Timing Off?

6 replies to this topic
  • cowboyona426

Posted April 12, 2002 - 02:45 PM


I just had my bike torn down so I could check the valve clearance. I attempted to follow the service manual in doing so, but ran into a few snags. First off, my rotor had two marks on it, and H and and I. When the I was lined up with the hatch mark in the case, the cam lobes were not opposite eachother, indicating TDC on the compression stroke according the service manual. The lobes were actually never truly opposite each other, and the E and I on the cam wheels were directly across from another. Am I just being dense, or is this normal? The bike runs fine, so I know the timing isn't as haywire as it seems like it should be. Any help would be appreciated.

  • John_Lorenz

Posted April 12, 2002 - 03:54 PM



The Timing is not off, it appears this way for whatever reason. I posted in "Question / Concern" Yesterday. Today I have found a few things out.

First, Thanks to Motoman for responding with his remarks this put me on a wild goose chase.

Here is a Snap of what you are talking about and I will explain below the pic

Posted Image

Ok the skinny on the miss align CAM divits.
I spoke to an old friend a very old friend who has a couple of thumpers running in the lacal area pro class's (No Surprise) He also has built or is building a awsome 426 for half miles. Here is his scoop. (BTW I took a chance and he was at his old shop, I have not seen hime for years).

Anyway, this is normal as Motoman points out, However the Cams should be adjusted at TDC mark the (I). The divits will appear at a slight angle but even on plain. This is the adjustment point

Slack Point
is when the divits are at the plain with the case about 1/8 past TDC (I). (AS shown Above

Valves can be checked the for Max allowance at slack, Although he says Idealy it should be just a slightly losser fit.

Again he stated you can sand with 400 - 600 grit to pollish down the shims to you liking (This is something Motman and others have used for fine tuning search that thread for more info.

All in all unless you are pumping 5- 10 more horse out of the beast set the clearance at TDC (I) as the manual states and dont worry about the appearnce of out of time..

Hope it helps :)

[ April 12, 2002: Message edited by: EgoAhole ]

  • freestyle111

Posted April 12, 2002 - 04:46 PM


the first time i changed timing on my wr i was concerned because when i lined up "I" with marks on case dimples on my cams were slightly off.i called up [yamaha]service dept and the mechanic told me the best way to align motor at "tdc" was to pull sparkplug and stick a dowel rod or long extension in sparkplug hole.just make sure its long enough that when the piston is at the bottom of stroke it still sticks out hole.

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  • cowboyona426

Posted April 12, 2002 - 06:20 PM


Thanks Ego, that makes me feel better. I don't trust the Yamaha mechanics around here, the only time my bike was at the dealer to get work done they *$^&!/ it up. Now I've got a new riddle for you- is it normal for compressed air to come out of the cylinder head breather hose? I never noticed my bike doing it until after I checked valve clearance today. I just hope its all sealed up alright. Let me know your thoughts.

  • John_Lorenz

Posted April 13, 2002 - 03:42 AM


Ya the back presure is normal on any combustion engine (HEnce the Breath holes).

Think about this for every action a reaction, So the Engine Builds presure on the compression stroke why ?
1: Sealed cylinder. i.e. rings,seals and valves
so becouse the engine is sealed hee the revearse is felt on the upstroke and down stroke. The moter is actually sucking in air from the tubes to equalize presure in the cases, and then pushing the air out on the down stroke.

So the techincle aspects of this is
1: Seal those tubs with filters they breath :)

Let the Fire Storm begin

[ April 13, 2002: Message edited by: EgoAhole ]

  • Mark_Cantrell

Posted April 13, 2002 - 05:00 AM


The vacuum and compression (just mentioned by EgoAHole) in the crankcase as the piston rises and falls makes up one of the 'missing' strokes on a 2stroke. The vacuum of the rising piston draws the air in through the carb (intake stroke) and when the piston comes down, the resulting crankcase pressure (reed valves keep it from going back out through carb) pushes that A/F mixture into the piston.

Since our bikes don't need this, and we don't have other pistons that rise out of phase with it, have to bleed the air out of the crankcase. I saw a picture of a wierd box on (Chad's?) SX bike that was to scavenge this air from the crankcase.

The other missing stroke (exhaust) bleeds the bottom 1/3rd of the power stroke using power compression to force combustion byproducts out exhaust ports.

Sorry, I'm bored.

  • John_Lorenz

Posted April 13, 2002 - 05:40 AM



Good point, Yes this is ture in 2 strokes, but adding that in the event of any moving part I.E. Trannie, clutch and so on the physics creates a vacum. This is built by on by sealed cases and so on. Man this can get real deep real quick

Bottom line Cowboy

Ya its normal.... :)

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