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TDC with a straw question?

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The flywheel markings on my 1986 XL250R are way off, took me a few days to figure that out when I first adjusted my valves.:lol:

After finally finding a new (used) head for my bike I put it all back together. I had always used the straw trick to adjust my valves but putting on the timing chain on my rebuild created a new issue/question.

When I'm turning the flywheel counter clockwise, the straw will be all the way up and then I can turn it a bit more (straw really doesn't go down) but it seems like the piston/connecting rod kind of move into an established position that it sits in. Do I need to hold the racket before it slips down into that position or is that the proper TDC?

Bike runs fine, top end speed is still lacking but that has always been the case.

Any help is greatly appreciated:worthy:

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Have you checked the flywheel woodruff key? Sounds like it might be sheared.

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I like to call that the "Floating point",,Pistons at the top and sort of flops about a bit when it's in that zone..,Personally I don't think anything goes out by it not being directly on the T when the engines at that point but the wisdom around here says different,,Lock the T on the mark somehow to be on the side of whatever anyone else says,,then there's no arguments..,,

and as Creeky says,,Check the flywheel woodruff key is intact and solid in its keyway,,

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Yeah, I know I should probably pull the left side cover and look into why the markings are off but after having rebuilt the top end I just want to ride it.:)

When I buy or borrow a band strap wrench to get the flywheel off, will the woodruff key make sure that the markings are correct or will I still have to find TDC with the straw and then insert the key and flywheel?

Possibly the previous owner pulled it all apart and just inserted the woodruff key when the flywheel was not on the compression stroke.:lol:

Thanks for the input fella's.

Edited by Born Again Ader
Because my grammer sucks.

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Oh well if you can't be bothered checking the woodruff key the worst that can happen is you'll destroy the engine when the valves hit the piston,,Happy with that then fair enough,,

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Oh well if you can't be bothered checking the woodruff key the worst that can happen is you'll destroy the engine when the valves hit the piston,,Happy with that then fair enough,,

Point Taken, I'll take it apart tonight or tomorrow.

I have ridden it over 300 miles the way it is and when I put the head back together I made sure that the lobes on the cam where not even close to touching the rocker arms at my perceived TDC.

I guess I am really wondering if I'm one link chain off or not and what that would do performance wise.

BTW, had the same bike 11 years ago in New Zealand, lived in Christchurch for the better part of a year riding it all over the South Island. How I wish I could go back.:lol:

Edited by Born Again Ader

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I think the best that any of us can do is get the timing within 1/2 link (do to chain stretch or tensioner).

So, if you set your timing based on piston TDC and the flywheel mark is not in the correct position, then this would indicate a missing or sheared woodruff key as "creeky" stated.

I'm just not sure if understand your problem... Is your flywheel timing mark off position, or is it just a floating point at TDC ???

BTW: You don't need to find TDC to install the key... It only goes one way! :lol:

Perc

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I think the best that any of us can do is get the timing within 1/2 link (do to chain stretch or tensioner).

So, if you set your timing based on piston TDC and the flywheel mark is not in the correct position, then this would indicate a missing or sheared woodruff key as "creeky" stated.

I'm just not sure if understand your problem... Is your flywheel timing mark off position, or is it just a floating point at TDC ???

BTW: You don't need to find TDC to install the key... It only goes one way! :lol:

Perc

Thanks for the reply.

The timing marks are totally off, not even close to TDC when I line up the "T" mark. I gave up on the flywheel markings the first time I adjusted my valves.

Therefore, I always use a straw to determine when I am at TDC on the compression stroke.

When I reinstalled the cam and installed the chain, that's when I noticed the floating point at TDC.

Probably best to fix the flywheel and woodruff key and not have to worry about what TDC is anymore.

Thanks for everyone's help, I'll try to take it apart tonight and see if I have a replacement woodruff key in the parts bike.

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My Bike finally sounds like a true thumper.:bonk:

Took me a while to get the proper flywheel puller but after putting her back together this morning, it seems like a new motorcycle. The timing was definitely off a link or two. Most likely the reason I was running lean and cracked my old cylinder head.:smirk:

Of course at the end of my test run the clutch cable snapped:banghead:

Nice dude at the gas station helped to push my bike to bump start it, I did finally get back home in 2nd and 3rd gear without stopping:worthy:

Thanks for all the help and happy holidays to everyone.

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Just curious. What timing marks are you talking about that were off when when the T mark is lined up? The marks on the cam sprocket that are supposed to be level with the head surface?

I'm thinking you might not have installed the cam chain on the sprocket correctly. With the T mark aligned, you set the cam in place and hold it so the sprocket timing marks are level with the head. When putting the chain on, you have to pull slack out of the chain(not so hard as to move the crank of the T mark) and wrap the chain around the sprocket from front to rear. All chain slack has to be on the back side of the sprocket. If not, then when you go to reinsert the auto tensioner it will pull the slack out of the chain on the front side of the sprocket when it does its tensioning and throw the sprocket timing off.

Thanks for the reply.

The timing marks are totally off, not even close to TDC when I line up the "T" mark.

When I reinstalled the cam and installed the chain, that's when I noticed the floating point at TDC.

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Initially when I aligned the flywheel on "T" it was not at TDC with the straw test, turned out that it was a sheared woodruff key.

Once I pulled the flywheel and installed a new woodruff key, I didn't have to guess at TDC and viola I was a link off on the cam chain.

Huge difference in performance.

Just curious. What timing marks are you talking about that were off when when the T mark is lined up? The marks on the cam sprocket that are supposed to be level with the head surface?

I'm thinking you might not have installed the cam chain on the sprocket correctly. With the T mark aligned, you set the cam in place and hold it so the sprocket timing marks are level with the head. When putting the chain on, you have to pull slack out of the chain(not so hard as to move the crank of the T mark) and wrap the chain around the sprocket from front to rear. All chain slack has to be on the back side of the sprocket. If not, then when you go to reinsert the auto tensioner it will pull the slack out of the chain on the front side of the sprocket when it does its tensioning and throw the sprocket timing off.

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