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MG Midget and Sprite Technical - Timing tape size reduction question

Recently I had to replace my harmonic crankshaft pulley (the rubber seal gave way) with the same type of pulley but had been machined down to make it lighter wieght

I changed out my timing marks for a pointer on top with a degreed timming marks tape that sticks to the pulley

with the new pulley machined down the tape is no longer accurate as the as the pully is now much smaller

My question is... can I measure both pulleys and find the amount of % (persentage) that the new pulley was reduced by and take the tape to a photocopy center and have it re-copied by the same % (persentage)

It seems like it would work, just not certian.

yes I have orginal copies of the tape on sticky paper that I use clear packing tape over the top of to protect... seams to work a treat.

thanks guys

Prop

I cant get a photo to post but here is the link to what the timing tape looks like... you can click on the photo for a better view


http://advanceddistributors.mybisi.com/product/1275-midget-sprite-timing-tape-kit

http://advanceddistributors.mybisi.com/product/1275-midget-sprite-timing-tape-kit
Prop

Prop,

The easy way to do this is to forget about the old pulley.

Make up a 'stop' from a piece of bar stock machined so it will fit into a spark plug hole (ideally thread it so it screws into the hole) such that it will prevent the piston rising to TDC (alternatively get an old spark plug and weld an extension onto the electrode).

With the stop in place, s,lowly rotate the engine by hand until the piston encounters the stop (and the engine can no longer be rotated). MARK the pulley against your timing pointer.

Now rotate the engine the opposite way until the piston can rise no further, Again MARK the pulley against your timing pointer.


TDC is the point equidistant between these two marks and can be marked as such.
Deborah Evans

>>TDC is the point equidistant between these two marks and can be marked as such.

Prop - as it's you - Deborah means the shorter of the 2 equidistances...

A
Anthony Cutler

..to further clarify (just 'cos its Prop) once you have a TDC mark on the top of your pulley you can time your engine dynamically, BUT you will need an adjustable timing light (The Snap On ones are the best I know of) fixed timing lights are useless in these circumstances...

JB
James Bilsland

Prop,

Yes, if you reduce the diam by a percentage you also reduce the perimeter by the same percentage.

But.. will the photo copy machine be accurate enough.

Why not make a new one from scratch

Measure the new diameter x PI divide by 360. Mark a piece of tape at these intervals stick it on the pulley.
tm wainwright

Thanks guys

I Do have the new pulley marked at TDC to a set pointer so not an issue .

I need the timing tape to graph paper out the timing curve of the new mallory dissy in a few weeks... inorder to find the best possiable curve with all the differant springs and wieghts that makes the mallory adjustable.

unless i purchase "Another" new timing light, no other way to do it that I can see without the timming tape

I took the orginal timing tape and had it photocopied exactly the same size, so I know the tape is the correct measurment, thats why I figure if the new pulley is ...say 29% smaller, then I would just reduce the new copy of the timing tape by 29%

Tim W.

.... that probably is the better way, but is also alot of work as Ive already got the new pulley installed, So Id have to unbolt the motor mounts remove the starter, lock down the flywheel, jack the engine up then re-break free the pulley bolt. then.... ect ect ect. So Id just like to stick the timing tape on the new "installed" pulley and be done with it

thanks
prop

Prop

OK I'm confused now.

You say you have a TDC mark on your pulley?

If so, get a protractor and mark up degrees before and after TDC on the pulley!
Deborah Evans

Gordon Bennett is there any hope whatsoever?

I think you should concentrate on sorting out the problems of the world Prop and get someone to start you engine for you!
Bob Turbo Midget England

Deb ... Thats a great idea, just to simple for my head noddle to concieve... I should be able to get a protactor on it with it already installed

Bob...I fear your correct, but I am getting there slowly but surly... just a few re-design issues and im driving

I got a new oil separator made last night that will fit the fuel pump crankcase pressure attachment, I modled it off the factory orginal on the timing cover so that should stop the oil vapor getting into the carbs... cool design I think, when I get it fitted in the next day or so Ill post some pics of it.

prop... 3 vents have got to be better then 1
Prop

This thread was discussed on 25/06/2010

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