Briggs & Stratton 6S - A Beginnig

[Deanofid]

Always glad to see more on this one, Bill.
You're right! More whittling to do, for sure, but after seeing how much you've
done on this build so far, it's sure to be an outstanding job.

Dean

 

[b.lindsey]

Thanks for checking in Kevin. With any luck I will at least get the cylinder bored out for the cylinder liner tomorrow and get the liner shrink fit into it this weekend.

Thank you too Dean. The exterior contours of the crankcase don't worry me as much as hollowing out the inside...all kinds of surprises lurking in there . Even when not making chips though, working on the drawings is a big help in planning things out.

 

[ozzie46]

Looks good Bill. You're doing an incredible job.


Ron

 

[b.lindsey]

During lunch today, I managed to bore and counterbore the crankcase block for the cylinder liner. Over the weekend I will heat the block, freeze the liner and hope it falls in smoothly and then equalizes to a good tight fit which should withstand engine operating temps somewhere between 250-300 degrees F. That's the theory anyway with thanks to Doug Kelley for his advice on this. The 2nd picture also shows the full size carburetor which I will be working on overr the long holiday weekend.

Ron, thanks for your comments too !

 

[rklopp]

Bill
I have a few recommendations for your shrink fit. First, machine a reduced diameter at the base of the liner to help you get it started straight. Second, make up a plug gauge to check the true diameter of the bore in the block and find out the true level of interference, find any taper, etc.. Shrink fits are no place for errors associated with comparing, say, telescoping gauge readings for the female part and direct micrometer readings for the male part. Third, consider assembling upside down with the liner supported on a loose-fitting iron or steel mandrel that is chilled along with the liner. Grab the cold mandrel with the liner sitting on it in your bench vise, then drop the hot block down over top of it. The extra chilled mass of the mandrel will help keep the liner from warming too quickly and seizing. Finally, calculate how much delta temperature you need to get lots of clearance. I would avoid heating the aluminum more than 400 deg F.
RKlopp

 

[b.lindsey]

RK, thanks for the advice. As it is calculated. the block bore is .0025" undersized. At 350 degrees F for the block and 30 degrees for the liner, that will give a clearance of .0014". Conversely, if the mated pair is operating at 300 degrees the aluminum will expand more than the liner but there would still be an interference fit of .0008" which should be more than sufficient. I suspect that 300 degrees is excessive as an operating temp for short runs, meaning the interference would likely remain at .001" or slightly more. There is also a chamfer on the bottom of the liner which should help it start in straight. I understand your idea of placing the block over the liner, but I feel I can have better control holding the frozen liner than the HOT block. It will be much easier to see and locate the liner over the bored block as well with the block oriented upright. I'll let you know how it works out.

 

[rklopp]

I would be scared to try this with only 0.0014 clearance during assembly. I am afraid the relatively thin liner will heat very quickly against the comparatively massive block, and ...bye bye clearance. Been there done that more times than I care to recount. I think you would be fine with a couple tenths interference at engine operating temperature. That liner is not going anywhere. I would reduce the current interference accordingly.

 

[Deanofid]

Bill, another route for this cylinder liner fitting would be to go with High Strength Sleeve Retainer, made
by Permatex. This is exactly the application this stuff is made for. It's also good up to 400°f.
It will give you some breathing room when it comes to shrink fit clearances for this piece. You could
make it an easy push fit, and rest easy about the thing getting forever stuck pressed just halfway
into the cylinder.

NAPA stores sell it.

Dean

 

[b.lindsey]

Hmmmmm....well I didn't get to these posts before giving it a try. The wife had taters baking when I got home so I stuck the block in the over with them...350 degrees on convection so good air movement. Put the liner in the freezer at the same time. Couple of hours later, after dinner, I get the block out, set it on a heat proof cutting board, quickly got the liner from the freezer and gave it a try. Was a little tight but a little wiggling to line it up and it literally fell right in. Rest assured though, I was ready to pull it out quickly if anything hadn't felt right...but it was all over in less than 5 seconds. Letting the block cool is gonna take a little longer. I'm bettin this thing is in there for keeps. Photo below. I do appreciate all the input though !! The only other thing i need to check is that the piston fit is still as good and as smooth as it was before in the loose liner.

 

[Deanofid]

Well, you have it done then! Good going, Bill. That's the way I did it for the Vacuum engine, too,
with oven and deep freeze. I thought the Sleeve Locker would make it less nerve wracking, but
you've got it knocked!
Hope you enjoyed the taters. ;D

Dean

 

[b.lindsey]

Thanks Dean, the taters were fine but the grilled ribeyes were even better ;D

BTW, the cylinder still fits the piston like a glove.

 

[rklopp]

:bow: Glad to hear the shrink went well!

 

[b.lindsey]

Thanks RK. Might have been just lucky, but I did breathe a sigh of relief when it fell in. You were right on one thing...it sure didn't take long for the liner to heat up.

 

[b.lindsey]

What a perfect almost Fall day today, mid 80's and low humidity...perfect for being out in the shop. Here though, I just have access to the Sherline equipment but that is perfect for getting started on the carburetor. Due to the irregular shape, the carb will be built up of numerous individual parts, soldered or threaded together. I started off turning the taper for the main body, then turned it around to drill the two bores of 3/16" and 1/4" which meet at the point where the butterfly valve body will go. This is shown in photos 1 & 2. Photo 3 shows milling out the 5/16" hole for the valve body after drilling a pilot hole first. I was worried about this step because there isn't much meat left on either side of the hole and while i half expected a mangled mess and a do-over, a very slow feed avoided that. Photo 4 shows milling the body on the outer end down to where the bore begins. A small end mill was used to open up this hole into the carb body before using the boring head to make the .250" radius on the end nearest the chuck. This flat is where the air filter seat will mate up with the carb body.

 

[b.lindsey]

Next up was the cylindrical part that the butterfly (for lack of a better term) valve will fit into and rotate to give more or less air/fuel mixture to the engine. Didn't take any in process pics of that since it was pretty straight forward. This does have a 3/16" opening on one side and a 1/4" opening on the other to mate with the two identical bores in the main carb body piece. I drilled/bored/reamed it to .250" which will be the OD of the butterfly whatchamacallit thingy that will fit into it. For now its just a snug fit into the carb body and the shank of a 1/4" drill bit was used to align it as shown in the second photo. The last pic gives some idea of size for this sub-assembly. Now onto the air filter seat...mainly some relaxing lathe work.

 

[b.lindsey]

Just as a reference, the below .pdf file will give some indication of where this is headed...lots of itty bitty parts and no idea yet that it will even work. If not at least it will make for an interesting paperweight :big:

Thanks for checking in.



View attachment BS6S-Carb4.pdf

 

[Deanofid]

Hey, you've made a $75 kazoo, Bill!

Just kidding. Looks great so far!

Dean

 

[b.lindsey]

Hey Dean....I knew it looked familiar and you hit it on the head...a kazoo. Gosh hadn't thought of those in years...senior year in high school to be exact...The Headland High School Senior Marching Kazoo Band...or something like that. Longer ago than I care to admit but back then we thought it was great fun...another and far more innocent time unfortunately.

More pics coming up shortly...

 

[b.lindsey]

The afternoon was still young so I figured I'd take a stab at the air filter seat. Ended up being as much mill work with the rotary table as lathe work but my luck is running good this weekend so what the heck. I think the pictures are pretty self explanatory so I won't comment. Besides it after 5PM now and time for my daily ration of Sierra Nevada Pale Ale...or wine...or better yet....

Oh and please no comments about this thing now looking like some sort of drug paraphenalia...after all this is a family type forum...more in tune with M&M's, Noids, Kazoos, etc. ;D

 

[b.lindsey]

And the last two...for now. Hmmmm....not much space there between the air filter and valve body, but neither is there much on the prototype engine. If need be I can round the bottom of the air filter housing a bit more and gain some there.

Happy Labor Day to those who will be celebrating it!!