Another 277 rephase question

[hotdog]

Hey all,

I have a question about the 277 re-phase, I have built heaps of dirt bike cranks before but never done a re-phase, so is a new adventure for me.

Here goes, the cam chain drive sprocket on the crank, when it gets notched for the drive locator/key is that for the 270 re-phase only.?

I have been doing some research on the web & seems to me this is the case, just would like some clarity on it from someone who's been there.

P.S. I have started an album for my build & will try to update regularly - search street tracker or Hotdog, not sure how to post or link pics to threads yet.

Cheers.

 

[bradical]

Im in the process of a rephase also. I am under the impression that you press the drive sprocket off and realign it with the notch in the other half of the crank so the timing marks are still usable on the left hand side case. If I am wrong someone please correct me.

Brad

 

[mrriggs]

The timing marks are relative to the left crank throw. You can re-phase the right side of the crank to any position and move the sprocket anywhere and it will not change this relationship, when the pointer says TDC it means that the left cylinder is at TDC.

When you separate the center of the crank, the sprocket comes off on the right half, pressed onto the shaft. You can leave the sprocket on the shaft and cut a new notch in the left side to receive it. Or you can press the sprocket off and align it with the notch in the left side before pressing it back together.

If you keep the sprocket on the shaft and cut a notch, then the sprocket will maintain it's relation to the right cyclinder. In this case you will want to keep the cam sprocket aligned to the right half of the cam when it is rephased.

If you press the sprocket off and keep it in it's original slot when the crank is assembled then the sprocket will maintain it's relation to the left cyclinder. In this case you will want to keep the cam sprocket aligned to the left half of the cam when it is rephased.

If you are already planning to degree the cam then it doesn't really matter which way you install the crank sprocket. The difference between the two positions is only 3 degrees.

 

[hotdog]

Thanks Mr Riggs,

I hav'nt pressed my crank apart yet so that does explain a lot.
Going off what you have written - if I Press off the crank sprocket to realign the slot to maintain it's relation to the left cyclinder, then when TDC is indicated the timing marks on the cam & cam sprocket should line up "as per normal".

I will be degreeing the cam also.

Cheers.

 

[mrriggs]

It depends on how you install the cam sprocket.

If the cam sprocket is lined up relative to the left half of the cam then, when the left cylinder is at TDC, the notch in the sprocket hub will face up and the dot on the cam sprocket will line up with the machined surface "as per normal". But the dowel pin on the threaded end will face up when the right cylinder is at TDC.

However, this would be true whether you kept the crank sprocket aligned to left side of the crank or kept it on the right side of the crank.

With the crank sprocket lined up to the right side of the crank and the cam sprocket lined up to the left side of the cam, you could still put the left cylinder at TDC and install the cam with the timing marks lined up as usual. At least, it will appear to be lined up correctly. If you degree the cam you will find that the cam is actually three degrees advanced. The reason for this is because you advanced the crank sprocket 83 degrees relative to the left half of the crank and then installed the cam four teeth retarded to get the marks to line up. Each tooth on the sprocket represents 20 degrees so you advanced it 83 degrees then retarded it 80 degrees (4X20) which leaves you at 3 degrees advanced.

Now that is assuming that you have a brand new timing chain with stock head and base gasket thickness. With an old timing chain you could actually end up pretty close to right on. With new chain and thicker gaskets you could end up WAY too advanced. That is why it is always a good idea to degree the cam whether you are re-phasing or not.

 

[hotdog]

OK thanks, yes motor will have new cam chain etc plus Athena gaskets -I beleive I have read the Athena head gasket is thicker than stock.

Anyone have a good link for degreeing a cam..??

Then would'nt pressing the crank sproket onto the left crank & not re-notching it be simpler.??
Wound'nt re-notching be a somewhat delicate operation to get it right without making a mistake.?
How are your cams set-up.?

Sorry soooo many questions, I'll have a better idea once I've done it.
People like yourself & Punklasar have good advice to give & I Just want to understand the reasons why & not just go through the motions.

Guess I better get a degree wheel.

Cheers.

 

[mrriggs]

I have also been discussing this with hotdog via PM and he suggested I post it here for others to see.

...I don't know if you include any information with your cams.? but please let me know what loctite has been used on the screws & how the timing (cam sprocket degreeing ) has been set-up in relation to the crank sprocket..?? E.G. what needs to be done to the crank once split & prior to re-assy (notching of sprocket..?? etc)
...

I don't send any info with them but I can answer any questions you have.

I use Red (high strength) Locktite on the screws.

I mark the cam sprocket on the right side of the cam before removing it. After re-phasing the cam, I put it back on and line up the marks.

When you separate the crank, leave the sprocket on the right side, and cut a new notch in the left side, then the cam should be timed correctly.

When timing the cam, the notch on the sprocket hub will point up when the left cylinder is at TDC.

When the right cylinder is at TDC, then the dowel pin on the threaded end will point up and the dot on the sprocket will line up with the machined surface.

I do recommend that you degree the cam since there are other variables that effect cam timing.

I assembled my motor this way and when I degreed it, it was right on the money, no adjustment necessary.
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