Topic: Question about valve clearances and crank position.

[Jayelwin]

So I'm adjusting my valve clearances and I have a question about crank position. I'm cheating and I have my engine dismounted and my valve cover off so I can see the camshaft. I've heard very specific things about the position of the crankshaft for each valve and it sort of doesn't make any sense now that I can see the whole thing. The camshafts at each point has a lobe but about 75% of the camshaft is just round. If the lobe is not under the rocker it seems crankshaft position would be irrelevant as it's just going to be sitting on a round portion of the camshaft and the valve will be closed. Can I just turn the crank until the lobe is a way from the rocker and test my clearances there or do I need to be precise about the position of the camshaft?

[City Boy]

Hi.For the most part you are correct but you might want to check clearance in various cam positions to verify the theory.There may be quieting ramps near the start and end of valve lift.

[DH]

There may be quieting ramps near the start and end of valve lift.

+1.......

[MCRider]

Setting the crank at 1-4 TDC will allow you to adjust 4 valves. Turn it 360° to do the other 4, per most manuals.

Other than that I wouldn't trust eyeballing the base circle of the cam. ITs not perfectly round and you should find top dead center twice, not too hard.

[lucky]

So I'm adjusting my valve clearances and I have a question about crank position. I'm cheating and I have my engine dismounted and my valve cover off so I can see the camshaft. I've heard very specific things about the position of the crankshaft for each valve and it sort of doesn't make any sense now that I can see the whole thing. The camshafts at each point has a lobe but about 75% of the camshaft is just round. If the lobe is not under the rocker it seems crankshaft position would be irrelevant as it's just going to be sitting on a round portion of the camshaft and the valve will be closed. Can I just turn the crank until the lobe is a way from the rocker and test my clearances there or do I need to be precise about the position of the camshaft?

Let me make this simple for you.
When you adjust the valves intake and exhaust for each cylinder
just make sure that the cam lobes for that cylinder are both facing downwards at 45º angles.

That is all you have to know.

Look at the crank indicator marks at that time.   LUCKY

This is NOT a theory.
IT is fact.

[Jayelwin]

I'm doing it so the lobe is visually about 180° away, pretty much turning until the lobe is on the other side. I do see the subtle rises. So maybe the camshaft is round only about 2/3 of the way around. But if the lobe is far away I'm good, right?

[lucky]

I'm doing it so the lobe is visually about 180° away, pretty much turning until the lobe is on the other side. I do see the subtle rises. So maybe the camshaft is round only about 2/3 of the way around. But if the lobe is far away I'm good, right?

No that is not correct.
Use the method I just described in the post above .
If you have just rebuilt the engine  my method will work too.
That is when it is most confusing.

[lucky]

I hope he is talking about a CB750. He did not tell us which bike.
It would be the same for the CB500 also.

[Don R]

 This looks like a good opportunity to use the book method and observe the location of the cam in relation to the rockers. Then maybe when you have to adjust in the frame you will be more comfortable doing it.

[Jayelwin]

Yes. 1975 CB750.

[MCRider]

I'm doing it so the lobe is visually about 180° away, pretty much turning until the lobe is on the other side. I do see the subtle rises. So maybe the camshaft is round only about 2/3 of the way around. But if the lobe is far away I'm good, right?

Just curious why the shyness about using the TDC mark? Eliminates any unknowns about ramps etc. IF #1 is TDC Compression; then #2EX and #3 Intake are ready also. Roll through 360°; #4 is ready, #3Ex and #2 IN. Done.

Problem with pointing the lobes away is you can't see them when the cover is on.

[Black 750K8]

I'm doing it so the lobe is visually about 180° away, pretty much turning until the lobe is on the other side. I do see the subtle rises. So maybe the camshaft is round only about 2/3 of the way around. But if the lobe is far away I'm good, right?

Just curious why the shyness about using the TDC mark? Eliminates any unknowns about ramps etc. IF #1 is TDC Compression; then #2EX and #3 Intake are ready also. Roll through 360°; #4 is ready, #3Ex and #2 IN. Done.

Problem with pointing the lobes away is you can't see them when the cover is on.

I'm with you this is the way I do it. I don't know why some people want to turn the crank just a little and do one valve at a time. I think Dave 500 likes to do it that way and he is pretty smart about this. But I just don't get it . Different strokes for different folks I guess. Still comes out the same when finished.

[Duanob]

You are waaaay over thinking this! I usually don't agree with Lucky but he's right, do what the manual tells you, millions of SOHC4 Honda owners can't be wrong.

[MCRider]

You are waaaay over thinking this! I usually don't agree with Lucky but he's right, do what the manual tells you, millions of SOHC4 Honda owners can't be wrong.

No manual I've seen tells you to do what Lucky is saying to do. They say what I've been saying to do.

[Black 750K8]

You are waaaay over thinking this! I usually don't agree with Lucky but he's right, do what the manual tells you, millions of SOHC4 Honda owners can't be wrong.

I agree that is the way the manual says to do it. Who is over thinking the OP?

[Jayelwin]

So using the TDC markers makes sense especially given future adjustments will be made with the cover on. But THEORETICALLY isn't what I'm saying correct. 

[TwoTired]

I've done the CB550 and the CB750 both by the book (two crank positions) and the 4 crank position method.  They both result in success.
The book method minimizes work time, that's all, which is important to Honda shop mechanics and their management.

If the piston is at TDC between the compression and the power stroke, the valve better be fully in their seats and that means the lowest portion of the cam profile.  To do this with each cylinder means four crank positions.

Honda figured out which valves were at the lowest cam follower position with only two crank positions, and (surprise) that works, too.

[MCRider]

So using the TDC markers makes sense especially given future adjustments will be made with the cover on. But THEORETICALLY isn't what I'm saying correct.

Could be, but...I wouldn't be comfortable acting on your theory. We just don't know, as mentioned, how much of the base circle is really the lowest part of the lobe. The only way  to be sure, unless you're a cam engineer, is to use the TDC mark. IMO.

Having just spent many hours degreeing a cam with a dial indicator, I see that you could use the dial indicator to confirm the lowest part of the lobe and how much. Lot of work for no great benefit.