1958 G80CS Valve timing

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Transatlantic
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1958 G80CS Valve timing

Post by Transatlantic »

I've nearly finished my 14 month total restoration of this beautiful machine BUT the valve timing is clearly wrong.
The problem is that at some stage the 2 cogs which control the inlet and outlet cams were changed for something else which does not have the original timing marks. Instead of the standard 2 marks there are just one on each cog, and when aligned with the half shaft pinion, the timing does not make sense. Its like both valves are opening together.
Can someone please advise how I can get the timing right in relation to the cam lobes? or verify the degree settings?
The timing marks are at "2 and 10 o/c" with respect to the cams, but the positions seem to be the reverse to what someone advised me.
This should be so easy with a single cylinder 2 valve engine , but I don't have any good data to work from - the degree settings in the manual that I downloaded seem suspect also. Any help much appreciated.

Supplementary info : I came to this conclusion after timing the magneto and adjusting the tappets to zero clearance at TDC , this made the engine so tight it wold not turn past a certain point so I'm certain the valve timing is wrong
Thanks!
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Rob Harknett
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Re: 1958 G80CS Valve timing

Post by Rob Harknett »

Assume you did watch the tappets stayed correct and a valve was not stuck?
Transatlantic
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Re: 1958 G80CS Valve timing

Post by Transatlantic »

Rob Harknett wrote:Assume you did watch the tappets stayed correct and a valve was not stuck?
That's a good question - I'll have to go back and take a look again - I'd assumed they're OK because I rebuilt the engine top end - any ideas on the lobes or timing marks?
Transatlantic
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Re: 1958 G80CS Valve timing

Post by Transatlantic »

Well i guess I'll have to figure this one out myself ! -super useful forum
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Rob Harknett
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Re: 1958 G80CS Valve timing

Post by Rob Harknett »

The correct workshop manual for your bike should be OK. If you think the one you have is incorrect try a different publisher to see if that is the same.
Pitmans or Neil etc. You think you have the wrong cams. The book will only be correct if you have the correct cams. The book will tell you of timing, 350, 500, and comp, heavyweights . The book may cover 1957 /1966 like this one http://archives.jampot.dk/book/Workshop ... .NEILL.pdf It gives all the degrees and cam/cog info, then goes on to the change in the degrees and cogs in 1960. as you seem to have the later cams/cogs have you tried the timing instructions for them. As you say the book is wrong, I believe the book would be correct if you had the correct parts. So you need the correct parts or try the timing instructions for the later cams/cogs you seem to have.
You cannot expect much comment it we have to guess what you have and what you are doing. It does however seem you are applying correct instructions from the manual to the wrong parts.
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dave16mct
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Re: 1958 G80CS Valve timing

Post by dave16mct »

This might help:

http://archives.jampot.dk/technical/Gen ... e_Dots.pdf

You have to realise that not many of us have these CS models. The guy in the article would be a able to help (Ken -de Groome) he advertises in the back of the magazine.
Cheers Dave.
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clive
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Re: 1958 G80CS Valve timing

Post by clive »

Transatlantic wrote:Well i guess I'll have to figure this one out myself ! -super useful forum
In the UK because of the time difference your question was only up for two days before you complain about the lack of response, the forum is just that, not an online interactive technical advice service. Having said that in the first day I had tried to find Ken's article in the archives but failed to locate it and awaited someone else to post a link to it.

If the timing advice there does not help one additional thought occurs to me. If you have high lift or scrambles cams is it possible that the timing side crankcase has been replaced? Some of the earlier cases will not take the high lift cams as there is not enough clearance for the tappet to lift as the foot becomes jammed. This would have effect of jamming the motor as one of the cams reached the critical lift. However if as you describe both valves are open at the same time then you will probably sort it out with the advice in the box in Ken's article.
clive
if it ain't broke don't fix
bjorn
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Re: 1958 G80CS Valve timing

Post by bjorn »

I would agree with Clive that a little patience is required while (hopefully) waiting for some answers. Now to the subject:

It would appear that your motor is fully assembled? If it were mine and had a "tight spot" or could not be rotated, I would take off the rocker box and remove the spark plug. It should then be possible to turn the motor without any tightness, irrespective of the cam timing. If it does not, there are a number of possible reasons for this.

However, assuming the motor now turns freely, the cause of the tight spot/binding when the motor is turned with the valves opening/closing is one of the following:
-cams so incorrectly timed that the valves are clashing (very unlikely)
-insufficient clearance between valve collar(s) and top of valve guide(s) to allow full valve travel (unlikely - but not unknown)
-one or both cams are timed incorrectly, allowing piston to hit valve
-both cams timed correctly, but (new) piston has insufficient cutout(s) for valve(s) with resultant piston to valve contact (usually this would be the inlet valve - just experienced this on rebuilding my 1960 CS motor)

With the rocker box off, but without further dismantling you can check the valve timing. Put a degree disc on the crankshaft, use some welding wire held down by an engine stud/nut as a pointer and set the disc to zero degrees at piston TDC. Use the pushrod lift to find cam opening and closing. Read the degrees for opening and closing of a cam at EXACTLY the same amount of lift on the pushrod - use an indicator clock - suggest record open/close degrees at 0.5mm and 1mm lift.

To be continued, depending on how you are going about the work...

regards
Bjørn
Transatlantic
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Re: 1958 G80CS Valve timing

Post by Transatlantic »

Thank very much everyone ! and apologies for being impatient - this should be the easiest task in the world -timing a 2 valve single cylinder engine, but it's been a massive frustration for me as the bike looks beautiful and is 99% finished.
I now suspect that either there is a stuck valve or top end problem , or the cams are marked incorrectly. before restoration the bike ran OK, it's just that I assumed that the timing marks were accurate, and really should have taken some pics.
Following the standard procedure of first timing the inlet then the outlet so the marks line up with the dot on the pinion produces valves opening at the same time, poor compression ( momentary 25PSI) when compression checking each alternate TDC, and once the tappets are adjusted to correct tolerance the engine wont rotate past a certain point.
It all rotates fine without the cams in. I'm going to take the head off and inspect the valves etc.
I'll try and post a pic of the cams maybe it would be obvious if the marks don't relate correctly with the cam lobes
Thanks!
Transatlantic
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Joined: Wed Sep 09, 2015 9:45 pm
Location: Vermont

Re: 1958 G80CS Valve timing

Post by Transatlantic »

dave16mct wrote:This might help:

http://archives.jampot.dk/technical/Gen ... e_Dots.pdf

You have to realise that not many of us have these CS models. The guy in the article would be a able to help (Ken -de Groome) he advertises in the back of the magazine.
Cheers Dave.
Thanks very much for this - its interesting , but the marks on my cams are lines, not dots, I know the previous owner sent then out for re profiling and they are not original to the G80CS
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