R975 Radial engines

Bob Phillips · #1 16-04-20, 04:09

Thanks Malcolm and David for your thoughts.
I think maybe you have it- aircraft plugs are too difficult to service in the field? seems to make sense. Much of what I have read suggests radials have a bad habit of fouling plugs and need frequent changes of plugs. So this could be due to a too rich mixture at low speeds or too much oil working its way up to the plugs? I have pulled apart engines where the top rings are all seized- probably due to oil leakage toward the combustion chamber. Too much oil will certainly foul the plugs, an ongoing problem in radial type engines.

Bob Phillips · #2 17-04-20, 21:06

Just a footnote to this discussions on sparkplugs. I was out rooting through one of my trailer, looking in boxes I put away 25 years ago and I found some more, radial/aviation style engine sparkplugs. The first another Champion C63, but with a twist. check out the twin electrodes. It the first one I remember seeing.
Second I found a couple of cartons of plugs for the Light Tank (Locust with Lycoming air cooled aviation engine) which are also Champion plugs. Note they are single electrode and unshielded.
Here are a few pictures.

plugsa.jpg plugc.jpg plugd.jpg

David Herbert · #3 17-04-20, 21:26

If anyone finds spark plugs with electrodes like the above, single or double, the thin piece welded to the threaded portion is platinum. Do not try to change the gap as they will fall off. However if the plugs are scrap it makes it easy to separate the platinum which is well worth doing - check the price !

David

charlie fitton · #4 18-04-20, 13:45

Quote:

Originally Posted by David Herbert

If anyone finds spark plugs with electrodes like the above, single or double, the thin piece welded to the threaded portion is platinum. Do not try to change the gap as they will fall off. However if the plugs are scrap it makes it easy to separate the platinum which is well worth doing - check the price !

David

$25.000/ kilo, here

Malcolm Towrie · #5 19-04-20, 05:18

You have a helluva stash of parts, Bob!

The Brits liked those "fine wire" plugs shown in your third photo. Ive seen them on Ferrets and an FV432. Like David said, the pins are platinum or ididium and they are a high-end plug for aviation use. Good for burning off lead deposits, which I found out aviation gas still has, much to my surprise.
Nowadays they cost over $100 each, so $1000 for a four-banger aircraft engine! Total overkill for a museum vehicle.

Malcolm

Grant Bowker · #6 19-04-20, 15:45

Most AvGas sold in Canada at present is 100LL. I.E. 100 octane Low Lead (max 0.56g/l of lead).
See https://www.shell.com/business-custo...uel/avgas.html for more information about AvGas.

Bob Phillips · #7 16-12-20, 02:55

I would like to revive this discussion of radial engines. The forum has covered a wide variety of topics from history and , identification of different engines, to common problems even fuel grades. In post 31 Dave Hebert mentioned that one issue was the failure of the 8 bolts holding on the crankshaft gear, meaning the rear gear case drive was disconnected from the front section. Thats what this new addition is about. I would appreciate input from forum members as I am looking for solutions to this problem. Anyway here is the story.
ABout a month ago, one of our fellow MV enthusiasts had his C4 equipped M18 out for a number of successful drives. At the end of the day when he went to restart it to garage it for the night, it would not start. The starter would run but the engine would not turn over. The engine could be turned using the cooling fan but there was no connection back to front. A magneto was pulled off and the fan rotated but the mag drive did not turn. So the engine had to come out and the rear case removed for a look see. It had, as Dave had pointed out, sheared off bolts otherwise fairly clean and had no apparent collateral damage. The bolts were removed without difficulty and the gear seemed to good enough to reuse. pictures enclosed.

breakage2.JPG breakage1.JPG breakage3.JPG

Note the unusual shape of the sheared bolts, they are essentially a tapered shoulder cap screw with a square driving head on top with holes to put through lock wires. The manual identifies C1 and C4 crankshaft bolts as
"Screw, machine, sq-hd, dld-f/1kg-wire, alloy -S, 5/16-24NF-2 (19/32) x 1 7/32 overall lgh" it is part number G104-0102120 or CO-200439 , also B206663. Not quite sure what all of the description means, can anybody translate ?

Now before I ask you for your respective opinions on how to repair this, lets look at the later -46 engine gears. The Wright R975 started out with much less power than the finished C4 version. It appears that one of the weak links remained the 8 bolts holding on the rear crank gear- a design unchanged since the mid 1930s?? By contrast, the late 1940s designed 975-46 was built much heavier to handle its boosted horsepower. Some of this has been previously referred to as we noted the heavier case construction, heavier rear main bearing etc. If you check out the next photo you will see a rear crankgear for a -46 and the much heavier method of attaching it. While it uses 8 capscrews, they are flat not tapered. The gear/crankshaft have an aligning dowel on one side. Most importantly, there is a heavy metal projection attached to the gear which is drawn into the rear of the crankshaft witha heavy bolt. A LOT stronger than the C1 and C4 version!