1989 Mach1 583 timing questions

[BrandonTKZ]

Hi Im currently doing a top end on my 583 that i got and i was looking at the timing while I have it apart and it doesn't make much sense to me. When the MAG connecting rod is at tdc the rotary valve lines up with the mark on the case like it should but the timing mark is like 1/4 rotation away. shouldn't the timing mark be on the 0 degree mark when the mag piston is at tdc? the first picture is when the mark is at 0 degrees

 

[pistonbroke800]

Im not 100% sure about the 583 but a lot of guys played with timing advancement and different rotary valves with the 670's to make a little more power. Maybe the guy before you was trying to get it to preform a little more.

 

[BrandonTKZ]

im not really worried about the rotary valve timing at this minute. im just asking about when the mag cylinder is at tdc should the timing mark on the crankshaft be at the 0 degree mark?

 

[pistonbroke800]

Ever check out dootalk.com? They have like a million doo guys that you could try and bounce that question off of also.

 

[BrandonTKZ]

ill check that out, I'm just quite confused about this

 

[BrandonTKZ]

i cant figure out how to post on there?

 

[lloydguy]

This should be the forum you want to post in,Mach Z / Mach 1 / Formula III Triples - DOOTalk Forums
or the S-chassisforum is here- MXZ / Legend / Summit / Grand Touring / Formula / etc. - DOOTalk Forums

 

[BrandonTKZ]

i put up a post on there a few days ago and no replies.. maybe i shouldn't worry about it? if it runs why stress it i guess.

 

[Modman]

OK first of all you are dealing with an incomplete engine to try and set timing so don't even bother, you need to assemble it first. Unless your crank has been twisted out of phase, once you assemble everything it will be fine. You need to get it fairly precise and you won't do that with just a pencil and trying to rotate the crank and guesstimate where TDC is.

Ignition timing is calculated before top dead center (BTDC) in most engine applications because by the time the ignition triggers the pulse, sends the pulse and ignites the fuel mixture, the piston has already travelled past TDC and is at peak or slightly on the downstroke (more or less - you want full combustion at or very shortly after TDC) and at max compression. If you left ignition until After TDC (ATDC) then you would not achieve full power as you would be igniting under decreasing compression/cylinder pressure as the piston travelled down, and full combustion may not be complete by the time the piston hits bottom of stroke. Also, in a 2 stroke application, your exhaust port would be opening and most of your fuel charge would escape before it ignited (or it would ignite in the pipe - backfiring - also one way to tell if your timing is wrong....).

Most of the Doo rotary engines were somewhere in the 0.065"-0.080" BTDC. I'd say the location of the timing mark on the mag and where the piston would be are pretty close right now. You need to assemble the motor and put a dial indicator on the mag piston, measure TDC and then line up the mark for the motor spec BTDC. Find the manual or call the dealer for the spec and set it up to that. But where it is now in relation to the piston being roughly at TDC is probably pretty accurate.

Hope that helps.