I know that it's not recommended to use a bushing engine as a pusher. The prop pushes the crankshaft assembly back into the backplate and quickly ruins the engine.

Would it be possible to buy a couple extra thrust washers and put them behind the drive washer. That would pull the crank forward enough to get it seated where it needs to run.

I know that when you set a bushing engine for standard tractor prop--the load pulls the crank forward and seats in against the rear side of the bushing.

Do you think it would work to put a couple extra thrust washers behind the drive washer to "adjust" the crank forward against the rear bushing seat in the pusher configuration?

Thanks

Chris:

A plain bearing engine will work fine as a pusher, without excessive wear, so long as you do two things.

First, no plain bearing engine will live long without castor oil. Many of these engines were used as pushers with good engine life in the days before the synthetic oils became predominant.

Second, very few of the older plain bearing engines did not have a steel washer between the prop driver and the front of the crankcase. Many modern plain bearing engines either have a fiber washer there, or no washer at all, leaving two aluminum parts to rub one against the other. A fiber washer, while better than nothing, will wear quickly leaving the two alloy parts rubbing, galling, and destroying themselves.

So. Make sure the engine you have selected either has the steel washer there, or install one. Then, with a goodly percentage of castor in your fuel mix you should have no problem at all.

Bill.

It's ironic that you asked that today, just yesterday I was checking out my LA .65 I converted to Diesel and I don't think there is enough room for a second washer on the front. What called my attention to it was the fact that on deceleration I was getting that rattling noise that some engines make at part throttle or when slowing. caused by the crankshaft pistoning in and out. I do not see how it can make that noise when there is so little room for the crankshaft to move in and out.

Bill:

When you say "plain bearing"--are we talking about a bronze bushing on the crankshaft??

I'm talking about a Bronze bushing engine. Like an LA or FP series engine.

They have a lot of end play in the crank. But--when used in a standard tractor setup--the prop force pulls the crank forward enough to keep it seated against the case bushing.

I've been told that when used as a pusher--the loads from pushing on the crank will force the rod pin into the backplate and make lots of shavings and other nasty stuff inside the engine as the rod pin wears a hole in the backplate.

This doesn't happen to a ball bearing engine because the crank is seated in the bearings and crankshaft end play is very minimal.

I always use Omega fuel. Usually 5% for break-in and then 10% for sport flying. I'm pretty sure that the Omega fuels are 30/70 blend with total oil content at 17%. Will this work for my pusher engine? I'm not opposed to adding a bit more castor to the fuel. If you REALLY think I should add oil--how much would you reccomend per gallon?

Thanks for the help.

Chris:

Not all "Plain bearing" engines have bronze bushings in them, the older K&B Sportsters, almost all Cox engines, for two examples, run the cranks in the base metal of the crank case. By saying "Plain" bearing they are all covered. Remember please, whether it has a cast in bush, runs in the base metal, or has some form of "Anti-friction" bearing be it ball or roller type, all rotating shafts have bearings of one form or another.

Synthetic oils do not have high enough film strength to lubricate a plain bearing crank properly. The engines will run with 100% synthetic, but they will run a lot longer with castor in the fuel. I use the Omega fuels in most of my engines, it seems to have a sufficiency of castor for my applications. I've not noticed any excessive wear in the four stroke cams, that's another high load place where the castor's film strength is needed.

Running a plain bearing crank as a pusher you might want to go to a higher percentage because not too much oil comes out the front, and it will have to for lubrication of what will then be your thrust bearing.

If the engine you've selected has enough crank float to allow the crank pin to hit the back plate you will definitely need to shim the crank to prevent it.

In shimming the crank you can use one or more washers, but try to use as few as possible, and keep them at least 0.020" thick. The thinner washers tend to crumple under load. Also, use hardened steel washers, with ground faces. If absolutely necessary, you can't find anything suitable, you can use a plain flat washer and lap the faces, then temper it.

As you adjust the end play remember the crank case is going to expand more than the shaft with heat, if the play is too little the shaft will bind when the engine warms up.

Possibly you'll have to use a thicker gasket on the back plate, or cut the face of it to keep the pin from hitting.

On the other end you can lap the front of the case if needed to get a washer in that's thick enough to last.

Bill.

I first used a Magnum GP15 on the tail end of my Sig Tri Star. The results weren't good. After two flights there was very noticible wear, with the drive hub pushing into and wearing the engine case. I switched engines to an MDS 18 and have not experienced any problems because of the configuration. Problems because of the MDS, yes .... but its much better now. [8D]

The engine I'm contemplating using for this pusher is an OS 40FP. It currently has a single thrust washer between the drive hub and the case.

I thought I could just order a half dozen stock thrust washers--for the FP-- from TH at $1.89 apiece and start shimming.

Good point about the different expanding rates on the case and crank. I'll shim it a little loose and run it for 5 minutes then pull it down and check wear from the back-end.

'Course--I could just break down and buy a ball bearing engine for the rear engine. Slap the 40FP on the front and avoid any troubles.[:-]

That would probably be the smartest thing to do. Money is just kinda tight right now. I've been hurt and off work since March 25, 2005. Have had 2 surgeries on my lower back. The temporary dissability payments from the work comp. insurance carrier---are a bit skinny at only 66% of my usuall wage.

The kids gotta eat and the bills need to be paid before I can justify spending too much $$ on the toys for now. My finance officer (wife) is keeping me on a tight leash right now. Darn financial responsibilities are cutting into my slush fund.[:'(] Can't wait to get back to work.

Its unlikely you'll find any parts for a FP at Tower unless they are also common with the LA series?

You could just go ahead and use the FP. If it doesn't turn out for you, Maybe, you'll be back to work by then?

Enjoy,

Jim

I measured both my LA .46 and .65 and could not get a .008 feeler guage between the crankshaft shoulder and the washer when the washer was against the prop driver. A Saito feeler guage would just slide in there with no wiggling room.

Jim:
Turns out there are parts available for the 40FP from TH. The 35 max and some of the 40LA parts will fit.

I went to the OS engines site and looked up the old part numbers and checked for compatability.
You can use the same con. rod for the .35--40FP and the 40LA.
TH also carries the crank, case, backplate, gaskets, wrist pin, and drive washer for the 40FP.

I was surprised that TH had that many parts available. But--as stated earlier--I did have to go to the OS site and get the OEM part numbers. Then enter them into the search at TH in order to locate them.

Best thing to do is use the FP on the front and get a ball bearing engine for the rear. I'm watching 65 engines on e*b*a*y right now. One of them has gotta go for cheap--and maybe I'll get lucky and pick up a decent .40-.46 runner with ball bearings for a good price.

Doc says I'll be back on light duty in 6--8 weeks. That is---if he didn't screw up this second surgery like he did on the first one.[]

The steel shim thrust washers only began to be fitted to plain bearing engines when electric starters came into vogue so they were only intended to come into play for the short time the starter was used but even then it's necessary to make sure there's a little oil between the rubbing face. Normally there's quite a bit of clearance between the end of the crankpin and the backplate. This is easy to check just by pushing the crankshaft back with no prop fitted to get some idea of the clearance. As Bill said, there has to be a small amount of free play when cold to allow for differential expansion, .005" or .010" should be enough but more doesn't matter.

The problem with using it as a pusher engine is that the steel shim will give a very good seal that would most likely stop enough oil from covering the surface. What I would do is to take out the crankshaft then use a triangular file to cut a small groove in the front face where the shim rubs against it to provide a channel for oil to flow outwards from the crank bush. If you think about it, all bushed engines already use a plain steel thrust bearing when used normally. In that case it's the steel crankweb running against the inner end of the bush but there's a heck of a lot of oil floating around inside the crankcase

The crankpin should never touch the backplate on an engine that was set up properly from the factory, even when used as a pusher. Most bushing engines come with a thin steel washer behind the thrustdriver. This was fitted to reduce the wear when using an electric starter and should work effectively when the engine is used as a pusher. They are easy to misplace, so make sure that your engine has one in place.