Thrust bearings? Aircraft vs. Automotive

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hdsadey
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Thrust bearings? Aircraft vs. Automotive

Post by hdsadey » Fri Jul 19, 2019 6:07 pm

First off I started this thread off in Airboat Talk since it includes both types of power. That being said I wanna know why everyone thinks automotive thrust bearings can't handle the pressure of a prop like aircraft thrust bearings? Other than the fact that aircraft have a floating thrust bearings and early sbc and sbf have them integrated into the main bearing, the way they operate is essentially the same.
Screenshot_2019-07-19-17-44-28.png
Newer engines like hemis and modulars have floating thrusts. Now other than a aircraft crank having an extra long rear main journal it's still a crankshaft with bearings that require oil as a cushion, just like an automotive engine. They both require a controlled oil bath out of the journal which contains the thrust bearing to keep it happy. At the machine shop we check thrust clearance and make sure there's no less than .003 oil clearance. I ran my 302 Ford for 4 years with no noticeable growing in clearances over the course of use. Please enlighten me on why one holds up better than the other because I'm confused.
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Re: Thrust bearings? Aircraft vs. Automotive

Post by keys2pines » Fri Jul 19, 2019 7:19 pm

hdsadey wrote:First off I started this thread off in Airboat Talk since it includes both types of power. That being said I wanna know why everyone thinks automotive thrust bearings can't handle the pressure of a prop like aircraft thrust bearings? Other than the fact that aircraft have a floating thrust bearings and early sbc and sbf have them integrated into the main bearing, the way they operate is essentially the same. Screenshot_2019-07-19-17-44-28.pngNewer engines like hemis and modulars have floating thrusts. Now other than a aircraft crank having an extra long rear main journal it's still a crankshaft with bearings that require oil as a cushion, just like an automotive engine. They both require a controlled oil bath out of the journal which contains the thrust bearing to keep it happy. At the machine shop we check thrust clearance and make sure there's no less than .003 oil clearance. I ran my 302 Ford for 4 years with no noticeable growing in clearances over the course of use. Please enlighten me on why one holds up better than the other because I'm confused.
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Re: Thrust bearings? Aircraft vs. Automotive

Post by terrible ted » Fri Jul 19, 2019 10:12 pm

Well I wiped out 3 small block cranks destroyed the thrust bearings in less than 5 years and I run an aircraft now for 9 years.

hdsadey
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Re: Thrust bearings? Aircraft vs. Automotive

Post by hdsadey » Fri Jul 19, 2019 10:31 pm

Ok I wonder if it's a sbc design flaw? By that I mean how they oil. Were those engines fresh builds or pull outs?
This is not to bash one side or the other, just curious if it's a common problem and why.
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Gary S
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Re: Thrust bearings? Aircraft vs. Automotive

Post by Gary S » Sat Jul 20, 2019 5:53 am

Aircraft engine was designed for a prop and a car engine was designed for a transmission. Its not just thrust that hammers away at it its a side motion that also takes a toll on it. Look at the size of a aviation nose bearing and compare that to a rear main on a car engine.

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Re: Thrust bearings? Aircraft vs. Automotive

Post by SWAMPHUNTER45 » Sat Jul 20, 2019 7:47 am

Without any doubt the auto engine was not originally designed to handle the pressure of a propeller making thrust.

Yet some do and have demonstrated the ability to do it for long periods without fail. The Cadillac 472/500, Olds 455 and Buick 455 have proven this over the past 45 years.

It is important to understand why they can do it and why some engines even in that family will fail. My understanding of the matter is the answer is several factors.

First is the engines have a sizable thrust surface and more importantly the thrust bearing of that period were of a very hard material. The tolerances at assembly were set tight and that worked in the airboat users favor.

Second oil of that period was formulated with a large dose of zinc and phosphorus and that provided superb metal to metal anti-wear protection.

Lastly with a DD auto the balance of the prop and the props own characteristics will add or subtract from your success. A out of balance prop and vibration will wipe out a thrust bearing very quickly.

The Branch car motors that are made for DD use are built differently than the ones which are ordered for use with a gear drive. This is because over the past 30 years building DD car motors Mr Branch has learned tricks of his trade to help get longevity from the platform.

The components today that most machine shops or auto stores sell are inadequate and inferior for DD airboat use. The materials are soft and will wear within 50 hours putting metal in the oil and plugging up oil holes. In many cases if tolerances can be set in spec using old vintage bearings can be your best choice but it's not always an option.

Regardless ALWAYS use a good oil that is well suited for this severe application. We brew our own and I will share.
4 qts Shell Rotella T 15w-40
1 qt. Lucas oil stabilizer
6-8 ounces CompCam 159 additive

That has been proven over the years to work extremely well and be a low cost solution to a high cost problem.

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Re: Thrust bearings? Aircraft vs. Automotive

Post by hdsadey » Sat Jul 20, 2019 9:38 am

Swamp so think about this! Those 3 engines you referenced have the thrust bearings located in the middle of the block like sbf. I'm wondering if these locations hold up better to a thrust bearing located at the rear of the block. Now if you have noticed the OEMs have all moved the thrust bearings to the middle with the exception of the Ford Modular 4.6/5.4 is now in the rear. I had read somewhere that the reason for a mid engine thrust bearing is from a leverage standpoint. Being in the middle with equal amount of cylinders on either side keeps equal pressure on the crank helping the thrust wear. High performance coated bearings may be a way prolong thrust wear. Aircraft engines are obviously are built to be twice as tough with an extra long rear main bearing because if it fails, pulling off the side of the road and walking isn't an option. Just the nature of the machine.

Now the other side like Gary said about the rocking motion of the prop on crank might do more damage to a rear thrust bearing as opposed to a middle bearing due to the short rear bearing. Aircraft having the bearing that long takes the rocking motion out and creates just a push/pull action not hammering the thrust.


I do believe a prop not properly balanced and setup correctly to minimize runout would have a huge effect on thrust wear.


I run Valvoline VR1 20w-50 Racing oil with high zinc for the reason of a solid flat tappet cam, but I'm thinking about running an extra additive. We use quality Clevite bearings in performance builds. We believe these are the best bearings made today.
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Re: Thrust bearings? Aircraft vs. Automotive

Post by SWAMPHUNTER45 » Sat Jul 20, 2019 11:00 am

Having the thrust centered in my opinion was to eliminate or minimize crank flex. In the case of the Cadillac platform having a rear mounted thrust would expedite it's failure as that is the last area to recieve oil in the engine and furthest from the pump.

As far as bearings go I am not sure which one you are referring to exactly when you say Clevite. I'm not well versed on that line as we do not use them. If your using the bearing known as the 77 which is a multi layer bearing and we find it is far to soft for building a direct drive. They are plated and lead and copper are a component of the bi or tri metal plating.

We have tried a host of different bearings in the engines I have run. My 555 stroker engine is running a bearing manufactured in Isreal.

Knowing your Ford has super high oil pressure that is going to be a benefit. I would consider adding in 10-20% Lucas as a cushioning agent as you get time on the engine.

Two things to watch for first is pressure dropping over time as it indicates clearances opening up and oil pressure bleeding off. Second and far worse is seeing oil pressure increase as you get running time on the engine. This would occur as soft bearing material sheds or distorts and covers the oil hole. The less oil moving through means enhanced wear and higher pressures.

I can tell you as I have seen many engines get opened up while visiting the Branch shop. His cheap and easy oil brew works. Remember I'm the guy who broke a pickup tube and had hardly any pressure and when we pulled it apart it showed only a light polishing to the bearing surfaces. Mr Branch didn't even change them. That is a clue that the "Branch Brew" works.

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Re: Thrust bearings? Aircraft vs. Automotive

Post by SWAMPHUNTER45 » Sun Jul 21, 2019 8:08 am

HD have you seen any engines that have been modified to utilize a roller bearing thrust. I know a guy who has a Chris Nelson twin turbo in a pro mod and in conversation he discussed that the engine and transmission are under such a load that a roller thrust must be used.

Next time he has it open I will see if he will allow me to take a few pics. It's a special block I know that they start at Brodix and go to another outfit for enhancements.

Found that to be interesting.

If Deano is still around maybe he can recall who it was that had tried to fabricate a second thrust on the Caddy platform. I have not seen one come through the shop but heard there was someone who experimented with that concept at the rear of the block some time in the early 1980s.

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Re: Thrust bearings? Aircraft vs. Automotive

Post by hdsadey » Sun Jul 21, 2019 9:45 am

I have often thought about some type of external thrust bearing. The problem I have come up with is having to put a spacer block between the flexplate and crank to allow a thrust bearing to be in between. On sbc with the starter bolted to the block poses a problem with pinion gear engagement. Sbf is a little easier. My idea would be to mill a billet rear engine plate thick enough to leave the flexplate where it is in a pocket, have the thrust bearing between the hub and and plate. The other problem is lubrication of the thrust bearing. As with other things ambitions turn to other projects and ideas get shelved.
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Re: Thrust bearings? Aircraft vs. Automotive

Post by Slidin Gator » Sun Jul 21, 2019 10:24 am

hdsadey wrote:I have often thought about some type of external thrust bearing. The problem I have come up with is having to put a spacer block between the flexplate and crank to allow a thrust bearing to be in between. On sbc with the starter bolted to the block poses a problem with pinion gear engagement. Sbf is a little easier. My idea would be to mill a billet rear engine plate thick enough to leave the flexplate where it is in a pocket, have the thrust bearing between the hub and and plate. The other problem is lubrication of the thrust bearing. As with other things ambitions turn to other projects and ideas get shelved.
So at that point you have most of the the cost and weight of a gear box. Might as well use a ratio other than 1:1.
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Re: Thrust bearings? Aircraft vs. Automotive

Post by hdsadey » Sun Jul 21, 2019 11:12 am

Yes sir conventional wisdom would certainly agree with that idea!!!!!
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Re: Thrust bearings? Aircraft vs. Automotive

Post by terrible ted » Sun Jul 21, 2019 12:17 pm

Gear box. Once you run an air boat you will have the TIM Tailor COMPLEX- That more power if you don't know.

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Re: Thrust bearings? Aircraft vs. Automotive

Post by terrible ted » Sun Jul 21, 2019 12:30 pm

My motors 2 were fresh built by a builder the other was a motor I assembled. I assembled The week before opening archery all junk used parts out of my garage of small blocks most were old ls1 motors. I need a motor to make opening day It ran as long as the fresh built motors ran. Before these I ran a sb 400 I killed it by blown hose in a rain storm. I do remember I could move the crank in and out enough to see it pop in and out.

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Re: Thrust bearings? Aircraft vs. Automotive

Post by hdsadey » Sun Jul 21, 2019 4:11 pm

Ted how many hours would you guess were on each before there was a problem? Same builder for the 2?
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Re: Thrust bearings? Aircraft vs. Automotive

Post by flcracker9 » Mon Jul 22, 2019 7:44 am

It will be interesting to see how the 5 Water Thunder DD LS boats hold up. Anyone know if they did anything differen't for the thrust bearing load? Are they running conventional oil?
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Re: Thrust bearings? Aircraft vs. Automotive

Post by John Fenner » Mon Jul 22, 2019 9:25 am

The water thunder dd engines have a custom built thrust bearing added to them built by Dave.
The thrust plates that are shown in the beginning post are of continental design for the C series 65-85-90 hp engines, the E series 470 cubic inch engines have a solid dual shell front main/thrust bearing, its ground power sister has bronze half circle plates with what I call the Achilles heel of the rotating assembly, as it is only located in the case halves by a bronze rivet, as they were designed to run a generator or water pump at 1100 rpm.
Lycoming engines for the most part use the case as the thrust surface.
Have had Chevy engines with thousands of hours with very little thrust wear due to proper oiling direction via a few massages of the thrust bearing.
If attention to detail is used during the build of any engine, zero corners cut, it will last for many hours.
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Re: Thrust bearings? Aircraft vs. Automotive

Post by terrible ted » Thu Jul 25, 2019 12:54 pm

hdsadey wrote:Ted how many hours would you guess were on each before there was a problem? Same builder for the 2?


Not sure but back then I was single so every weekend was a hunting, fishing, or air boating. My old logs show i was out 140 to 160 days a year doing one or the other. Those motor also were tuning big wood paddle props i was running a 72 34 paddle.

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