This is my first post here.
I helped a friend with her newly purchased 2005 VN750 which had no compression in the rear cylinder (was running on the front cylinder only).
Disassembly revealed that both intake rockers were completely displaced, one lobe of the intake cam was deeply gouged (from rubbing on the displaced rocker), and both intake valves were bent.
We replaced the cam, both valves, both rockers, the valve guides for the two bent valves, and all 4 valve seals (might as well do it while you're in there). During that process I discovered that Kawasaki didn't really have their act together when it comes to identifying these cams. If you don't know, each of the 4 cams in the VN750 engine is different -- no two are alike.
So, from the front of the engine to the rear, in order you have:
- Front Cylinder Exhaust
- Front Cylinder Intake
- Rear Cylinder Intake
- Rear Cylinder Exhaust
For either cylinder, telling the intake cam from the exhaust cam is easy -- the exhaust cam is shorter than the intake. OK, that's the easy part. Now, how do you tell the front intake from the rear intake, and the front exhaust from the rear exhaust?
According to the service manual, it's easy. Here's a screen shot from a 1987 VN750 service manual:
Well, that's just confusing isn't it? According to that diagram, the camshafts on the left are the front and the rear -- but of course they have to be one or the other.
Fortunately, in the 2006 service manual they fixed that little blunder:
OK, that's clearer. So the ones on the left are the rear cylinder camshafts, and should have grooves on the sprocket end to identify them, and the ones on the right are the front cylinder camshafts and should not have the grooves.
OK, that's great. Except. In our engine, all 4 camshafts have the grooves. In a donor/reference engine, none of the camshafts have grooves. Since the chances of both of these engines having 2 wrong camshafts, and yet be able to run, are pretty slim, I decided (after some initial frustration and swearing) that the "groove" method just wasn't going to cut it.
Let me stop here and say that when you are disassembling an engine you should tag or bag parts like this to ensure that you don't mix them up. If you do that, then you won't really have to worry about which is which. But what if you didn't know any better and just put them all in a box? Or what if you had to order a replacement and wanted to know you had gotten the right thing, etc.? In our case, at this point I'm just wanting to make sure this engine does indeed have the right cams before I put it back together and put it back in the bike. The whole groove thing gave me reason to question it.
So, I sought to determine the physical difference between a front/rear intake and a front/rear exhaust. Looking at the so-so pics in the service manual, and comparing to the cams in the two engines, I determined that both engines do have the correct cams in the correct locations. The way you can tell the front from the rear shafts is by the orientation of the lobes relative to the reference holes in the sprocket.
In the pictures below I have the reference holes aligned in the same orientation they would be when you are verifying the cam timing. When facing the sprockets the holes are at 9 o'clock (exhaust) and 3 o'clock (intake). In each picture the cams are laid out as they sit in the bike (in the same order as the list up at the top of this post). That said, there are 3 views, top, left, and right, to show you what the cam sets look like in "timing check" position for each cylinder
As shown here all 4 cams are in the orientation they would be if doing a timing check on the particular cylinder. As the cams normally sit in the bike, you will not
see all 4 cams aligned like this, ever
. When the front cylinder is at 9 o'clock and 3 o'clock, the rear cylinder will not be, and vice versa. I present them as I do to make it easy to compare the cams.
OK, so here's the overhead view. You can easily see that the exhaust cams are shorter than the intakes, and you can see that (with both cylinders set in timing check position) the front cylinder lobes point out from the middle, and the rear cylinder lobes point in toward the middle. It is sort of hard to see this in the overhead picture however, and you can't see the reference holes in the sprockets.
Here's the view as it would be looking at the cams from the (rider) left side of the engine. Now you can see the reference holes in the sprockets, and it is easier to see that the lobes are pointing outward from the center (relative to that set). While you can't see the reference holes for the rear cylinder cams, you can see the lobes of the rear cylinder cams are pointing inward toward the center (relative to the set). Just a reminder, you will never see all 4 cams in this orientation in the motor at once (as explained earlier).
Finally, here's the view as it would be looking at the cams from the (rider) right side of the engine.
OK, well that's it. Given these pictures you should be able to identify any VN750 cam.
Regarding our repair job, it was a great success. The bike is a lot more peppy with two functioning cylinders than it was with one.
Hope this guide helps save someone some frustration. If nothing else, some day maybe it will remind me of all these details if we have to tear into her engine again.
P.S. All of these pictures are black and white photos I shot of the actual cams from the project. I shot in black and white to give the best contrast so you could see the details, and it also had a nice benefit of keeping the file sizes small.