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Fixing the how NOT to make an engine

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bogstandard:
This is a follow on post from this article,

http://madmodder.net/index.php?topic=1361.0

I thought I would show the members how I go about rescuing an engine that should really have been consigned to the recycle box.

After finding out that the machined port faces were square to the base bottom, I made up a quickie ali plate, with two parallel faces so that is could be remounted accurately into the vice after a little work was carried out on the casting.




Once the ali plate was tapped down onto a parallel, I levelled the port faces and tightened it to the plate when I had it running 0-0 along the parallel I was measuring against.




I was very surprised to find out that the casting is in fact brass, rather than the normal bronze. It must be that ST are cutting back on quality even further. They can't get much worse than the crap undersized cast iron castings that they are knocking out nowadays.

Anyway, getting away from my personal gripe, I roughly centred a 1/8" (3.2mm) endmill over each port hole and cut down to a depth of 50 thou (1.25mm).




Once all eight ports were machined out, I made some slugs of brass to fit in each hole.




A bit of flux (I am trying a new one and don't know what it will turn out like, it is Tenacity#5, supposedly even better than my favoured 4A) down the hole, a plug inserted, and a small ring of easiflo 0.5mm wire around each one.




A bit of heat until the solder flows, then a quick quench followed by half an hour in a citric acid pickle bath. I did notice that the new flux was still very active while the job was heating up, also I noticed that there was a lot more copper plating from the pickle bath than I would normally find. It looks like the whole casting is made of copper, whereas normally, there would be just areas around the soldering that were copper plated.




After a good dose of surface grinding and a little bit of mill work, the casting is ready again to be machined, this time with the holes in the correct place.
I did remove a few thou of casting thickness, but there is still plenty of meat on it to take it. The new port holes won't be as deep as the originals, as I will only be penetrating the slugs and picking up on the oversized and out of place holes that were in there before.



I did no more work on the crankshaft, as I need to get the cylinders into their correct positions first. I will eventually mod the crank disc thickness to take into account the thickness I have removed off the casting, only then can the crank pin be fitted.


Bogs

Brass_Machine:
Holy cr@p that is a slick fix John. I am impressed.  :bow: The plugs, were they press fit or was there some clearance?

Nice job as always.  :clap:

Eric

bogstandard:
Eric,

When silver soldering, there should always be a gap of around 0.002" (0.05mm). This is to allow the silver solder to flow under capilliary action into the gap and make a super strong joint. The mistake a lot of people make is to have the bits press fitted into the hole. Then when it is silver soldered, the solder only sits on the surface. When you come to do a bit of machining as I have done, the slugs would then not be fixed in position, and liable to be blown out when pressure is applied.

I have been rescuing these sorts of engines and castings for many years, so to me it is just another little job. you tend to remember how you have repaired bits in the past, so no learning curve to go through each time. Excluding the pickling stage, this was less than an hours work, so well worth doing, considering a new casting would be about 35 to 40 squid.

Very rarely do you come across a casting that can't be repaired and got back into a useable state. A coat of paint also helps in covering up a repair if it can't be blended in too well, as would happen with a silver solder repair on a cast iron casting.


John

shoey51:
 :bow: :bow: :bow: great work John I wish I had your skills.

back to square 1 with my loco project I was a bit slap dash with some of my measurements :(

bogstandard:
Shoey,

All my 'skills' have been picked up and fine tuned over the years, so don't worry, you will get there in the end. Time is a great leveller.

I too still make mistakes, but I am now a dab hand at covering things up and doing quickie rescues. So even though it looks like I have everything spot on, sometimes it is just a good cover up and modify job.

We are not talking about life threatening things here, so if it can be made to work after making a mistake, then do it. The sky won't fall on your head if you make a slightly thicker rod to fit in an oversized hole.

John

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