Engineering versus Medication.

[cardiffrob]

Just changed my medication and am having a bit of a problem. One of the side effects is a loss of concentra....Umm, Y'know......thingy, like what I was talking about. Sorry, where were we?


Anyway, all joking aside, I'm struggling to think through a technical issue and for the life of me I can't get it sorted in my noggin. Can someone help with the mathematics for me?

Distributor has a 15 degree baseplate (23D4 Cooper S one) and I want it to give about 34 degrees at full chat so I want to set the static timing about 4 degrees at static.

The crank pulley is 129mm diameter which means 129xPi for the circumference? If so, equals 405mm circumference. So, to get 4 degrees BTDC I need the timing mark to be how far shifted? Is it 4 degrees times 405/360?

Really quite scary how this stuff has affected me this week. I made myself 2 cups of coffee this morning without remembering that I'm not allowed to drink coffee. Fortunately I forgot both of them and they went cold on the table.

 

[Chris Stevens]

Very easy way to do this type of thing is to put an accurate TDC mark on bottom pulley, and time it with a light which has advance/retard feature. One of those also allows you to see exactly what the distributor is doing and alter it if needs be.

 

[Crater Creator]

No, it's 4/360 times 405mm
So, 4.5mm for 4 degrees.
And 38.25mm for 34 degrees


Another way to think of it is the 4/360 is a "fraction of the full 360 angle", multiplied by the circumference.

 

[Chris Stevens]

No, it's 4/360 times 405mm
So, 4.5mm for 4 degrees.
And 38.25mm for 34 degrees


Another way to think of it is the 4/360 is a "fraction of the full 360 angle", multiply my the circumference.

Might be easier to time from TDC mark?

 

[Crater Creator]

Yeah, those figures would be used to measure round from the TDC mark.
It's a simple enough way to do it if you have a simple strobe without advance/retard or anything. Just dab a bit of tippex at 4.5mm and one at 38mm round from the TDC notch and time to them.

 

[Chris Stevens]

Yeah, those figures would be used to measure round from the TDC mark.
It's a simple enough way to do it if you have a simple strobe without advance/retard or anything. Just dab a bit of tippex at 4.5mm and one at 38mm round from the TDC notch and time to them.

If you are building special purpose distributor for a tuned motor, timing light with advance retard feature is a very useful piece of kit. My Snap On one cost over £200 about 20 years ago, but think you can get ROC ones for £50-60 now?

 

[gordon stephenson]

I would divide the 405mm circumference by 360 to give a linear distance scale at the circumference.

 

[cardiffrob]

Thanks everyone.

I'm still feeling somewhat befuddled but that lot seems to make sense. 1 and a bit mm per degree. So, for static timing I need to stop the crank some 4-5mm short of TDC timing marks and then turn the dissy the opposite direction to the rotor arm travel until there is 12v between the points terminal and earth.

This engine has a waterpump sitting right above the timing mark arrow and it isn't possible to see the marks at all, not even through the rad. I have to work the TDC-to-timing marks with plasticine squidged in. The rad has a big overhang rearwards that prevents you from seeing it from above. the original design had you looking through the fins of the rad core but mine obscures the timing pointer and the pulley. Best of British design work!!

 

[Chris Stevens]

If you cant see the timing marks to strobe it, then its going to be a lot more difficult to set up. Without being able to use the marks, then turn motor forward till No1 cylinder is on compression stroke, and I would guess using a TDC tool intended for bikes, and a DTI with magnetic stand, you should be able to accurately get TDC position? When you have that its a matter of turning the motor back so piston is at static advance position (measure with DTI), and making sure points are just opening at this position (a fag paper works well for this).

 

[Crater Creator]

CradiffRob,
Yep, your plan for static timing sounds exactly right.
What about an inspection mirror - any way to get it down the side of the pulley to see the TDC mark?
Or a borescope if you have one?
What kind of a beast is that anyway!? It looks absolutely mint (and what's with the sweetie jar at top right?).

 

[cardiffrob]

Thnaks again.

Yes, I've managed to set TDC using the plasticine method and then got it warm so I could turn the dissy to get the highest manifold vac (minus a bit for safety) so I could at least get up and down the driveway. getting the correct advance at speed is the next trial now that someone with a clear mind has confirmed the numbers for me. I think I may have to remove the entire front end and get the rad out to mark the pulley permanently. Man....this stuff is wooooooo...weird.

Tried a 5mm Ebay endoscope but it is hard to get it in place. I've got a load of metalwork in my spine that is not very bendy, leading to lots of trouble when I bend forwards a bit too much, hence the meds. removing the rda looks to be a better bet in the long run.

CC. Alta engine in a Morris Minor, 1949. The bottle is a sweetie jar with a Lucas pump on top that looks a bit like an original Trico bottle. I couldn't afford a real one.

 

[Chris Stevens]

Guessing the timing by

Thnaks again.

Yes, I've managed to set TDC using the plasticine method and then got it warm so I could turn the dissy to get the highest manifold vac (minus a bit for safety) so I could at least get up and down the driveway. getting the correct advance at speed is the next trial now that someone with a clear mind has confirmed the numbers for me. I think I may have to remove the entire front end and get the rad out to mark the pulley permanently. Man....this stuff is wooooooo...weird.

Tried a 5mm Ebay endoscope but it is hard to get it in place. I've got a load of metalwork in my spine that is not very bendy, leading to lots of trouble when I bend forwards a bit too much, hence the meds. removing the rda looks to be a better bet in the long run.

CC. Alta engine in a Morris Minor, 1949. The bottle is a sweetie jar with a Lucas pump on top that looks a bit like an original Trico bottle. I couldn't afford a real one.

Its fiddly to set timing using the piston position method as I outlined earlier, but a lot less trouble than messing around with plasticine etc. If it were my engine I would establish TDC accurately, put a mark on where it can be easily seen on bottom pulley and time using a variable light..........

 

[Turbo]

Is there any way you could extend the rad pipework so you can set up the engine with the rad to one side, giving you access to the timing marks. You could rig up an electric fan to keep the rad cool.

Btw, my sympathies are with you over the side effects of your meds. I'm currently taking gabapentin for pain relief and when I started taking it last year I suffered with poor concentration and bad co-ordination. It got so bad I stopped driving for a while after having a near miss. Thankfully the effects eased though I still get relapses every time my dosage is increased.

 

[cardiffrob]

Its fiddly to set timing using the piston position method as I outlined earlier, but a lot less trouble than messing around with plasticine etc. If it were my engine I would establish TDC accurately, put a mark on where it can be easily seen on bottom pulley and time using a variable light..........

Therein lies the problem. You cannot see the crank pulley at all once the car is assembled (unless your head is resting against the exhaust manifold) but I can turn the crank with the starting handle an splob the plasticine on to see if the notch in the pulley is 4.5mm from the timing mark by pulling it away and measuring it with a ruler at the bench. Putting the TDC mark on would require taking the head off and there still aren't any head gaskets available for this engine. Some hopefully being produced in South Africa this year. I think you're 100 right in that I really need to pull it apart and make new timing marks based on accurate dimensions and will do that when it comes apart for any maintenance. I have the DTI and Mag stand in the shed.
The original SV engine had the plugs over the valves but the head conversion puts them inclined near the bores. I contrived a bodgers' DTI with a length of TIG rod with a short bit in the bore and the long end hanging out. That's as good as I can get until the head comes off. Is there a gadget that gives TDC from the pistons with plugs like the 45 degree angled ones in the pic above???

Woke up this morning with a mouth that tastes of copper coins and old batteries. Gak! Sat on the bog and it was like a Saturn V launch! I hope the side effects wear off soon.

 

[Chris Stevens]

If you have a lathe its very easy to make a tool which screws into plug hole, and has a rod through the centre which if the angle isnt too acute can be used to measure piston position. To be honest though on an engine like that you could set timing by ear as soon as you can get it running, and not be very far out.

 

[ajlelectronics]

How about grafting in an electronic sensor ?

 

[Jim Davey]

Threaded rod down a plug hole, gently turn the engine until it contacts the rod and stops. Mark the position on the flywheel, reverse the direction and rotate until the piston again comes in to contact with the rod and make another mark. TDC will be exactly at the point between your two marks. There is a chance of a few degrees of error if you try and find the TDC by finding the point where the piston stops moving at the top of it's stroke.

 

[Crater Creator]

Threaded rod down a plug hole, gently turn the engine until it contacts the rod and stops. Mark the position on the flywheel, reverse the direction and rotate until the piston again comes in to contact with the rod and make another mark. TDC will be exactly at the point between your two marks. There is a chance of a few degrees of error if you try and find the TDC by finding the point where the piston stops moving at the top of it's stroke.

^^^^ Now THAT's a good idea. Very useful forum, this.....

 

[wookie]

Putting the TDC mark on would require taking the head off and there still aren't any head gaskets available for this engine.

Can you get sump gaskets ? you could take the sump off and set the engine at TDC by looking up from underneath rather than whipping the head off.

 

[cardiffrob]

Just to clarify, I have TDC, it is just that I can't see the marks unless the crank is maybe 70-80 ATDC when it briefly comes into view. If I put my hands in there I can no longer see the mark.

I've now put the crank 4.5mm BTDC so that I can set the timing, static, to give 34 at max advance. If I ever have to pull the engine or remove all of the front panels I'll contrive a better method of finding TDC and the various other positions of interest. The electronic idea sounds good, as does drilling a hole in the flywheel end of the crankcase so a pin can be slipped through and into a similar hole drilled into the flywheel for TDC.
The magnetic crank position sensors also sound a nifty idea.