Plunket Jr. Build

[swilliams]

So next I made the liner. This needs a 1" hole bored in it that is 3.2" long. I started by putting some cast iron in the lathe and drilling it with a 7/8" drill. Note the use of the lathe carrier to eliminate the chance of the drill spinning in the Morse taper

Then I bored the liner out to about 50 thou undersize using a carriage stop to get the depth right

The outside diameter of the liner was made to about 2.5 thou bigger than the housing inside diameter.

 

[swilliams]

I needed to put a 10mm by 1mm pitch thread in the other end of the liner for the spark plug. As I didn't have a tap this size and couldn't be bothered tracking one down I just screw cut the thread. I have a 44 tooth change gear and by putting this on the tumbler stud instead of the usual 20 tooth gear, then setting the gearbox to cut 56 tpi, my lathe was set to cut a pitch of 0.998mm which was more than good enough for this job.

The boring bar for the threading is just one I made from silver steel.

 

[swilliams]

I then heated the housing up with a propane torch and put the liner in the housing

The inlet exhaust hole is not lined up perfectly between the housing and the liner but I think it's good enough. I'm reasonably happy with how it's turned out.

 

[b.lindsey]

Steve, you have made a lot of progress since i last check in. The silver solder work looks great by the way.

Bill

 

[NickG]

Beautiful fabrication work there. :bow:

 

[ozzie46]

Some really nice work here. That lathe dog trick for the drill bit is one I will stuff away for use later on. Thanks for the tip.

Ron

 

[cfellows]

Some very nice work there, Steve. Looks like you've done a lot of heavy lifting and it's turning out very nice. I'll be interested in seeing the process of making the engine base. That looks like another fabrication job.

Chuck

 

[swilliams]

Bill, NickG, Ron and Chuck, thanks for checking in and for being interested.

Bill, I hope none of the silver solder leaks, I think it's ok (cross fingers)

Chuck, yes the base should be an interesting part of the project. It is held together with screws and then silver soldered. You have just reminded me that I need to order some taps for the small screws I bought for the job.

Cheers
Steve

 

[swilliams]

I did some more work on the exhaust valve assembly today.

Here's a fuzzy pic of the main three parts. There is a steel housing that the valve seats against, the bronze valve guide which I made a press fit in the steel housing and the valve

There is an 1/8" hole through the valve guide which is not put in until it is in the housing.

 

[swilliams]

Here's a pic of the guide assembled in the steel housing. You can see the hole in the side that the exhaust exits through.

The next step is to drill the hole through the guide. I drilled a 3mm hole which needs to be 1.5" long which is more than 12 times the drill diameter. I find when drilling very deep holes like this in the lathe that having the drill held dead true makes a big difference with respect to the hole being straight. For this reason I used an ER collet chuck. Next I put a 3.1mm drill and then reamed it 1/8". The hole was still running true when it came out the other side. I know if I used one of my drill chucks that wouldn't have been the case.

 

[swilliams]

The valve seat was then turned in with a boring bar. This was done with the same chucking as used for drilling the valve guide.

Here's the whole thing put together. I lapped the valve seat a little with valve grinding paste

That's all for now 8)

 

[swilliams]

The last significant job on the cylinder assembly was to bore out the cylinder to it's final size. I did this with a 5/8" boring bar with a HSS cutter in it. The finish came out good and the bore is parallel. I think I will be able to get away without lapping the cylinder bore.

You can see the exhaust valve guide assembly now installed in the cylinder assembly. I made it a light press fit in the housing.

 

[swilliams]

Now that the cylinder assembly is largely finished next is the conrod. This is another job involving lots of milling.

This is how it started out, a piece of 1" diameter aluminum meets a 1" diameter endmill

 

[swilliams]

So the round is converted into rectangle section with a couple of holes that will become the big and little end

My basic strategy for making this is to base everything around a pin which will locate the big end. Here's the pin in the embryonic conrod

and here it is bolted to the mill table

I've set the dials to zero with the spindle in line with the pin. The conrod has two angles. I'll pick these up by swiveling on the pin attached to the table and then make use of a smaller pin in the little end.

 

[swilliams]

So now I start milling and can pick up the two angles by running an indicator across the pins

So the different pin diameters pick up the two angles by coming at either side with an indicator

 

[swilliams]

Then after some time things start to look more like a conrod

from here I move to the rotary table

and eventually

Finally I made up some bronze bushes and put in a small slot and hole at the little end for the oil passage.

It took quite some time but it's done

 

[NickG]

Lovely job on the conrod Steve, i've always been scared of doing complex shapes like that but you made that look easy. Sure it wasn't easy but will be a good method to follow.

Thanks for showing

Nick

 

[swilliams]

Thanks for the nice comments and for checking in Nick, much appreciated.

I've been doing some work on making the piston, here's a couple of shots of it after doing the basic turning

The grooves were put in with a tool I ground from HSS and the smaller diameter at the end is just to hang onto it while machining. I'll cut it off when I've finished.

 

[swilliams]

From here I stuck it on the rotary table and drilled and reamed the hole for the gudgeon pin. There is also a smaller hole for a little oil pipe to lubricate the little end.

I then set the rotary table up vertically and milled the clearance for the conrod as well as spotting a couple of holes for some grub screws which will secure the gudgeon pin.

 

[swilliams]

Here's the inside of the piston

and here's the piston assembled with the conrod

Next job will be to have a go at making the rings. I'm hoping to have a go at that on the weekend