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gs650g timing issue?

  • Thread starter Thread starter apprentice-mark-maker
  • Start date Start date
A

apprentice-mark-maker

Guest
Hey guys and gals,
I just finished an engine rebuild (new piston rings, and gaskets) and have noticed there are 2 timing marks. one looks like " T|" and the other "T|F|". put the bike back together and cranked it over by hand and did not feel any pistons banging into valves, however I am not getting any compression (0psi,0psi,0psi,3psi). if i place my finger over the spark plug hole there is a strong vacuum however. any help would be great, thanks!
 
Hopefully,your advancer gizmo is legible. "T" mark is TDC.."F" mark is about 10 degrees btdc...then another mark way to right in pic is about 40 btdc (full advance)
Are your camshafts oriented correctly?


image.jpg
 
Ive double and triple checked the position of the cam shafts according to the gs650g maintenance manual (though my manual calls for 20 pins not 18 between the 2 and 3 mark), and the timing was set to the T|. Currently the timing marks on the shaft are facing cylinder 4 furthest to the right from the position of the rider. Im about to give everything a once over and check the position of the cam lobes at top dead center and will report back.
 
You might want to make sure the notches in the cams are facing each other. And remove the ignition plate so you can see the 1.4 T mark clearly.
 
I am not sure this is even possible, but I will throw it out there anyway, did you accidently install the exhaust cam on the intake? Look for the tach drive teeth.
I always assumed it could happen which is why they are marked with a big EX sometimes.
 
apprentice-mark-maker said:
Ive double and triple checked the position of the cam shafts according to the gs650g maintenance manual (though my manual calls for 20 pins not 18 between the 2 and 3 mark), and the timing was set to the T|.
Click to expand...
Please check at least one more time. :-k

What you need to be SURE of is where you start and end your counting.

- First, line up the T| 1-4 mark on the crank with the index mark.
- Make sure the #1 arrow on the exhaust cam is pointing at the edge of the head.
- Look at the #2 arrow. The pin directly over it is Pin #1. It is not Pin #0, and you start counting the one next to it. Pin 1 is OVER arrow #2.
- When you get to Pin #20, it will be OVER arrow #3.

Very technically speaking, yes, there are 18 pins BETWEEN the two arrows, but the instructions call for including the pins over the arrows, so the count will be 20.

I can't (won't :oops:) tell you how many times I mis-counted the pins by saying that Pin #1 was the next one after the #2 arrow. Yeah, the bike didn't run so well, so I went back and did it again. And again. And again. It finally hit me that I was counting incorrectly. My bikes run great now.

.
 
So ive double checked the engine with a second pair of more experienced eyes, and have cross referenced the manual a few more times, but its still stumping me. By everything Ive seen the timing should be correct. When the |T 1.4 mark is lined up with the timing mark pistons 1 and 4 are at BDC and pistons 2 and 3 are at tdc. The cam lobes are both facing out at the same angle when piston 4 is at bdc and the timing mark is in line. The pins are counted and are correct as well as the arrows being flush with the gasket surface. Leakage i dont think is a huge deal cause when the spark plug hole is covered with my finger and is cranked by hand durring the down stroke before the valve opens, it holds a vacuum for a long time. When I put the engine back together the first time I may have not put the valve cups back in their proper places, I know it isnt prudent, but the bike only has 6k on the engine, so I dont know if it would make a huge difference as there isnt much wear in. Ill go take some pictures of the cams and piston positions and post them.
 
Lets step back here and think....when 1 and 4 fire, their pistons will just about be at TDC. As Nessism said, the notches on end of camshafts will be facing each other like in this pic...if you need a bigger pic let me know

image.jpg
 
apprentice-mark-maker said:
So ive double checked the engine with a second pair of more experienced eyes, and have cross referenced the manual a few more times, but its still stumping me. By everything Ive seen the timing should be correct. When the |T 1.4 mark is lined up with the timing mark pistons 1 and 4 are at BDC and pistons 2 and 3 are at tdc. The cam lobes are both facing out at the same angle when piston 4 is at bdc and the timing mark is in line. The pins are counted and are correct as well as the arrows being flush with the gasket surface. Leakage i dont think is a huge deal cause when the spark plug hole is covered with my finger and is cranked by hand durring the down stroke before the valve opens, it holds a vacuum for a long time. When I put the engine back together the first time I may have not put the valve cups back in their proper places, I know it isnt prudent, but the bike only has 6k on the engine, so I dont know if it would make a huge difference as there isnt much wear in. Ill go take some pictures of the cams and piston positions and post them.
Click to expand...

The bolded part above could be your problem. Not sure if you just mistyped, but pistons 1 and 4 should be TDC, not BDC.
 
Are you sure your crank is not 180 degree out of time here. I thought piston 4 should be a TDC if both the cam lobes are facing out.
 
THATS IT BOYS! WE'VE GOT COMPRESSION AT 140 ACROSS THE BOARD!!!! The timing mark T|F| is apparently for pistons 1 and 4 where as the timing mark T| is for 2 and 3. which is odd as the manual says to "line up the timing mark T". I find it weird that only the 1 and 4 mark have the fire mark, but oh well. Thanks for all the help guys! Wouldnt have done it without the suggestions that 1 and 4 needed to be at TDC when cam lobes where out.
 
Hooray! While you've been messing with innards, did you fiddle with camchain tensioner to ensure it's working properly?
did you reinstall it correctly? And release the lock screw? Then tighten the locknut?

I gotta ask....why did you have to do this work? And at how many miles?
 
The reason for the work was because I had a bubble in the watch glass, didnt recheck the oil after i started the bike, and pushed the engine too hard. revved it to about 7 grand with half a quart too much oil in it and started puking oil out the vent at the top. Figured it was either head gasket or piston rings but I also wanted to see the inside of the engine to check the condition and clean stuff out. History on the bike is it was a craigslist barn bike with 6k miles on it, but the last registration on it was from 1981(the year it was made) so shes been sitting for a while probably 35ish years. bought for 800 figuring it would last a while before any major work...

This is my first bike, and have no previous experience with anything bigger than a 5hp lawnmower engine. So my blunder with the oil was a sore mistake that will not be forgotten. and the cam tensioner is installed properly, and takes up the slack. I gave it a small crank backwards and the chain was still tight.

good news is the bike runs like a hot damn now. Better than before the rebuild! and all the sludge from engine break in is gone so oil should be nice and clean for a while.

Also if there is a place on this for entertaining stories, Ive got some pictures from this rebuild. As a college student I did the whole topend rebuild in student housing and in a parking lot including using a 30 rack to drop the engine. where theres a will theres a way.
 
"Also if there is a place on this for entertaining stories, Ive got some pictures from this rebuild. As a college student I did the whole topend rebuild in student housing and in a parking lot including using a 30 rack to drop the engine. where theres a will theres a way."

us old guys like to hear these stories , knowing that there are still some youngins who will perserve!
keep up with the maintenance and this critter will treat you well....Mine still runs nicely at 58k miles, 50+mpg easy
Enjoy it
 
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