william hanshaw

Hello, all.

I've been running my 1954 beam-mount McCoy 049 diesel, and it's been a great runner even after storage since then. Now the contra-piston (with O-ring gas seal) has sheared in two at the O-ring notch. I'm wondering if anyone by chance has a contra piston that I can purchase to put my engine back in running shape. I've contacted David Owen today and am waiting for his reply. The contra piston doesn't look as though it'd be too difficult to machine if one has a lathe. The O-ring accomplishes the gas seal, so all the contra needs is a gentle sliding fit in the sleeve. Help anyone? This little jewel is too neat to put on a shelf as a closet queen! Please advise.....Bill Hanshaw

Diesel Die-hard

I probably have an original spare that you can use, William.  If you don't find anything elsewhere, let me know.

earlwb

There are usually someone on Ebay that is always selling parts too.

qazimoto

My Feedback: (1)

One of my 049 McCoy's also had the CP broken at the o-ring grove. I'd guess that the damage was part of a heavy handed attempt to remove the o-ring.

It was an ebay orphan as well. Fortunately I also had a spare.

As mentioned above it would be a simple machining job to make a replacement but as you've found spares are fortunately plentiful.

A replacement made of brass without an o-ring would be an interesting experiment considering how successful brass/Aluminium conversions are in other motors.

AMB

Sounds like the O ring grove was too close to the edge of the contra , my guessmartin

Dan Vincent

The idea of making a brass contra-piston is also my thought. Brass would provide excellent heat. If not try steel.

Seems to me you could chuck a brass rod in a drill, use a file to cut a notch for the O-ring and then cut the piston to vertical size with a hacksaw while the drill is running.

The O-Ring would make up for any sloppiness in your contra-piston.

Anyone know the diameter of a McCoy .049 contra-piston?

qazimoto

My Feedback: (1)

Yes the McCoy CP o-ring grove is cut perilously close to the bottom. It looks like it's made from Cast Iron which is clearly more brittle than either Steel or Brass.

It's also concave on the combustion side which doesn't help it's strength.

Some of my friends now use Leaded Steel for CP's with entirely satisfactory results.

Perhaps the CP from the beam mount version is more robust?

I make the diameter to be 10.31mm or 0.405", a rather difficult size for "Dutch Turning" since Brass comes in 3/8" and 10mm and the next size up means lots of work.

Diesel Die-hard

I think that steel would be perfectly satisfactory for this service, and doubtless far more durable.  I also think that brass would likely work very well.

Gazimoto, since you have a contra-piston out of the cylinder, can you supply the depth of the component and also the dimensions of the O-ring groove?  It seems to have a square base - is that correct?  I'm not sure why they located teh O-ring groove so close to the bottom - it actually makes no differece in practical terms as long as the contra-piston is a reasonably close fit in the cylinder.

qazimoto

My Feedback: (1)

My CP is from a radial mount McCoy, I've just realized that Bill's is from a beam mount example. Are they the same?

Anyway the pics show the dimensions.









The thickness of the CP botton is in inches. The metric equivalent is 0.74mm

It does have a square base.

Dan Vincent

Gazimoto, thanks for the dimention info.

william hanshaw

Gazimoto, Thanks for sending the pics of the contra....it surely appears to be the same as my beam-mount contra. Now the challenge will be to get one made! My contra is too shattered to be used for reliable measurements. My calipers are analog and in ihches, so I have to be very careful in transferring numbers these small to english dimensions. Thanks so much for your lending hand.

If you were of a trusting mind to do so, your contra could be sent to a friend to make another, and returned. I would gladly defray the postage and other costs.

It's very encouraging to see how generous and friendly the fellows in this very specialized hobby are!

Regards, Bill Hanshaw

william hanshaw

Fellows, I just took a second look at my shattered contra's pieces, and sure enough its top end has two features that I don't see in the pictures:

1. There is a small lip on my contra that rides over the top of the cylinder sleeve - to prevent it from being thrust too deep into the sleeve. The lip is only .035" thick with a diameter of .460". So when it's inserted all the way into the sleeve (max compression), it hits the top of the sleeve's rim, to stop further depth of the contra into the sleeve. To me, the pics don't seem to indicate this lip on the top of the contra.

2. The bottom surface of my contra is slightly concave, matching the convex top of the piston. I don't know if this is an actually-required feature, however.

It may be that these twp minor contra upgrades in the 1954 beam-mount version may have been as a result of field suggestions of users of the older radial mount model. Just an uneducated guess, admittedly!

Regards, Bill.

qazimoto

My Feedback: (1)

Bill,

I'm in Australia, it's late and I have to be up early tomorrow for a special event.

When I can manage it I'll convert my metric dimensions back into Imperial for you and do a sketch and post it.

If you can PM me your address then I can pop the Contra Piston into the post.

regards

AMB

Looks like the "lip"may have been done to prevent folks form lowering the contra to far as not to strike the op of the piston??, interesting feature martin

william hanshaw

Gazimoto et all: Yes, the top lip on the contra on my beam-mount model was to prevent the contra's being pushed too deep into the sleeve. If I can have your email address, I can attach my drawing of the contra. Or better yet, I can post my sleeve and contra parts, with drawing, to you and you can then make sure that the new piece fits as planned. If you agree, give me your email and adress and we can get this little project underway. My other friends on this thread have also kindly offered to either give me their only spare, or machine a contra for me....all seem to mutually want to help and get this little jewel running again. What a screamer it has been! Another future project might be to make a new piston as well. But for now this is surely enough! Let me hear from you if you want to pursue this avenue.

Best regards