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post #1 of 11 (permalink) Old 06-22-2011, 12:49 PM Thread Starter
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VN750 cam (camshaft) guide

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:
  1. Front Cylinder Exhaust
  2. Front Cylinder Intake
  3. Rear Cylinder Intake
  4. 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.

Important note: 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.
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Last edited by MotoCache1; 06-22-2011 at 12:52 PM.
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post #2 of 11 (permalink) Old 06-22-2011, 02:04 PM
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Excellent write-up MotoCache1!

I find it absolutely mind boggling that the front cams had the grooves but the alignment hole was opposite of the rear. Crazy. How does that happen?

Did you keep the cam caps with their respective cams? The manual says that they are machined to match the cams specifically.

Street
1985 VN750 Acquired Feb, 2011 - 13,676km
Mods - Ear Shave, Pickup Coil Gap, Drilled Clutch Basket, Shift Tie Rod, Mosfet R/R, MF Battery, De-Goated (H-Pipe), MCCT, Heated Grips, Plexistar 2 Windshield

Dirt
2004 KTM SX 125 - 1979 Can-Am Qualifier 250 - 1971 Kawasaki F6

Video Tutorials - Engine Rebuild - Fork Seal Replacement - Grease Swing Arm Bearings - Carb Rebuild - Spline Lube - Refilling Rear Shocks - Grease Steering Bearings
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post #3 of 11 (permalink) Old 06-22-2011, 02:12 PM
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A question,

Are the rear cams in the pictures from the original bike, and the front cams from the donor bike?

Do you have pictures actually showing that the grooved front and rear cams were different?

Street
1985 VN750 Acquired Feb, 2011 - 13,676km
Mods - Ear Shave, Pickup Coil Gap, Drilled Clutch Basket, Shift Tie Rod, Mosfet R/R, MF Battery, De-Goated (H-Pipe), MCCT, Heated Grips, Plexistar 2 Windshield

Dirt
2004 KTM SX 125 - 1979 Can-Am Qualifier 250 - 1971 Kawasaki F6

Video Tutorials - Engine Rebuild - Fork Seal Replacement - Grease Swing Arm Bearings - Carb Rebuild - Spline Lube - Refilling Rear Shocks - Grease Steering Bearings
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post #4 of 11 (permalink) Old 06-22-2011, 03:33 PM
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Thumbs up Thank You Motocache1

I'm the friend whose bike Motocache1 is referring to, and I can confirm all that he is saying is true. My bike is much happier and is a lot more fun to ride now.

Moto, I have to say, when you said you were going to post a write up, I wasn't expecting such detail. Thank you very much for taking the time to do so.
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post #5 of 11 (permalink) Old 06-22-2011, 03:38 PM Thread Starter
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Quote:
Originally Posted by Roach View Post
Did you keep the cam caps with their respective cams? The manual says that they are machined to match the cams specifically.
Everything was labeled and kept with its original location. In top end work I'm really detail oriented like that -- even to the point of each rocker going in a labeled bag that says where it goes (e.g. left rear intake rocker, etc.).
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post #6 of 11 (permalink) Old 06-22-2011, 04:07 PM Thread Starter
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Quote:
Originally Posted by Roach View Post
A question,

Are the rear cams in the pictures from the original bike, and the front cams from the donor bike?

Do you have pictures actually showing that the grooved front and rear cams were different?
Assuming the "grooves" are what I think they are, they are very very faint lines radially on the face of the sprocket in the center. They didn't come out in the photographs, but if I shine a light correctly I'm sure I could get pics of them.

In the picture the rear exhaust cam is from the bike that had no lines on any of the cams, and the rear intake cam is from the bike that had lines on all 4 cams.

The cams in the pictures are all still loose and available to be photographed further if needed. In the engine that's back in the bike, the front intake and exhaust cams have lines, and the rear exhaust has lines, but the rear intake does not have lines because it came from the engine that didn't have lines on any of the cams.

Maybe the "grooves" I'm supposed to be looking for are something other than these radial lines I was seeing on the flat machined surface in the center of the face of the sprocket.

Next time I'm over at her house I can take a picture with the light hitting at the right angle to show the lines that I'm assuming are the "grooves".
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post #7 of 11 (permalink) Old 06-22-2011, 04:49 PM
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Quote:
Originally Posted by MotoCache1 View Post
Assuming the "grooves" are what I think they are, they are very very faint lines radially on the face of the sprocket in the center.
I don't think they are.

They are very distinct round grooves around the shaft.


Street
1985 VN750 Acquired Feb, 2011 - 13,676km
Mods - Ear Shave, Pickup Coil Gap, Drilled Clutch Basket, Shift Tie Rod, Mosfet R/R, MF Battery, De-Goated (H-Pipe), MCCT, Heated Grips, Plexistar 2 Windshield

Dirt
2004 KTM SX 125 - 1979 Can-Am Qualifier 250 - 1971 Kawasaki F6

Video Tutorials - Engine Rebuild - Fork Seal Replacement - Grease Swing Arm Bearings - Carb Rebuild - Spline Lube - Refilling Rear Shocks - Grease Steering Bearings
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post #8 of 11 (permalink) Old 06-22-2011, 09:55 PM Thread Starter
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Quote:
Originally Posted by Roach View Post
I don't think they are.

They are very distinct round grooves around the shaft.
Hahahahaha, well, that's awesome. Talk about not seeing the forest through the trees. Guess if I'd ever faced all 4 cams the same way at once I might have noticed that no-to-subtle feature.

Ah well, the pics are bound to be useful for something to someone someday.

If nothing else, if someone is wondering how to tell the cams apart, and doesn't have a service manual, this thread will give them everything they need and more. Thanks!
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post #9 of 11 (permalink) Old 06-23-2011, 06:49 AM
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I have an '86 with about 20k miles. I get this clacking noise from the top of the front cyclinder that comes and goes, at idle, sounds really smooth when not doing it. First, the owners manual says the valves never need adjusting, true? 2nd, with the issue you had with the cams, was this just a random deal, or should all the older bikes be opened up to check positioning? Other that the clacking mine runs fine, good power. Having had the motor partially out once, not sure if I want to deal with that again if I don't have to.

1986 VN750
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"STUPIDITY SHOULD BE PAINFUL"
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post #10 of 11 (permalink) Old 06-24-2011, 12:38 PM
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Quote:
Originally Posted by MotoCache1 View Post
Hahahahaha, well, that's awesome. Talk about not seeing the forest through the trees. Guess if I'd ever faced all 4 cams the same way at once I might have noticed that no-to-subtle feature.

Ah well, the pics are bound to be useful for something to someone someday.

If nothing else, if someone is wondering how to tell the cams apart, and doesn't have a service manual, this thread will give them everything they need and more. Thanks!
Yeah I still think it's handy and well written.

Street
1985 VN750 Acquired Feb, 2011 - 13,676km
Mods - Ear Shave, Pickup Coil Gap, Drilled Clutch Basket, Shift Tie Rod, Mosfet R/R, MF Battery, De-Goated (H-Pipe), MCCT, Heated Grips, Plexistar 2 Windshield

Dirt
2004 KTM SX 125 - 1979 Can-Am Qualifier 250 - 1971 Kawasaki F6

Video Tutorials - Engine Rebuild - Fork Seal Replacement - Grease Swing Arm Bearings - Carb Rebuild - Spline Lube - Refilling Rear Shocks - Grease Steering Bearings
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