Briggs & Stratton 6S - A Beginnig

[b.lindsey]

Arnold, thanks for checking in. I went back yesterday and re-read your thread on the elbow engine too after seeing the pictures you posted recently in the finished projects section. That is one of the most elegant interpretations of the elbow that I have seen. Its somewhere on my to d0 list and when i do get to it I can' only hope it turns out as nice as yours.

Bill

 

[b.lindsey]

Got more done on the cam gear today. Photo 1 shows the blank after the lathe work was done Photos 2,3 and four show the set-up on the mill using the angle plate, rotary table and gear cutter mounted in a modified slotting saw arbor. The teeth are being cut ar a 25 degree angle as per the original. I am happy so far with the results thoug the final test will be how it meshes with the 18 tooth gear which has to be cut now for the crankshaft. I'm keeping my fingers crossed.

 

[b.lindsey]

The last four pictures for today show the cam gear after the teeth were cut and next to the prototype. The cam lobes still need to be milled but that will wait until the crank gear is cut to make sure the two gears mesh correctly at the calculated center distance. I have also left the angle plate/rotary table set-up just as it is so the teeth angles will be the same. Since this is the first gear I have ever cut I can only hope the calculations were all done correctly. I checked them over and over on paper and with CAD but not confident enough yet to cut the cam lobes until I actually see the gears working together as they should. A simple fixture will be made to simulate their relative positions in the crankcase.

 

[kustomkb]

Looking really good Bill!

All the best with the test fit.

 

[steamer]

I have also left the angle plate/rotary table set-up just as it is so the teeth angles will be the same. ...

Hi Bill,

I think the helix angle has to be opposite for the crank gear.....I think.... ???

Might want to check that for sure.

Dave

 

[b.lindsey]

Dave,
Yes you are right. What I should have said was that I am leaving the 25 degree angle set on the angle plate and leaving the rotary table attached as it is. If I then turn the angle plate around facing to the right rather than the left and still cut the teeth from the back side, then the helix angle should be reversed. Great observation on your part though and I very much appreciate the warning. I'll let you know how it turns out.

Bill

 

[b.lindsey]

As Dave pointed out, the helix angle of the crankshaft gear has to be opposite to that of the cam gear. To achieve this the angle plate and rotary table were just turned around 180 degrees from the way they were when cutting the cam gear. This is shown in photo 1. The18 tooth crankshaft gear was then cut. A simple fixture was made with a 3/16" post for the cam gear and a 7/16" post for the crank gear spaced .964" center to center which is the calculated center distance for the gears. After a little deburring of the teeth on the crank gear (1018 steel) and filing the tooth points of both gears by a few thousandths they were checked on the fixture with good results..no apparent interference and little if any slop in the mesh of the gears. Finally I could take a breath again!! The fixture is shown in photo 2 with both gears. Photo 3 shown the gears alone with the obligatory M&M for size reference. Finally, if it posts, is a short video of the gears turning on the fixture. The .964 center distance will now be used to locate the cam gear axis in the crankcase relative to the crankshaft.

View attachment Cam Gear.wmv

 

[gbritnell]

Boy the gears really came out nice. I had reservations about the straight teeth but in the video it looks like there's no problem at all. I think I might have opted to press the cam into the gear just in case something happens to one of the lobes, then the whole thing would need to be made over.
Are you doing any work on the block? I can't wait to see this thing come to life.
Very nice work so far.
gbritnell

 

[b.lindsey]

Thanks George. Lets hope nothing happens while cutting the cam lobes. Once I reference and mark the location of the timing mark on the cam gear, all of the angles for cutting the lobes have already been worked out and drawn up. As always some patience (especially with the Sherline equipment) and thinking before cutting will hopefully avoid such problems.

As for the block, nothing has been done recently other than what has been posted already. Several things needed to wait on the successful completion of the cam and crank gears. Their positions in the block (the crankshaft location has alread been machined into the block) determine the locations of the valves, etc. Now I think I am at a point where block progress can continue and I am excited about that too and it will make this collection of stray parts look much more like an engine.

If nothing else I have a newfound respect for how Briggs turned out tens of thousands of these and similar engines in the 40's and 50's. Its such a simple looking engine...very basic and no frills...until you get into it and try to duplicate that simplicity.

Thanks for checking in...more on the block soon

Bill

 

[swilliams]

Very nice job on making the helical gears Bill :bow:

 

[steamer]

Great Job Bill!

Can't wait for the cam!

Dave

 

[b.lindsey]

Thanks Steve and Dave. For a first go at making gears I have to admit I was pleased with the outcome as it had been one of the things I was worried about doing. Now I'm all smiles and will have them run in well just from spinning them 'round on the fixture before they ever see the inside of the block.

Bill

 

[Deanofid]

That is definitely a 'wow' thing, Bill, cutting gears like these as your very first ones!
They look lovely the way I see 'em. Great work!

 

[b.lindsey]

Thanks Dean. Still haven't had the time to work on the cam lobes yet but am hoping to do that tonight. One of the "optional" projects which our students can choose to do in the machine shop lab here at the university is an 18 tooth spur gear done out of aluminum. I have been teaching the theory as part of the lecture part of the course...the various formulae, use of dividing head, etc. but being honest with them I have had to say that I had never cut a gear before. If nothing else, that monkey if off my back now ;D

Bill

 

[b.lindsey]

The Big Brown Truck delivered a few goodies today...some O2 drill rod for the crankshaft and valves and tappets and through pin for the cam gear, 1/4-28 LH tap and die for threading the flywheel end of the crankshaft and making the locking nut, and some .037 and .045 music wire for the intake and exhaust springs. Which leads me to a question for the IC guys that make their own valve springs. I need the ID of both springs to be .312" How much undersized should the mandrel be for winding the springs in order to achieve the correct ID needed. The music wire is still pretty stiff even in these smaller sizes so I am sure it will tend to spring back some over the OD of the mandrel. Is this just a trial and error thing or are there any guidelines out there for this. The springs will be identical except for the wire guages. With a pound of each size wire on hand there is definitely material for error if needed but am hoping someone can give some guidance here.

Thanks,

Bill

 

[Deanofid]

Bill, I have a couple of articles in the Tips and Tricks section for making springs. I've made a gob of them
and find it to be a bit of a trial and error thing to get them the exact diameter you want. I think Marv put
a program in one of those two threads that helps to figure mandrel sizes, though. Have a look:

http://www.homemodelenginemachinist.com/index.php?topic=8253.0

http://www.homemodelenginemachinist.com/index.php?topic=8258.0

These tell how to make extension and compression springs, and also easy heat treating for them. Your music wire will make springs you can use just as they are, but they will last longer and perform better
through high cycle counts if you heat treat them. It's easy.

Oh, second link shows compression springs, but you might want to have a look at both threads, as the
basics are laid out in the first.

Dean

 

[BlakeMcKee]

Where do you get your material from Bill? There is this place called metal express that I found here in Charlotte but I was wondering if you get it from somewhere local, and cheaper? Your engine looks good, keep it up. Looking forward to your future post! Thanks.

- Blake.

 

[b.lindsey]

Dean, thanks for the links, I will look at both of them. I have access to a small heat treat furnace at work that may come in handy too and plan on using it for the tappets at least. If I have any further questions I will ask. Thanks again!!

Blake, I have used Metal Express yes and i use them a lot for school as well. They have been a good supplier generally though not necessarily the cheapest. There is also a good scrapyard up near Harrisburg but you have to kind of look around or ask for what you want. For things like drill rod, I usually use MSC. The stuff I got today I ordered yesterday and it shipped ground from PA and still arrived today. Other than that I have lots of brass and aluminum that I have collected over the years from doing mold work

 

[b.lindsey]

Dean,

Those were both wonderful tutorials and I have downloaded Marv's MANDREL program as well. As soon as I get back from a Thanksgiving trip to Atlanta I will get started on making the wire guide since both spprings will be from wire larger than .025". Certainly looks very do-able as does the heat treating process for the wound springs. As noted above, with a pound of each size wire there is plenty of practice material until I get it right. Thanks for pointing me to these posts written with your usual clarity. Another adventur to look forward to now

Bill

 

[b.lindsey]

The semester here is finally over (except for grading final exams) so things have quieted down enough to squeeze in a little shop time. First up were the inlet and exhaust valve springs depicted below. Thanks again to Dean for his great tutorials and to Marv for the MANDREL program which both helped a lot. Just a few pictures for now before I fall off the board completely, but there will be more shortly as the valves and tappets take shape and now that I can get back to finishing up the camshaft too.

Nothing too exciting, but the first three pictures show the mandrel as the spring is started and finished and once the mandrel is removed from the chuck. The last picture shows the finished springs (except to Dean's recommended heat treating which I will do). Didn't have an M&M handy but the ID of the springs is .312 and both are .635-.645" tall. The inlet spring is .037" music wire (on the left) and the exhaust spring is .045" music wire (right).