Camshaft phasing

[Kool_Biker]

As I am inching towards my 1K Km service, I know I will be confronted, again, with the same dilema I had when I was assembling my engine about a short while ago: Despite using a brand new cam chain, I was unable to align the two exhaust cam gear marks (in red) with the head surface at TDC.
So I settled for the compromise shown in the attached pic, with the exhaust cam probably 'advanced' by 1 tooth, which really does not feel right to me.

P1090392 (1).jpg

The bike works well and pulls wonderfully (although I've never ridden another CBX before to compare )
I do not want to go into cam indexing at the moment, this can wait for a later time if ever.
But, I should be able to adjust a little bit better, and wonder how?

Two questions:

1. Is the 'TDC' mark line on the crank, consistently accurate?

2. To what extent does cam phasing affect compression?
When hot and with valves set deliberately on the loose side, my engine does between 136 & 150 psi, i.e. somewhat less than I would expect.
Could this be telling us something about cam phasing?

Best, Aris

[daves79x]

Aris:
I would say your exhaust cam is one tooth off. Your intake cam is about where all mine seem to fall at TDC, just slightly forward of horizontal. The exhaust should closely match that. If your top tensioner is not tight in the photo, once you tension it, the cam will be off even more, relative to the intake. Your bike obviously runs reasonably well as is, but upon your next service, I'd try re-indexing the exhaust cam and see how that looks. Post up some photos and I should be able to tell you if it's correct. Don't know if this affects compression or not only one tooth off, but 150 is pretty good. I've never measured close to the factory spec on any engine I checked, and most of them ran very well.

Dave

[Kool_Biker]

Thanks Dave, this is very useful.

From your extended experience re my 1st question? "Is the 'TDC' mark line on the crank, consistently accurate?"

Cheers, Aris

[daves79x]

Aris:
You would have to use a piston stop and degree wheel to find absolute TDC. For duffers like me, the factory mark has always served well. I would think it would be pretty close since no chain stretch comes in to play. The only error would be the factory mark on the crank being slightly off. Not sure if that answers your question.

Dave

[Kool_Biker]

Dave, yes it does.
If the factory mark serves you well, it should surely cover puny my needs as well!
Thanks again, Aris

[Kool_Biker]

As the engine is ready for its 1000 Km service, I would like to decide whether to change the existing positioning (phasing) of my cams relative to TDC, or not.

So here's what I found, earlier on today:

P1090737.jpg

Crank position at TDC

P1090735.jpg

Exhaust cams position at TDC

P1090736.jpg

Inlet cams position at TDC

CLEARLY, for now, I would prefer not to touch them , as I am sure there will be many opportunities to play with them in the near future.
Your thoughts?

Cheers, Aris

[daves79x]

I spoke incorrectly in my first post - no wonder this is confusing. I meant to say that the EXHAUST cam marks are usually slightly forward of the head surface - as your pictures show. The INTAKE marks should be relatively the same, and it looks like yours in the first photo (without all the tensioners and oil pipes) may be rotated backwards a tooth. Now see below:

From that photo, it looks like you are OK, but I'd need to see both dots on both cams. I know that's near impossible to photograph. With the tensioners and guides in place, it looks nearer to correct than the previous photos. Usually, the exhaust marks are just slightly forward of the head surface and you want to match that with the intake. When assembling, if you move the intake cam one tooth either way, it usually becomes clear where it should go. See if you can get a shot of the entire top that shows all 4 dots.

Dave

[Kool_Biker]

Dave

Please help me with my reasoning, and forget the inlet cam gear for a minute.

As I think is clear in my latest attached pic and the position of the red index mark: at TDC the EXHAUST cam sprocket is ADVANCED by ~ half tooth.
Now I KNOW that if I move this sprocket backwards by 1 tooth, the red index mark will move ABOVE the feeler gauge datum, probably by the same amount.

So unless I am missing something, the issue is reduced to whether I want my EXHAUST cams slightly advanced (as is) or slightly retarded (in which case I will HAVE to move the exhaust cam gear one tooth backwards).

Thanks for your patience, Aris

[daves79x]

Aris:
I'm sure your exhaust positioning is correct. That's exactly where all mine end up. I'm saying that the intake should be relatively the same degree of 'forward' rotation, instead of 'backward' rotated. I'd just have to see what the intake looked like rotated forward a tooth. You are correct to get the exhaust cam right first - and you have. It will never exactly line up with the head surface. I'm just saying that I match the intake the same way - slightly rotated forward. You may be there in the final analysis, I just can't tell from your assembled photo and I was just noting that in the first photo in the thread, it looks like the intake may be one tooth off. That's about the best way I can describe it. I'm going out for a while until evening (it's 11:30 AM here right now) so I'll check back when I get home this eve. Hope I'm not further confusing you!

Dave

[Kool_Biker]

Dave, you are not confusing me, you are helping me out immensely!
Now that we have established that in the state the engine is right now (1000 Km), the exhaust positioning is correct, I will focus on the inlet and report back, hopefully with better pics.
Thanks a lot, Aris

[Kool_Biker]

Yeap, definitely Dave, my inlet cam sprocket is RETARDED by 1 tooth!
Question: What is the minimum I've got to do to move the inlet sprocket forward by 1 tooth?

Would removing the oil pipe, inlet cam chain guide and removing all tension from the inlet tensioner provide the chain with enough slack to rotate the inlet sprocket by 1 tooth? (he wished ... )

Thanks, Aris

[daves79x]

Aris:
I think that will do it for you. I'm sure you can slip the chain one tooth that way. I suspect you know by now. Hope it wasn't too much trouble!

Dave