Finding TDC with spark plug stopper?

allanrps

allanrps

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I was trying to set my timing today. I don't have the stock flywheel on, so I was trying to find top dead center and measure the timing using a degree wheel. I went about doing this by making a stopper that screws in to the spark plug hole out of a plug and some hardware. Then I opened the intake valve peek hole and inserted the stopper in when the cylinder was on the compression stroke. However, I turned the engine over like 1 1/2 times before it stopped, and it stopped when the intake valve was coming down. It didn't occur to my idiot self that the stop was likely hitting the intake valve and not the piston until I heard a terrifying pop when unscrewing the stopper with the valve partially open. I had also leaned into the crank shaft when bringing what I though was the piston to the stop and screwed in the stopper several turns after meeting increased resistance when the valve was partially open. So I am terrified that I've f'ed up my valve. I don't get though why it would hit the intake valve but not the exhaust valve. And I don't remember hitting any valves with a screw driver down the spark plug hole. Can somebody shed any light on this? Did I really mess up? Is there another way to find TDC?

Thanks,
Allan
 
use a dial gauge, much more accurate.


I would check the valve as it could be bent and let go when running, ruining all your hard work
 
If the valve is bent, it will have noticeably more clearance than it had before. That would be the first place to check. A leak-down test would be the next option, followed by a compression test - if the engine can turn over freely by hand.
 
You can stick a pencil(or whatever) into spark plug hole(while holding it) and simply feel piston go up and down while turning crankshaft with a wrench, TDC is between moment pencil stops going up and the point it starts going down. To make TDC mark you do not care what compression cycle it is. Once found - make a scratch on the flywheel and you got the mark. It is also ok to turn engine 5-10 degrees back and forth around TDC to get a feel that you mark is in the right spot.
 
I used the pencil trick when finding tdc to set the valves, but I want to have a more accurate mark for setting the timing. I wanted to measure the degrees where the piston hit the stopper on either side of tdc, then mark tdc in the middle.

Drewpy, what do you mean by "let go"? You mean it might release from the cam shaft and get chewed up by the engine? I figured I was just going to start it and hope nothing got messed up, but upon further consideration, that doesn't seem like a good idea....

I'll check the valve clearance and hope it's where I left it. I still don't understand how one valve could hit but not the other. Aren't the intake and exhaust valves symmetrical?
 
Ah ok.... I guess at one time I knew that.

Sorry for asking lame speculative questions, but I don't really want to pull the engine and check. Do you guys think its likely I bent the valve? I didn't use a whole lot of force turning the crankshaft and I didn't screw the stopper in much after feeling resistance from the valve either. If there's any give in the system and the valve is tough I'd imagine the valve itself wouldn't be damaged.

Also, would I be able to do as I planned with a thinner stopper? Does anybody who's been in the engine know if there's any clearance there at all?

Thanks a bunch for all the help
 
I am thinking, that a compression test, will be your test. bad compression, will or may signifie that you will be opening your case up, to see your valves. a good compression, should be good.
 
Ditto on the compression test.
If you can turn the crank manually and nothing sticks, catches, or breaks. It's probably ok for a comp test.

Do a dry compression test then a wet compression test.
If the wet test gets close to 150psi I believe you can assume the valves are OK.
 
Last edited:
allanrps said:
Drewpy, what do you mean by "let go"? You mean it might release from the cam shaft and get chewed up by the engine? I figured I was just going to start it and hope nothing got messed up, but upon further consideration, that doesn't seem like a good idea....
Click to expand...

the head could possibly break off the stem, they are hardened steel but brittle with it.

If it was me I would take the head off and check the valve for lip/stem damage.its not a big deal to do
 
allanrps said:
Ah ok.... I guess at one time I knew that.

Sorry for asking lame speculative questions, but I don't really want to pull the engine and check. Do you guys think its likely I bent the valve? I didn't use a whole lot of force turning the crankshaft and I didn't screw the stopper in much after feeling resistance from the valve either. If there's any give in the system and the valve is tough I'd imagine the valve itself wouldn't be damaged.

Also, would I be able to do as I planned with a thinner stopper? Does anybody who's been in the engine know if there's any clearance there at all?

Thanks a bunch for all the help
Click to expand...

I have to be honest, I do not fully understand the "stopper" trick. Can't comment on that.

If you already have TDC scratch(mark) you can set valve clearances. Measure 12degrees from first scratch and make another scratch(mark), now you can set ignition timing using it.

As for bent valves scare - doubt you broke something. I would remove spark plugs, put bike in first gear, roll it few feet and listen. If no scary noises I would do "compression test" by closing spark plug holes with my finger, put everything together and start the bike :)
 
Thanks for all the help guys. I checked the valve clearance and that did not change, so I guess I'm pretty safe, right? Engine isn't making any funny noises. If there is still doubt I'll try to get a hold of a compression gauge.

I did find tdc and set the timing successfully with the stopper. Just hit the stopper with the piston on either side of tdc and then marked tdc in the middle using a degree wheel. Then set timing forward 10 degrees.
 
Started the thing today. Had to use stater fluid to get it going, and once it started I heard this pretty loud clunking noise. I guess I know that means... I'll check the timing again just to make sure it's not premature detonation, but it doesn't sound like it to me. Off with the head I guess

Posted via Mobile
 
allanrps said:
... Off with the head I guess
Click to expand...

...........
images
 

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allanrps said:
Started the thing today. Had to use stater fluid to get it going, and once it started I heard this pretty loud clunking noise. I guess I know that means... I'll check the timing again just to make sure it's not premature detonation, but it doesn't sound like it to me. Off with the head I guess

Posted via Mobile
Click to expand...

Never mind, its all a learning curve
 

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