Problems with settin cam chain on a 1976 honda xl 125 engine

[swordheart]

Could someone help me with this, i am rebuilding a honda xl 125 engine ( i have had the casings vapour blasted )I bought the bike as non working and thought it would be a nice cheap intruduction to learning how to rebuild an engine. My problem is when i set the tdc on the rotor, the cam sprocket mark is slightly to the left of where it should be and when i set the cam sprocket mark to where it should be the rotor mark is at the F rather than the T mark, its doing my head in. Am i doing something wrong. I have no idea how the cam chain tensioner works but it does seem tight.

[Fizzer Thou]

Getting the cam timing correct should be your main concern.If you get the timing out by one tooth,it will throw out your ignition timing

Adjusting the correct timing chain tension you can do once the engine is running.
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[davebike]

Unless the chain is very stretched and
I guess you using a new chain or have checked its condition?

The crank been rebuilt and when the cam chain sprocket was replaced they not got it right
BTDTGTS

Dave
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[Robby]

If it's anything like similar engines, the tensioner will a spring loaded slipper blade that fits behind the cam chain on the back side of the engine (inlet side). If you have the rocker cover off the bike then the tensioner will be relaxed and not putting any tension on the chain.

If you have any slack in the chain while setting the timing, you want the slack to be on the tensioner side of the chain run.

Getting everything to line up perfectly can be tricky. 1 or 2mm is ok, you just want to be on the correct tooth of the sprocket.

[swordheart]

Thanks for replies
No it isn't a new cam chain and to be honest I wouldn't know how to tell if its stretched. Here's a photo of how far past the mark it goes, the rotor mark is set and the position of the cam mark is just over the top of the previous tooth. The picture isn't quite right the mark is directly over the top of the previous tooth.

https://i1244.photobucket.com/albums/gg579/swordheart/IMG_0923.jpg[/URL]

[Fizzer Thou]

How tight is the cam chain tension when in this position?If there is any looseness on the chain it may well move the cam timing with respect to the crank position.Do not set the valve clearances until the cam timing is correct or the best that you can make it with regard to the alignment markings.

The other year I helped a friend to do a top end rebuild of a Honda XR250R engine.We had a similar situation to what you are now experiencing.No matter what we tried,it was always half a tooth out of alignment.In the end we set it as best we could and hoped for the best.After several hundred miles the engine runs perfectly.

From what I remember the cam chain tensioning is done by removing the rubber cap,loosening off the locknut and adjusting the centre screw until there is no rattle from the cam chain.The empty bolt hole at 4 o'clock to the cam sprocket is for the cam chain tensioner blade upper mount bolt,so install that and see how the chain tensioner adjusts things.
____________________
Just talk bikes.What else is there?

Always have a 'Plan B'

[swordheart]

The cam chain is very tight, I forgot to say I removed the cam chain bolt to see if the cam chain tensioner blade would slacken and allow the cam sprocket mark to move more to the left so it was a whole tooth away, but as you can see it didn't it stayed still
When I screw down the adjuster bolt it has no effect on the cam blade mechanics ( I have the rotor cover off ) I presume from earlier posts it only comes into effect when the engine is running ?
I am tempted to leave it half a tooth out and just see what happens

[Nobby the Bastard]

I used to rebuild an XL185 every weekend (it really needed scrapping but the owner needed transport).

You can move it forward (or backward) one tooth with no damage to the valves. It's quite difficult to identify what is the correct timing.

It sounds like it needs to be moved 1 tooth because you got it wrong.
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[swordheart]

That's good to know about it not damaging the valves. I think I will try it as it is first, then if it has problems I'll take it to pieces and totally rebuild it again