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Finding TDC without the indicator? '80 GS550

  • Thread starter Thread starter ChicagoRob
  • Start date Start date
C

ChicagoRob

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Hello All.

While doing a valve adjustment I messed up the timing. (Took the cam chain tensioner off to replace the gasket and it must have skipped a few teeth.)

The problem is that the PO replaced the ignition signal sender with a taller unit, so he couldn't put the TDC indicator back on. (He replaced it with a simple washer.)

Anybody have a sure-fire way to find TDC on an '80 GS550?

Thanks,

Rob
 
Pull a spark plug, stick something in there (a metal rod of some sort, but nothing that will marr the piston), rotate until the stick comes out the furthest...
 
If the ignition is still using the factory advance mechanism even with an aftermarket igntion system the TDC marks shoul still be in place, you may need to remove the ignition pickup plate to see then though. the timing mark is cast into the upper crank case half and the TDC, and firing marks are on the advance mechanism for both cylinders 1-4 and 2-3.
 
Skyboy8950 said:
Pull a spark plug, stick something in there (a metal rod of some sort, but nothing that will marr the piston), rotate until the stick comes out the furthest...
Click to expand...

This is good advice!
I was gonna tell him he's screwed.:)
 
I've done it before on cars when I couldn't see the TDC mark. It is simple and gets the job done.
 
You can also drill through a plug & insert a soft bolt through it. (I think this is the procedure I've only read about it but I can look it up again or try to if you're interested).

Put it in & slowly turn the crank till the piston touches, mark the crank, reverse the engine the other way until it touches again & mark the crank again. The exact middle of the marks will be TDC.

This is meant to be more accurate than the "stick in the hole" trick (unless you use a dial gauge) but I have used the stick in the hole trick with success on car engines.

Dan :)
 
If you use the stick method make sure that its on No 1 piston not No2 or your timing will be 180 degree's out.

Suzuki mad.
 
Thanks

Thanks

That was my next question, which piston? Thanks, it's number one.

I'll try pulling the ignition plate off first to see if there are any factory marks, if not, it's the stick for me.

Thanks everybody.

Rob
 
They made tools for that use.
I still have mine left over from when I had a GT-380.
It was a dial indicator that screwed into the spark plug hole.
I have not seen any in stores lately though.
 
Saltymonk has the right idea.
Use a degree wheel. Bolt it on the end of the crank on the ignition side. Make a pointer out of a piece of wire and connect it to a clutch cover bolt. Point it anywhere on the degree wheel.
Modify a spark plug by drilling out an old spark plug and inserting a bolt long enough to stop the engine before the travel down.
Insert the modified plug into the #1 cylinder. Rotate the engine one way till it stops. Note number on the degree wheel. Go the other direction till it stops. Note this number. Add the two numbers together and divide by two. Take out spark plug stopper and rotate the engine to that number. TDC as close as you'll ever get it.
 
Just a thought, should it matter if the valve is TDC on the compression stroke? i know on cars it has to be on the compression stroke don't know if it's different for bikes.
 
TDC is on the compression stroke at #1.
It does matter especially on the installation of the cams.
 
GQROD said:
Just a thought, should it matter if the valve is TDC on the compression stroke? i know on cars it has to be on the compression stroke don't know if it's different for bikes.
Click to expand...
Since he is resetting the cams, all he has to do is set the crank to the top. Then, when the cam goes in, it will determine whether it's the compression or exhaust stroke.
If he is only moving the cam a tooth or two, yes, he will have to pay attention to which stroke it is.
 
Thanks Everybody.

Thanks Everybody.

I always wanted to play with a dial indicator and Harbour Freight had one for $15, so I went that route.

I tried the "stick in the hole" method first and was still two teeth off.

I really liked the degree wheel idea. If I hadn't bought the indicator, I would've gone that route. That's a true shade tree mechanic hack, simple yet accurate.

Thanks again,

Rob
 
If it has a long enough probe... mount it somewhere solid & stick it down the spark plug hole, the dial will accurately tell you when the piston is at the top as it will count up until it starts falling away, much more accurate than by feel with a rod, probably no better & a little more messing around than the way you & I described though once you have all the parts (drilling a plug etc is a PITA).

Dan :)
 
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