Hestitatin' and a Judderin'

[edd_barker]

Hi all,

Two problems in one this week!

Friday I gave the Green Baron a full service, new points, coil, condenser, plugs, leads etc. Re-gapped the points to .015 which they weren't at previously. Ran fine. Drove 220 motorway miles up to Manchester with no problems other than an oil top-up. Slowing down after motorway speeds I have two faults now:

1. The engine is hesitant at low revs, or when accelerating from lower speeds in a higher gear. I'm reluctant to say hesitating as its more like its vibrating differently without the performance being affected, but definitely wasn't doing that before. Fine at higher revs. Plugs are light brown/grey and I haven't touched the carb for fear of upsetting it.

2. The brakes now judder. The front drums/pads/cylinders are all brand new. Mintex pads. It had been fine with these for a week, but now juddering.

Any thoughts? Its the engine that concerns me more as guessing brakes are just bedding in, I will have a look tomorrow. I have a carb re-build kit as it doesn't look like its been touched in donkey's years, is there a guide anywhere for where to start tuning and adjusting it from? I've only done an outboard carb before with a low/high speed adjust.

Many thanks,

Edward

[chesney]

Did you alter the ignition timing at all?

[bmcecosse]

Put the old coil back on.......it's never the coil. In fact - could be just about anything you have changed - try the old condenser too - and regap the points again. 12 thou is fine. Don't touch the carb!!! If it's not broken - don't 'fix' it!!

[mogbob]

Edward
Although the carb hasn't been touched...does it have oil in the damper to the right level ?
Bob

[mike.perry]

Check all electrical connections are tight, plugs, HT leads, wires to coil & dizzy. Check points have not closed up

[beero]

Yes, points heel can wear quickly if not lubricated closing up the gap. As others have said, put old coil, condensor etc back on, but one by one, so you know which component is at fault.

[edd_barker]

Hi all,

On examination today, its only running on 3 cylinders. Cylinder no. 3 (3rd from the front, 2nd from the back) isn't firing, but I have spark. Ground the plug against the head and it looked like it was firing OK to me.

Tried to get a compression reading but my comp gauge, despite being brand new, doesn't work. So I will try to borrow one.

Any thoughts on next step/likely cause? Assuming I'll have to delve into the engine

What's weird is that performance isn't affected at all. Whole way to Manchester and back I sat at 65 MPH happily, and as soon as it hits higher revs it's fine.

Thanks again

[beero]

It may be sparking but not at the right time. This could be a stray spark from 1 or 4.
A rotor arm or dissy cap problem may cause this.

[edd_barker]

Rotor arm and dizzy cap were both new with service, have swapped back to the original ones and still the problem remains. Almost looks like there is 2 sparks in different places on the plug?

Anywhere else I could look for problems? Or is a compression test the next step, but surely even if I've dropped a ring it would still fire?

I could have the leads on in the wrong order but then surely the other 3 cylinders wouldn't fire properly? Removing a lead from any of those causes the engine to falter but still run, but removing Cylinder no. 3 does nothing.


Anyone with more experience near Kingston/Surrey/West London?

Thank you

[MarkyB]

It could easily be a leaking valve, take all the plugs out and put the leads out of the way.
Then spin the engine over and cover each plug hole with your thumb, if the compression doesn't blow your thumb off the hole, that cylinder has a problem and the head will need to come off.
Otherwise check the HT side of the ignition.

[minor65]

If you have fitted new drums and mintex shoes as I did. I would advise you to remove the drums and get them checked for distortion, at a local engineer/machine shop. As the new drums now are terrible quality. Here's a link to my post reference my brake judder.

http://www.mmoc.org.uk/viewtopic.php?f=1&t=48631

[Dean]

Are the new plugs champion or nyk's?

Champion are better, but I would try putting an old spark plug in. I've had dodgy spark plugs before now.

[mike.perry]

Turn the engine over on the handle, you will feel a low compression

[bmcecosse]

If you have tracked it down to that cylinder, and a plug swop doesn't fix it (and you are sure the HT lead and cap are well connected - then it is a burned valve. Off with it's head!

[edd_barker]

Hi all,

Many thanks for the replies and advice. The tip to use your thumb as a compression gauge confirmed that cylinder 3 was way down. Then my forum request for local help was unwittingly answered by the man over the road (from here-on known as 'Super Tim') who has rebuilt several mini engines!

One borrowed compression gauge and: Cylinder 3 has ZERO compression. All the others are a shade over 120.

So plan for tomorrow:

Remove head and have a look. Pray it is a burned/split/slipped seal valve and not a piston ring.

I have a spare engine that was going to be for the 12G940 rebuild. I have taken the head off, so I can swap it over with the one currently in the car.

To my mind all I need to do is:
1.Remove springs and valves (Tim lent me a compressor)
2.Clean the head with a soft, brass wire brush and decoke until shiny
3. Grind the valve seats until smooth with paste.
4. fit with new stem-seals
5. refit the cleaned head with all new gaskets.

I only need this engine to run until I can finish the 12G940 rebuild, so I want to minimise engine work before that.

Anything I've missed?

Also, are there only valve seals on the exhaust valves? My 2nd head didn't have any on inlets.

Many thanks,

[bmcecosse]

It's normal to only fit the top hat seals on the INLETS..... Your 65 mph bash may have closed up an exhaust valve gap -and then the valve and seat burn very quickly. In future - set exhaust gaps to 15 thou - actually - I use 18 thou now...and check/reset every 3000 miles.

[edd_barker]

That is very likely, I didn't check the gaps as rocker cover wouldn't come off without removing heater tap

Lesson learned!

Is is the BMC manual I need for tappet check advice? Never done before.

So inlets are the larger valves...I thought exhausts were bigger? Also didn't have circlips on the valve colletts, can I live without them?

EDIT

One last question...how do I clean the cylinder head/block faces? Obviously I don't want to do any damage or affect the head gasket seal. Brass wire brush ok?

Thank you

[bmcecosse]

No!! Carefully scrape with a small paint scraper - no brushing - or emery paper etc..... And no collet clips required.....

[edd_barker]

Thank you sir, much obliged.

[edd_barker]

Problem solved, exhaust valve on 3 was missing a large chunk. Didn't look like a burn, more like a section had sheared off as was a clean break. Fingers crossed that chunk of metal went whizzing straight out the exhaust!

Will try and swap with a valve off the donor engine if I can get it to seat properly.

Thanks everyone for your help

Edd