Cam Timing Way Off

[gaillarry]

Working on a donor engine to replace the tired out engine in my 83. The p.o. says he put in a new cam chain but never ran the engine.

I wanted to double check things so removed the valve cover. Chain looks new but the timing is way off. At TDC its about 4 teeth off.

To reset the cam this what I plan - pls correct me if I'm wrong

1) remove the cam chain tensioner
2) remove the bearings on the cam
3) realign the cam/sprocket
4) install bearings
5) install cam chain tensioner.

 

[5twins]

That sounds correct.

 

[I am Carbon]

sounds like a plan to me too

 

[CDNTX650]

i dont even understand how the hell people can screw that up. But its on here all the time.

 

[gaillarry]

I read a lot of older posts on cam timing before posting. I suspect the chain will jump a few teeth when putting the tensioner back in place.

 

[deadchef]

i went through the exact same thing this summer with cam timing almost identical.

 

[CDNTX650]

even stupider....marks dont line up...better put it back together.

 

[XSLeo]

In the Clymer book it isn't as clear as it could be on the cam timing. They don't refer to left and right on the notch and dot. If you don't look well enough at the pics you may get the cam in with the marks on the wrong side, left to the right.
Also sometimes getting a new chain on the cam sprocket can be a bit tough.
It's not as hard to get wrong as some think.
Checking like you did was a good thing. With the timing marks on the rotr at tdc the notch should be straight up and the dot level with the gasket surface.
Once you get the marks lined up you can hlod the cam with tension on the chain at the front while you screw the tensioner back in.
Leo

 

[XSLeo]

You may get enough room just by removing the tensioner to work the chain back one tooth at a time with out removing the bearings. I know this can be done with a worn chain.
Leo

 

[scharny61]

Is it possible to set your cam up 180° out? What I did was I sighted my left piston to be at the top of the stroke. Lined up the cam notch vertically and made sure the dot on the cam was set as per the manual. Is this correct?

 

[5twins]

I don't think it's possible. Both pistons rise and fall together on this motor (unless it's been re-phased). If the left piston was at TDC, the right one was too. You should be OK.

 

[I am Carbon]

5twins is right on as always

 

[rebel542]

At TDC, 2 lobes up on left, 2 lobes down on right. Timing marks should align.
Hope this helps.

 

[scharny61]

The lobe positions sound right from memory. Does a 650 fire every time the pistons hit TDC? I thought a four stroke meant that the first time the pistons rise, the fuel/air mixture is compressed and ignited and the next time they rise is when the exhaust gases are being pushed out. Does this sound right? If it is and you have the spark igniting on the exhaust stroke ; no ignition. Thanks for you interest and answers.

 

[aldo5468]

Yes, both plugs spark at TDC. In the cylinder on its compression stroke, the air-fuel mix fires. In the other cylinder on its exhaust stroke, nothing happens. This style of ignition is sometimes called a "wasted spark" design.

 

[scharny61]

That makes sense, thanks for clearing that up.

 

[5twins]

Well, that's partly correct. You get both plugs firing at every TDC and a waste spark in one of the cylinders with the later TCI and with a Pamco. With the old points set-up, only one cylinder fires at TDC, the one on the compression stroke.

 

[aldo5468]

I stand corrected and enlightened - I composed my response in the context of TCI taht I used to have (now BB).

 

[scharny61]

I remember having to set the points up to fire separately. Now I'm running the Pamco setup. The bikes running now so I reckon I did something right. Thanks again.