Gypsy Engine

[byawor]

I have been working on my Gypsy on and off for awhile. Would it be ok to post some experience and pictures here or should I start a new thread?
Bob

 

[Ringsnapper]

Sure, I don‘t see any issue with you adding your experiences to this thread.
I would suggest that if you have an extensive build story it might be best to start afresh as this thread has already rambled along over a number of topics for some time all be they Gipsy related.
Your choice though.

 

[byawor]

Trial fit of rocker arms. I had a lot of trouble finishing the supports, the castings are almost impossible to hold so it is difficult to get them right. I ruined a bunch so I made some replacement castings. If anyone is interested will post some pictures of the process. Time well wasted!!
Bob

 

[Peter Twissell]

Yes please Bob.
Photos of the process are always interesting.
Glad to see I'm not the only one who works on the bench of chaos!

 

[Richard Hed]

Trial fit of rocker arms. I had a lot of trouble finishing the supports, the castings are almost impossible to hold so it is difficult to get them right. I ruined a bunch so I made some replacement castings. If anyone is interested will post some pictures of the process. Time well wasted!!
Bob

This is why people read books--to gain experience without haveing to do the same processes that have been tried time and again thru the ages. Your experiences, particularly the one that finished the product, can be helpful to others doing something smilar. I am particularly interested n how you held the thing in the end.

 

[byawor]

This is how I did it. Drill and tap the three holes with center hole at x0y0. Rotate the block 90 degrees y stays at zero, set x0 at the base move y to y.495 and x to .687 these are the dimensions in the drawing. Picture shows where the hole would be and it just does not look right. I think it is ok in y but should be further up in x. I think the problem is that the "base" is too thick by about 50 thou. However there is no dimension given in the drawing. I hade the push rods adjustable so The hole maybe doesnt have to be exact but its kind of hit and miss. The casting is made using the original as pattern.
Bob

 

[Peter Twissell]

Thanks for the explanation, Bob.
I assume you machined the base flat before drilling and tapping the holes?

 

[Ringsnapper]

Yes can’t wait to get started on the heads.
Just an update on the crankcase casting. I’m hoping to fit the oil pump to the crankcase so I‘m working on the various gearing for the cam, timing, and oil pump. Most of the spur gears and the helical gears I found as stock items in the HPC Gear catalog. I looked around in the US , Boston Gear etc. but didn’t get much joy. I only needed to cut one gear in the end for the crank shaft as the bore on the HPC gear is 5/16 and the crank shaft is 1/4 in.

I expect they would have made a custom gear if I’d asked. (The cost of shipping from UK to US is really expensive).

Also fitted the oil pump gears after drilling the inlet and outlet ports.
One point to note, and kind of obvious but the drawing calls for a 1/2 in dia recess to be drilled for the helical gear pinion shown below ( the upper most bore with a steel insert in it ). It’s really 3/8 in dia. , 1/2 in would break through the casting side wall.

Rgds
RS.

 

[byawor]

Had a look at the HPC website gear pricing seems really good. I have all the gears I need but paid a lot more than what it would cost from them.
Bob

 

[byawor]

Couple attempts at rocker arm supports. First thought I would try lost wax. Made silicone mold and cast the wax. Worked ok but I had trouble making the plaster mold, tried couple times but could never get it to fill properly. The silicone mold will stand low melt alloy and makes a pretty nice piece but heavier and not as strong as aluminum. Second attempt is a steel mold as shown> tried it with wax and it seems ok will melt aluminum later this week. If anyone wants the waxes to try casting I will send them to you.
Bob

 

[Ringsnapper]

I’ve never tried casting with lost wax, the burnout procedure always seemed long and complicated with temperature profiles etc. to get the wax out and dry the plaster sufficiently. I guess the original Chenery castings were lost wax.

I finally got around to fitting the lower half of the crank case. This is the casting bought from Keystone. I’d been putting it off because it needed a good bit of hand filing to remove metal from the front and rear beneath the flanges and get them wide enough to drill for the attachment bolts. The front is particularly awkward with many compound angles to contend with. The foundry left a lot of metal presumably to help with pattern removal in the sand.


Spot drilling for the 7BA screws but will use 3-48 UNC.

 

[peterl95124]

great work on a great engine !

my favorite sources for small gears are stock-drive-products in the US and rpcgears in the UK,
I'm in the US but have used rpcgears for some 15/48 helical that SDP doesn't stock.

 

[byawor]

Couple of pictures of a "real" Gypsy head

 

[Ringsnapper]

In the quest to get the sump, crankcase and oil pump fitted together I needed to complete the crank shaft which meant get the oil ways blanked up where needed , cut a key way for the 15 tooth gear and generally fit the bearings and end caps with properly sized shims.

A bit of skimming on the bronze bearing ends was needed here and there but generally the crank fitted well enough and I got the bolts down tight with the shaft turning smoothly.
Also shown is the camshaft assembly trial fitted with the cam segments in place. Cams are not hardened yet, might need to wait for warmer weather.
I was a little concerned that the cam dimensions (lengths) might need adjusting given the crankcase is a DIY effort but in fact the segments worked out quite well with only a little adjustment required.

Here‘s the set up for cutting the cams with a blank bolted onto an eccentric shaft about 0.528 in offset and using a graduated disc to keep track of the profile cutting. The profile is cut 10 degrees at a time. Its a very similar set up to Les Chenery’s V twin engine design. Cut the first profile surface ,stop, advance 10 degrees, cut the next profile and repeat 23 times. 22 for the exhaust cams.

With much of the internal assemblies and gearing in place I made a trial fit of the three castings.
The oil pump was cast before the crankcase and I had not made any allowance for shrinkage so it was a relief that it more or less went together without too many problems. I was worried there would not be sufficient metal for the studs around the gear casing, but it just made it. It was nice to turn the crank nut and see the oil pump gear turn smoothly. Just roughed out the gear case profile on the crankcase here.
Can‘t wait to get on to those heads!

 

[johnmcc69]

Fantastic work!

John

 

[Ringsnapper]

Decided to keep going with the oil pump casting and complete all it’s machining just in case there is a hidden gotcha that might hold things up.

Ready to assemble the oil pump.

So the bearing for the magneto drive shaft was completed along with the cross shaft. The 90 degree helical gearing mated up OK and seemed to turn freely. My version of the oil pump housing seems to be a bit wider (front to back) than the original so all the shafts are longer than the drawing. I was keen to test the oil pump but I had to re cast a pump housing cover as there are bumps in it to take the bronze bushings and on my original casting the bumps did not align correctly with the pump gear shafts. Fortunately it was a one and done exercise.

I can say there was quite a bit of ‘fitting’ involved in getting the pump working but eventually it did draw oil in and and push it out.

As I had needed to make the pipe fittings for the pump I decided to keep going with the brass work and make the oil distribution pipe that feeds the main bearings which runs down the outside of the crankcase. There are six 0.25 in banjo fittings that are silver soldered up to accept the copper pipe. One has 7/32 “ pipe fitting that connects up to the oil pump.

These are fiddly things to make so I made a jig shown below to hold all the parts for soldering.

 

[mole42]

Lovely work! As ever, it’s the jigs and fixtures that takes the time but the work would be impossible without them!

 

[Ringsnapper]

‘A little while later’ …..I finally get around to the cylinder heads and boy did I underestimate the work needed to get them finished. There is a lot of machining on these guys and ample opportunity to mess up. These were the final four out of about ten attempts, though two of them didn’t get very far so maybe call it eight attempts. I have to agree that the rocker support arms are challenging. I couldn’t bring myself to try another casting so milled them from block using the drawings and some photos of a completed engine. Made about six of them in the end, they are tricky to keep hold of as mentioned above.

 

[Ringsnapper]

It seemed that the drawing leaves some of the geometry of the exhaust porting to the builder to figure out and it was that triangular arrangement that cost me at least one or two attempts before I got it so the there was clearance for the head bolt in that corner and the port lined up with the valve. I found that until you actually try it it’s very difficult to see how it works. Probably would have been better to draw it out in CAD first.

 

[D and D]

Lovely work! As ever, it’s the jigs and fixtures that takes the time but the work would be impossible without them!

So true.