Cam timing GS1000

[Guest]

Hey all, feel a bit crazy for posting this but I'm about to pull my hair out. I put the cams back together on my 78' GS1000, carbs, airbox etc..etcc.. started her up and was having a hard time getting vacuum to synch the carbs, and she didn't sound right. Figured I must have gotten the cam timing off by a bit or something. Pulled the valve cover and sure enough when I rotated to the "T" mark just past 1-4 the cam mark "1" was way off, I was actually surprised the bike started as easily as it did. So, three attempts later I am stumped. I make sure the bike is at TDC by pulling the number 1 plug and putting my thumb over it as I hand crank, as soon as I feel the pressure on my thumb I start looking for the #1-4 "T" mark, get it lined up with the timing mark and then put the exhaust cam so that the #1 mark is parallel with the head, just as described in the shop manual, and carry on setting up the intake cam as per the manual, the 20 pin count is perfect, install the cam tensioner, etc...etc... BUT when I go to check that everything is correct I again put my thumb on #4, feel the pressure and line up the "T" mark, when I look at the exhaust cam, nothing is lined up!! it's 180 degrees off. I've rotated the crank multiple times and get the same result. I've done this twice now and can't figure out what I'm doing wrong.

 

[Sandy]

Are you actually turning the crank 2 revolutions when checking or just one?

 

[Guest]

2, 4. Maybe I'm thinking about this wrong, do I need to worry that TDC is on compression? It's the cams that determine compression, so if both cams are not hooked up, as long as the "T" mark is lined up right, everything should be good.... right? I just have it in my head tjat when everything is buttoned up and I line up the "T" mark for TDC and see that the cam marks are correct the bike should be at the TDC of the compression stroke..... but maybe that's wrong....??

 

[sharpy]

Cam lobes on #1 facing away from each other?

 

[Guest]

Yup, I only took the cams off to replace the valve seals

 

[chuck hahn]

T mark lined up with the mark on the cases.
Pull slack from chain at the front of the engine and lay on Exhaust cam being sure the "1" arrow is facing front of bike and even with head surface. Keep tension on the chain.
Slide in the intake cam and set the "3" arrow facing straight up.
Let the cam chain tensioner forward and count pins. If there are 19 then its correct. Double check the T mark is still on. If all thats good then your problem isnt cam timing. May be a stuck open valve??? Sure all the keepers on the stems are seated right?? Its something but it isnt the cam timing.

NOTE. with the carbs off crank it and put your hand over each intake manifold and feel for some suction on the intake strokes.

 

[Steve]

One other little diagnostic tip: make sure the crank is intact. :-k

You say you are checking TDC on #1, then on #4, so make sure they are both hitting TDC at the same time.

Something as simple as a pencil in each spark plug hole so you can watch them reach TDC will do the trick.

Also be sure you are counting cam chain links correctly. The pin directly over the #2 mark on the sprocket is #1, not the one next to it.
Can't tell you how many times I got that one wrong when I started working on engines.

.

 

[bobgroger]

One other little diagnostic tip: make sure the crank is intact. :-k

You say you are checking TDC on #1, then on #4, so make sure they are both hitting TDC at the same time.

Something as simple as a pencil in each spark plug hole so you can watch them reach TDC will do the trick.

Also be sure you are counting cam chain links correctly. The pin directly over the #2 mark on the sprocket is #1, not the one next to it.
Can't tell you how many times I got that one wrong when I started working on engines.

.

+1 It ran fine when he took it apart though so the crank probably isn't an issue. Start with the simplist thing, work your way down the list. I am thinking yopu are one tooth off on the intake. 20 pins from 2 to 3, at least on a 16V

 

[Guest]

It's all sorted fellas, thanks for the tips. Turns out it was the carbs but I am pretty sure I shouldn't be worrying about the compression stroke when I'm getting TDC and putting cams back in.

 

[Steve]

... but I am pretty sure I shouldn't be worrying about the compression stroke when I'm getting TDC and putting cams back in.

Not sure what makes you think that. It is absolutely CRITICAL to ensure proper timing between the crank and the cam. As already mentioned, the crank is lined up with the TDC mark for cylinders 1 and 4, the #1 mark on the exhaust cam is lined up with the gasket surface, then the proper number of pins between the #2 mark on the exhaust cam and the #3 mark on the intake cam.

Technically, there is no "compression stroke" until you install the cams, but the timing of the cams and crank is what makes it possible.

.

 

[TeamDar]

T mark lined up with the mark on the cases.
Pull slack from chain at the front of the engine and lay on Exhaust cam being sure the "1" arrow is facing front of bike and even with head surface. Keep tension on the chain.
Slide in the intake cam and set the "3" arrow facing back and even with head surface.
Let the cam chain tensioner forward and count pins. If there are 19 then its correct. Double check the T mark is still on. If all thats good then your problem isnt cam timing. May be a stuck open valve??? Sure all the keepers on the stems are seated right?? Its something but it isnt the cam timing.

NOTE. with the carbs off crank it and put your hand over each intake manifold and feel for some suction on the intake strokes.

Chuck, this is not correct for a GS1000. Number "3" points straight up and there are 20 pins counted. Dar

 

[Guest]

Not sure what makes you think that. It is absolutely CRITICAL to ensure proper timing between the crank and the cam. As already mentioned, the crank is lined up with the TDC mark for cylinders 1 and 4, the #1 mark on the exhaust cam is lined up with the gasket surface, then the proper number of pins between the #2 mark on the exhaust cam and the #3 mark on the intake cam.

Technically, there is no "compression stroke" until you install the cams, but the timing of the cams and crank is what makes it possible.

.

No, no..I didn't mean timing wasn't critical. What I meant was that I shouldn't be worried about "compression stroke". As you said, it's the cams that determine the compression stroke. I kept checking for the compression stroke after I put the cams in and had it in my head when #1 comes to compression, and I line up the "T" mark at 1-4 the #1 mark on the exhaust cam should be in it's correct place, which it wasn't, so I thought I was doing something wrong, which I wasn't. As everyone here has said, and the shop manual describes, you just line up the "T" mark properly, ignore anything to do with "compression". Again sure appreciate the clarification, I must have been low blood sugar yesterday..