first classic-Herald 1200 ..weak valve springs??

[redratbike]

Aug 26, 2024 16:42:44 GMT Darkspeed said:

When you are convinced its fuel its probably electrical....

it’s done my head in the past few months but i hope its now sorted and i can now start to fit the lowered springs ,rear block and alloy wheels as i wasn’t going to do anything till it was running right.

[redratbike]

well it seems to running bad i didn’t get to road test it last time and jumped in this morning and it feel like a backfire through the carb as per the video inpost a few weeks back


so rocker cover and tappers off i can push the valves open by hand .. i shouldn’t be able to do this should ? in that case and they are weak this points to the car running ok till about 2.5-3k then just getting worse the higher you rev it

am i right in my thinking here guys ??

in which case new valve springs and we would be good to go ?

[Darkspeed]

Sounds like timing to me - or electrics at least - points coil condenser related, power, earths and the rest.

[redratbike]

Sept 11, 2024 17:42:01 GMT Darkspeed said:

Sounds like timing to me - or electrics at least - points coil condenser related, power, earths and the rest.

thanks for the response

i ‘ve changed everything i can up to this point , dumped the points for an electronic module….set the timing etc

earths mmmnnn, should i have an earth lead from engine block to chassis 🤷🏻‍♂️ i know my motorbike does .

edit: Engine earth strap usually goes from bolt through bottom of front plate of engine on right (looking from front) to underneath of nearest mounting of steering rack


What did you think about the valve springs should i be able to push them down with my fingers ?

[stealthstylz]

By "push down" how much are you talking? Make them deflect a bit - yes. Push the valve fully open - no.

[redratbike]

Sept 11, 2024 21:35:41 GMT stealthstylz said:

By "push down" how much are you talking? Make them deflect a bit - yes. Push the valve fully open - no.

1/8-1/4” maybe a little more

[igor]

Sept 11, 2024 22:21:39 GMT redratbike said:

Sept 11, 2024 21:35:41 GMT stealthstylz said:

By "push down" how much are you talking? Make them deflect a bit - yes. Push the valve fully open - no.

1/8-1/4” maybe a little more

Unless you have excessively strong hands this would seem to indicate that valve spring tension leaves something to be desired. Does it valve bounce at medium to high revs?

[Darkspeed]

Do you have a workshop manual that provides the spring pressure and installed heights? Pressing on a set of bath room scales positioned at the same height will give you an indication of the force you are applying if you duplicate the action you are employing.

Does the engine rev normally and freely without load.

ETA

The reason I ask is because being an old cast iron engine it could be that the valves have been ground or receded into the head and lost some of the original preload.

On the electrics - fitting new parts is no guarantee of good operation these days when it comes to parts for classics - Plus if the dizzy is not installed correctly, has the advance weights seized, the advance plate not earthing properly as the strap has disintegrated, The cap carbon not in contact with the rotor arm, the posts on the cap a mile from the rotor - the rotor not aligned with the post at ign' point. The coil resistance incorrect. Issues with voltage. Other components failing that are connected to the coil earth or feed. - There is a far longer list of potential electrical issues than there is of fuel.

E of the ETA - should have stated - many more electro mechanical issues than fuel.

[vitesseefi]

Herald 1200 has feeble valve springs from the factory. To the extent that it doesn’t have collets but a strange double hole arrangement in the valve cap. WSM says the caps can be removed by hand, and they can!

It’s a feature not a fault. Can still manage 5,500 rpm before valve bounce.

spitting back through the inlet can be caused by
-lean mixture (lean mixture burns very slowly so is still burning when the inlet valve opens)
-Retarded ignition (as above)
-plug leads in wrong order

[redratbike]

thanks for the reply guys i’m going to go back to square 1 and start re-checking everything.

unfortunately the car is in a council lockup some way from home with no power etc hence why the posts have been a little sporadic

[Darkspeed]

This link works to the factory manual.

app.box.com/s/c970f3ab0c2635962ef5

And yep, those valves are not going to be hard to push open



Previous owner getting it all wrong with the cam timing is also a possibility.

[redratbike]

thanks Darkspeed wow they are pretty soft aren’t they !

iz’ve been through the timing before maybe o am missing something obvious it was an allegedly rebuilt engine so anything is possible .

[Darkspeed]

Sept 14, 2024 7:42:52 GMT redratbike said:

...allegedly rebuilt engine...

Hopefully you will find the issue is an external one.

[kevins]

One thought, have you checked the exhaust is not blocked?