Jump to content

Unreliable timing marks


Waynebaby
 Share

Recommended Posts

Hi All,

I felt a bit guilty about not participating in Johns damper survey but when he asked for views I wasn't sure if I had a degraded damper or not. I think I now know that I do.

I've been trying to trace the source of a "soft misfire" under load for over 12 months and finally resolved it by re-setting my ignition timing. Rather than using the strobe gun (I'd previously used it to set the engine to 7-8 degrees advanced) I thought I'd try the suggested method of finding the distributor position that gives the fastest tick over and then backing it off a gnats. Not only did this get rid of the hesitation but it has transformed the engine response without (as far as I can tell - I'm getting deafer) any pinking. I can't stop grinning when I drive it now.

Out if interest I thought I'd use the strobe to see what the timing marks claimed the timing to be and I found that if I am to believe them my timing is now set at 25 degrees advanced BTDC!

I don't believe the timing marks any more. Can anybody think of a reason why I shouldn't ignore them from now on?

Regards

Wayne

Link to comment
Share on other sites

if the do it by ear has raised a smile i reckon you have just what john was looking for.

you could stick a probe down the plug hole and get a rough tdc to conform your feelings about 25deg,  as that sort of error should 

be detectable with a little up an down of the piston and a bit of stiff wire.

get the piston to drop 1/2" in both directions mark the pulley , dive in half gets a reasonable guess at tdc.,  

Pete

 

Link to comment
Share on other sites

I'll try that next time I've got the plugs out Pete.

That reminds me of something similar my mate once did back in the day with his CZ175 motorbike (a fine bit of Czechoslovakian engineering at its agricultural best) He was trying to find the top of the stroke using the outside of a BIC ballpoint pen in the plug hole. He kicked(!) over the engine and I watched in horror as the pen casing disappeared out of sight down the spark plug hole only to be smashed to tiny pieces against the head as the piston came back up the barrel. Off came the head. Being a 2-stroke some of the plastic shards had gone through the transfer ports down into the gearbox. Being a CZ the engine didn't seem to mind!  

Happy days

Wayne

Link to comment
Share on other sites

Wayne,

Invest in a piston stop, that screws into the spark plug hole, and - er - stops the piston.  It's longer than a plug, with a rounded end so as not to damage the piston face.  Lots on ebay, for pennies: https://www.ebay.co.uk/sch/i.html?_sop=15&_osacat=0&_odkw=piston+stop&_from=R40&_trksid=m570.l1313&_nkw=piston+stop+14mm&_sacat=0

Fit the stop, turn the engine by hand until it meets the stop.  Mark the pully at the timing pointer.

Turn it the other way and do the same.

TDC is EXACTLY halfway between your marks.    If that doesn't coincide with the TDC mark on the pulley, then yes, it has moved.     You'll need a new one, or to get it rebuilt.  There are people in the US and New Zealand who do this, but not the UK, AFAIK!   If it is bad, and you can find another, then may I have it, please?  I will need some 'known bad' pullies for testing.

JOhn

Link to comment
Share on other sites

Thanks for the reply John and the link for the stops. If the pulley does need to come off it won’t be for a while though.

I’ve not read your paper yet. Are you able to say whether running with a goosed damper is harmful or if it just makes setting your timing reliant on e.s.p. rather than a timing gun?

Wayne

Link to comment
Share on other sites

Jesus, Pete!   Just do a piston stop test!  Non-destructive!

Wayne, sorry for the slow reply.    Good thing I got back in time to warn you about that hooligan above!   If the outer ring of the damper shifts, the you have no idea where your timing is.  Could be a few degrees, could be dangerously advanced, could be unrunnable.    

But the primary purpose of the damper is to suppress torsional vibration on the long crank.    Broken cranks have been known, how many due to faulty dampers unknown, but a vibrating crank can't be good.   Nor have outer rings that let go completely, although they have in other engines, when they become a flying, lethal discus of death under the bonnet!

John

 

Link to comment
Share on other sites

Hi All,

You'll be glad to know that I drew the line at cutting holes in the bell housing (I'd sort of assumed Pete was pulling my leg!) and this afternoon followed John's advice and used a Piston stop. This has resulted in what could be described as a Good News - Bad News - Bad News scenario.

The good news is that the timing marks on my damper ring are exactly where they should be.

The first bit of bad news is that this means John no longer has a failed damper to perform an autopsy on and the second bit of bad news is that I now have the mystery of why my car seems perfectly happy running with 25 degrees ignition advance.

Confused Wayne

 

Link to comment
Share on other sites

Wayne,

Check you timing light.  Does it have an advance control adjustment on it?    Engines of an inferior type (pace, some Spitfires) may have merely a mark on the pulley and and a pointer on the front of the engine.   Owners can't look at the pulley and see exactly how much advance they have.    So kindly strobe makers provide a knob to advance the light, so the poor benighted owners can set the mark and pointer together, and know that they have X degrees of advance.

But the knob is easily turned by accident and may not be obvious.   I have one of these (with a Gunson's label but identical) 

Advance Timing Light ADVANCE TIMING LIGHT

That black knob on the back of the barrel, is the adjuster.   I admit - I've carefully set my timing and then had an uneasy feeling about the engine's response, to discover the the knob was presetting a significant amount of advance, that I had then set yet more advance!  More than  once, so the knob is now taped to keep it still, at zero.

John

Link to comment
Share on other sites

Ia good few years ago before I had a classic I donated a smart sun gun from our closed down  emmision dept.with large thumb wheel and a large meter which showed the  degrees , and a 6 " Vacuum gauge to check the vac advance, its all went to the Ecurie Ecosse team , then I got a classic and ended up with a Snap On  unit same as johns pic,  this played up and I purchased a unbranded one from halfords , exactly the same but in a black case

There was a thought to swap the cheap into the expensive,, the guts were identical, and hey presto the shock spurned the snapon to 

Revitalise and both work well,  agree the  advance control is a bit to easy to alter 

Tape sounds a good plan     pensioner's like the simple fixes  !!

Pete

 

Link to comment
Share on other sites

Thanks for all the replies. I am always impressed by how the people on this forum rally around.

I have an Accuspark strobe gun with an advance control adjustment knob but I'd forgotten about the handedness of the pick up Pete, so that's the first thing I'll try tomorrow.

Wayne

Link to comment
Share on other sites

3 hours ago, Pete Lewis said:

 

Moving the leads wont change anything other than now it wont run

I do beg to differ sir, having done this myself, and my timing was wayyyy out by tens of degrees. the timing marks were out of sight and when turned to anything close to normal wouldn't run at all. I had to tune it by ear, rotating the dizzy until the engine ran perfectly. It was only once I realised that the leads were on one terminal too far round, and moved them back, that the timing marks aligned where they should be, since the strobe being on the normal lead - in the wrong position however - was firing too late for the timing marks.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...