Topic: My Cam Looks Retarded...

[74750k4]

or am I...   

According to Jay...

"Re: 1st attempt at degreeing a 750 HiPo cam - consults please
« Reply #16 on: March 18, 2012, 12:21:02 AM »QuoteThe general consensus on the single cam motors is the intake timing is important. Put that in and let the exhaust fall where it does."

So going with that plan, my Dynoman Performance DP117KHD specs say to make measurements with .020" of valve lift, at 0 valve lash...
Adjusted intake to 32 Deg BTDC with the 20 thou lift, checked EXH closure at 37 deg ATDC also with 20 thou lift. Measurements agree.

Big notch at end of cam is not vertical, it is retarded roughly 15-20 deg. as are the cam bolts in the slotted sprocket. The bolts are not centered, not at end of slot either...  about half way between centered and end. So does this matter? Am I, or is it, retarded?

[MRieck]

I don't get checking at .020...the rocker arm is barely off the lobe base. I have always used .040 or .050 so you are more "into" the profile. What are the opening AND closing #'s for both the intake and exhaust....that's how figure out your lobe center. Don't take those cam card #'s as gospel or you will be in trouble. Also....I take the readings at the actual lash I will be running....I find it more accurate. Your opening/closing #'s will be different BUT don't worry about that. Just get the opening and closing number so you can calculate the lobe center.

[HondaMan]

I don't get checking at .020...the rocker arm is barely off the lobe base. I have always used .040 or .050 so you are more "into" the profile. What are the opening AND closing #'s for both the intake and exhaust....that's how figure out your lobe center. Don't take those cam card #'s as gospel or you will be in trouble. Also....I take the readings at the actual lash I will be running....I find it more accurate. Your opening/closing #'s will be different BUT don't worry about that. Just get the opening and closing number so you can calculate the lobe center.

Yeah, what he said ^^^ ...

The Dynoman literature confuses the heck out of me. I have been doing it like MRieck, finding the lobe center of the intake and balancing that around the open/close, at .040" lift. What I have found with their 41/a cams is: they end up timing in much like an old Dodge V-8 cam, with equal open/close timing on both sides of the stroke, on both intake and exhaust. Dodge did this to improve the midrange torque for any given engine, but it does make them tend to run hotter due to the tendency to trap some of the spent gases in the cylinder during exhaust cycling.

[jmtuccini]

I believe the politically sensitive term is mechanically disabled

[MRieck]

I don't get checking at .020...the rocker arm is barely off the lobe base. I have always used .040 or .050 so you are more "into" the profile. What are the opening AND closing #'s for both the intake and exhaust....that's how figure out your lobe center. Don't take those cam card #'s as gospel or you will be in trouble. Also....I take the readings at the actual lash I will be running....I find it more accurate. Your opening/closing #'s will be different BUT don't worry about that. Just get the opening and closing number so you can calculate the lobe center.

Yeah, what he said ^^^ ...

The Dynoman literature confuses the heck out of me. I have been doing it like MRieck, finding the lobe center of the intake and balancing that around the open/close, at .040" lift. What I have found with their 41/a cams is: they end up timing in much like an old Dodge V-8 cam, with equal open/close timing on both sides of the stroke, on both intake and exhaust. Dodge did this to improve the midrange torque for any given engine, but it does make them tend to run hotter due to the tendency to trap some of the spent gases in the cylinder during exhaust cycling.

Right Mark....this is why Web stopped with the timing cards and said to "split" the opening and closing numbers. It is much more enjoyable working with separate In/Ex cams when engaged in cam timing. These SOHC are married to lobe separation. At least car guys get grinds that take that fact into consideration. Megacycle will work with you in regard to lobe centers (custom grinds) but it is still a disadvantage. Well.....I'm up to the challenge because I love these engines.

[MRieck]

I believe the politically sensitive term is mechanically disabled

....and yes.....I get it.

[Jerry Rxman Griffin aka MuthaF'er]

No, I think the correct term is metally challenged 

[70CB750]

No, I think the correct term is metally challenged 

^^ 

[MRieck]

So.....whats the deal. Are you looking for answers or talk??

[74750k4]

Looks like I'm getting both, but...

I thought a bit about this, changing the measured lift start to .040" from .020" will advance the cam timing a bit, as will measuring with the stated .005" lash instead of 0.0 lash. So I'm going to try it. The new problem is the degree wheel is removed now, and no way to check true TDC, so a piston stop is on order. Since I know for certain though that at .020" intake lift I am at 32 Deg BTDC, I might just use that measurement point to temporarily set up the wheel again, until I get that stop.

[MRieck]

Looks like I'm getting both, but...

I thought a bit about this, changing the measured lift start to .040" from .020" will advance the cam timing a bit, as will measuring with the stated .005" lash instead of 0.0 lash. So I'm going to try it. The new problem is the degree wheel is removed now, and no way to check true TDC, so a piston stop is on order. Since I know for certain though that at .020" intake lift I am at 32 Deg BTDC, I might just use that measurement point to temporarily set up the wheel again, until I get that stop.

I would use the piston stop and get a fresh baseline. Changing the lift point to .040 and increasing the lash to running spec won't physically advance the cam....it will give you different opening and closing #'s. Example...if the intake was opening 30 degrees BTDC it will now open at 25 degrees BTDC (with the .005 lash). Same basic thing with the .040 measurement point. I forget what cam you are using but you will probably come up with something in the 15 to 20 degrees BTDC for the intake opening.
 You sound like you have the basics down for cam timing which is a very good thing. You have to sit and wrap your head around it (and read about it) but once it clicks it is a great feeling.
 The only other thing I'd say is start with the exhaust timing as that is more critical as the piston is ascending as the valve is closing. If the timing is very late the crown will hit the valve. If ANY contact is felt....ie...the crank will not turn.....stop and make some changes. Again...I'd get a piston stop (or make one from an old sparkplug) and get your TDC exact.

[74750k4]

Currently I set the cam to open the intake at 37 Deg. BTDC of crank rotation, at .020" of lobe lift per the Dynoman Performance DP117KHD (Kenny Haraman D Grind)Cam card (attached as PDF in 1st post.) If I still use their 37 Deg. BTDC crank angle opening measurement position, at the crank, and then change to your 0.040" of lobe opening lift, I will have to physically advance the cam to get to that extra .020" of lobe lift. No???  If I also add in .005" of valve lash... again, I will be physically advancing the cam to make up for that .005" loss of lift, at the crank manufacturer's stated measurement point of 37 Deg. of Crankshaft angle. This all assumes of course that using the opening measurement point of 37 Deg. of BTDC crank angle is correct. If that is not correct, what crank angle should it be? Jay seems to like setting the intake position, and let the EXH end up where it will. So there seems to be some disagreement here. Alternatively, there is always setting the cam lobe centers to the cam manufaturer's stated crankshaft angle values, and then check openings, and closing positions. Seems like the opinion is, that I can't trust any of the Mfg's data??? So make up my own??? Seems a bit scary.

[74750k4]

oops 32 Deg BTDC, not 37...

[HondaMan]

Currently I set the cam to open the intake at 37 Deg. BTDC of crank rotation, at .020" of lobe lift per the Dynoman Performance DP117KHD (Kenny Haraman D Grind)Cam card (attached as PDF in 1st post.) If I still use their 37 Deg. BTDC crank angle opening measurement position, at the crank, and then change to your 0.040" of lobe opening lift, I will have to physically advance the cam to get to that extra .020" of lobe lift. No???  If I also add in .005" of valve lash... again, I will be physically advancing the cam to make up for that .005" loss of lift, at the crank manufacturer's stated measurement point of 37 Deg. of Crankshaft angle. This all assumes of course that using the opening measurement point of 37 Deg. of BTDC crank angle is correct. If that is not correct, what crank angle should it be? Jay seems to like setting the intake position, and let the EXH end up where it will. So there seems to be some disagreement here. Alternatively, there is always setting the cam lobe centers to the cam manufaturer's stated crankshaft angle values, and then check openings, and closing positions. Seems like the opinion is, that I can't trust any of the Mfg's data??? So make up my own??? Seems a bit scary.

You're getting the right idea!
This is where tuners 'agree to disagree' on what is 'best' for an engine, which is what makes different tuners valuable to different racers. You can shift the cam (among other items) forward or back in time to adjust your powerband RPM, within the confines of a given cam. In short, it depends on what you want to get from the engine in the end.

For example, looking at Honda's stock cam for the "F" series engines:
The intake valve opens at 0 BTC from Honda (give or take about 1 degree) if you just bolt it in. This setting causes the intake tract to be unsteady until about 5500 RPM, at which point the flow speed and mass of the air itself smoothes out by pushing the unsteady 'wave' (that is caused by pushback during the overlap cycle) to become swallowed up inside the chamber. By about 6000 RPM, it starts to let the air inertia (i.e. mass*velocity) push harder and pack a little extra air into the chamber, swishing it across the top of the piston (called "sweeping") and out the exhaust, so less leftover exhaust is contained in each piston pop. This causes a noticeable jump in power, starting right at that RPM. This is sometimes called the "lower power peak" point of the cam. As the RPM rises further, the amount of time the inlet valve is open (duration) determines HOW MUCH air gets packed in, and more air/fuel mix makes more power. As the RPM rises further still, the timing of the exhaust valve comes more into play to try to prevent loss of the "sweep" charge out the exhaust: if the valve closes too soon, old gases are left in the chamber: if too late, then the 'good' stuff escapes out to the pipe as lost efficiency. In DOHC engines, the In-Out can be separately controlled, on which entire libraries are written: in the SOHC engine, your choice is limited by the cam builder's ideas.

If you were to advance the [stock] cam 5 degrees (like the earlier "K" engines), the intake's flow smoothes out by around 4000 RPM. "K" riders will notice this as a point on the tach where the engine changes the way it 'feels', in about 200 RPM between 4000 and 4200: it changes from a sluggish, smooth feeling to a snappier, power-on-tap feeling. This increases until about 7000 RPM, then starts to go the other way again. By about 9500 RPM (if the valve springs are in good condition) it feels about the same way it did at 4000 RPM again.

The tradeoff: if you graph the amount of torque the engine is making (as you see in typical HP dyno charts) and whip out your calculus, you will find the area below the curve as drawn is the same regardless of how you time the cam. But, if you find the precise rpm where the valve sizes and their flow is optimized for the burn rate of the fuel you are using, and set the inlet cam to push the most air in at that speed, you will get a higher, narrower peak in the curve. Some folks call this "more power".

I am in a little different camp, however. This narrow peak means you must run the engine there to get that power. Since the small-bore 187cc engine of the CB750 needs about 6000 RPM (K cam) or 7000 RPM (F cam) to reach into this peak, you don't enjoy riding the bike in traffic very much as the result. If you 'detune' the cam by advancing it, the power comes on sooner, creates a lower peak, and spreads the peak out over a wider RPM range, so the bike feels more responsive, more of the time.

So, what we SOHC4 builders experience is simpler than the DOHC strugglers' trials. We get to adjust the point where the powerband starts, and the band is as wide as the lobes were built to manage, with never a 'flat spot' in the midst of the peak (DOHC tuners can spread this powerband thing too far, making the middle "flat").. Typically, we get about 4000 RPM powerband with a stock Honda cam, less with cams that have wide lobes (i.e., more duration) and higher power peaks. An example: the Webcam 41/a grind makes power start about 7000 RPM, show is over by 9500 RPM (2500 RPM powerband). Below 7000, the engine is sluggish and tends to foul plugs in heavy traffic. But, when it comes 'on cam' it can lift the front wheel (if it's not a cafe' with the rider laying on the tank), which some folks really like!

[MRieck]

Currently I set the cam to open the intake at 37 Deg. BTDC of crank rotation, at .020" of lobe lift per the Dynoman Performance DP117KHD (Kenny Haraman D Grind)Cam card (attached as PDF in 1st post.) If I still use their 37 Deg. BTDC crank angle opening measurement position, at the crank, and then change to your 0.040" of lobe opening lift, I will have to physically advance the cam to get to that extra .020" of lobe lift. No???  If I also add in .005" of valve lash... again, I will be physically advancing the cam to make up for that .005" loss of lift, at the crank manufacturer's stated measurement point of 37 Deg. of Crankshaft angle. This all assumes of course that using the opening measurement point of 37 Deg. of BTDC crank angle is correct. If that is not correct, what crank angle should it be? Jay seems to like setting the intake position, and let the EXH end up where it will. So there seems to be some disagreement here. Alternatively, there is always setting the cam lobe centers to the cam manufaturer's stated crankshaft angle values, and then check openings, and closing positions. Seems like the opinion is, that I can't trust any of the Mfg's data??? So make up my own??? Seems a bit scary.

  You are getting hung up on the numbers. I have NEVER had a cam measure out exactly to the manufactures specifications....there are to many variables.
 Let's start over.....you have 37 opening as it sits.....what was the closing #??? Did you record the closing #? The lobe center can be calculated as long as you have both #'s. You can subtract the opening # (37) from the closing # (65 or so I'd guess). Take that product, add to 180 and than divide by 2. That gives you your lobe center......that is the only number you should really be concerned with.
 The lobe centers are supposed to roughly be 106 Intake and 110 exhaust. You are roughly there. The information I gave you on how to measure is, IMO, more accurate in regard to judging actual opening/closing events.
 Do not worry about "advancing" the cam. The only way that is possible at this point is if you actually move the cam sprocket. You are not doing that. You are merely changing where you measure at.
 You have to measure both the intake and exhaust. Many, many times you have to split the difference between the intake and exhaust lobe centers. NO CAM IS GROUND PERFECTLY. God....you should measure some Web cams. As you go through the opening/closing cycle on the intake and exhaust it is a good idea to record total lift....the actual # will surprise you.
 As I said before.....do not get hung up on the opening closing #...you want the lobe center.
 As an aside...I'd go for 105 lobe center on the intake and see what exhaust lobe center is. Look at just about any Yoshimura cam made and it is the ubiquitous 105/105 lobe center.
 Last thing.....use a piston stop to do the work. I do not know how you achieved absolute TDC without one.

[74750k4]

To confirm TDC, I used a dial indicator at the piston crown....  and yes, the measurements I made as far as duration (open to close), and lift at the lobe, did not match the MFG's specs. If the cam needs to be adjusted to get the lobe centers correct, I certainly will be moving it...  that's why adjustable sprockets are sold. No???

[MRieck]

To confirm TDC, I used a dial indicator at the piston crown....  and yes, the measurements I made as far as duration (open to close), and lift at the lobe, did not match the MFG's specs. If the cam needs to be adjusted to get the lobe centers correct, I certainly will be moving it...  that's why adjustable sprockets are sold. No???

Dial indicators do not work with side loaded spark plugs. On a central located spark plug OK. I am out of this thread....you are smarter than me....frustrated.

[74750k4]

Hmmm...  but that's you assuming the head was on, when I was using the dial indicator to set absolute TDC   ...It wasn't.
But since you're gone now, you'll never know that.

Here's Megacycles take on it...  similar to yours , but still there may be some adjustments needed to the cam position...
It's their version of the same grind.

125-D             .345" 265° 105.5° Kenny Harman “D” grind. OK with stock pistons.       26 btc/59 abc .005"
billet               .325" 280° 110° UseHD springs. Mid-range and some top-end.                70 bbc/30 atc .005"



B) All overhead cam type engines:

1) Stated lift is the gross lift AT THE VALVE.

2) Durations and opening and closing angles are given at .040"valve lift, with zero checking
clearance (lash). For engines with shim-adjusted valve lash it may be desirable to check the cam
timing at running lash rather than zero lash, to avoid having to re-shim the valves after degreeing-
in the cams. If you wish to check the cam timing at running lash, simply deduct the lash from
.040" to obtain the correct checking lift. For example, if your running lash is .008", check opening
and closing points at .032" valve lift (.040" minus .008" = .032") . In this way, you should obtain
the specified timing figures.
When trying to compare different cams using quoted specifications, is is important to be sure that all
specifications are given at the same checking point. Otherwise, direct comparisons are not valid. Mega-
cycle chose .040" as a standard since this corresponds closely to one millimeter, which has become a
standard checking point with most Japanese motorcycle manufacturers. Be aware, however, that many
catalogs and workshop manuals quote cam timing figures at other, often unspecified, checking points.

SOME GENERAL NOTES PERTAINING TO CAM INSTALLATION

1) Don’t check only valve opening OR closing. Check both opening AND closing and split any
deviation from specifications equally between them. This way, you should come within 2 or 3 degrees of specifications.

2)ALWAYS check valve-to-piston clearance before running the engine. A quick and easy way to do
this is to hold the crank at top dead center on the exhaust stroke, (overlap) and with the crank held
in this position, pry the valves open with a lever. You should have a minimum of 1/16" movement
before you feel the valve touch the piston

[bwaller]

You know sir, when you have people taking the time to type long responses to help you sort through issues it's best to pay attention....and be respectful. Some of these folks do this work in their sleep, good guys to have in your corner I'd say.

Keep reading & good luck with your cam

[PeWe]

Very interesting thread with very good answers from people that know what they talk about when they have decades of practice!   maybe centuries...? 

I have never timed a cam before, got it done by my local tuner once then followed the made markings on cam vs sprocket next time I had to take it apart and together again.

I'll soon have my engine together again with new pistons and hotter cam than before. I'll need a printout of this thread and turn my engine around measuring and thinking.... I have already decided to advance the cam with 3-5 degrees to get more on lower rpm's. CycleX CX-7.

I'll start to have the APE cam sprocket in the center, measure what happen and make sure that the valves will not hit each other or attacked by an angry piston!    Clay on the piston crowns will indicate how close the engine failure is...

I'll advance until I feel mechanical contact, mark the sprocket vs cam, then retard until contact again and mark to see the points I have to avoid. After this make a serious setting and make sure it will be tolerances from mechanical contact positions. It is the exhaust valves that are hunted by the pistons if I have understood the threads here correctly..

[bwaller]

You really need to start with a positive piston stop to find true TDC....when the engine is assembled. Use as large a degree wheel as you can mounted on the left end of the crank. Use a pointer that isn't too flimsy in a position that won't get moved by contact. Whatever tool you use to turn the engine, make it as long as possible so that small movements are easy. Be methodical in these first steps and the test numbers will be accurate (whatever they are)

It may be necessary to assemble/disassemble the engine several times checking clearances etc.

[PeWe]

You really need to start with a positive piston stop to find true TDC....when the engine is assembled. Use as large a degree wheel as you can mounted on the left end of the crank. Use a pointer that isn't too flimsy in a position that won't get moved by contact. Whatever tool you use to turn the engine, make it as long as possible so that small movements are easy. Be methodical in these first steps and the test numbers will be accurate (whatever they are)

It may be necessary to assemble/disassemble the engine several times checking clearances etc.

New base and head gaskets are not used when I might need to assemble/disassemble it many times? Use old ones until the correct setting is found and marked on cam and sprocket, right?

[70CB750]

This got me thinking - bad habit, I know  - the K0 has the power band right on the money at 4000 rpm and I love it.

Now the F engine if I stick with the original cam, it will have similar kick @ 6000 rpms.  According to gear calculator (for K, not for F but it will not be far):

18/48
rpms   1st 2nd  3rd  4th 5th
6,000   36   52   67   81   95
16/48
6,000   32   46   60   72   85
15/48
6,000   30   44   56   68   79
14/43
6,000   31   45   58   71   83

Hmm, seems like it does not make much sense to go that way, to make the F be more streetable, or at least legal for pete's sake - 70mph is the highest speed limit in our area.


Edit:  14/43 is what JT lists as stock for 78 F2 - I quess Honda did go through the same process.

[74750k4]

Piston stop on the way...  but originally checked/set TDC with dial indicator when head was off, and torqued with stud spacers on.

Similar to this photo by Brantley  http://forums.sohc4.net/index.php?topic=112544.0

Only in the center, not the edge of piston.
oh by the way...   my cam WAS retarded.

Eliminating any doubt...  I sure appreciate all the expert opinions here...

[HondaMan]

This got me thinking - bad habit, I know  - the K0 has the power band right on the money at 4000 rpm and I love it.

Now the F engine if I stick with the original cam, it will have similar kick @ 6000 rpms.  According to gear calculator (for K, not for F but it will not be far):

18/48
rpms   1st 2nd  3rd  4th 5th
6,000   36   52   67   81   95
16/48
6,000   32   46   60   72   85
15/48
6,000   30   44   56   68   79
14/43
6,000   31   45   58   71   83

Hmm, seems like it does not make much sense to go that way, to make the F be more streetable, or at least legal for pete's sake - 70mph is the highest speed limit in our area.


Edit:  14/43 is what JT lists as stock for 78 F2 - I quess Honda did go through the same process.

Yeah, the 14/43 combo on the "F" bikes made them very 'buzzy" in the touring crowd's minds (3.07 final drive ratio), and installing a 15t front was common back then if you were pushing a Vetter fairing. This made it close to the K0/K1 gearing, much more pleasing to the ear, but then it was almost 1000 RPM off of the bottom end of the "F" powerband. This contributed greatly to the lost sales in the post-1976 SOHC4 750 bikes (IMO), as we heard MUCH about it from those who had worn out their first 750, then bought another, only to be disappointed on the open road. Historical trivia...