Author Topic: Valve timing  (Read 8562 times)

Offline billy192

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Valve timing
« on: December 22, 2012, 09:38:38 PM »
Hi,
I think I have put the cam back in correct,,,,,,,,, but is there a way to make sure. I have turned the roto around by spanner and not valves hitting the piston. but doubt has crept in.
I do know where TDC is but how do i know when TDC on the compression stroke is?
 
Billy
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Billy

Offline tom400f

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Re: Valve timing
« Reply #1 on: December 22, 2012, 10:02:03 PM »
I would expect the static ignition timing marks will tell you (this is a 250G5 right? They are 180 degree twin if I remember)

Anyway, if you have aligned the crank and camshaft markings OK then its unlikely you have made a mistake. You have to be a whole tooth out one way or the other so it would have been obvious. Not sure how easy it is to measure accurately but if you know the timing specification (inlet opens x degrees before tdc etc) then you can may be see with the tappet covers off and check the crank position.

Last resort - whip the rocker cover off....
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Offline billy192

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Re: Valve timing
« Reply #2 on: December 23, 2012, 08:31:41 AM »
Thanks,
yes its a G5 250 I think its dead on the timing marks. after checking last night it looks like the carbs are not working correctly. the slides are not rising at all. i will check the diraphram's next.
Billy.
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Billy

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Re: Valve timing
« Reply #3 on: December 23, 2012, 01:29:53 PM »
To answer your original question about compression stroke......it's the cam that defines the compression stroke as if you move it one revolution out from where it is the compression stroke moves with the cam, if that makes sense.

The other part of your concern you seem to have covered yourself in that the timing accuracy is correct as even one tooth out will show as a deviation on the marks.

I always think it's good practice with turning by hand as you've done, if it meets any resistance at this point at least you can work backwards through it to correct it without bending a valve.

Offline billy192

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Re: Valve timing
« Reply #4 on: January 13, 2013, 06:28:48 PM »
Hi,
Ok update. got the engine running, well running on one cylinder. the Left is purring like a cat the right nothing at all.

things i have checked
1 spark ....yes
2 fuel ... yes plug is wet when i take it out
3 swapped around plugs still the same
4 swapped the diaphragm from each carb
5 cleaned all jets
6 points  gap checked more than once
7 used a bulb on the points to the left and light comes on when LF on stator
8 if i rev it up i get a bake fire on the right once
9 can the engin run like this with the cam in 180 degrees out?

fed up as i am nearly there :'( :'( :'(
Billy


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Offline Bryanj

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Re: Valve timing
« Reply #5 on: January 14, 2013, 05:40:57 AM »
Are you re-fitting the points cover as it was a common fault for the cover to earth out one set of points

Offline billy192

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Re: Valve timing
« Reply #6 on: January 14, 2013, 07:38:22 AM »
No points cove not on  :(
Billy
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Offline andy_c101

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Re: Valve timing
« Reply #7 on: January 14, 2013, 09:47:34 PM »
I've not worked on the 250G, (so this is more speculative, & not authoritative)

but my experience on a 550 points timing, I find that I can set the static points timing with a bulb, to light on the "F" mark, BUT.... I then have to be extra extra careful that on re-tightening the points baseplate, that nothing moves.
I go round the (three) baseplate screws by just a fraction of a turn to tighten it it all down so that nothing moves.
- in the past. that has caused me to 'loose' ignition on one coil.

Otherwise be methodical, and patient; you will get there!

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Re: Valve timing
« Reply #8 on: January 14, 2013, 10:04:24 PM »
I see what you mean in asking about the cam being 180deg out......but trying to think through it I'm struggling with the sequencing to come up with any answer.

It is a 180deg crank on this bike? isn't it?
Are the points running on the crank?

As another thing to compare....can you switch the points wire to the opposite coils and also the plug caps to in effect swap the coils over to verify if both are ok.

Offline billy192

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Re: Valve timing
« Reply #9 on: January 15, 2013, 12:46:29 PM »
Thanks for the reply K2-K6
spent hours on U tube last night found a great guy timing a CB360 1974 virtually the same engine.
he was changing the points gap to suit the timing marks and said to disregard the manual when it came to timing.

so currently i have the right points gap at 0.040 and the left at 0.030 and both cylinders are firing,,,,not smooth but BOTH firing.
so i feel some minor tweaks and I will be there.

 Billy
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Re: Valve timing
« Reply #10 on: January 15, 2013, 04:21:38 PM »
Well that is progress and at least allows you to move it closer to running well.

I researched a bit more about the firing intervals of these engines to try and answer the original 180deg question you posed, and as far as I can see it should make no difference as the ignition operates on a spare spark principle i.e. it also sparks during the exhaust stroke  as well as compression so if the cam was out by 180-crank-deg then it should still run on both cylinders.

If anyone else think that's wrong please add to this.

Just a thought about the points gap....if it runs better with a bigger gap, then it could be the condenser not functioning well as this is supposed to help the points switch cleanly....you could try switching the condensers over between each other to assess this.

Offline billy192

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Re: Valve timing
« Reply #11 on: January 15, 2013, 10:08:17 PM »

I think your correct with the cam. as for the condenser there is only one between the two sets of points.
i will keep fiddling til i get there
Billy
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Offline billy192

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Re: Valve timing
« Reply #12 on: January 16, 2013, 04:13:02 PM »
Hi Oddjob,
It is one of those where you need to average out the gaps between both sets and they are both new and Honda.
will clean the advance mec tonight
Billy
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Billy

Offline billy192

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Re: Valve timing
« Reply #13 on: January 19, 2013, 07:33:01 PM »
Sorted,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, took the plunge and striped the top end and yes it was 180 degrees out. I dont know how I did not see when I first did it.  Re set the valves which for some reason were way out on the right cylinder. started first turn checked with a strobe and a minor adjustment now sweet as a nut. thanks for all the advise.
Billy
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Billy

Offline UK Pete

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Re: Valve timing
« Reply #14 on: January 19, 2013, 07:43:38 PM »
Well done Billy, bet your well pleased,
Pete

 

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