loss of power

[moray]

My traveller has developed a loss of power problem.

It starts fine, and idles well, and drives well for about 10 minutes or so.
Then it starts misfiring and losses power, before chugging to a complete stop.
If I leave it for a minute, it will restart easily and let me get a bit further down the road, before it happens again.

The fuel pump has been rebuilt, and has a healthy tick, and is delivering fuel as per normal.

The engine has been fully rebuilt and has only done about 500 k's.
The plugs, leads, points, wiring loom are all new. The car is negative earth.

I have tried two different condensors, new rotor arm, a new distributor cap.
I've checked the coil voltage, 13.8 volts. also checked the polarity is correct.
checked and adjusted the points to 15 thou
the plugs are all gapped to 25 thou, and are a tan, brown colour.

the oil on the dipstick is clean, and also in the filler and under the rocker cover.

I've ordered a replacement electronic distributor bundle form accuspark, and will replace the lot, just to rule out the ignition system.

I've noticed the radiator cap was dirty inside, with what seemed like grease.

just wondering if it could be a head gasket issue? Is there anything else I could check?
I don't have a compression tester.

[moray]

If I pull the plug leads while its idling I notice it drops revs on all cylinders, except number 4.
there is no noticeable difference on it.

when reconnecting the leads I can see a spark on all leads between the plug and lead.

[ianmack]

New condensers,cap and arm are a clue. Try substituting them, one at a time, with old ones. Some of the new ignition parts currently available are defective.

[bmcecosse]

Obviously there is a problem with #4 - either a burned valve , or less likely a head gasket problem - since that usually affects two adjacent cylinders. However that doesn't really explain the 10 minute running. Run it till it stops - is the fuel pump ticking away mightily? Take the tank filler cap off - listen for an inrush of air, which would indicate a vacuum is forming in the tank.

[chickenjohn]

Try swapping the plug from no 4 cylinder to another cylinder and if the misfire moves to that cylinder- you have a faulty plug! (Rare but new parts can be faulty).

Also, new stock rotor arms can be iffy, on a customers car I saw a intermittent misfire that was eventually traced to a rotor arm with a loose rivet, you could try changing to a known good (i.e. off a friends car that runs well!) rotor arm.

Other than that, a compression test on no 4 will tell you if there is a valve or gasket problem causing misfire due to loss of compression.

[moray]

Thanks guys,

if it was a blown gasket or stuffed valve wouldn't it be misbehaving all the time?

when it occurs the fuel pump ticks as per normal so because of that, and the fact it has only just been rebuilt I had ruled it.
Will try the fuel cap vacuum thing. Will probably have to wait till the weekend.

will try the plug/cylinder swap and see what happens.

The accuspark ignition has turned up today, so will also fit that and see if it resolves the problem, fingers crossed

[kennatt]

it could be that one of the v alves Tappets on no 4 is too tight and when hot and the valves expand not letting the valve close,thus giving the symptoms of burnt out valve. when cold its ok. Check the tappets on no 4 as a matter urgency because if it is as above very soon you will burn the valve or seat.

[bmcecosse]

There are two problems here -stopping after 10 minutes - and seemingly 'no power' from #4. They are not related - fix the 'stopping' problem , and then worry about #4 - although yes - it will only take a couple of minutes to check the valve gaps.

[minor65]

I pressume when you rev the engine with cyl 4 pluglead on, it is 'on' the cylinder. As apposed to it being 'off" it when the lead removed. If there is just no difference when at idle, then the valves may just need rubbing in a bit on 4. Compression check would reveal all.

[bmcecosse]

If the exhaust valve gap is ever allowed to close up - then the valve will be burned - and the seat damaged, Hence the advice from MG/Rover to run the gaps at 15 thou. You should also check/reset every 3000 miles or so.

[moray]

Had a quick go yesterday and think I've made some progress.
I re torqued the cylinder head to 59NM ( 44lbft), each nut took about a 1/4 to 1/3 turn to get there.
I then checked valve clearances and set them to 15 thou exhaust and 12 thou inlet.
The gaps were closer, probably around 10 - 12 thou.

I also fitted the new accuspark red coil, electronic dizzy, plugs and leads.
I got it to start, but I think the timing still needs tweaking.

to get it correct do I let it warm up, then adjust the timing by rotating the dizzy clockwise until it starts stumbling, then back it off slightly? followed by a road test to make sure it's not pinging.

stupid question, but what does pinging sound like?

[bmcecosse]

Light metallic rattling - like dried peas in a tin can. And only there when the engine is working hard. Just swing the dizzy gently back and forth till you have the best/smoothest/fastest idle. I wouldn't have changed the coil.....

[moray]

The saga continues.

I went to drive her last weekend. Turned on the ignition, waited for the petrol pump to finish priming.
turned on the starter, there was a loud bang and then nothing.

Had a look under the bonnet, and the sealed battery had exploded, covering the engine bay in acid !!

I removed the battery and hosed everything down, then mixed up some sodium carbonate and water in a watering can, covered everything with that, let is sit for a while then hosed it all off.

I've got a compression tester on ebay, and today, armed with a new battery I started her up for about 5 mins till warm, then whipped out the plugs and tested the compression.

cylinders 1 and 4 only got to 90 psi, 2 and 3 were 140 psi

I guess the head will have to come off ?

[bmcecosse]

The question really is - why the explosion? Had you been charging the battery? Did the non earth terminal come in contact with the clamp bar? Was the engine perhaps 'solid' and a big current drawn from the battery when trying to crank it? The two cylinders at 90 psi are desperate - so well worth investigation - but since not together, hopefully it's just valve / seat problems.

[SteveClem]

Can't claim to have the expertise of some of these guys,and no idea why your battery went pop, but I have encountered your previous symptoms in the past on my '61 saloon. Ran great for 10mins then an embarrassing loss of power. Leads just needed tightening up in the dizzy. Some kind of screw that pierced the lead.

[Johnny]

I had similar trouble once and it turned out the coil was shot, quick replacement and all was fine. Might not be but thought I'd mention it.

[bmcecosse]

Errrr - it's NEVER the coil

[Johnny]

Well it worked for me!

[bmcecosse]

Was it a 'good old coil' - or a modern replacement? What's the primary impedance on the 'failed' coil ?

[trabant]

If I had 90 psi I'd be very worried this is somewhat similar to what happened with mine and like bmc says it does sound like you had two problems mine was down to shoddy new ignition components specifically the condenser mine went through three in six weeks the exploding battery usually only occurs with over charging or severe load.