changing a head

[david vaughan-birch]

hi-a word of advice please? I'm putting a new left hand head on; I've followed Steptoe's advice and ziptied the camshaft chain to the sprocket but the indent is facing down rather than up on the head as fitted at the moment, and according to Haynes it should be pointing up so that its on TDC compression stroke. Presumably with the indent facing down this means its on TDC exhaust stroke? Can I fit the head like this, and then cycle the engine to TDC to set the valve gaps? Or alternatively get a grown up to look at it? Advice appreciated!

 

[waterloo700]

If if came off that way - AND you haven't turned anything over while the head was off - all will be OK

BUT

for God's sake turn the motor over by hand when its all back together to check and - if in doubt get expert advice and not from dummies like me on't t'internet.

Advice is easy when its not your own bike

 

[MattW]

hi-a word of advice please? I'm putting a new left hand head on; I've followed Steptoe's advice and ziptied the camshaft chain to the sprocket but the indent is facing down rather than up on the head as fitted at the moment, and according to Haynes it should be pointing up so that its on TDC compression stroke. Presumably with the indent facing down this means its on TDC exhaust stroke? Can I fit the head like this, and then cycle the engine to TDC to set the valve gaps? Or alternatively get a grown up to look at it? Advice appreciated!

Yep - just refit the new head with the cam rotated so that the key on the cam lines up with the key way in the sprocket.

Make sure you drench the camshaft / followers etc with fresh oil before you rotate the cam. Bear in mind, with the cam at TDC exhaust, the valves will not be on their seats and will be proud of the head face - don't put the head down on it's gasket face or you could bend the valves.

Then with it refitted turn it over by hand until the head is at TDC compression (always a good idea to turn it over gently by hand anyway after fitting a head etc to make sure nothing is clashing).

 

[Steptoe]

hi-a word of advice please? I'm putting a new left hand head on; I've followed Steptoe's advice and ziptied the camshaft chain to the sprocket but the indent is facing down rather than up on the head as fitted at the moment, and according to Haynes it should be pointing up so that its on TDC compression stroke. Presumably with the indent facing down this means its on TDC exhaust stroke? Can I fit the head like this, and then cycle the engine to TDC to set the valve gaps? Or alternatively get a grown up to look at it? Advice appreciated!

So, this "new" head isn't the same head that came off - Judging by what you've explained and if i'm interpreting it corrrectly you can't just fit it back in place as it is, you'll need to rotate the cams etc so the timing sprocket lug will line up with the sprocket and the cams and valves will be in time with the piston at TDC and the rest of the engine.

 

[david vaughan-birch]

thanks chaps-thats what I thought. As you say Steptoe its a different head so I need to make sure that everything's in phase. Just so that I can understand whats going on, am I right in thinking that (apart from the need to fit the head at TDC so that theres no pressure on the valves from the cams) its simply a question of aligning the keyway with the timing sprocket lug?

 

[MattW]

thanks chaps-thats what I thought. As you say Steptoe its a different head so I need to make sure that everything's in phase. Just so that I can understand whats going on, am I right in thinking that (apart from the need to fit the head at TDC so that theres no pressure on the valves from the cams) its simply a question of aligning the keyway with the timing sprocket lug?

If you fit the head at TDC exhaust (which you'll have to), there will be slight pressure on the valves from the cams but it doesn't matter (as long as you don't put the head down on its gasket face as above). As long as the new head is at the same 'TDC' as the one you removed, the keyways will line up.

I did just this when I removed my 1100's head to fit a new head gasket - mistakenly set it at TDC exhaust before I removed the head. I then dismantled the head (removed the cam carrier) so that I could take it to get the head face skimmed. When I bolted the cam carrier back on I mistakenly set it at TDC compression.

I realised my mistake when I came to try to refit it (keyway 180 degrees out of phase) - I just spun the cam to bring it to TDC exhaust and it refitted with no problem.

You might find it hard to spin the cam with no sprocket on it - I unbolted the cam carrier, spun it and bolted the cam carrier back down.

Edit: As Steptoe says in his how-to, be ultra careful to make sure that the keyway is properly engaged before you tighten the sprocket nut.

 

[david vaughan-birch]

now this is odd-set the keyway on the lefthand side so that it faces up as per manual, and checked the other side to make sure it was facing down. They are both up! very confused now so will have a cuppa and think again.

 

[MattW]

now this is odd-set the keyway on the lefthand side so that it faces up as per manual, and checked the other side to make sure it was facing down. They are both up! very confused now so will have a cuppa and think again.

There's not really any reason that the keyways should face in different directions - they are timed independently (or at least run from separate sprockets on the jackshaft which runs under the crank) and are probably handed so they aren't interchangeable.

As long as you make sure the keyway on the cam and the sprocket line up, it'll be fine (but still spin it over a few revolutions with a spanner on the crankshaft to make sure!). Remember the cam runs at half crank speed.

 

[david vaughan-birch]

True-but I never underestimate my own ability to make a simple job complicated...

 

[MattW]

True-but I never underestimate my own ability to make a simple job complicated...

Just thought - you are using a new head gasket aren't you?

 

[david vaughan-birch]

yup-I did remember to get a new gasket! I think I didnt torque up the sprocket enough so when I cycled the engine it stayed put. Get there in the end I'm sure. thanks for the help so far chaps

 

[MattW]

yup-I did remember to get a new gasket! I think I didnt torque up the sprocket enough so when I cycled the engine it stayed put. Get there in the end I'm sure. thanks for the help so far chaps

Re read Steptoe's how-to - it really critical to get the sprocket keyway engaged before you torque it. Otherwise you can mash the keyway / sprocket.