timing

They list the timing to be 2.2mm BEFORE TOP DEAD CENTER. I'd rather take the guess work out of it and use something that's 2.2mm thick on top of the piston to measure it exactly. While the engine is being assembled with the head off. We could snug the cylinder with the nuts with spacers. What do you think?
A digital caliper could be used or a depth Gage too.

Bill, don't see any reason it would not work and would be accurate. Suggestion: drill the ends of a straight piece of bar stock to fit over the studs, then drill and tap a center hole for a fine threaded bolt. You could then adjust the bolt to protrude 2.2 mm from the bottom edge of the bar for the piston to come up against, use a lock nut to retain it at 2.2 mm. With different stud holes could be used on different engines and could be easily adjusted for different timing specs.

Steve

why wouldnt you have the head installed and use a dial indicator like husqvarna engineers in the manual want you to? are you saying this is guesswork?
besides with a the dial indicator its very easy to run something other than a set measurement.

I use the dial indicator method myself, but I take the step of finding true top dead center first using a piston stop. Bill's idea seems to have merit if the engine is already apart.

i can see using the piston stop, but how does that work differently than just using the needle on the dial indicator, and zeroing at tdc? (just wondering)

With the dial indicator installed, as you approach or leave top dead center there is a small amount of crankshaft rotation that does not move the dial indicator (dwell time). This amount varies dependent on stroke and rod length. Some feel that this amount is small enough to not be concerned with, I just have a preference to take the step to find TDC using a piston stop. I make a timing pointer that points to the flywheel, rotate the engine one direction up against the stop, make a temporary mark on the flywheel aligning with the pointer, then rotate the opposite direction up against the stop and make another mark. Half way between the two marks on the flywheel is TDC. Make a more permanent mark there. From then on, I can easily install my pointer, bring the engine to my TDC mark, set my dial indicator to 0, then back the crank to my correct timing on the dial indicator.
If I was using Bill's suggestion above, and using a tool as I described, I would use the tool to find TDC while rebuilding the engine, mark the flywheel/ rotor mark and set the timing all during the rebuild. Dial indicator timing changes would then be easier for me.
Sorry for the long winded response.
Steve

What do I think? What was the world like before the internet.

I like degrees instead of distance, I like a timing light though the pin in hole seems to not have a lot of error. If the spark plug thread is perfectly vertical that is the way to go. If the spark plug thread is on an angle the head off has it's advantages. Still top dead center can be located and then move onto degrees. I found the dial indicator more accurate than lining up the crank with the pin up and no cylinder. Depending on the health of your parts there is going to be some play in the big end and wrist pin, I was suprised how little on the one I did last.

Now how about which would you get a nice new Lecton carburetor or a nice new ignition with advance function?

no problem steve, i kinda figured you were going for precision, and theres certainly nothing wrong with that.. i have played with timing quite abit to where i do not feel such a small amount is worth troubling over unless you are blueprinting all your port timing heights as well and so on. thanks for the explanation though, no such thing as too much information here at the cafe.

fran, thats a great question...my answer is "both". at least the lectron will be going on my 87 430 project this summer. the motoplats will stay until they fry, i have good luck with them. more lighting output and an actual advance curve would be nice tho

Ahh, slight hijack Bigbill, but related.
I'm about to do 2 x new ignitions on my WR400's
One is a new power dynamo,
the second is an NOS motoplat I have.

I've never done one before, I have my dial guage and understand the 2.2 BTDC.

I believe the power dynamo has an ignition advance?, does this mean the 2.2 BTDC is still valid? or is there a different setting?

PS, I'm not sure what I'm lining up with the dial guage........must pull out the manual

Timing is not that critical, the 2.2mm figure is just a starting point, but the method would work. I don't know why you would need to do that since if you have the head off it is easier to use a dial indicator than with the head on.

Doesn't the original husqvarna ignition have the advance in them? The motoplat and the SEM?

Timing is timing unless the new ignition comes with other settings.

the motoplat has no advance, thats why they are sensitive to kickback.
not sure but i believe the sem has advance built in, they do not kick back as much.
the new ignition retard timing at low rpms (startup) then advance later for power...setting timing with motoplat is compromise. so timing is not timing.
if you look at timing specs, its often different between bikes equipped with plats or sems. different ignitions require different base timing settings. its a good question where to set a new ignition's timing as they often say "we can can only give you a starting point, tune on your own".

If we set the timing with the new ignition at 2.2mm then we're 2.2mm advanced more on the top rpm. The more the timing is advanced the higher rpm we achieve. If we set the timing exactly at "0" tdc then we lose that static setting of 2.2mm at the bottom end and top end. Now do we want a lion or a lamb.

The timing( static setting), the carburation(jetting), the porting, the pipe(chamber) play a key role all together in tuning for performance. While one thing will improve the performance when all the changes are done and they work together is were the excitement happens at the twistie.

What do you mean by the 2.2mm being the starting point? Have you gone more advanced? I have advanced the port timing. I advanced the static timing in the ported engines. My '81 husqvarna 250cr was ballistic at the higher rpms. Otherwise normal at the lower rpms till you wicked it and it was like riding a missile. Advancing the exhaust port timing is moving it up in the middle and arching the port half the distance of the middle at the sides. Example if I move the port up 1/8" in the middle I raise it up 1/16" on the sides arching it. The exhaust exits sooner.

are you confusing port timing and ignition timing?, advancing igntion timing does not usually increase top end power or rpm.. advancing favors bottom end and retarding favors top end to a point

Here:

In my 82 Cr 250.

Sheet says 1.95 mm BTDC or 18 Degrees.

So if I use degree wheel and dial indicator, both match.

That's how I verified I'm gee hawing!

i think you lot are thinking too far into it
if you are doing it in mm then it really is simple and the dead spot of crank rotation at tdc is irrelivent . set the timing when the piston is 2.2 mm lower than the highest point the piston travels to .

if you are doing it in degrees then yeah a piston stop will be needed

my 82 500 is at 2.2 currently . is there anything to be gained from working towards the first stated factory figure of 2.8 ? or will it just make it even more voilent through the midrange ?

how do you like the digital indicator? i have an ancient suzuki indicator, lol

Love it! Made my own spark plug holder out of spark plug bottom, two sleeves I pressed in and clevis pin.

Whopping $3 bux. Had nother one but it for water cooled engines. Had to come up with something longer for air cooled fins. View attachment 55755

Advancing the timing gives you more rpm. At some point the power will drop off but we're not going that far advanced. Port timing is totally different. With advancing the exhaust port by raising it the hot exhaust gasses start to leave sooner into the chamber at the same time the intake suction starts to draw in sooner. The two stroke cycle is being advanced port timing wise.