Need help with Timing Adjustment (find TDC) on 8 valve 1979 GS850G

[seanarthurmachado]

Hello everyone,


My old Suzuki gs850GN (8 valve 1979 model) is not starting due to timing.

Need aid in adjusting. I own a clymer manual and have downloaded a shop manual but still need a little help.


I have the side cover off.

I need to pop the top case off the engine to get to the valves and set the position.

Am I correct in thinking:

Intake Lobes are towards the BACK of the bike ?

Exhaust lobes are to the FRONT of the bike ?


am I remembering that I need to:

Have the INTAKE VALVE LOBE on Cylinder 1 (clutch hand when sitting on bike) pointed UP
and
have the EXHAUST VALVE LOBE on Cylinder 1 pointed to the FRONT ?


Thanks for any answers.

 

[Guest]

Hello everyone,


My old Suzuki gs850GN (8 valve 1979 model) is not starting due to timing.

Need aid in adjusting. I own a clymer manual and have downloaded a shop manual but still need a little help.


I have the side cover off.

I need to pop the top case off the engine to get to the valves and set the position.

Am I correct in thinking:

Intake Lobes are towards the BACK of the bike ?

Exhaust lobes are to the FRONT of the bike ?


am I remembering that I need to:

Have the INTAKE VALVE LOBE on Cylinder 1 (clutch hand when sitting on bike) pointed UP
and
have the EXHAUST VALVE LOBE on Cylinder 1 pointed to the FRONT ?


Thanks for any answers.

TDC on compression stroke for #1 should put the intake and exhaust cam lobes pointing outward toward the gasket surface. Intake pointing towards the rear and exhaust pointing forwards.

 

[Big T]

Take off the ignition cover and look in the hole in the plate. Rotate the motor clockwise via the big nut until you see T 1-4 F. The mark next to T is TDC

 

[Guest]

In the larger scheme of things, you don't need to know where the cam lobes are pointing. According to all the manuals, the "T" mark for cylinders 1 and 4 gets lined up under the ignition cover, then look at the SPROCKET on the exhaust cam. Yes, that would be the cam directly over the exhaust pipes on the front of the engine. At the front edge of that sprocket, you should see an arrow, along with the number "1". The arrow should point to the gasket surface of the head. When it's in that position, there will be another arrow with the number "2" pointing up. Starting with the pin that is just above the arrow, count the pins. REMINDER: the pin over the arrow is #1, not Zero, then starting with the next pin. It will be difficult to keep track of pins while the chain goes under the idler sprocket in the center, but the 20th pin should be directly over an arrow on the intake cam that has the number "3" next to it. Again, you don't care where the cam lobes are, just the timing marks and the arrows.

If all of those are lined up, your (lack of) starting issue is not "timing". At this point in the season, it is usually more common to have gummed-up carbs, so make sure they are clean and your valve clearances are good.

 

[bwringer]

Finding TDC: http://www.bwringer.com/gs/tdc.html

Also, when the timing is correct the rectangular notches on the ends of the camshafts will be parallel with the surface of the cylinder head at TDC. They'll either be pointing directly away from each other, or directly toward each other. Don't worry about the lobes; look at the notches and it's pretty plain if you're a tooth off.

And follow the procedure for counting cam chain pins and aligning the arrows on the cam sprockets carefully. Read and follow the manual. Use the "big vice grip" trick shown in the manual to clamp the exhaust cam before installing the cam caps.

One thing to remember is that when you get everything in place correctly, the notches won't really line up until you install the idler, install and release the cam chain tensioner, and turn the engine through a revolution.

 

[jbrewer8]

So, I bought this bike from to OP last week. I had it running a bit, but with some serious backfiring. I took the cams off to check/adjust the timing, and want to be clear before I reassemble everything. The manual says the #1 arrow should be at or 1-2 mm below the gasket surface at TDC. When I first checked, it seemed slightly above, so I took out the intake cam and adjusted following the manual. The photo below is where it's at now, but I'm thinking it looks too far below the gasket surface. the photo where you can see the arrow makes it look just right, but since it's looking down on it, it's a bit of an illusion. In the other photo you can see that looking straight along the gasket surface, you can just barely see the '1'.

Can someone let me know if it's right the way it sits, or am I 1 tooth too low?

Thanks for the help!!

Here's the other photo since I can only attach 1 per post (This is my first post here, so still learning the ropes.): https://photos.app.goo.gl/R7Y7OVEzwgKMv0TJ3

 

[Guest]

Seems rather ambitious to pull the cams before actually checking the timing, but, ... too late now.

Just as important as where the #1 mark on the cam is pointing is where the CRANK is lined up. If it's not on the T mark for 1-4, what's showing on top doesn't matter.

Did you bother to check the valve clearances before pulling the cams? If the valves are tight (especially the intakes), you can easily have hard to start conditions, with accompanying backfiring.

Hope you didn't go through a lot of extra work for nothing.

 

[bwringer]

The alignment of the #1 arrow looks correct.

As mentioned, getting the crank lined up exactly is also extremely important.

It's a chain and sprockets, so if it's one pin off it's actually fairly obvious.


One thing that commonly happens is that the cam chain bunches up where it passes around the sprocket on the crank. So if you haven't done so already, make sure this hasn't happened -- pull on the cam chain and rotate the crank back and forth just a bit. Make sure there's no slack in the front run of the cam chain from the exhaust camshaft to the crank; rotate the crank clockwise a wee bit and make sure there's tension.

The other thing, of course, is that the chain always wants to skip as you tighten down the cam caps and idler -- the spring tension on the lobes causes the intake camshaft to rotate. Use the trick shown in the manual to secure the exhaust camshaft with a large pair of locking pliers so it can't rotate. As you're tightening the intake camshaft caps and idler, keep a close eye on the sprockets (if you have an extra pair of hands, keep a finger on the chain where it passes over the sprocket). I usually put a dab of paint or fingernail polish on the pins used for timing so I can make sure it didn't skip before installing and releasing the cam chain tensioner.

Once installed, rotate the engine slowly through a couple of revolutions and make sure everything lines up again. Pay attention to the notches in the ends of the camshafts. These should be pointing directly at each other and parallel to the gasket surface at TDC. Rotate the crank one revolution and they should be pointing directly away from each other. (If you put paint on the chain pins, they won't line up again, at least not for a while.)

 

[jbrewer8]

I did check before I removed the cams and the arrow was SLIGHTLY above the gasket surface (although, sometimes I do get carried away taking stuff apart!). In the photo the crank is at TDC and the arrow is just below the gasket surface with no slack in the chain, I was just afraid it was too far below. If you are looking at eye level with the gasket surface, you can just barely see the '1' so I was afraid it was too far. If what I have now is right, it was off by 1 tooth.

Eye level view...


I did not check the valve clearances though. The OP did say he had already checked & adjusted, however that would have been easy to verify before I pulled the cams. Oops. I guess that's how you learn though.

Thanks for the help!!

 

[bwringer]

I did check before I removed the cams and the arrow was SLIGHTLY above the gasket surface (although, sometimes I do get carried away taking stuff apart!). In the photo the crank is at TDC and the arrow is just below the gasket surface with no slack in the chain, I was just afraid it was too far below. If you are looking at eye level with the gasket surface, you can just barely see the '1' so I was afraid it was too far. If what I have now is right, it was off by 1 tooth.

Eye level view...
View attachment 55150

I did not check the valve clearances though. The OP did say he had already checked & adjusted, however that would have been easy to verify before I pulled the cams. Oops. I guess that's how you learn though.

Thanks for the help!!

Hmmm... man, this shows why hands-on is so much better.

In the eye-level photo, you're definitely one tooth off. In the first photo, it looked OK from that perspective.

You should be able to see the upper half of the arrow at eye level. The diagram in the manual is pretty clear.

 

[hannibal]

Is the crank lined on up the line next to the "1-4 T" or on the T? It looks like you're in between links at the "1" mark.

 

[jbrewer8]

Unfortunately, life has gotten in the way of putting this back together until today, we've been preparing for my oldest son's graduation, which was yesterday, so now I should have more time for it. This bike is actually for him, and he's impatient to get it running!

So, I got it back together and checked the valve clearance. Too tight on cyl 2 & 3 but 1 & 4 seemed OK. Anyone know where the best place to get shims is? I also need to get a tool. I wish I would have checked the current shim sizes before I put the cams back in though.

Thanks for the help so far!!

 

[cowboyup3371]

Look up the shim club here on the forum under the GS Services section. If you have done the clearance once than you know the process and can do it again with your calipers to check the size of each shim. If need be, I'm in Miamisburg (south of Dayton) and can come down to help if you want.

 

[jbrewer8]

That would be AWESOME!! I'm just kind of guessing on most of this stuff. I'm actually in Fairfield Township, just North of Cincinnati, so I'm only about a half hour away.

My son (that I'm fixing this for) is a chef and offered to cook you anything you want for helping out! (I can't get that out of him for me & my wife!)

 

[bwringer]

That would be AWESOME!! I'm just kind of guessing on most of this stuff. I'm actually in Fairfield Township, just North of Cincinnati, so I'm only about a half hour away.

My son (that I'm fixing this for) is a chef and offered to cook you anything you want for helping out! (I can't get that out of him for me & my wife!)

Crikey, you're pretty much right in the middle of a whole nest of experienced GSR people. Many of them will be in Indiana for the rally this weekend, but take advantage of the nearby expertise.

 

[Dogma]

Unfortunately, life has gotten in the way of putting this back together until today, we've been preparing for my oldest son's graduation, which was yesterday, so now I should have more time for it. This bike is actually for him, and he's impatient to get it running!

So, I got it back together and checked the valve clearance. Too tight on cyl 2 & 3 but 1 & 4 seemed OK. Anyone know where the best place to get shims is? I also need to get a tool. I wish I would have checked the current shim sizes before I put the cams back in though.

Thanks for the help so far!!

I get my shims from Z1 Enterprises. I have the shim tool, and never use it. Look up the zip-tie method.