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MG MGB Technical - MGB 1964 wouldn't start
|I have just replaced the head gasket on my MGB and mostly it went reasonably well, except for losing the heater valve to cable connector. |
The problems started with starting it again. It turned over, fired once on one cylinder and the starter released. Again and again, with full, half and no choke, full, part and no throttle and all manner of combinations.
So I worked systematically, checking the points, cleaning them and replacing them, setting the static timing each time. Measured the resistance of each HT cable, through to the plug tips. Cheched the firing order, whether there was a spark at each plug. Checked the float chambers, at which point, the needle valve in one carb started to leak. Checked the manifold was bolted on properly. Scared myself with the dismal cold compression. (I suspect my 30 year old tester isn't the greatest.)
It was only when I took the air filters off to see if something was blocking the carbs that I discovered that one of the carburettor dampers was empty. That was it!
Has anyone had the same thing happen to them? I still can't believe it.
|It doesn't sound like the cause of the non starting to me.|
|1. Was the engine running reasonably before you did the gasket?|
2. What gasket did you use?
3. Did you check the valve clearances after head replacement? You don't mention it so assume you didn't and the valve train is the most likely cause of compression loss.
Putting oil in the carburettor dampers (filling the front and topping up the rear) was really all I did! (The front was completely empty). I worked round checking and adjusting one thing at a time until it ran. OK, I also took the air filter off but that was to see if anything was stuck in the carburettors. I was clutching at straws by this time.
1. The engine was running reasonably before I did the gasket.
2. The gasket is a Payen gasket, the first time I've seen one. It looks very nice, a work of art. It seems almost a shame to hide it between the block and the head.
3. I checked the valve clearances after I replaced the head. The old gasket was of a different type so I assumed the thickness could be different. I also took the opportunity to put some extra shims under the rocker pedestals as one of the valves was right at the end of its adjustment. I assume the (unleaded) head had been skimmed before I bought it.
My MGB has the early starter motor which disengages when the engine rotates faster than it does. One cylinder firing accelerated the flywheel fast enough to make the motor disengage. I assume that the piston in the carburettor, was sucked up too quickly and provided a mixture which wouldn't burn. By which time the starter had disengaged and then the engine stopped.
I would have thought the later starter would have got it running, if a little roughly.
At least I have the valves set, new points fitted and the static timing adjusted.
|If it had started it would have idled exactly the same with oil in the dampers or no oil in the dampers. The damper only comes into play when you open the throttle.|
Unless perhaps you were starting it with throttle and choke, and the first cylinder to fire each time was No.4, I can't really see one empty damper causing it. The pistons barely rise at idle, and there is always a bit of lost motion in the damper anyway.
|It would need a major change in settings for it not to at least fire and run roughly. Sounds like there is something Odd here. The head would have to have a great deal shaved off it to lose adjustment at the rockers and then they would all be affected. I would take the head off and the valve chest covers and check everything in the valve train, including the followers (did you find the heater valve nipple?) AND the valve seats, they have been known to fall out. Why did you think the gasket needed changing? If it was losing water or mis-firing the head might be cracked.|
Hi, Paul, the car was firing one one cylinder before disengaging the starter. When the engine fired, it disengaged the starter as the inertia starter pinion did as it's supposed to do and wound itself onto the helix.
Surely the caburettor butterfly is opened a little when the choke is pulled out? The piston could be lifted easily and quickly when I removed the filters; they normally need quite a force from my little finger and even then move slowly. So if the piston moved up quickly, that would result in slow moving air across the bridge and a weak mixture. Exactly what the engine doesn't want at a cold start.
Allan, I changed the gasket due to a spot of oil in the water, noticable by a thin layer of mayonnaise on the inside of the radiator filler cap. I have heard of heads having been skimmed and then needing shims under the pedestals, on this site! It was just at the end of the adjustment on the exhaust valve of cylinder no. 4. It was like that when I fitted the head ten years or so ago. I now have adjustment in both directions.
Anyway, the car ran fine on my test drive and starts easily. I suppose I should empty the dashpot again to see what happens.....
something you *might* like to try - John Twist recommends "90 weight gear oil" in the dashpots, I (in UK) and Rod (in Aus) have tried it and have been very please with the smooth running results (well Rod used 75w/90)
90 gear oil isn't as 'thick' as many think, it's within the 40 to 60 engine oil range
see 1:50 here - http://www.youtube.com/watch?feature=player_detailpage&v=v9QI3NlvwiY
|Mike - the piston would rise quickly, it just wouldn't move very far. And if one cylinder fired enough to accelerate the engine to the point where the pinion was flicked out of engagement with the flywheel, why didn't didn't others and so keep the engine going? Quite odd, but not as odd as the MGB that wouldn't restart after buying vanilla ice-cream at the local supermarket but would after buying chocolate.|
This thread was discussed between 12/09/2013 and 15/09/2013
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