Timing 180 degrees out ???

[David McHugh]

Hi all, once again your expertise help is sort.

 

1973 Spitfire IV 1300cc

 

Following a rebuild I am not getting fuel to the plugs, in fact the carbs are not suckling when placing my hand over the air intake of the carbs. From the tests I have done,it am pretty certain that it is a timing problem. The Haynes manual says that in order to check if the rotor is 180 degrees out. When turning the crank to bring no1 to tdc no4 exhaust valve should be closing and the inlet value should be opening, however it would be more logical to me if this was happening at no1 and not at no4 as it is no1 that is at tdc, likewise the rotor is pointing to no1.

 

In a case where I am not 180 degrees out, could it be to do with the distributor adjustment ? I am setting no1 at 8 degrees btdc with the rotor directly central to the no1 terminal in the distributor cap, is this correct? or should it be that the rotor be just on the leading edge of the terminal?

 

All comments, recommendations etc will be appreciated.

 

Best wishes

David

[Mjit]

The cycle is suck/squeeze/bang/blow.

For suck you want the inlet valve to be open, so the fuel/air mix can get in to the cyclinder.

For squeeze you want everything closed - if either the inlet or exhaust valves are open the rising piston will just push everything back out the cylinder via that valve.

For bang you also want everything closed - if either valve is open it will be easier for the gases to exit the cylinder that way, rather than by pushing the piston down and turning the crank.

For blow you want the exhause valve open so the rising piston can get the spent gases out, before swapping exhaust and inlet valves as you go over TDC and back in to suck.

 

So it sounds like things are broadly right on the timing front.  As #1 approached TDC with both valves closed (squeeze) the rotor arm approaches #1 plug lead.  Mean while #4 is at the other end of the cycle, approaching TDC on the blow (exhaust open) and moving in to suck (inlet open).

 

 

All that said nothings going to work if you're not getting any fuel - and even if you were times 180 degrees out you should still be getting suck through the carbs.

 

1. Are you getting fuel to the carbs?  Crank for 30s and check you have fuel in the float chambers.  If you don't check back towards the tank to work out why.
2. If you do start with the jets flush with the carb body and screw then down 3 turns.  That low fuel should just bubble through.  If it doesn't start unscrewing the pipe from the float chamber to the carb.  Fuel should starts leaking and it suggests the pipe is blocked (and if there's fuel in the float chamber and it doesn't leak you're breaking the laws of physics!).
3. Have you checked your rocker gaps and are they actually going 'loose' when closed.  If not the exhaust valves could not be closing fully, so you'd be sucking air back past them rather than fuel/air through the carbs/past the inlet.
4. Grab an assistant and a can of Easy Start.  Get them to crank the engine and squrt Easy Start directly through the carbs.  That should get some caughing and spluttering (and maybe a little back-firing so keep your eyebrows clear) if nothing else.

[JohnD]

David,

Fully agree with Mjit, good explanation.   I'd add:

 

No suck at the carbs, "when you put your hand over the air intake of the carbs"?  There are, as you know, two carbs!   And a 'balance pipe' between them, so you need to block both at the same time.

Difficult to do that, and turn the engine, unless you have recruited an assistant.

 

 

It's difficult too, to feel the compression strokes as you turn the engine by hand, as there is always one cylinder doing it, but take out a spark plug and block the hole with your finger.  You may be able to feel it, or hear the gas escape when you take it out.   Or, take them all out bar one and feel that as you turn it.     If your cam timing (not to be confused with ignition timing) is out, then there may be no compression.     If you have a compression gauge, that will read very low across the block.

 

Of course you may need some of this:

 

 

 

John

[Pete Lewis]

when you say rebuild was that the car or the engine ??  was the engine stripped and rebuilt ??

 

has it run ok in the past .. whats been done to upset cam or ignition timing 

 

Pete

[David McHugh]

The cycle is suck/squeeze/bang/blow.

For suck you want the inlet valve to be open, so the fuel/air mix can get in to the cyclinder.

For squeeze you want everything closed - if either the inlet or exhaust valves are open the rising piston will just push everything back out the cylinder via that valve.

For bang you also want everything closed - if either valve is open it will be easier for the gases to exit the cylinder that way, rather than by pushing the piston down and turning the crank.

For blow you want the exhause valve open so the rising piston can get the spent gases out, before swapping exhaust and inlet valves as you go over TDC and back in to suck.

 

So it sounds like things are broadly right on the timing front.  As #1 approached TDC with both valves closed (squeeze) the rotor arm approaches #1 plug lead.  Mean while #4 is at the other end of the cycle, approaching TDC on the blow (exhaust open) and moving in to suck (inlet open).

 

 

All that said nothings going to work if you're not getting any fuel - and even if you were times 180 degrees out you should still be getting suck through the carbs.

 

 

• Are you getting fuel to the carbs?  Crank for 30s and check you have fuel in the float chambers.  If you don't check back towards the tank to work out why.
• If you do start with the jets flush with the carb body and screw then down 3 turns.  That low fuel should just bubble through.  If it doesn't start unscrewing the pipe from the float chamber to the carb.  Fuel should starts leaking and it suggests the pipe is blocked (and if there's fuel in the float chamber and it doesn't leak you're breaking the laws of physics!).
• Have you checked your rocker gaps and are they actually going 'loose' when closed.  If not the exhaust valves could not be closing fully, so you'd be sucking air back past them rather than fuel/air through the carbs/past the inlet.
• Grab an assistant and a can of Easy Start.  Get them to crank the engine and squrt Easy Start directly through the carbs.  That should get some caughing and spluttering (and maybe a little back-firing so keep your eyebrows clear) if nothing else.

Mjit, thank you for your response. I understand the 4 stroke cycle of suck, squeeze, bang and blow, however I failed to run through the sequence to understand why the Haynes is telling me to check the valves on no4 and not no1 when bringing no1 to tdc.

I have adjusted the tappets but I have not checked that they are going loose when closed. I will do this as my next step.

I have got fuel in the carbs, that was my first check.

I have tried Easy Start, I don't get any firing just a blow back through the forward carb, this happens after turning it over for about 3 secondseries and seems to be consistent.

 

I think I have covered all of your points, thank you, I will check that the valves are actually going loose when closedo, as my next priority now to John's reply.

[David McHugh]

David,

Fully agree with Mjit, good explanation.   I'd add:

 

No suck at the carbs, "when you put your hand over the air intake of the carbs"?  There are, as you know, two carbs!   And a 'balance pipe' between them, so you need to block both at the same time.

Difficult to do that, and turn the engine, unless you have recruited an assistant.

 

 

It's difficult too, to feel the compression strokes as you turn the engine by hand, as there is always one cylinder doing it, but take out a spark plug and block the hole with your finger.  You may be able to feel it, or hear the gas escape when you take it out.   Or, take them all out bar one and feel that as you turn it.     If your cam timing (not to be confused with ignition timing) is out, then there may be no compression.     If you have a compression gauge, that will read very low across the block.

 

Of course you may need some of this:

 

 

 

John

John, Thank you for your reply too.

I did check only one carbs with my hand over the intake while turning over with the key not by hand, I thought it would be enough. Covering both carbs is something I can try.

As for cam timing, this is where I originally thought the problem my lie, this was why I have checked that the valves on no4 are doing what the manual said they should be doing ie. as no1 comes up to tdc no4 exhaust valve should be closing and the inlet value should be opening, if this is happening surely that means the cam timing is correct? It would help to know what stage the valves on no4 should be at tdc, this would be more accurate.

I have a compression tester but have not tried it because I didn't think that the engine being turned on the key would be fast enough to get a reading.

 

I will try the compression tester, if it doesn't work, I will try my finger in a plug hole with the rest in place. Sorry to say I didn't understand what you meant by taking all but one plug out and then??

 

Thank you to for the video clip, very funny lol

 

David

[David McHugh]

when you say rebuild was that the car or the engine ??  was the engine stripped and rebuilt ??

 

has it run ok in the past .. whats been done to upset cam or ignition timing 

 

Pete

Pete, thanks for the reply. The engine has been completely stripped down, so the timing chain has been off and the camshaft out. When I put it back together in checked that I had aligned the timing markers. I have had the engine in pieces before and rebuilt it and hado it on the road after without any problems.

 

David

[Pete Lewis]

As the triumph sprocket can fit in 1/4 tooth increments its possiblemto fit it on the cam with the marksm(if it had some) aligned but the cam is 180 out

 

the idea of cam timing checks in most books dont explain all you expect to see

 

I would set the rockers on 7and 8 rocking , and open the rockers on 1and 2 to 40 thou

then rotate crank to tdc and check the clearances on 1 and 2 doesnt matter what they are but should both be the same

 

if theres a difference then the sprocket needs indexing to another set of holes and re check

each pair of holes gives 1/4tooth, so two sets of holes are available and turn gear over for next two

 

if the timing is miles out then its start from scratch

 

Befors you do anything, use johns thumb over plug hole to determine no1 is on a compression stroke , make sure the rockers

1 and 2 have clearance

[JohnD]

 

Yes, that is what the cams should be doing.     No.1 both closed as piston is TDC while No.4. also approaches TDC and the valves are both slightly open.    This is so reliable that is you have the means to measure their opening (dial gauges) it is s simple method of setting the cam timing, called Equal Lift On Overlap.   (The overlap is of the two valves being slightly open at the same time)  As you are using it, it is also a useful way to check that the cam timing is correct.

 

You mention that you get consistent blow back when you use some 'Easy Start'.    This make me wonder about your ignition timing, given that the cam timing is OK.    Look under the Dizzie cap, with No.1 at TDC and both valves closed.  This is the start of the ignition/power stroke, when the spark plug should fire.      Is the rotor arm pointing at No.1 terminal?     

Then, have you installed the plug leads in the right order 1-3-4-2, going ANTI-clockwise?

 

If all these are true, then try starting the engine with the dizzie slightly loose, so that you can turn it by hand, a few degrees either way, until it catches.

Mark the dizzie in some way so that you can return it to the original position easily, and not get lost!

 

John

[David McHugh]

Yes, that is what the cams should be doing.     No.1 both closed as piston is TDC while No.4. also approaches TDC and the valves are both slightly open.    This is so reliable that is you have the means to measure their opening (dial gauges) it is s simple method of setting the cam timing, called Equal Lift On Overlap.   (The overlap is of the two valves being slightly open at the same time)  As you are using it, it is also a useful way to check that the cam timing is correct.

 

You mention that you get consistent blow back when you use some 'Easy Start'.    This make me wonder about your ignition timing, given that the cam timing is OK.    Look under the Dizzie cap, with No.1 at TDC and both valves closed.  This is the start of the ignition/power stroke, when the spark plug should fire.      Is the rotor arm pointing at No.1 terminal?     

Then, have you installed the plug leads in the right order 1-3-4-2, going ANTI-clockwise?

 

If all these are true, then try starting the engine with the dizzie slightly loose, so that you can turn it by hand, a few degrees either way, until it catches.

Mark the dizzie in some way so that you can return it to the original position easily, and not get lost!

 

John

Hi John,great we are thinking along the same lines, what you have suggested is what my Dad said except you have explained it far better, so thanks once again.

It probably won't be today but I will try your method in the next couple of days.

 

Happy New Year to you John

[David McHugh]

As the triumph sprocket can fit in 1/4 tooth increments its possiblemto fit it on the cam with the marksm(if it had some) aligned but the cam is 180 out

the idea of cam timing checks in most books dont explain all you expect to see

I would set the rockers on 7and 8 rocking , and open the rockers on 1and 2 to 40 thou

then rotate crank to tdc and check the clearances on 1 and 2 doesnt matter what they are but should both be the same

if theres a difference then the sprocket needs indexing to another set of holes and re check

each pair of holes gives 1/4tooth, so two sets of holes are available and turn gear over for next two

if the timing is miles out then its start from scratch

Befors you do anything, use johns thumb over plug hole to determine no1 is on a compression stroke , make sure the rockers

1 and 2 have clearance

Pete,very well explained, now that I have all the answers for what I was looking for thanks to John and yourself, i am just waiting for a slightly warmer day to implement the checks and adjustments where needed. It's not nice handling metal for hours in 2 to 4 degrees.

Happy new year to you Pete.

[Pete Lewis]

A dash of something nice in a strong cuppa the breath should help defrost the pinkies

 

pete