Centaur Gas Engine

[Dr Jo]

Hi guys,

I was lucky enough to acquire a part built Centaur gas engine at my club auction last week and over the weekend have been examining my purchase. Yes there are good bits and badly machined bits but it is the crankshaft that is puzzling me.

The crankshaft is 3/4" too short and has been machined 7/16" dia rather than 1/2" scratch.gif. Does anyone know of a mod for this engine that has a shorter 7/16" crank? I am aware of an article in ME where someone enlarged the crank diameter to 9/16" and extended the length.

Jo

 

[Jasonb]

Maybe it came out bent after fabrication and they took it down a size to suite their next smaller available reamer. Or you have a bit of wyvern in there as well.

Can't think why it would be shortened, it was more usual to see them longer for an extra flywheel or pully.

Jason

PS your two engines looked good at Sandown

 

[Dr Jo]

Thanks Jason, I am pleased you saw my two beam engines .

The Centaur: I had my suspicions that the items in the box may have been tackled by more than one person previously, so there is no reason why they should not have been confused with parts from other engines, it just helps to make life even more interesting.

Having reviewed the all centaur parts I have decided that calling the engine "part built" may be stretching the imagination a bit. A few of the parts are beautifully machined, I can only assume that the other previous owner was not very sure on threads as almost every hole that had a fine thread has been drilled out at the thread clearance diameter ???, which accounts for the second cylinder head as the spark plug thread in the original had also been drilled at 10mm clearance!

My plan is to fill the "chewed" aluminium castings with plastic padding in the areas that do not matter. I will look to recover the over sized holes by applying inserts. Question: should I use Brass, stainless or BMS for the inserts in the aluminium?

Jo

 

[Admiral_dk]

I will look to recover the over sized holes by applying inserts. Question: should I use Brass, stainless or BMS for the inserts in the aluminium?

I have great experience using Heli-Coil inserts in full size engines - unfortunately not cheap.

Are you worried about corrosion or is there another reason for the question about witch metal to use ?

There's also the possible use of special Aluminium solder.

 

[Dr Jo]

The reason I question the metal for the inserts is that I know that aluminium, which is what the Centaur castings are made of, reacts with some metals, I just cannot remember which.

Heli coils are out as the threads needed are 40 tpi ME threads and consequently are likely to be rare as hen's teeth!

So my current plan is to make inserts. The missing threads do not require much in the way of mechanical strength so I may even consider making them a "hot casting/ cold insert press fit" (or even loctite). Unless some one can advise me of a better way.

Jo

 

[Jasonb]

Jo you could tap them out to a bigger size and locktite in a threaded alloy stud, machine or file flush and then cut the correct size into that. Sparkplug should be easy to get a helicoil if you want to use one for that.

As For Plastic padding you may be better off with JB Weld which is a higher temp rated epoxy, just a little less viscous than plastic padding but stronger and not affected by the heat the engien is likely to see. You can get it from Hemmingways or e-bay for a fiver.

 

[Lukas Pils]

Hello

I also have a set of castings for the centaur laying under the bench waiting for the right moment! ;D Do you have the helical gears for the cam shaft or do you know a source for them or even dimensions?

Lukas

 

[Jasonb]

I think the nearest center to centre you could get is 0.858" using 32DP gears of 12 T & 24T which is not too far below the suggested 0.875"

In the UK HPC Gears will have them, in the US try Boston Gear.

J

 

[Dr Jo]

In the original article E Westbury only identified the use of 2:1 skew gears with about 7/8" between center lines, adjusting the camshaft up or down to suit what was available. He suggested acquiring some for either a car distributor or from a speedometer drive but that was back in 1957. (Reeves will sell you a set of gears for the vast sum of £57.)

I will have to look out some JB weld, thanks Jason.

Jo

 

[Blogwitch]

Jo,

I have a job sitting in my workshop, waiting to be done, a tacho drive from the Westbury era, complete with skew gears.
This one needs to be made to rotate in the opposite direction, which is a main casting modification.

If you search old British motorcycle sites or breakers, they can still be obtained.

John

 

[Dr Jo]

That looks idea just what Lukas needs.

I guess that the handing should be able to be over come by an appropriate adjustment to the cam positions.

Jo

 

[Jasonb]

Bogs could you not get L/H skew gears instead or R/H? HPC do either handing if its a standard gear profile. May cost the client a bit more but a lot less work than modding the casting.
J

 

[Admiral_dk]

Sorry about the late answer but look here http://corrosion-doctors.org/Definitions/galvanic-series.htm

You should be able to pickup some pointers there.

Raw aluminium is a problem in a moist environment, the best cure is anodizing but none of the cures are any good with a insert and that's the reason I suggested filling the holes again with alu-solder. In a dry environment you got nothing to worry about with steel or bronze.