Author Topic: Valve Clearance Question  (Read 306 times)

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Offline MAllen

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Valve Clearance Question
« on: October 20, 2020, 11:40:32 pm »
Greetings all
I have just reset my valve clearances and am wondering if the setting (.0003) should remain when the piston is at TDC? When I spin it and re-check the setting, it seems to have closed. Is this normal or is something else going on?
My C11G was running well until I replaced a worn rocker cover washer and throttle slide valve. It has been running badly ever since, so working my way around possible problems. I have stripped, cleaned and replaced parts in the carb, checked fuel lines and now having a go at valve clearances. Spark plug has been consistently lightly sooty so indicates richness. Not sure where to go next, so your thoughts are appreciated.
Cheers
Mark

Online Owen

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Re: Valve Clearance Question
« Reply #1 on: October 21, 2020, 07:11:37 am »
Depends which type of cam shaft you have. Standard or the later ramped cam
Check using the following:

'If there is any doubt as to the type of camshaft fitted, rotate the engine until it is at top dead centre on the compression stroke. This can be simply ascertained if a long piece of wire is inserted through the sparking plug hole so that the top of the piston can be felt. On some SV models it is necessary to remove a compression plug in the cylinder head in order to reach the piston.
At the top of the compression stroke both valves will be closed and slight movement of the engine backwards or forwards will not cause either valve to open appreciably.

Check the valve clearances in the top dead centre position. If the earlier type of camshaft is fitted. The clearances will be substantially the same as when they were set up as described under Valve Clearances.
If the replacement (RAMP) type camshaft is fitted the valve clearances will be considerably reduced.
So if a model with the replacement (RAMP) type camshaft fitted is set up with the smaller valve clearances applicable to the original camshaft, the clearance will be completely eliminated when the engine is at top dead centre on the compression stroke.
Early Pre 54 model Cams were marked C10 or C11.
Later pre 54 model Cams were marked C10 8 or C11 9
So there you have it!
Note: I did not reinvent the wheel as these instructions are from a C user manual
1940 C12 (350cc)
1945 C10 & C11
1953 C10 & C11

Online Ginge

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Re: Valve Clearance Question
« Reply #2 on: October 21, 2020, 08:13:10 am »
It also depends on on what piston stroke you are on. 

It’s a four stroke so the first TDC is the compression stroke ( both valves closed therefore valve clearance is present). The second top piston position is the end of the exhaust stroke, in which case the exhaust valve will be open ( no valve clearance).

True TDC when you set your clearances is at the end of the compression stroke, as the spark occurs. If you set valves at the wrong TDC unhappiness will occur.

For my money though you changed the slide so I’m thinking the rough running is carb related. Carb too tightly bolted on  and warping the body, or maybe the pilot needs to be tweaked to match the new slide.

Keep at it!



Ginge.

Online hampshirebiker

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Re: Valve Clearance Question
« Reply #3 on: October 21, 2020, 09:28:16 am »
Excellent advice from Owen and, of course, you need to be on compression stroke TDC. I would make sure you have a slight clearance on each rocker in this position and investigate the rough running as a separate issue; most likely carb related.
Postal - Liphook Hants - But just into West Sussex.

Offline MAllen

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Re: Valve Clearance Question
« Reply #4 on: October 22, 2020, 12:15:42 am »
Thanks for the responses. The carburettor has always been my focus however no success so far; I’ll keep trying. What would “tweeking” the pilot look like Ginge? I’ve fitted a new Amal 25 pilot jet. The new fitted slide is a 3.5.
I have also found an air pocket in the in-line fuel filter which may be contributing to the problem.
Cheers
Mark

Online Ginge

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Re: Valve Clearance Question
« Reply #5 on: October 22, 2020, 05:49:03 am »
Tweaking would just be adjusting it in and out on the air screw to ensure it transitions into the needle and slide circuits.

Pilot jet provides background fuel to the whole carb generally so if it is off, the new slide might be amplifying the richness or leaness.
Ginge.

Online haddy

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Re: Valve Clearance Question
« Reply #6 on: October 25, 2020, 10:05:57 am »
The more you ride it you will be able to solve all the problems

Offline griff

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Re: Valve Clearance Question
« Reply #7 on: October 25, 2020, 01:12:51 pm »
  I wouldn't worry too much about a sutty plug. Can't get mine to burn 'clean' whatever I do . New carb fitted. The core is the correct colour but the outer rim looks like the chimneys we had to go up in the 40's..... Modern fuel seems to be the cause...    ::)   Griff
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Online Jim S

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Re: Valve Clearance Question
« Reply #8 on: October 26, 2020, 12:00:14 pm »
On the original post, I think there are too many digits to the right of the decimal, or do I need to go out and find a really thin feeler gauge.

 :o

Online camman3

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Re: Valve Clearance Question
« Reply #9 on: October 26, 2020, 12:34:27 pm »
Yes three tenths of a thou is going to be a really delicate thing!.....should be three thou off course .003....just a typo I guess
Graham
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In sunny (sometimes) Christchurch, Dorset, UK

Online timsdad

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Re: Valve Clearance Question
« Reply #10 on: October 27, 2020, 07:34:42 am »
Point Oh Oh Oh Three is about the play you need in a new little end bush - the thickness of a thin film of oil.

And 'off course' means it's not being measured in the correct place, Graham!


Ray
Just a motorcyclist.

Offline MAllen

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Re: Valve Clearance Question
« Reply #11 on: October 30, 2020, 04:05:55 am »
Yes, very small feeler gauges required.........no wonder my eyesight is deteriorating!
 :)