Lakeside53
Stihl Wrenching
I needed to make some accurate and repeatable port timing measurements.
It's not all that difficult in concept- print out a degree wheel, tape it the flywheel and point something at it. But... if you want to use it over and over again, get repeatable results, and be able to accurately calibrate TDC each time, something better is required.
I found a scrap of sheet aluminum about 2mm thick, scribed a 4.25 inch circle (so it will fit on most still saws), rough cut it on the bandsaw (you could also use a jig saw), then just because I have one... trued up the edges on a lathe... The center is bored out to 10mm, but I'll probably make it 12 then put in sleeves to suit different cranks.
Go to www.machinerycleanery.com, and download their nice degree wheel. Load it into Microsoft paint or whatever, and scale the PRINT output until you get it to fit exactly on the disk you made. In my case, it was 24%. Squirt a little spray adhesive on both, slap togther, and cut the excess off with a razor knife.
Mount it on the flywheel stub with a washer in front and behind and tighten until it has a firm friction fit. For a pointer, I used a scribe mounted in magnetic base holder. The cheap holders work great for this type of stuff and are only about $20.
Now the part that's tricker.. how to determine exactly where TDC is... it's not as easy as it looks.. but there is a dead easy way!
Set your wheel to about TDC. Either screw in a piston stop, or as you can see in my case, with an open cylinder, put a 1mm washer on top of the piston. Turn the wheel to the left, record the reading, then to the right and do the same. Adjust the wheel until you read the same measurement left and right. Remove your stop, and the zero mark is TDC...
My "stop"
Left = 15 degrees
Right = 15 degrees
TDC and BDC are at zero (on this scale)
It's not all that difficult in concept- print out a degree wheel, tape it the flywheel and point something at it. But... if you want to use it over and over again, get repeatable results, and be able to accurately calibrate TDC each time, something better is required.
I found a scrap of sheet aluminum about 2mm thick, scribed a 4.25 inch circle (so it will fit on most still saws), rough cut it on the bandsaw (you could also use a jig saw), then just because I have one... trued up the edges on a lathe... The center is bored out to 10mm, but I'll probably make it 12 then put in sleeves to suit different cranks.
Go to www.machinerycleanery.com, and download their nice degree wheel. Load it into Microsoft paint or whatever, and scale the PRINT output until you get it to fit exactly on the disk you made. In my case, it was 24%. Squirt a little spray adhesive on both, slap togther, and cut the excess off with a razor knife.
Mount it on the flywheel stub with a washer in front and behind and tighten until it has a firm friction fit. For a pointer, I used a scribe mounted in magnetic base holder. The cheap holders work great for this type of stuff and are only about $20.
Now the part that's tricker.. how to determine exactly where TDC is... it's not as easy as it looks.. but there is a dead easy way!
Set your wheel to about TDC. Either screw in a piston stop, or as you can see in my case, with an open cylinder, put a 1mm washer on top of the piston. Turn the wheel to the left, record the reading, then to the right and do the same. Adjust the wheel until you read the same measurement left and right. Remove your stop, and the zero mark is TDC...
My "stop"
Left = 15 degrees
Right = 15 degrees
TDC and BDC are at zero (on this scale)
