Topic: CAM Timing - Advance, Retard, Early, Late, BTDC, ATDC - I'm So Confused

[RSchaefer]

Well just to confirm again - The degree wheel is on the point base (crankshaft).  I did not use the spark plug stopper to measure "true" TDC, I used HondaMan's method - align the "T" for 1-4 on the point base with the pointer on the block, line up the horizontal line on the end of the CAM with the hash marks, notch up - that's TDC.

Then I set the intake and exhaust valve lash per HondaMan, intake 2-3mm, exhaust 3-4mm.  I set the dial indicator on the top of the valve keeper (#1), parallel to the valve and rotate the engine in the proper direction to go from zero on my dial indicator to .040."

With what appeared to be the same mounting position as my stock CAM sprocket (now using the Dynoman adjustable sprocket) I appear to be at 5-degrees BTDC.  I shift my dial indicator over to #2, rotate the engine until I get .040" on #2 intake and the degree wheel indicates 5-degrees BTDC from 2-3 "T" mark.  So I am consistent from intake #1 and #2 with this setup - 5-degrees BTDC.

Then I adjusted the Dynoman sprocket to were #1 & #2 are set to 10-degrees BTDC at the .040" lift.  Consistent from #1 to #2, same setup.

So it seems this is a 5-degree advance from the stock "F" setting?

[RSchaefer]

Jerry thus the heading of my thread - Advance, Retard, Early, Late, BTDC, ATDC - I'm So Confused

[RSchaefer]

I think it equals this:

Advance equals early and BTDC, intake valve opens sooner then stock
Retard equals late and ATDC, intake valve opens later then stock

[Don R]

Sounds right to me. the pros will say to use the intake lobe centerline method but you seem to have it correct this way. Be sure to rotate the engine slowly by hand to check rotation clearances.

[scondon]

Well just to confirm again - The degree wheel is on the point base (crankshaft).  I did not use the spark plug stopper to measure "true" TDC, I used HondaMan's method - align the "T" for 1-4 on the point base with the pointer on the block, line up the horizontal line on the end of the CAM with the hash marks, notch up - that's TDC.

Then I set the intake and exhaust valve lash per HondaMan, intake 2-3mm, exhaust 3-4mm.  I set the dial indicator on the top of the valve keeper (#1), parallel to the valve and rotate the engine in the proper direction to go from zero on my dial indicator to .040."

With what appeared to be the same mounting position as my stock CAM sprocket (now using the Dynoman adjustable sprocket) I appear to be at 5-degrees BTDC.  I shift my dial indicator over to #2, rotate the engine until I get .040" on #2 intake and the degree wheel indicates 5-degrees BTDC from 2-3 "T" mark.  So I am consistent from intake #1 and #2 with this setup - 5-degrees BTDC.

Then I adjusted the Dynoman sprocket to were #1 & #2 are set to 10-degrees BTDC at the .040" lift.  Consistent from #1 to #2, same setup.

So it seems this is a 5-degree advance from the stock "F" setting?

Looks right to me, RSchaefer.

 If possible, I would measure the exhaust lobe as well to make sure your set-up is measuring correctly. One thing to notice is that the stock cam has a "square" profile i.e the open/close numbers on the intake lobe are mirrored on the exhaust lobe(Intake o/c 5/35, exhaust o/c 35/5). Before advancing/retarding a square cam I make sure I am getting mirror readings from intake/exhaust lobes. You've already advanced your cam, but If your technique is good your exhaust lobe should also read 5 degrees advanced( o/c 40/0.....I think that's the right).

 HondaMan has surely done this procedure MANY more times than I have, so if you've followed his write up, and it looks like you have, then you should be good to go

[dave500]

dial the cam first and see what you have,,then alter the timing if you want,dont use the centre line method,its not as accurate.

[RSchaefer]

Well I got a PM from Mark and he seems to be continuing to state what I have been saying, EXCEPT he is now saying the stock "F" cam intake starts (0.40") at 0-degrees TDC and that I should be moving it to 5-degrees BTDC in order to pickup my 5-degree advance.

BUT, I thought the "K" was at 0-degrees and the "F" was at 5-degrees so to advance 5 more degrees I should be at 10-degrees BTDC.

I sent him a PM with this question, he is on the road for a few days!!

[Hinomaru]

I have not personally degreed the following cams listed below and cannot verify their accuracy. However, the Honda shop manual shows the following numbers published under the model specification pages:
 
14101-300-020: K0 to K6: Intake opens @5 BTDC and closes @30 ABDC

14101-392-000: F0 / F1 and K7 / K8 - Intake opens @0 BTDC and closes @ 40 ABDC

14101-410-000: F2 / F3: Intake opens @5 BTDC and closes @40 ABDC
 
Also, some limited discussion found in these threads:
 
http://forums.sohc4.net/index.php?topic=105567.0

http://forums.sohc4.net/index.php?topic=105053.0

[RSchaefer]

The Cheese is Getting Binding!

I THOUGHT ALL of the "F" CAM's were the same relative to advance, realizing the F2/3 have a different overall profile, specifically more lift and open longer.  In other words what I thought HondaMan said in his book was that ALL 4-years of the "F's" were a 5-degree advance over prior "K's."  I thought at some point K7/8 CAM's also advanced 5-degrees from prior K's.

Anyway this most recent info generates substantially more confusion as it seems the "K" was at 5-degrees BTDC and the "F0/1" was retarded to 0-degrees and then the F2/3 went back to the "K" at 5-degrees?

[scondon]

BUT, I thought the "K" was at 0-degrees and the "F" was at 5-degrees so to advance 5 more degrees I should be at 10-degrees BTDC.

That's what the supplements in my Honda shop manual state as well, but Hinomaru has conflicting info, also from Honda. I don't blame ya for feeling a bit confused.

Seems no matter what year or model those cams all have one thing in common....a "square" profile. Get the reading on your exhaust timing. Those numbers, when compared to your intake readings will clear it up for you what cam you have, and what the timing is.

Post your intake and exhaust readings here if it's not making sense to you

[RSchaefer]

OK when all else fails READ:

This is from the Honda Shop Manual for the CB750, ALL years with ALL supplements

K0-K4:
Intake Open 5-degrees BTDC
           Close 30-degrees ATDC

Exhaust Open 35-degrees BBDC
              Close 5-degrees ATDC

Nothing on K5/6 (assumed to be the same as K0-4)

F0-F1: (Longer duration on intake valve)
Intake Open 5-degrees BTDC
           Close 35-degrees ATDC

Exhaust Open 35-degrees BBDC
              Close 5-degrees ATDC

K7-K8: (Retarded from earlier models)
Intake Open 0-degrees BTDC
           Close 40-degrees ATDC

Exhaust Open 40-degrees BBDC
              Close 0-degrees ATDC


F2-F3: (Longer duration on both intake and exhaust from earlier models)
Intake Open 5-degrees BTDC
           Close 40-degrees ATDC

Exhaust Open 40-degrees BBDC
              Close 5-degrees ATDC

Soooooo it would appear that ALL of the "F's" were the same advance as the earlier K's "5-degrees."

AND to set the intake opening (.040") on my F0 at 10-degree BTDC would be a 5-degree advance from stock!

[KJ790]

OK when all else fails READ:

This is from the Honda Shop Manual for the CB750, ALL years with ALL supplements

K0-K4:
Intake Open 5-degrees BTDC
           Close 30-degrees ATDC

Exhaust Open 35-degrees BBDC
              Close 5-degrees ATDC

Nothing on K5/6 (assumed to be the same as K0-4)

F0-F1: (Longer duration on intake valve)
Intake Open 5-degrees BTDC
           Close 35-degrees ATDC

Exhaust Open 35-degrees BBDC
              Close 5-degrees ATDC

K7-K8: (Retarded from earlier models)
Intake Open 0-degrees BTDC
           Close 40-degrees ATDC

Exhaust Open 40-degrees BBDC
              Close 0-degrees ATDC


F2-F3: (Longer duration on both intake and exhaust from earlier models)
Intake Open 5-degrees BTDC
           Close 40-degrees ATDC

Exhaust Open 40-degrees BBDC
              Close 5-degrees ATDC

Soooooo it would appear that ALL of the "F's" were the same advance as the earlier K's "5-degrees."

AND to set the intake opening (.040") on my F0 at 10-degree BTDC would be a 5-degree advance from stock!

Going by this information, it looks like the F2/3 models had the intake retarded slightly and the exhaust advanced from the K models. You need to look at where the lobe centers are in relation to the crank. By keeping the same opening point but adding to the duration they increased the overlap and tightened up the lobe center separation.

[Hinomaru]

Rschaefer,

Your Honda shop manual w/all the supplements is more up to date compared to my old one. I would go with your shop manual numbers until if/when more info becomes available. Sorry for any confusion and like you say: READ