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1999400F

1999 YZ400F Update!

31 posts in this topic

Well we went riding Thursday and the smoke smelled of oil so I'm currently in the process of taking the head off and replacing the piston and rings. I ran into a few problems/concerns. upon getting the bike to TDC we loosened the timing chain and slid the 2 cams out and suspended the chain with wire from the frame-some how we lost TDC when I checked after removing the cams, will this be an issue upon reinstall? We loosened all the head bolts except for the 1 in front and the 1 in back of the engine reason being is it was so damn tight we started to strip the nut facing the rear-any ideas on how to get the nut off? We thought about heating it up with a torch or dremeling it off-any suggestions? and the final concern is do I need to remove the shims in order to pull off the head? Thanks for your input guys and girls!

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what i did to find TDC after losing it was take a thin flat screwdriver and insert is into the spark plug hole. move the wire on the cam chain allowing you to place your hand in a relative position to where the cam sprockets meet up with the cam chain. rotate the nut on the crank while letting the chain move in the palm of your hand and not bind up. watch for the screw driver to reach TDC.

by stripped do you mean to say that you've begun to round the nut off making it harder to grab or has it somehow been cross-threaded and is actually stripped somehow not allowing it to back off, the former being what most likely happened.

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TDC will be no problem...just be sure the timing chain is engaged on the crank sprocket and you keep a bit of tension on it when you move the flywheel, otherwise it will get all wadded up in around the crank and could get damaged or bent. As far as those nuts, you need something like this http://www.motionpro.com/motorcycle/tools/category/torque_wrench_adapter/

to be able to get a box end on it and apply some torque. If it's already too rounded to do that, cut with a dremel tool and buy a new stud/nut. Don't use a torch!

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the nut is starting to round off...so to my understanding its just a stud thats coming out of the head and it is easily replaced?

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I just ordered new studs all around can't hurt to have the extra studs layin around..more updates on friday!!

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TDC is no problem. Just set it back to TDC by the marking on the stator (is that how you did it previously or no?) That's the only way to be exact about it anyways

I'd recommend seeing how stretched the cam chain is while you're in there.. that's one thing you do not want to fail..

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when i popped the valve cover off it was tight as a mofo, also check tension-er and it seemed to be in working order. I did not mark TDC on the cams or chain...I looked in the manual and made sure the dots (indents) on the cams were evenly aligned when the "I" on the crank was aligned.

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...I looked in the manual and made sure the dots (indents) on the cams were evenly aligned when the "I" on the crank was aligned.

This is how it should be done.

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when i popped the valve cover off it was tight as a mofo, also check tension-er and it seemed to be in working order. I did not mark TDC on the cams or chain...I looked in the manual and made sure the dots (indents) on the cams were evenly aligned when the "I" on the crank was aligned.

of course it's tight..the tensioner keeps it tight

that doesn't mean it isn't stretched

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This is how it should be done.

question, in the manual it pictured the cam on the exhaust side with the indent (dot) aligned on the left but when i got it to TDC the first time it was aligned on the right, could that be an issue...also it is a hot cam stage 1.

of course it's tight..the tensioner keeps it tight

that doesn't mean it isn't stretched

Well then how would I check to see if it is stretched?

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The camshafts turn at half engine speed, so there are two TDC's for each revolution of either cam. At one TDC (compression) the cams will be aligned, at the other (exhaust) they will appear upside down.

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If your doing the top end anyways replace the timing chain. They are cheap and easy to replace. You will need a flywheel puller though and they are cheap as well.

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The camshafts turn at half engine speed, so there are two TDC's for each revolution of either cam. At one TDC (compression) the cams will be aligned, at the other (exhaust) they will appear upside down.

does it matter which TDC I use..I was just gonna align the "I" then place the cams in how they look in the manual

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The spark is triggered by the crank, so it fires the spark plug each and every time around, producing a "waste" spark during the end of the exhaust stroke. Any TDC you choose to time the cams will become the compression stroke because the cams are what determines that.

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Intake - compression - power - exhaust plug fires every other storke

You know what I mean. I meant stroke as in piston going up.. not in the literal intake/compression/power/exhaust

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ok got the head and cylinder off this weekend and there is quite a bit of carbon build up-how should I go about cleaning the head,. sandblast? Also I could tell that there was oil getting in the gas but the rings look ok, does this mean anything? could oil be getting in from the valves?

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