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Relationship between Timing & tappets

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Sprunghub:
Ok - I'm going to preface this with an embarrassment warning.  I'm not an engineer, I do my best, I get by, but a lot of the time it's luck.  I have '0' mechanical "instinct".

My CB750 F1, 33,000 miles runs like a 'clock'.....which is an unfortunate analogy, because it has developed a "tick", in the last few days or, more to the point a click.....click, click & a whirring sloosh ??? ::)

It sounds, as best I can tell "top end"....but it doesn't sound unduly 'tappety'.....& it is the click/ticking which has attracted my ear ( I mean lets face it, it's a pretty noisy engine even when "pefect") so the slooshing, may be normal "top end" noise.

The only thing I have done to what was an otherwise sweet running, non-ticking, bike, is add the Dyna S electronic ignition & time it to perfection with a strobe light.

The question is, if the timing was slightly out before the Dyna S was fitted & the tappets set to run on a slightly "out" timing, is the fitting of the perfectly adjusted ignition likely to have induced the tappets being 'out' ?

I have double checked the fitting of the Dyna S - nothing is "catching", it does speed up with engine revs but gets pretty much "lost" in the engine noise at higher revs, on the stand or rolling & is most obvious when at low revs, low speed or static.  It's there when the engine is warm or cold ? & doesn't seem to get better or worse.  Sometimes it seems imperceptible & then like a spanner in a tin can.   

The bike is running with good power, carbs have just been set/balanced ( since the ticking started ) & touch wood nothing horrible has happened.

Any suggestions.......

Bryanj:
Adjusting the timing can have no affect whatsover on the tappets, but altering it can make different mechanical noises appear and dissapear, check the exhaust gaskets are not blowing at the head as that can sound very much like a tappet

SteveD CB500K0:
The tappets are set at Top Dead Centre (TDC) which is the "T" mark if you have a Honda points backing plate. This is when the piston is at the top of its throw and both valves are closed.

The timing is set "before TDC" (the "F" mark). This is a few degrees before TDC to allow the ignition a few milliseconds to fire the plug (which should happen a fraction of a second after TDC).

Hope this generic info helps.

I'll leave your other question to the 750 guys...

Sprunghub:

--- Quote from: Bryanj on April 07, 2010, 02:37:04 PM ---Adjusting the timing can have no affect whatsover on the tappets, but altering it can make different mechanical noises appear and dissapear, check the exhaust gaskets are not blowing at the head as that can sound very much like a tappet

--- End quote ---

I wonder......in my last, re. the abortive re-fit of the exhaust, I noted & "fessed up" to the fact that one of the Motad pipes had split around the lip cum flange where it fits against the head.

I've had a 'calm' listen, tonight.......I'm wondering now if it could be coming from there.  It really is the most peculiar.....& alarming, to be honest 'noise'.  That's what made me think it wasn't tappets, it's like a szzzuzzing & a tap ??? ::) :-[.  If it was likely to be a commonly found issue, I'd get a sound file & 'post' it, but it's obviously something obscure ! so there isn't much point. 

I may just hold fire & see what happens when I fit the OEM system.

Sprunghub:
Is there anyone on the Group using a Dyna-S ignition ? particularly with the Dyna coils ??

Still trying to suss the origin of this 'noise'.

It may still be the exhaust, but I've re-bedded the rims & got them tightened down.  I can't put the 'old' set up on until the collet's arrive, but there is no sign of any escaping gas- although that still may be the issue.

In the meantime, I have set the tappets - or rather 'checked' they were pretty much perfect anyway.  Have 'tweaked' the timing chain, which again, was pretty much bang on as it was only done about 1,000 miles ago.

I'm still getting the szuzzing & 'crack'  - I'm just wondering if you get such an enhanced spark with these Dyna S systems you can hear it & if anyone who is running one can comment ?

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