PVL-Do the math?

[wfopete]

While putting a PVL ignition on my Jackpiner the instructions for making the initial timing adjustment only give millimeters or thousandths references as opposed to degrees.  Why is that?  To get it right you need a dial indicator set up ($$), when a degree wheel would be much less expensive.  I can't understand why accuracy would have that much to do with it, since it is only a initial setting. Also by using millimeters to set the timing, every time the stroke of an engine changes it will require different timing settings, where as degrees will remain constant regardless of the engine (2 or 4 cycle) or stroke of the engine.  Has anyone converted the millimeter timing specs to degrees for a Jackpiner, so a degree wheel can be used to set the timing? Thanks.

Peter Petrick

'01 KTM EXC 520, '74 YZ 250, '86 Honda XR 250, '71 Hodaka 100, '74 SUZUKI TM 400, '73 Penton Jackpiner

[TGTech]

The amount that the piston moves, is proportionally relative to the length of the stroke AND the centerline distance of the connecting rod. If I have the stroke and the rod length, I can calculate the linear measurement's comparison to the radial measurement.

The linear measurement is more accurate than a radial measurement because of the tolerances that you encounter in the connecting rod bearings and piston pin fit.

Dane

[wfopete]

I agree, but heck measuring by degrees is good enough for timing millions of autos engines, why not here? Anyway Dane, I got the unit on and the bike fires up and runs great.  You just don't want to know how I made the measurement;). Thanks for the explanation. Dogone you engineers have a way with words!

Peter Petrick

'01 KTM EXC 520, '74 YZ 250, '86 Honda XR 250, '71 Hodaka 100, '74 SUZUKI TM 400, '73 Penton Jackpiner

[TGTech]

Pete,

   The difference between all those cars and trucks,is that they aren't two strokes and aren't anywhere "near the edge", like the KTM engines can be.

   On a number of different forums, I have explained that KTM has a history of going after horsepower by using high compression. High compression creates heat, as does ignition advance. If you have too much advance, you can create enough heat to toast your engine. Admittedly, the 175's weren't as bad as the 250's and 400's, but it's still worth paying attention to.

Dane

[firstturn]

As a Wise Man once told me and I stand by it;

 Not only that, but you have to take into consideration, the surface
quality of the polish on the muffler bearings too. Otherwise, all the
power can slide right out the exhaust before it is transfered to the
pinion.

Now that is pushing the limit on these 2 strokes.

Ron Carbaugh

[Big Mac]

A word from the cheap seats on tools for timing...

I'm all for not cutting corners and the benefits of quality tools, but hey, if I could afford that approach, I'd probably leave the wrenching to my private mechanic.

I finally broke down a couple of years ago and spent $13 (on sale, $10) on a 1" travel cheapo Chinese-made dial indicator, which I bought at my favorite cheap tool place, //www.harborfreight.com. As far as I know, no one sells a 14mm adaptor to screw into a plug hole that will easily accept a standard dial indicator...

...so I took an old spark plug and drilled the center of the electrode out of it, and then hacksawed off all but the threads I needed. It fit about snug in a 1/2" copper pipe coupling. I stuck a short piece of 1/2" copper pipe in the coupling on one end, leaving about 1" sticking out, and the 14mm threads in the other end, soldered it all up w/ the Benzomatic, and ended up with a tube threaded on one end to twist nicely in the spark plug hole.

I found about 4 o-rings that rolled up on the shaft of the dial indicator nicely and which offer a snug fit with enough resistance to keep all in place when the dial indicator is stuck into the tube. The o-rings used to roll off and get left in the tube until I applied the magic of a few thin swaths of duct tape below the rings, which did the trick to keep them in place.

This hokey excuse for a timing indicator has been a champ for the past 5 years now and I've been able to make it fit around the fins of CZs, Huskies and Pentons just fine. On the bikes with opposing plugs at about 45 degree angles (CZs) I even have the math somewhere to deal with the angle factor. Hope this helps someone!  Mac

[TGTech]

Thanks for the tip Mac. When I started reading your post, it immediately brought to mind the fact that I'd done the same thing, but perhaps with a little more complexity. I took a spark plug base and machined an aluminum sleeve that fit the indicator and then drilled and tapped the side of it for a set screw. End result, the same thing you have. Thanks again.

Dane

[DKWRACER]

Hummmmmm, got mine from MSC, only about 16.00...good ole Yankee engineering, the mind is a terrible thing to waste..Great post BIGMAC, think I got my threaded end from Checker, anti-fouling plug.................Tom...