Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: TwiggsiiieS on May 24, 2018, 01:24:12 PM
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Hi all,
Having issues sorting the dreaded pilot cct, rides best with the air screws almost out (4 Turns)
All stock #40 pilot,#75 main, filter, filter box, Carbs clean.
So decided to check everything Vacuum synced, Ignition timing good etc.
Valve timing:
I assumed that if i were to just detect the movement of say the inlet rocker on 4 I could look at the timing mark through the points plate and see it ~ 5° before the 'T' mark( roughly on the 'F' mark). However it is just before the two advance timing marks! probably about 30° BTDC. Checked it twice! I must misunderstand something?
Is the spec 5 BTDC when the valve is fully open?
So took the rocker cover off to check the Cam Markings. Set crank to 1-4 TDC and the marks on the cam sprocket are almost flush with the casting, if I line them up exactly the fixed timing mark lines up with the left hand edge of the letter 'T', about 2 or 3° ATDC.
Is this chain stretch? I don't think its far enough out to be a link out. Is it too far out?
Great to solve this one thanks in advance.
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Yes that is caused by chain wear (they do not "Stretch!") but not far enough out to cause a running problem
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Thanks Bryan,
Obviously the valve timing must be ok but just for infomation, do you know about the Valve timing, at 5° BTDC should the inlet valves just start to open?
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I've not got detailed figures for the 400 but the information given for the 750 quotes; inlet opens 5 BTDC at 1.0mm valve lift. At 0mm lift it's 56 BTDC.
You can see that you're in the right area without having a degree disc to work with. So it doesn't look like any thing to worry about at first look. With the motor at TDC for 1/4 cylinders and the cam positioned correctly, then you are just looking at production tolerances plus wear of chain.
As Bryan has said, it's the chain internal bearings and pins that wear rather than chains stretching. If you try to lift the chain away from the sprocket at the middle of its engagement, then it will give you a good indication of how much wear is in place.
A new chain you can't pull away at all really as the "pitch" of both components matches. Any appreciable movement indicates the chain has a longer pitch than the sprocket.
If the head or barrels have been skimmed it comes out of this dimension too.
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Thanks K2-K6,
That's great info, the chain cant be lifted off the sprocket :).
I will put it back together and ride with the dead spot until winter.
I know the compression on ALL is low but starts and pulls well apart from the dead spot(gets worse with heat)?
I guess the low compression is a valve seat issue as it doesn't burn oil.
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The engine on my CB400/4 was running really well, before I took it apart and found it had eaten 3 pistons and sets if rings.....just saying ;D
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Lol
I'm looking forward to it now!
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Lol
I'm looking forward to it now!
So was I :'( :'( :'(