Topic: What is the best way to determine which CAM I have?

[Ira]

I've searched through a lot of threads about cams, but I'm too much of a rookie to understand what I'm looking for.  The short story is I have a '75 engine of unknown history.  There's evidence suggesting it's been modified: bored to 836, head is ported,etc. I took the top end apart to replace the rubber parts, but due to the other modifications, I'd like to determine if the cam is still stock.  What should I do?

1) Are there markings I should be looking for?
2) Is there a set of measurements for the stock cam?
3) Should I try to measure it myself, or can I take it to an engine shop?  What are the essential tools for doing this?

I measured the lobes with a basic caliper and they're slightly over 35 mm.  Based on what I've read, that's not precise enough?

Thanks and advance, and if there's already another thread I should be looking at, please point me in the right direction.
 

 

[Don R]

Look on the end of the cam for markings. Sometimes they will be stamped in the middle. Look at the lobe, if it is shiny and on the side you can see another lobe shape in a darker metal it is a hardwelded cam made from a stock core.  Look in the Honda manual, it shows measuring a stock cam with a caliper, you compare the width to the lobe height.

[Ira]

I measured the width and the height - width is 28 mm, height is around 35.5mm? Do I need to be more precise?

The formula I found for lift is height - width * rocker ratio.  Is the rocker ratio in the manual?

[ekpent]

As mentioned look for any markings. Most stock 750 cams had a mold number or an 'R' number on them around the sprocket area. If you see that number than as mentioned see if its been hard welded. You do not see any markings anywhere ?

[lucky]

1. Do not take it to an engine shop or machinist they
would just have to do what you are doing.
Automotive shop -forget it.

2. There are measurements for the stock cam in the workshop manual
usually. But they tell you the amount of LIFT.

3. That measurement you took is useless.

You could have a cam that does not have higher lift  but just has longer duration.

A close visual inspection will get you a better result.

IF you do not know what cam you have how did you adjust the valve clearance?
Performance cams do not have the same valve clearances as a stock cam.If I was you I would try to contact the person you got the motorcycle from.

One more thing. IF you have a stock cam (KNOWN)
You can compare the two together. That is a fast way to do it.

Also even if you find out that it is not a stock cam you will still need to know how to set the clearances.

I would at least set the intake valves .001 thousandths extra clearance.
If everything is adjusted correctly and the compression is low then I would slack off those adjustments intake clearances and see if it makes a difference.

[Ira]

Lucky,

The person I bought this engine from did not know its history.  He got it from someone else and it was sitting in the corner of his shop until I bought it for $150.   I used it last summer, found it was leaking oil externally, and pulled it to rebuild the top end.  I have not adjusted the valves, although they sounded loose when the motor was running. I don't have a stock cam for comparison.  I could easily get my hands on one though.

[ekpent]

My mild Andrews cam I put in my RC836 called for both intake and exhaust at .004.

[PeWe]

Photos of the cam can help the pros here to help you...
Usually printed marks at the end as mentioned earlier. Marks everywhere else can help too.

If the cam sprocket has oval holes for the 2 screws attached to the cam, it's most likely a hotter cam.

[Ira]

It doesn't have oval holes.  I'll check for markings and take some photos.

[lucky]

My mild Andrews cam I put in my RC836 called for both intake and exhaust at .004.

I think I would go with the .004 (thousandths) and .004 thousandths myself.
Intake and exhaust.

One other reminder...
IF it will not idle that is often caused by valves set too tight, if all other things are right.

[Ira]

To be clear, if it turns out this is the stock cam, I'm going to purchase a hotter one, of which I know the specs.  I'm just hoping the PO did this already.

[754]

Check your clearance and WRITE IT DOWN.. Before taking apart..

[Ira]

Check your clearance and WRITE IT DOWN.. Before taking apart..

too late. it didn't occur to me that i might have anything other than a stock engine until it was apart.

here are the markings (i took a couple quick photos last night, will get better ones).

[754]

Ends of cam..lookat the ENDS..

[Ira]

10-4.

Like I said, that was at a glance. I'll get shots of the ends, as well as the profile of the lobes. The "R" and "L" mean nothing at all?

[Ira]

Ok, here are pictures of the ends.  Do these qualify as markings?

[74750k4]

hmmm... No marks,  looks pretty squared off too, lots of duration in there.

[nilsey]

Hey Ira, have you found the cam lobe specs for the stock cam? for my 550 the factory service manual lists the cam lobe height for intake and exhaust. do you have the FSM for the 75 bike? maybe start there and see if the lobe heights are in the ballpark of what you have?

[Ira]

Nils - Clymer says intake minimum spec is 35.86mm and exhaust is 35.36mm, while base circle is 27.93.

The cam I have is in that ballpark.

[HondaMan]

Nils - Clymer says intake minimum spec is 35.86mm and exhaust is 35.36mm, while base circle is 27.93.

The cam I have is in that ballpark.

One way to check for stock cams (which yours is not) is to set the valve clearance at .045" in intake #1, then insert a .005" feeler gage and turn the crank until it just traps the thin gage between the rocker and valve. Then look at the spark advancer marks: if it is between the "T" and the "F" mark at this spot, it is stock duration (that is, it's either 5 BTC or 0 degrees TDC opening). The 1975 engines had both versions, the latter being the "F" cam, which also appeared in the K6 engines.

[Don R]

I just had a thread on degreeing my Kenny Harmon F cam in the hi perf section. You might find some good info there.  With a dial indicator, degree wheel and a piston stop you can learn how to measure the cam for lift and duration.  And set it up properly.

I should have made a how to thread while learning it myself.

[Don R]

In our case the rocker ratio is approx. 1 to 1 so you don't need to figure that in.  In some cases the lobe lift WILL tell you something about the cam. Just not always.

I laid my cam in the cam towers in an old head on the bench and set up a dial indicator to measure the lift. My particular cam is a bit different than the markings on the end would suggest. The KH/F cam cards say .385/.330 mine is .370/330.

 I'd be happy to check it, I'm about a 3.5 hour drive away though.

[754]

Its not a really hot cam,looks like it may be stock.
 Dang now i wish i had taken an end pic of the Andrews A cam I had in my hand today.. Its a mild grind.. Could hav made a comparison easier..

Look in 4sale, pic f an A grind up near the top.