Mery Explosive Engine

[Jo]

These little valves can be really tricky, well done for overcoming the challenge Andy 

Jo

[Chipmaster]

Thanks Jo, I’m waiting for a 7/16” ball nose slot drill that I want to use to form the valve pockets. It was due to be delivered today April 15th. While the slot drill is in transit I’ll start work on the eccentric straps.
Andy

[Roger B]

Hi Roger, you’re looking at a family heirloom. It’s a brass toffee hammer that was used in my great grandmother’s shop in Bristol about 1900. Do you remember slabs of toffee being broken up in sweet shops? I also remember what that toffee did to my teeth.

Andy

I remember toffee hammers which came together with a slab of toffee although I think they were cast iron rather than brass. My father's side of the family comes from Bristol. Grandad was a travelling salesman for a sweet company, Callard and Bowser???

Nice progress on the complicated parts of the engine. Small valves are tricky 

[propforward]

Excellent work on this engine - just been catching up - really excellent. Quite a challenging one to build.

[Chipmaster]

Hi Roger, you probably know all there is to know about small valves.
I'm a Bristolian and remember Frys who used to make chocolate in Bristol. I think their creme eggs were far better than Cadbury's but they probably haven't been made for fifty years. Callard and Bowser were Scottish according to the Internet.

A lot of cast iron swarf has been made as I hacked the two Explosion Chamber Covers out of a piece of 50mm square cast iron bar. I wanted the covers to be about 1/8" thick with a raised mound for the spark plug, I couldn't think of an engineering term.

IMG_1418 by Andy, on Flickr

IMG_1424 by Andy, on Flickr

IMG_1426 by Andy, on Flickr

IMG_1427 by Andy, on Flickr

IMG_1436 by Andy, on Flickr

Also began work on the eccentric straps that started out as one bronze casting.

 IMG_1433 by Andy, on Flickr

IMG_1435 by Andy, on Flickr

Thanks for the encouraging words Stuart AKA Propforward

Andy

[Chipmaster]

I found the Exhaust Chambers very challenging especially after I broke off part of the flange on one of them when it broke loose in my milling vice. 
The following picture shows the piece that broke off alongside the casting that I was in the process of repairing.

IMG_1370 by Andy, on Flickr

I didn't feel in the mood to take pictures of the recovery, I got on with it. There was enough casting for me to machine the damaged flange down to 5/8" then cut a 5/8 BSF thread on the stub. A piece of cast iron bar was then tapped 5/8 BSF, JB Weld applied to the threads and screwed on to the stub of the casting. After allowing a day for the JB Weld to cure I machined the new flange down to the appropriate dimensions. I also contacted Martin Models who confirmed that they could supply a replacement casting, thought I would wait in case I had more accidents and needed to order other replacement castings.

This is a side on view of the exhaust chamber casting, the red lines indicate the ports that have to be drilled to come out one above and the other below the valve seat. There is the risk of breaking through the valve seat so great care is required.

Exhaust valve chamber by Andy, on Flickr

I set the casting up in a four jaw chuck to bore out the chamber 19/32" to take a 3/8" BSP plug then a 7/16" Ball Nose slot drill for the valve pocket. A small boring bar was used to machine the flat surface where the valve seat would be cut. It took ages to set the casting up in the four jaw chuck but all went well finishing off by tapping the 3/8 BSP thread. Incidentally I bored the casting out a few thou beyond 19/32" because I felt there was the risk of cracking the side of the casting with the strain of driving in the 3/8 tap, probably wiser to use the lathe to cut the thread. I forgot to take pictures of this stage.

Anyway the thread was satisfactory so I could move on to drilling 1/2" holes 3/8" deep into each of the flanges as per the drawings. For this 'repaired' casting there was the risk that such a hole would destroy the thread holding the flange on. Fortunately it was Ok, I had reasoned that the core diameter of the thread approx 0.6" would be ok if my measurements and set up were correct.

IMG_1469 by Andy, on Flickr

IMG_1470 by Andy, on Flickr


The half inch holes lead on to the 1/4" holes to be drilled through to above and below the valve seat, one at 8 degrees the other at 10 degrees as per the drawings. After spending much time trying out various means of drilling those critical holes I decided to rely on my lathe. I put about a 1/4" of 3/8 BSP thread on the end of a five inch length of brass bar that could be held in a quick change tool holder with the casting screwed up tight on the end. A drill chuck was mounted in the lathe spindle and a 1/2" dowel pin used to align the casting.

IMG_1471 by Andy, on Flickr

The topslide was then set to the appropriate angle and drilling commenced.

 IMG_1473 by Andy, on Flickr

IMG_1474 by Andy, on Flickr

Here are some views of the results, some with a torch shining through the ports.

IMG_1487 by Andy, on Flickr

The repair is visible in this picture.

IMG_1488 by Andy, on Flickr

IMG_1489 by Andy, on Flickr

IMG_1477 by Andy, on Flickr

Phew glad that's done, I think the repair will be ok so I won't bother with replacing the casting. However, there's still the second Exhaust Chamber casting to be done.

Andy
 

[Dave Otto]

Nice recovery Andy, hopefully number two goes more smoothly.

Dave

[Jo]

Well done Andy nice repair, no one will ever know 

Jo

[Vixen]

Andy,

Good recovery 

Mike

[Chipmaster]

Jo, Mike & Dave - Thanks for your supportive comments, I was in two minds whether to confess to that embarrassing accident. I think the repair or is it a bodge will be strong and reliable.
Should anybody else get to this stage with this model I suggest checking those 8° and 10° holes into the valve chamber before you drill, I increased the angles on mine to ensure the valve seat wasn’t touched. Also due to drills and centre drills wandering I had to use a 1/4” slot drill to produce a flat surface that I could start drilling through. Also start with a small say 1/8 drill and check where it emerges. Using a burr in a Dremel I was able to open and clean up the ports.
Andy

[Chipmaster]

By the end of Sunday afternoon having finished various jobs I had just enough time to machine an Exhaust Chamber Cap casting.

The cap is sawn off this casting.

IMG_1497 by Andy, on Flickr

Then on to the lathe to be machined and threaded 3/8" BSP.

IMG_1495 by Andy, on Flickr :
IMG_1498 by Andy, on Flickr

Screwed in to the top of the exhaust chamber.

IMG_1499 by Andy, on Flickr

IMG_1500 by Andy, on Flickr

Andy

[Chipmaster]

Forming the ports in the second exhaust valve chamber went well.

This was a better way to hold the exhaust valve chamber casting for drilling 1/2" holes 3/8" deep into each flange.

  IMG_1510 by Andy, on Flickr

IMG_1513 by Andy, on Flickr

Followed by drilling 1/4" ports into the chamber, one above the other below the valve seat.

IMG_1514 by Andy, on Flickr

Video

IMG_1515 by Andy, on Flickr

IMG_1518 by Andy, on Flickr

IMG_1521 by Andy, on Flickr

Followed by a flange and 1/4" BSP elbow for each chamber

IMG_1541 by Andy, on Flickr

IMG_1544 by Andy, on Flickr

IMG_1548 by Andy, on Flickr

The two exhaust pipes were just a quick fit for the pictures

Andy

[Admiral_dk]

Your model is really starting to take the shape of the finished Engine - looks good 

Per             

[Chipmaster]

Cheers Per 

Machined one eccentric strap this afternoon. Following standard procedure I used an offcut of brass to mount the casting then centred it in a four jaw chuck.

 IMG_1554 by Andy, on Flickr

IMG_1555 by Andy, on Flickr

IMG_1557 by Andy, on Flickr

The strap has a retaining groove which registers with the eccentric. Fortunately I had a 1/6" internal groove tool.

  IMG_1558 by Andy, on Flickr

IMG_1561 by Andy, on Flickr

IMG_1562 by Andy, on Flickr

IMG_1564 by Andy, on Flickr

Will do the second strap tomorrow and the straps will be mounted on an arbor for tidying up the outer surface.

Andy

[Roger B]

That was a nice set of family shots    It's coming along well