grease with a high percentage of molybdenum disulfide get a can of "Nevr-Seez" and use that. MoS2 greases are commonly used as break-in lube for cam lobes and their matching lifters, but using them anywhere else in an engine is not encouraged. The two elements will separate under high heat and pressure, the remaining crystalline sulfur acts as a polishing agent. If used in excess more places will be polished than desired, and this is nothing but preliminary wear.
If you want to use a grease on the rocker gear it's better to use a white lithium grease such as "Lubri-Plate" in your engine.
Ball bearings
New precision steel bearings and new ceramics are equally smooth. After ten hours the steel bearings are starting to get loose, after 30 hours the steel bearings are due for replacement. The ceramics, after 30 hours, still feel like new.
OK everybody, OK! I know the steel bearings will often run 100 hours, ‘specially if you get them with the polycarbonate retainers. But to get that life you have to run the engine dry every time, use after run oil religiously, and castor oil is needed in the fuel.
I’ve seen both open and shielded bearings as OEM in Saitos, they are now being supplied with a true sealed bearing in front. At the same time, I don’t think I’ve ever installed anything other than sealed bearings in front. As a matter of fact, on some engines I’ve used stainless front bearings instead of ceramic when Paul (RC-Bearings) didn’t have the right ceramics to fit.
I don’t feel too bad about stainless in front, it’s the rear that has the high loadings, and using the –2RS front bearings I leave both seals in place, so lubrication is not a problem. Paul assures me the original grease is good for the life of the bearing even in the high rpm use. So far I’ve had no failures, or even questions, about the completely sealed front bearings.
The rear bearing MUST be an open bearing, otherwise oil to the cam and tappets would be either restricted or eliminated. Cant live with that.
”Paul” is Paul Macintosh, RC_Bearings.com
You need to get the –RS or the –2RS bearing for the front of the Saito engines.
In your case the 698 (8x19x6 mm) is the base number for the front bearing, ordered by that number alone you would get a plain bearing with open construction. The “Stock” Saito bearing is a 698-ZZ, still a standard bearing but with the addition of steel shields. These are supplied packed with a high temperature grease, but after running a while the grease can be forced out, then your leak will come back. A 698-rs or a 698-2rs will have a true seal, or double seal in the –2RS, and will not leak until it’s well worn.
The best is the 698C-TH9, which has the “Polymite” ball retainer and the double seals. Supplied with the double seals it is, again, packed with the high temp grease, and so long as the seals are not disturbed the bearing is lubricated for its life. Which is, as stated earlier, about ten times the life of a conventional steel bearing.
Forgot to say the 698C is the bearing with ceramic balls.
All the comments are good, but in my experience I've found that in sport use one $30 set of ceramic bearings outlasts ten sets of "Stock" bearings. This does depend on not crashing or running lean.
The ten sets is a guess. Using ordinary bearings in an engine with "Normal" service I replace them every year or two. None of the engines I've put ceramics in have needed a replacement set.
Standard bearing sets for $10 and ceramics at $30? I think it's well worth the extra money.
We hear about the crashes, and we hear about the engines damaged by lean runs. We do not hear about the successful flights, and the engines that just keep on running.
In my club I'd say the successful flights out number the failures by at least 100 to one. This makes the ceramics a good buy.
The bearings I have been getting from RC-Bearings.com are, in appearance, made with high chrome stainless steel races. I haven't worried about any specification beyond high quality "Ceramic" ball bearings. They have worked fine for me, I have yet to experience a failure.
The "Side" load is an axial force. The propeller thrust is a side load. I have seen no sign of excess wear, or any wear at all, in the ceramics.
On crash damage. With steel balls, stainless or not, the crash loads can Brinnell the balls and races. This puts flat spots on the balls, and dents in the races. The bearing is ruined. With ceramic balls, the balls do not get the flat spots, the dents in the races are on the "Non" thrust side, so many times the ceramics will survive where the steel bearings will not. Might hear a little noise with a starter, but when running the thrust will pull all the parts to run on undamaged areas. This part is speculation, I've not crashed a set of ceramics.
At the same time, do remember that no bearing will survive a lack of lubrication.
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