Lycoming Main Bearing Dimensions

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RJW

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A couple questions: What are the nominal standard dimensions of these Lycoming main bearings—width and thickness or OD and ID. I really need the width so I can check the loads this size bearing can sustain. The bearings I’m interested in are marked number 7 in the drawing. The part number that I have for them is 18D26096. I think they are for the 2.625” diameter crank. Also, are these bearings sold as individual halves? Or are they like car bearings where one bearing includes both halves? Price is around $30 but I don’t know if that’s for one or both halves.

Dan? Are you there?

Thanks,
Rob

Lyc Bearing.jpg
 

Dan Thomas

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A couple questions: What are the nominal standard dimensions of these Lycoming main bearings—width and thickness or OD and ID. I really need the width so I can check the loads this size bearing can sustain. The bearings I’m interested in are marked number 7 in the drawing. The part number that I have for them is 18D26096. I think they are for the 2.625” diameter crank. Also, are these bearings sold as individual halves? Or are they like car bearings where one bearing includes both halves? Price is around $30 but I don’t know if that’s for one or both halves.

Dan? Are you there?

Thanks,
Rob

View attachment 20060
I'm no longer at my former job where I could have checked those dimensionally. Working on turbines now. Knowing Lycoming, the $30 is probably for the pair, but you'd have to call a dealer to find out for sure.

Dan
 
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ekimneirbo

Compare the Lyc bearings to a smallblock Chevy 400 or an LS1-LS7 engine and you will be pleasantly surprised. Note that the Lyc uses the aluminum case as its thrust face and the contact area is decided by the flange on the crankshaft. Notice also that the contact area of the actual bearing surface is two raised areas on the bearing shell roughly equivalent to two main bearings.
Lycoming bearing dims.jpg
 
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ekimneirbo

Here are some more pictures for comparison between Lycoming Continental and Chevy Engine Bearings I'll follow this up with some more pictures.Be sure to measure your self to insure accuracy, but these should get you a rough idea comparatively.GO 300 Redrive 031.jpgThrust Faces 1.jpgLS1 Crank Dim 1.jpgIMGP0321.jpg
 
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ekimneirbo

There is a Federal Mogul page here that shows how they deal with getting oil to thrust surfaces in cars. Don't consider this as being blessed by them use on an airplane, its just to show a possible adaption that you may use at your own risk. There is an exploded view of a GO-300 Continental which show a small splined shaft as part of the drive system. It slides into the splined end of the crankshaft. The picture with the ruler gives reference to the size of their rather compact gear drive extension compared to some aftermarket drives.GO 300 Redrive 031.jpg4 Thrust.jpgGO 300-2 001.jpgGO 300 Redrive 045.jpg
 
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ekimneirbo

Yet some more pictures. Remember these are for reference only and you need to do accurate measurements yourself..........but these should work ok for comparisons. The next and final email in this group will show you some of how I'm thinking about proceeding.IMGP0318.jpgIMGP0325.jpgIMGP0329.jpg
 
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ekimneirbo

OK, here goes the last one. I hope this info helps others in at least thinking about building a prop drive. Again, its not proven or engineered beyond redneck standards. Proceed at your own risk if you emulate any of this. At least when someone tells you Lyc/Cont have humongous thrust bearings compared to a Chevy, you can decide exactly how much difference makes one humongous. GO 300 Redrive 077.jpgIMGP0333.jpgIMGP0337.jpgIMGP0346.jpg
 
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ekimneirbo

One more thought here. The idea I am working toward is that the axle shaft will drive the propeller. It will be driven by a splined adapter on the rear of the crankshaft. This hopefully will allow for any minor (.003 ?) misalignment. It will also hopefully relieve the engines thrust bearing from any thrust loads from the propeller....or at least make them minimal. The hollow shaft around the axle will be driven by its front face being bolted to the rear face of the axle. Bolts will pass thru the propeller, then thru the axle face, and screw into the face of the hollow tube. They may then be further secured by nuts and cotter pins. The hollow shaft will have two forward thrust surfaces because of some difference between the face areas of automotive bearings and aircraft bearings. I can't just use the Continental aircraft bearing because it is apparently no longer made, and if you do find one, its $$$. The double thrust face area should be larger than even the aircraft bearing area. The auto bearings are also available cheaply in undersizes which will allow me to grind the hollow tube to a new finish (.003-.010). If someone were to make this shaft from scratch, they could make the bearing surface diameter to suit what ever size they wanted. The hollow tube with the combination of two thrust bearings and one plain bearing should (hopefully) provide plenty of support for the propeller gyrations. It worked for Continental with the GO-300 so hopefully it will work for me.........even if I put more hp thru it with a direct drive LS 418. Again, none of this is proven and I'm not recommending it to anyone........just providing insight on how I plan to proceed. So if you use any of these ideas, do so at your own risk.
 

RJW

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I just saw your posts. Sorry for not responding sooner. Thanks for posting all the pictures. These will be a great help to anyone thinking of using hydro bearings. Currently my work has returned to roller bearings. But I think hydro bearings are a very good idea. The old Geschwender chain drives use hydro bearings on the prop shaft and I think the EPI boxes use hydro bearings throughout.

Excellent info on the design of these bearings. If you look at design books on bearings you will find that these things are anything but cylindrical with flat thrust surfaces. They are very carefully shaped to distribute oil across the journal. It’s a very interesting design problem with, as usual, much more going on than meets the eye.

Concerning adequate thrust surface, using two surfaces is ok as long as you are careful about differential expansion between shafts and cases. You want to provide even loading for both bearings. I’m not sure but this might be kind of difficult to achieve. One advantage here is that light airplanes don’t produce much thrust for long periods (climb). Make a guess about the actual thrust and calculate the surface area required to react it using a giving type of oil and flow rate. It might even turn out that a single bearing will be enough depending on the regime you are designing for.

I also think that your drive scheme is a good one. The difficulty here will be designing an effective drive axle. That quill in the GO300 is a very carefully designed part that must be made from the proper materials, very carefully machined, and precisely heat-treated to work with the entire system being put together (again, much more going on with this apparently simple little part than meets the eye). Still, a proper quill is the way to go for coupling drives. The only reason not to use one is the difficulty in careful design and manufacture. Most prefer avoiding the difficulty involved and go with clutch centers or rubber couplings. However, your drive axle will work if you are careful in its design. It will be much more efficient (lighter) than flywheels, springs, rubber, and clutches.

Rob
 

Toobuilder

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One more thought here...
Trying to isolate one thrust surface (engine) from another (drive) with sliding splines was my initial thought as well. However, even in the Corvette splined coupling, the joint is clamped down tight after assembly. To keep it loose enough to slide will also accelerate wear significantly. Ultimately, you may just have to calculate the thermal expansion of the system and allow enough clearance so the two thrust surfaces are not fighting each other.

I do like the quill shaft however... I keep coming back to that, but am running into problems with the short length because I'm trying to match the installed length of the Lyc 540. I think that the longer it is, the less critical the design and manufacture has to be. The driveshaft on my 63 Pontiac Tempest was a type of quill, but it was about 5 feet long. Trying to accomplish the same thing with a one foot shaft is a whole different story. I can gain length like you do by passing the quill through the driven shaft and grabbing the front side, but I'm also looking to pressurize the hub with oil for a C/S prop, so I have not figured that one out yet.
 

Toobuilder

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OK,

If you use the axle as a quill, then it woulld be fairly easy to machine the GO-300 drive piece to be a press fit out near the flange. This would allow me to pass governor oil through the drive and into the axle to supply the hub. A press fit and some sealant would significantly reduce the complexity of sealing the two for 300 PSI oil. All I would give up is an inch or so of "quill real estate".... Hmmmm....
 

PTAirco

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I remember there used to be a handful of scaled down Curtiss P6 replicas that used small block Chevrolet engines, with the prop simply bolted to the flywheel with a 6" or so spacer/adapter/hub. The standard main bearings wore out rapidly. They switched to those Federal Mogul bearings and seemed to do fine after that. There used to be a forum that discussed these aircraft and this particular conversion, but it seems to have died.
 

Toobuilder

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One more thought here. The idea I am working toward is that the axle shaft will drive the propeller. It will be driven by a splined adapter on the rear of the crankshaft. This hopefully will allow for any minor (.003 ?) misalignment. It will also hopefully relieve the engines thrust bearing from any thrust loads from the propeller....or at least make them minimal. The hollow shaft around the axle will be driven by its front face being bolted to the rear face of the axle. Bolts will pass thru the propeller, then thru the axle face, and screw into the face of the hollow tube. They may then be further secured by nuts and cotter pins. The hollow shaft will have two forward thrust surfaces because of some difference between the face areas of automotive bearings and aircraft bearings. I can't just use the Continental aircraft bearing because it is apparently no longer made, and if you do find one, its $$$. The double thrust face area should be larger than even the aircraft bearing area. The auto bearings are also available cheaply in undersizes which will allow me to grind the hollow tube to a new finish (.003-.010). If someone were to make this shaft from scratch, they could make the bearing surface diameter to suit what ever size they wanted. The hollow tube with the combination of two thrust bearings and one plain bearing should (hopefully) provide plenty of support for the propeller gyrations. It worked for Continental with the GO-300 so hopefully it will work for me.........even if I put more hp thru it with a direct drive LS 418. Again, none of this is proven and I'm not recommending it to anyone........just providing insight on how I plan to proceed. So if you use any of these ideas, do so at your own risk.

Lots of good stuff here. Took me a little while to comprehend what you were saying, but really did get my brain back into high gear. Your idea has removed the biggest stumbling block from my concept... How to get enough length in the quill. Anyway, some random thoughts- some have been previously posted in my other threads:

Grab a Corvette flexplate for your "splined adapter"... they're essentially throw away items and can be had brand new on ebay for about $25.

You can have custom race axles built in almost any length, spline and flange configuration. I called one shop and they will build an axle that matches the SAE prop flange dimensions and the Corvette flex plate spline. You may have to do some post processing and grind the quill part down to your spec, but they will do the hard stuff for a pretty reasonable price ("aircraft reasonable", that is).

Rather than "bolt" the two flanges together, I'd consider pressing drive lugs through both, just like a "normal" prop flange. That, and a press fit down at the shaft will keep things from moving around.

Did you ever consider using the Lycoming snout bearing at the front and a roller thrust bearing at the tail of your stub shaft?

With all the work you have into the mods on the GO-300 stub shaft, why did you not go with a custom unit, using more typical bearings?

What are you going to do for a housing? I'm thinking a couple of blocks of aluminum bolted in halves just like a split aircraft case should do the trick. Besides, I can do most of the work with a drill press and lathe.
 
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ekimneirbo

Lots of good stuff here. Took me a little while to comprehend what you were saying, but really did get my brain back into high gear. Your idea has removed the biggest stumbling block from my concept... How to get enough length in the quill. Anyway, some random thoughts- some have been previously posted in my other threads:

Grab a Corvette flexplate for your "splined adapter"... they're essentially throw away items and can be had brand new on ebay for about $25.

You can have custom race axles built in almost any length, spline and flange configuration. I called one shop and they will build an axle that matches the SAE prop flange dimensions and the Corvette flex plate spline. You may have to do some post processing and grind the quill part down to your spec, but they will do the hard stuff for a pretty reasonable price ("aircraft reasonable", that is).

Rather than "bolt" the two flanges together, I'd consider pressing drive lugs through both, just like a "normal" prop flange. That, and a press fit down at the shaft will keep things from moving around.

Did you ever consider using the Lycoming snout bearing at the front and a roller thrust bearing at the tail of your stub shaft?

With all the work you have into the mods on the GO-300 stub shaft, why did you not go with a custom unit, using more typical bearings?

What are you going to do for a housing? I'm thinking a couple of blocks of aluminum bolted in halves just like a split aircraft case should do the trick. Besides, I can do most of the work with a drill press and lathe.
Thanks for the replies from everyone. I'll try to address the different points. First the difference in expansion. I don't see that to be a problem as this is essentially the same situation that a steel crankshaft encounters in an aluminum block using the same bearings. As far as expansion affecting two thrust faces differently, I think the end play tolerance will make that a work ok, but I may have to adjust the tolerance to suit the situation. As for roller bearings, they are definitely easier to adapt to a housing, but they will need to be pressed onto the shaft. I want something thats easy to disassemble, and I just like the ruggedness of automotive bearings. They will make the machining of a housing to hold them much more difficult. Pins or dowels to align the 3 components is something I also plan to do, so we are thinking similarly there. I looked at several different ways to attach the adapter to the engine. There are some lightweight magnesium bellhousings fo a smallblock that might be usuable. You can find used ones on Ebay. I have one. I think the LS flywheel is too big for it, but the flywheel could be machined down and a smaller starter ring mounted. That would then require something like a reduction gear starter to be adapted. The LS Corvette with the encloseddriveshaft has a nice shaped bellhousing that would seem to lend itself to the adapter for my design. I do have some concerns about using aluminum bellhousings because of some of the thin walls on them. There are some steel bellhousings available in the racing industry that are very strong and reasonably lite......bout $400. I think I am going to machine a 2" thick aluminum plate to be the initial adapter from the engine, and then make my secondary adapter so that it inserts into the primary housing with either a slip fit or maybe a slight interference fit. Heat one, chill the other and slip it in place. It would then have 4-6 bolts to anchor it firmly. I'm going back and forth on whether to buy some flat stock and use them to make two halves or buy some round stock and saw it in half. I think I'd rather have some flat stock for ease of initial machining, and then turn it to a round shape later after its bolted together........but round stock would be cheaper I think. The custom splined axle route is what I plan to do. If someone makes the hollow shaft from scratch, they can use larger diameter racing axles and machine the hollow shaft to work with it. Don't forget to make sure you leave enough wall thickness for the bearing diameter you want to use. The axle in my pictures was just one I had laying around from an old truck project.
 

Toobuilder

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Not sure what you mean with the Corvette flywheel being "too big"... it fits inside the bolt pattern of the LS, which is essentially the same as a SBC. The Corvette unit is little more than a flexplate with a splined hub in the center.
 
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ekimneirbo

Not sure what you mean with the Corvette flywheel being "too big"... it fits inside the bolt pattern of the LS, which is essentially the same as a SBC. The Corvette unit is little more than a flexplate with a splined hub in the center.
There are two different size flywheels that I am aware of for smallblock Chevys. The bolt pattern for an LS flywheel is different than the smallblock. (Also you have to watch out for smallblock flywheels that fit the externally balanced 400 smallblock or certain big blocks) I would prefer not to use a flexplate because I think the rotating weight is complimentary to the engine and propeller for smooth operation. One other thing about smallblock flywheels is prior to 1986 or so they used a two piece rear seal. From 1986 till 1996 they used a one piece rear seal and were internally balanced engines. The bolt pattern for the one piece seal engine is different from the two piece seal engine. I'll post a few follow on emails here to get some pictures in order. The Corvette housing has a nice shape for an adapter but I don't know about its strength. Note the bolted and welded tube adapter. For anyone considering a Buick/Olds/Rover conversion the Rover auto trans has a nice removable bellhousing with ribs that looks worth checking out. Picked up one of those for $25.Corvette 1.jpgCorvette 2.jpgCorvette 3.jpgCorvette 4.jpg
 
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ekimneirbo

The magnesium bellhousing that Nascar uses. I don't know if new versions are available that work with the LS type of engine. This is for a smallblock Chevy.Magnesium 1.jpgMagnesium 3.jpgFord PTO 1.jpgFord PTO 3.jpgFord PTO 7.jpg
 

Toobuilder

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Once again, I'm not following... The bolt pattern I was talking about earlier was the bellhousing. Since you planned to use a LS engine, I just figured you would use a LS flywheel/flexplate (or, since you want a splined hub, the LS Corvette unit). The magnesium bellhousing piece you have looks interesting - and if its the same bolt pattern as the SBC, it will "mostly" bolt to the LS block (one hole off). Are you sugesting that the unit will not clear a Corvette flywheel for some reason?
 
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