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Timing question

  • Thread starter Thread starter jdion81
  • Start date Start date
J

jdion81

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The 1982 GS850GL engine I am rebuilding didn't have the ATU attached so I am not able to mark the position of the ATU plate and find TDC accurately using this. I have held the ATU plate to the crank and found approximately TDC which I have verified through the spark plug hole.

1. How important is it to find TDC accurately before removing the cams?
2. How do I accurately set the timing after the rebuilt as I have no index mark (which would have been made when removing the ATU)
 
As many years as I have owned and worked on 850s, I have never heard the term "ATU". What is it? :-k

1. You can remove the cams regardless of crank position, but the only reference point you have for putting them back in is TDC, so it's just easier to put it there before you remove the cams.
2. Cam timing is explained in detail in all versions of the service manual that I have seen (Suzuki, Clymer, Haynes). It requires setting the crank to TDC first. Without marks, you will have to make some by visually observing the piston to determine TDC. You then set the exhaust cam so the timing marks line up with the appropriate places, count the proper number of chain pins, then set the intake cam. Finally, install the idler sprocket and the tensioner unit.

.
 
Steve said:
As many years as I have owned and worked on 850s, I have never heard the term "ATU". What is it? :-k
Click to expand...

The Haynes manual that I have calls the electronic ignition unit thingy the Automatic Timing Unit and shortens it to ATU. Babbitts online calls it [FONT=&quot]SIGNAL GENERATOR ASSY[/FONT]


Steve, Since I have your ear for a minute or two, what do you think of stainless bolts in the aluminum head/engine casing? I would like to replace the bolts with allen head bolts and kind of like the idea of stainless, but heard warnings of chemical reactions between the aluminum and stainless.
 
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Most people you will find around here use the OEM Manual and antiseize on their SS hex bolts.
 
I agree, I do like the OEM manual, but I wanted something that I could afford to get covered in oil and crap rather than my laptop screen.


Do you have a recommendation on where to get the SS stuff? And you would use hex rather than allen?
 
OK the Signal Generator assembly is on a plate that fits in there, but why was it removed? Unless you are splitting the cases or changing the oil seal behind it, there is no need to ever remove it. You will need to use a degree wheel or something similar to make sure you get it back EXACTLY like it was, so it will work properly.

Stainless bolts are OK, as long as it is not structural. Holding covers onto the crankcase is not structural.
As posplayr mentioned, use anti-sieze (copper is preferred) when putting the bolts in.

Have you been given the keys to our "library"? It is otherwise known as "BassCliff's site".

Click HERE to go to the site. Bookmark it, you will be using it A LOT. :-\\\

While you are there, note at the top that you can download a factory manual for an 850, or just click HERE.

There is also a wiring diagram there, but the one in the right column just below that is better. Click HERE for the diagram.

Yes, the manual and the diagram say they are for an '80 850. The manual covers all years, so read carefully to make sure you are in the right section.
The diagram is lacking the side stand warning switch that is on your '82, but it is otherwise the best diagram that shows all the colors and connections.

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Steve said:
OK the Signal Generator assembly is on a plate that fits in there, but why was it removed? Unless you are splitting the cases or changing the oil seal behind it, there is no need to ever remove it. You will need to use a degree wheel or something similar to make sure you get it back EXACTLY like it was, so it will work properly.
Click to expand...
The engine that I am rebuilding didn't come with the signal generator assembly attached, so the assembly was pulled from the other bad engine. Is there a published procedure for this degree wheel thing that you speak of? I sure hope so.
 
jdion81 said:
The engine that I am rebuilding didn't come with the signal generator assembly attached, so the assembly was pulled from the other bad engine. Is there a published procedure for this degree wheel thing that you speak of? I sure hope so.
Click to expand...

The simplest thing by far is to get the correct OEM parts.
 
posplayr said:
The simplest thing by far is to get the correct OEM parts.
Click to expand...
What do you mean, correct OEM parts? I have those, its just that they were not on the engine when I got it, so I have no index for re-assembly. I could through the timing assembly on there and hope that its in synch with the cams.. but I dont think that is prudent.
 
jdion81 said:
What do you mean, correct OEM parts? I have those, its just that they were not on the engine when I got it, so I have no index for re-assembly. I could through the timing assembly on there and hope that its in synch with the cams.. but I dont think that is prudent.
Click to expand...

If you had an OEM manual you could see there is a plate that has marks on it.
 
Yeah, I have the plate and found where TDC should be - approximately anyway. Within a few degrees or so. How important is it to get it dead nuts accurate before starting it up though?

I think I have figured out the wheel process though, and can get it a lot more accurate to true tdc.

Steve - thanks for mentioning the degree wheel and I do have the OEM manual up on my work computer, hasn't been closed in a few weeks.
 
jdion81 said:
Yeah, I have the plate and found where TDC should be - approximately anyway. Within a few degrees or so. How important is it to get it dead nuts accurate before starting it up though?

I think I have figured out the wheel process though, and can get it a lot more accurate to true tdc.

Steve - thanks for mentioning the degree wheel and I do have the OEM manual up on my work computer, hasn't been closed in a few weeks.
Click to expand...

Timing varies between 4 deg(idle) BTDC to about 28 deg(2500) BTDC.This is from memory the numbers are in the manual(under specs).

I used a degree wheel to check the factory marking (GS1100ED) and it was within about the width of one mark.

For timing figure +/- 2 degrees. I don't know how far that is till you are off by a link in the cam chain. You can probably rotate the motor one tooth and see how far the mark moves.
 
One link is about 24 degrees, at least on the 1100. 720 / 30 teeth = 24
 
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I know that it will be different amounts for different bikes. The 650E and 650G use the same cams, but the SPROCKETS are different.

I discovered that when I put an engine together from some different donor bikes. With the E cams in the G engine, I could only rotate the crank about 1 1/4 turns before it locked up SOLID. Watching carefully, I noticed that one of the valves seemed to be opening too early, so I re-checked the cam timing AGAIN (and again). Finally took the cam out and counted teeth on the sprocket. The E sprockets have fewer teeth, so will turn quicker when driven by a G crank sprocket. I changed the sprockets, put the E cams (with the G sprockets) in and it did the full rotation test, so I closed everything up and hit the starter button. :encouragement:

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