Honda Twins banner

1 - 13 of 13 Posts

·
Registered
Joined
·
84 Posts
Discussion Starter · #1 ·
Hi All, I've been lurking here for a long time, this is my first post. Long story short, I'm rebuilding a CB350 to race in Novice Production Lightweight at the Topeka AHRMA race in June. Personally I'm not a brilliant mechanic, nor do I have any special knowledge of motorcycles or engine building. I started on this project 2 years ago with a much different goal in mind, but the race opportunity has presented itself and it sounds like fun. I'm just about done rebuilding the engine, the head is at the machinist today being decked and getting a valve job. This weekend I plan to install that head, and then the cam box, cam, rockers, etc.. Here's my quandary:

1) I have 3 engines currently deconstructed that have come back together into the 1 (hopefully) running race engine
2) I wasn't extremely meticulous in tearing down the engines. I might be able to mate 4 rockers with their original cam, but there's no possible way I could tell you which cam lobe each rocker originally lined up with.

My question is how I should proceed with filling the cam box. Since I can't match rockers to their original cam lobe, should I have the whole shooting match serviced by my machinist? Or is that overkill? Will a cam that passes visual inspection, when installed with 4 rockers that pass visual inspection, ultimately perform the way it is supposed to regardless of the fact that they haven't worn together over whatever number of miles may or may not be on them all?

I'm at my office right now, when I get home tonight I should be able to add photos of the cam/rockers I intend to use if necessary.

Thanks!
 

·
Sensei
Joined
·
27,168 Posts
You do know there are two types of cams and you must use the correct rockers for that cam, and its easiest if you use the matching cam box as well (one can work for either type cam, the other not so much)......
 

·
Registered
Joined
·
13,085 Posts

·
Registered
Joined
·
84 Posts
Discussion Starter · #4 ·
Thanks guys. Sprint, yes, I'm aware that there are 2 different cam types. It's a fact that has caused me a little bit of concern of late. We'll get to that briefly though.

Ancientdad, thanks for the direction. I made my introduction post.

So, last night I got in the garage and started gathering cams and rockers so that when I pick my head up from the machinist tomorrow I can ask him what he thinks about my intentions. What I found was that of the 3 cams I have, one is "fat," one is "skinny," and one is "missing, presumed skinny." Here are a few pictures of the "skinny" one, which is the one I hope to use.
20190225_185234.jpg
20190225_185240.jpg
20190225_185248.jpg
20190225_185254.jpg
20190225_185259.jpg

Now, back to the "fat cam, skinny cam" discussion. This is a skinny cam. I am 99.9% sure that the cam box I intend to use also originally housed a skinny cam, but it's the box from the "missing, presumed skinny" cam. Is there a visual difference between boxes? I was able to twist the cam I hope to use into the box I hope to use. Does that guarantee compatibility, or do the problems begin when the sprocket and rocker arms are added to the box? This is the box I intend to use:

cambox.jpg
 

·
Sensei
Joined
·
27,168 Posts
TWO different cam TYPES, but FOUR different cam possibilities...... How did you determine which cam you actually are using?
Visually is not always a correct answer........

Were I you, I would verify your possibilities by engine serial numbers and how many "312" rockers you have from the three engines......
That might also verify if the missing cam was "skinny"..........
 

·
Registered
Joined
·
84 Posts
Discussion Starter · #6 ·
In this case, visually is the answer. The "fat" cam has some pitting on the lobes.

Unfortunately the missing cam is in a bag with its associated rockers. I have 2 cams readily available; one fat one skinny, and 8 rockers, 4 stamped "312" and 4 that go with the fat cam. So, let's assume for a moment that the missing cam doesn't exist, or that it's at the bottom of a lake (It does, and it isn't, but let's assume). What should I look for in the cam that I do have? How can I be certain that the cam I have goes in the box I want it to go into?
 

·
Sensei
Joined
·
27,168 Posts
IIRC, IF the parts can all be "trial" fitted atop the engine, chain on sprocket, and sprocket in position on camshaft (NO sprocket bolts installed YET), and camshaft in the head covers (bearing blocks) and fit together, you can use that box......excessive force should NOT be required....If the parts don't just slip into place...STOP..........
 

·
Registered
Joined
·
84 Posts
Discussion Starter · #8 ·
Ok, that covers that "How can I be certain" question...what about the cam? You said a visual inspection is not always the correct answer, what kind of tests would you put the cam through to decide whether or not it would be returned to service?
 

·
Sensei
Joined
·
27,168 Posts
I would GUESS from the information you provided (and ASSUMING the missing cam has its correct rockers with it)
that you do have a "skinny" cam and probably should use the 312 rockers with it....
Sorry, that's the best I can do from here.....:confused:
 

·
Registered
Joined
·
84 Posts
Discussion Starter · #10 ·
I get all that, I'm returning to the initial inquiry which is "How do I know if I need to have this cam ground or if it's good to just put back into the engine and run?"
 

·
Sensei
Joined
·
27,168 Posts
That can be measured IF you have lift and duration specs, and the correct tools...I don't have the specs.....

I'd just run it as-is unless the pics don't show the imperfections.....
 

·
Registered
Joined
·
879 Posts
I looked at your photos and I wouldn't have any issues using that cam. Check the shaft where it runs in the covers and also the thrust surface that controls side to side. All should be smooth.

The FSM says you can lightly dress the cam with an oil stone. I use a fine diamond knife sharpener to check for ridges and flats. You need something rigid that is wide enough to go across the width of the lobe. It will show up any issues very quickly. You can do the same with your rockers. There is usually some small flat area on the rocker and with a few swipes it can certainly be corrected. Also look for discoloration of the parts, you can usually ID the exhaust rockers by the baked oil browning .... if there is bluing then check them very carefully as that indicates high temps.

I soak all my cams and rockers in Evapo rust for a period of time, two or three days, as it removes all the old oil and reveals other possible issues. I repeatably rinse the parts in hot soapy water then force dry with a heat gun then coat with engine assembly lube.


After checking the cam and rockers there is no issues that I have found in putting them in any position.
 

·
Registered
Joined
·
84 Posts
Discussion Starter · #13 ·
Ok, great information all. Thanks! Tonight I'm going to locate the missing cam and its rockers. Tomorrow I will have the machinist take a look at it all when I pick up the head. With any luck I will be zipping this engine up this weekend! Goal is to test-fire it before the end of March.
 
1 - 13 of 13 Posts
Top