Valve timing...

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Matt Hale
Posts: 75
Joined: 08 Oct 2020 10:00
Location: London

Valve timing...

Post by Matt Hale »

Hi All
SIMPLE VERSION OF MESSAGE BELOW= QUESTION: Should my LOWER drive gear for the cam belt be easy to remove? (it is) and how do I know where it should be positioned on it's shaft? (The belt is off and I've turned crank and cam...ooops..).

PPREAMBLE>>>>>I have had my pickup and magnet checked by a well known Morini mechanic who tested them on their bike and all fine....so I put them back on my 350 Electric start 1979 bike.
I also decided to replace my cam belt and new one is tighter and less floppy consistency which I understand is a good thing...

...HOWEVER...stupidly I have moved the bloody crank and cam and lost cam timing I think... I have not removed the top camshaft gear from it's shaft and it has a clear timing mark to align with the mark between cylinders on casing at 12 O'clock...so that is reliable I think..
...What I have a problem with is the lower drive gear which the belt also goes on. On my bike this gear is easily removed and with the half moon key in the crank slot it can be placed back on at least two various positions with key in place. This is a bloody nuisance as I therefore can't rely on the timing marks- it has one yellow dot on outer edge of the drive gear and a punch mark on inner casing around 2 o'clock. I believe the yellow dot on it's outer edge is supposed to line up with the punch mark on the casing when the mark on the upper drive gear is at 12 o'clock as in diagram in Blue Manual page 4, top left image.

QUESTION 1>>>>If the lower drive gear can go on the crank shaft in different positions how do I know which position it should go on?

In an attempt to answer this Q1 - The crank should be positioned so the front cylinder is on TDC compression stroke at this point?

QUESTION 2: How do I know when I have TDC on compression stroke? (WITH CAM BELT OFF) The Workshop Manual says "with engine at TDC on compression stroke" but no advice as to how this is achieved. People write on internet to "put finger in plug hole and you will feel the compression rise"...ALSO presumably both valves must be closed... but the belt isn't on so they don't move unless I turn the cam manually with socket spanner.
SO...
QUESTION 3...Should I put the valves in closed position (visible with lid off) by turning cam (top drive gear) then find Compression TDC on front cylinder by turning the crank? Then put lower drive gear on aligning the marks? ....I have tried this but the mark on the upper drive gear (cam) is NOT at 12 o'clock. To have the calves closed it has to be at 3 o'clock ish.

HELP !!!!
350 Sport 1979 electric start model (missing)
Curry yellow tank etc paint work, navy blue frame, silver wheels.
70sbikes
Posts: 96
Joined: 13 Nov 2014 11:44
Location: Melbourne Australia

Re: Valve timing...

Post by 70sbikes »

The slot on the crank (where the woodruff key fits) lines up with the mark on the pulley, which is then aligned with the mark on the crankcase. So, just align the slot on the crank with the mark on the crankcase, then fit the pulley.
Matt Hale
Posts: 75
Joined: 08 Oct 2020 10:00
Location: London

Re: Valve timing...

Post by Matt Hale »

Thank you 70sbikes-,Very clear.
Matt
350 Sport 1979 electric start model (missing)
Curry yellow tank etc paint work, navy blue frame, silver wheels.
3potjohn
Posts: 1243
Joined: 02 Jun 2007 13:58
Location: Devon

Re: Valve timing...

Post by 3potjohn »

P68 of the Blue Book shows exactly this. I have only found the crank pulley to be a fairly tight fit. You can double check the rocker movement just by way of reassurance.
John
Matt Hale
Posts: 75
Joined: 08 Oct 2020 10:00
Location: London

Re: Valve timing...

Post by Matt Hale »

I’ve understood how and in which position lower belt drive gear fits…but when the belt is off how do I def know I have achieved TDC of compression stroke? I think I need to be at this point to check valve gaps?
Thanks John + - Matt
350 Sport 1979 electric start model (missing)
Curry yellow tank etc paint work, navy blue frame, silver wheels.
mbmm350s
Posts: 666
Joined: 22 Jun 2018 10:18
Location: Reading UK
Location: Berkshire UK

Re: Valve timing...

Post by mbmm350s »

Hi Matt,

The lower cam pulley should be a light interference fit on the shaft, if not and is very loose, and I have done this, use loctite 601 or similar.
The manual says to use Loctite 242 and make sure to clean the shaft.
The first time we did this with a very loose pulley we phoned Loctite and explained the application
and were told that the bearing retainer should be used.

The pulley itself provides vernier adjustment of the valve timing. New pinions were not marked and the process of checking the timing as described in the manual should be observed.
Not mentioned in the manual is that the reference key way, the one that is normally fitted to the woodruff key, is the inner spline which is exactly bisected by the right hand edge of an outer spline.
You can check to see if this is the one that has been punched with a dot, I expect that it will be.

Mark
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