Werowance builds a webster

[Brian Rupnow]

If you have anything that can work to 5 decimal places, go for it. As a general rule, numbers used in mechanical drawings are rounded off to three decimal places, or even two, depending on the degree of accuracy required. Only very critical fits may be given a fourth decimal place, because most shops don't have machines that will work to such close tolerances. When you get the crankshaft set to 15 degrees, (before the piston reaches bottom dead center) the cam should be positioned so that the rocker arm is just touching the valve, but not lifting it yet.

 

[Mechanicboy]

You can make a 15 degree angle of cardboard or plywood and place it on the crankshaft and set as the baseline is in parallel with the base of the motor, align the crankshaft and crankpin with line of 15 degree angle . Turn camshaft until the rocker arm touches the valve stem without opening the exhaust valve before attaching the gearwheel/flywheel to the crankshaft.

 

[werowance]

Hi Mechanic boy, I modified my crank to have counter balance weights so mine is not flat as the plans called for. but had I done it like that then yes I could have used my angle blocks and 123 blocks to get the proper angle. thanks for the input and hopefully someone else building this engine who does make it by the plans properly will see this and it will help them.

 

[Mechanicboy]

Hi, Werowance. My engine has balance weight on crank, no problem --> Align the measure tool with the circle who are visible on crank shaft and let the crank pin lay on the measure tool before setting the cam and fastening.

 

[Bill Lawson]

I dropped algebra when they told me That Pi are square and I was smart enough to know that pi are round. Enough of that, I too am building a Webster in my winter habitat. I don’t have the drawings with me, so I am following your progress with interest. I am not very keen on cross drilling the flywheel to secure it to the crank. I will if I have to, but I wondered if a small key way would work and the cam being a slip into the flywheel hub and secured with a small setscrew

 

[werowance]

got the muffler made, next I realized I forgot to make the flywheel spacer as well as mill the flats on the piston wrist pin, and still need to make the carb adapter. getting close...

 

[Brian Rupnow]

Looking really good.--Brian

 

[werowance]

very slow going lately, u joint on my trucks right front axle went out this weekend then after that I had a couple days fight with the dreaded "cant stay out of the bathroom" thankfully that's over with. anyway I managed to get the carb adapter done and started on the flywheel spacer last night.

 

[Brian Rupnow]

If it runs as good as it looks you are going to have a real winner there.--Brian

 

[werowance]

got the flats milled on the wrist pin, realized I hadnt drilled the oil hole in the rod so I did that, finished the flywheel spacer and installed the rings on the piston. I then did a little break in by hand. compression seems good. all that's left is to make the jig to drill the cross holes in the flywheel and then drill / pin it and to make ignition circuit. then if it runs ill make a proper fuel tank.

a tip that might help others installing the piston in the cylinder after the rings have been installed - a zip tie. it compressed the ring and without to much fuss I got it in.

only picture I have is of the flats milled.

 

[CFLBob]

Looking forward to seeing it run. Like Brian said, it runs as good as it looks that's going to be a real winner.

 

[werowance]

made the jig last night to hold the crank in place so I can drill the flywheel. before I do that I just wanted to double check, the drawings show the crank hole to be 2.0 from the bottom, then add .162 for a total of 2.162 from bottom to where I need to drill the hole in my jig? that's what I did and it appears to be right but I want to double check and show some photos before I actually drill the fly wheel. on my jig its just rough sawn on the top but where it matters the bottom is milled and square and the hole measured from the bottom up.

 

[Brian Rupnow]

However, in this case, the small gear is attached to the flywheel and this is kind of a two part deal. Webster wants the crank throw positioned so that the piston is 15 degrees before bottom dead center, and also wants the cam set in a position where the rocker arm is about to begin lifting the exhaust valve, hence the exact positioning of the flywheel in its rotation.

 

[werowance]

but is the crank in the proper 15 deg spot by the measurements I called out? it looks right to me. but just questioning my measurements. if that is correct then next I will rotate the flywheel with the crank locked in place until the rocker arm just "starts to lift the exhaust valve off of its seat" as the plan says. I assume that just a barely move it description?

 

[werowance]

now I have another question, I think its called valve lash. the space between rocker arm tappet and valve tip. when the cam is at the fullest possible closed position - or at the lowest point of the cam and rocker arm how much space or gap should there be between the rocker arm tappet and valve stem? I cant find any info on it in the instructions, the drawing - where it shows the engine fully assembled shows a gap but it doesn't have any dimensions on that page. should it be 0 lash adjust till it just touches or almost touches?

 

[aka9950202]

I set it to .25mm and it runs. Just a lucky guess on my part.

Andrew in Melbourne

 

[Mechanicboy]

For the mostly of all model engines the valve gap is 0,04 mm-0,1 mm. The gap is determined by heat of expansion in the material. 0,25 mm is too much for the small engine due the timing will be reduced affected by big gap since the small parts in the model engine do not expanding so much as the large engines. (0,25 mm for intake valve can you find in the car engine, too much in model engine. Also i am car mechanic)

 

[Brian Rupnow]

Leave about .010" to .015" gap when the cam is not influencing the rocker arm. This gap can be between the rocker arm and the valve, or the rocker arm and the cam, or a combination of both.For setting the valve timing, the cam should be touching the rocker arm and the rocker arm should be touching the end of the valve , but not yet lifting it. That is where they should be before you drill the crankshaft and flywheel at the position of 15 degrees before bottom dead center. The ONLY reason that gap is there is to make sure that the valve isn't held open by anything on the compression stroke.

 

[werowance]

Brian and Mechanic boy, thank you very much!

last night I disassembled everything for final inspection and cleanup and discovered yet one more thing I had forgot to do. countersink the hole on the bottom plate for the screw that holds the head block down. at the time I didn't have the right size screw to go by - now I do. finished that all up, took the mating surfaces between the head and valve block and put them on a surface plate with 1200 grit and now they are nice and flat - hopefully I can get by without a gasket but ready to if I need to. my wife bought me a belated birthday gift yesterday to, a large shop fan. said I was sweating profusely the other day when working on my truck. shes wonderful.

 

[Brian Peters]

up .25 is correct but to be 0.25 off the diagonal line which looks like 60 not 90 to the horizontal line you would need to calculate the offset to the right as
right = cos(60) x 0.25 = 0.125 should get you there if I still remember how to do trig.