Briggs & Stratton 6S - A Beginnig

[Rustkolector]

Many years ago there was a group of model builders that built a dozen or so Briggs and Stratton model FH engines in half scale from patterns made by Norm Brockelsby. I have only seen one of these engines, but I remember that the air shroud on the model FH was made of cast brass. It was a very true likeness of the original shroud, but obviously was made thicker due to the casting process. Unless you looked closely, or tapped on the shroud it was hard to tell it was cast. The external finish was polished smooth. Your mockup shroud method could be revised to make a good lost wax type casting pattern. Brass foundries are not usually hard to find. Good ones are a bit harder to find.

Jeff

 

[b.lindsey]

Jeff, that is also a good idea and you are correct that the FDM RP method can readily be used forcasting patterns with minimal changes to the 3D models for draft, shrinkage, etc. This entire engine lends itself to castings and at some point I may look into that but then there would have to be a market for it too to make it worthwhile. Meanwhile, as time permits I am developing 3D drawings as well as the 2D working drawings. Thanks to you and others for all the ideas!

Bill

 

[b.lindsey]

Several hours today were spent doing some very light milling and a lot of hand filing to finish up the con rod, wrist pin retainers, and final reaming/countersinking/oil groove cutting in the split crank pin hole. Picture 1 shows the whole sub-assembly. Picture 2 shows the additional contouring (mostly filed) on the lower end of the con rod. Picture 3 shows the teeny internal retaining ring installed on one side of the wrist pin. Finally Picture 4 shown the size of the cutter abd the remaining retaining ring.

 

[b.lindsey]

Monday I want to bead blast the con rod as a final finishing step but now on to other things. Tomorrow I hope to start on the rings for the piston and maybe the small oil flicker arm and keeper that fit on the lower end of the con rod so the whole sub-assembly can be finished. One other picture for today and that is of all the bits and pieces done thus far.

 

[Deanofid]

Oh, the con rod ended up really nice, Bill. The factory guys have nothing on you!

Nice 'family' shot.

Dean

 

[Maryak]

Bill,

The piston and conrod are works of art. :bow: Not to mention the whole engine. :bow:

Best Regards
Bob

 

[b.lindsey]

Dean and Bob,
Thanks for checking in. The "family" shot still looks a little sparse but still growing at least.

Bill

 

[Speedy]

Monday I want to bead blast the con rod as a final finishing step but now on to other things. Tomorrow I hope to start on the rings for the piston and maybe the small oil flicker arm and keeper that fit on the lower end of the con rod so the whole sub-assembly can be finished. One other picture for today and that is of all the bits and pieces done thus far.

hi Bill that is a great shot!
following with great interest.
Michael :bow:

 

[Noitoen]

:idea:To make the shroud out of thin aluminium :hDe:, you could use the temporary part to cast a male/female mould out of epoxy and then press a thin sheet of aluminium. Not the whole part, just the curved back side, then a rim around would finish it off with some soft aluminium solder discussed somewhere else in this site. scratch.gif

 

[b.lindsey]

Thanks Speedy, I did blast the con rod today and it looks ever better now i think.

Noitoen...I think at a minimum, the shroud needs to be 1/16" thick...that might form well enough, especially the soft aluminum sheet stock, but would have to factor in the time and cost of making the epoxy mold halves and making the solder joints still worries me some as far as getting all the edges rounded properly. I am sure with some practice the overall approach might work well, but it might take a few attempts to get there. I am too much a perfectionist, especially on a part that visible. Thanks for suggesting the idea though.

Bill

 

[b.lindsey]

Its been a few days and nothing new to report really since I have been out of town for 4 days and thus, no shop time I did tak a few shots of the piston and con rod after bead blasting though and include them here. Now that I'm back, i will be finishing up the oil splashing finger for the con rod and starting on the shroud this week. I have a lot of catching up to do on many of the other threads too.

Thanks for looking in.

 

[4156df]

Bill,

The bead blast is just the right touch. It's a shame to have to hide this part inside the crankcase. Maybe you need to sneak in a viewing port.

Dennis

P.S. The two center pops reminded me of my Dad, gone for many years. He taught me to always mark the cap and rod with a center punch so they'd go back together in the same orientation. Funny how little things can take you back.

 

[b.lindsey]

Thanks Dennis. I know it will be hidden but at least I will know whats inside. Even with a viewport I'm not sure much could be seen as there will be a lot of oil splashing around in the crankcase, but its a thought anyway. I still like nice shiney parts but for some the bead blaster has worked very well in replicating a nice cast look...most notable the cylinder head and the con rod.

Thanks for checking in. I am hopeful that over the summer, progress will accelerate.

Bill

 

[Deanofid]

It's a work of art, Bill. Craftsmanship, even if hidden inside a crankcase, is still craftsmanship.
Someday, we will all be gone, and some museum fellow will be taking this apart to clean it. He's going to see that the inside is just as nice as the outside and he'll think to himself, "This guy did nice work!".

Dean

 

[b.lindsey]

Thanks Dean,
Actually I think I should be taking lessons from you but if someday, someone were to say that, I can certainly think of worse epitaphs. For now...I am just happy to have gotten this far without too many major scrap box additions :big:

Bill

 

[b.lindsey]

Had some good shop time today and tackled the piston rings using a no heat treat method which Doug Kelly (Snow Tandem Engine) told me about and uses exclusively now. This was my first attempt at making rings so there was more than a fair amount of nervousness. I roughed out the OD and ID of the short piece of cast iron on the big lathe at work...could have been done on the Sherline but would have taken a lot longer. The final finishing cuts were made on the Sherline however, bringing the OD to the bore size of 1.000" + .030 and the ID to about .875"

After that Iparted off 2 sets of rings (hoping that would be enough). Each set has 2 compression rings and 1 oil ring. This is shown in photos 1 and 2 below. Next a .030 slottint saw was used to cut a gap in each ring as shown in photo 3.

 

[b.lindsey]

With the ring blanks done, a simple fixture was made so that the gap could be closed and held closed between the two halves of the fixture. A shoulder was turned on the chucked side of the fixture to hold the ring approximately centered while the OD was turned to the 1.000" bore size. This is shown in the photos below.

 

[b.lindsey]

After turning the OD, releasing the holding pressure of the fixture allows the ring to spring back open, but the ID still has to be machined. The next step of this method, and no doubt others, is to make a sleeve that the rings will very snugly fit into, again holding the gap closed meaning that the ID of the sleeve matches the OD if the rings at 1.000" The original bore of the ring blanks was apprx. .875" and the final ID needed was .902" Since the 2 compression rings are .040" thick and the oil ring is .094 thick, the sleeve was turned to the 1.000"diameter for a depth of only .094" leaving a slight internal shoulder to act as a back stop and very fine cuts were taken since only the snugness of the fit was holding the rings in the sleeve. In this case it worked well and the rings didn't even try to slip inside the sleeve. Both the fixture and the sleeve were made of aluminum. The first two photos show the sleeve and the third photo shows one of the finished rings...after 320 grit paper was used with some elbow grease to bring the final ring thickness to the required .040" (or .094" for the oil ring).

 

[b.lindsey]

I would like to say that the whole process went without a hitch and it pretty much did, but one of the compression rings was killed while turning the OD. I think insufficient pressure allowed the gap to open slightly and the tool bit grabbed it and the sudden stress snapped it. A second compression ring broke during installation on the piston, likely due to some overeagerness on my part. I was happy I had cut the two extras since I ended up needing them. Other than that I breathed a huge sigh of relief when the third ring finally snapped into place on the piston. The three installed rings are shown in photo 1. The other three photos show the piston fitted into the cast iron cylinder liner and I was very pleased with the fit. Obviously it will need some running in to seat the rings and to better lap in the cylinder bore, but for now the piston slides in the liner (with a good coating of oil) with what seems a "just right" amount of friction.

Thanks for checking in.

 

[Deanofid]

Just like the full sized example. Excellent work, Bill, and great work in writing it up, too.
Sure is looking good. (And still marveling at that fabulous piston rod.)

Dean