Crab frustration:-)

Sorry to hear that, Tommy. It can be very frustrating sometimes, trying to get things right. Two years ago, I was getting very annoyed about all the exhaust problems that were happening and began to get rather disheartened with it all. Still, came through it with some help and advice from other 'crabbers.

You know it will be worth it when she's working properly. Even if this is a one off "rogue" car, you have others which work well and should be enjoyed.

Reading through the threads again, it all comes back to the engine. It seems to be a "performance" rebuild - perhaps they have pushed things a little too far? Before you give up, have a word with PETER BURGESS. He is the recognised authority on what can and can't be done to a B motor and is also a throroughly nice bloke. I rather think that my friend Mike has a Burgess motor in his rally crab, so they've seen them before.

If you want an "off the wall" idea, how about dropping the compression ratio? The rebuilders may well have decked the cylinder head as part of their work. As a quick (and temporary) test, fit a second cylinder head gasket, re-gap the valve clearance and see what happens.

It would be a shame to just give up and walk away.

Chris.

Thanks for your help and sympathy guys, I really appreciate it:-) I agree it's to bad to give up, and the car would be wonderful if I could sort this problem. I would regret it, I'm sure. Imagine seeing it again at a car meet or so and find out the new owner had fixed it with little work... Hopefully a week away from it will bring my motivation back:-) Putting it away for some days alwas helps:-)

The strange thing, and the most frustrating, is that it will work ok for periods, however it's never as smooth running as the Marina or even my recent crab, which has been standing for years. Sadly they are not road legal, don't have plates and MOTs, so I'm not able to try them on the road yet. I've put them on hold until the 1800 was sorted, which has taken a long time for sure. Perhaps I'll fix the Marina now, which needs very little work. At least I can enjoy some classic motoring then.

I will try to check out the new engine when it comes to compression ratio. Surely, the block was skimmed, but I will have to find out how much. The head has been rebuilt earlier and it has most likely been skimmed, too. Are there thicker head gaskets around for the 1800/ MGB?

However I can't help thinking it's down to fuel or electrics/ ignition or possibly a combination, as it behaves very similiar to what it did on the previous engine. Except the oil burning, at least there has been some progress:-)

To boil it down again: Rough idle when hot, coil gets too hot (again), impossible to establish a steady mixture, same goes for the timing which will make it pink occasionally it seems. Fuel related smoke when revving hard (soothy), no smoke when driving. Starts instantly in all conditions, from - 30 Celsius to + 30. Usually fine on the road, except hesitating/ vibration at steady speed in around 70 kmh. Also some hesitation when driwing slowly. In short, the quicker I drive, the better it behaves.

So, when does the trouble start? Engine starts right away cold, and runs fine, the engine is steady. However, after a couple of minutes or so there is a slight miss now and then and idle speed varies, like slight hunting. This shows on the Gunson tach too, the needle won't keep steady, typically it will miss every 10 seconds or so, dropping about 50 - 100 rpm and then catch up again. This behaviour is repeated, and typically it will be even worse after driving. Engine will then vibrate badly and exhaust note is uneven. I can then make it run somewhat better by weakening the mixture, however it will then drop and stall when lifting the lifting pin.. Also the engine seems to run somewhat hot, although it's never above the N area on the gauge.

There's one thing I haven't replaced on the car, the petrol tank. The original one was rusted, so i fitted a rust free one from a early mk 1 spares car. Is there an internal filter in these tanks, and could this be something to look at? The manuals are unclear on this. Anyway, it would be impossible to change I suppose:-) The pump is a nos genuine SU, with filter in it. The filter is absolutely clean.

When it comes to the electrics I still find the coil too hot. Problem occurs as it heats up, so could be a connection here. Is the spark too weak for some reason? It's yellowish/ blue. I tried a new wire from the ignition switch to coil yesterday, in case there was a bad connection at the A3 therminal. No difference. Could something mess up the current to the coil? I've read about North american mgbs starting when applying the brakes, because the current from green wires will short through the ignition switch red white wire or something. Sorry I don't remember the details.
Could something be wrong in the car's wiring? It's been converted to negative earth. Voltage stabilizer, which ignition related circuits are connected to? Partial short somewhere, shorting the ignition/ coil lead now and then? Using the strobe the ignition marks jump a little, seems related to the miss/ hunting. The vacuum gauge reads 18 or so at idle, drops and goes up to about 25 and back to 18 when revving. Needle shakes slightly all the time. However, it's a very cheap gauge..

When it comes to cam timing I'm sure this is spot on for this standard cam, after all the headaches with the cam issue.

Well, it seems I haven't given up completely:-)

Regards, Tommy

Can't see why you'll need a pressure regulator. When the float valve(s) close in the carb(s), the back pressure stalls the output from the pump by holding the valve shut.

I have one of these fitted on my car:



German, not that expensive and works well. It sits behind the tank.



I'd keep it as simple as you can, Tommy. If the carbs are working properly, they cycle the fuel flow automatically.

Enjoy your holiday and forget about it for a while.

Chris.

Well, time for an update!

Regarding the fuel pressure regulator, I only considered using one if I went for the universal electric pump, which could put out more than 4 PSI pressure according to specs. As Dave says, I've also read that the float valve could have problems with pressure above 4 PSI.

Anyway, I fitted the original Princess type pump. The other one, also NOS, must have a leak as pressure drops rapidly. I also changed the needle and seat and installed a fuel filter. It was still hard to obtain a steady mixture according to the lifting pin test. Typically it seems to be too weak.

I went back to the engine and ignition then, as I understand the engine itself and ignition has to be spot on before attempting carburation adjustments. I changed the oil separator for the original one, as Dave suggested, as I noticed traces of oil in the breather valve. Coil still got abnormally hot, so I fitted another coil again. This time a ballasted one from a Marina, with the resistant wire from the Marina too.

Thinking about sticking to the original, I swapped the Bosh (70 A, from a Granada) alternator for a Lucas 16 ACR and this swap seemed to make the biggest difference on the engines behaviour. I set the dwell to 50 percent and the timing to around 12 degrees at 600 rpm. By using the lifting pin I was able to find a reasonable mixture setting where the rpm also would rise clearly when opening the oil filler cap. I use the diaphragm breather.

It behaves very well on the road, loads of torque, no hesitation/ misfire and no pinking even up steep hills in 4th gear. The engine is very quiet for a B, so I think I should be able to detect any pinking etc. So, things are a bit brighter now. As you may have understood, I'm extremely picky when it comes to engine tune up but I intend to drive it like this now, perhaps taking it for a longer trip to smooth things out. The coil stays cool when driving, and wil only get somewhat hot at idle. I'm not to concerned about that.

At idle, there's still a slight hunt when it gets hot, but perhaps I'll have to live with that. the idle whill then drop after a while. When revving it will be fine for a while, then drop again. At this state it's still difficult to get steady behaviour from the lifting pin. It will behave as too weak one moment, correct the next. If I revv it at hot idle, there will be a light puff of black smoke from the exhaust too, even though the lifting pin suggests it's too weak.

I'm not sure how to judge the vacuum gauge either. At least there's nothing critically wrong I guess. At idle, about 700 rpm it's around 18. The needle is not steady, flickering rapidly. It sure looks to follow the engine's slight hunt too, falling to 17 when eninge misses, then up again. Running at faster idle it shows a steady needle at 20. Revving rapidly, it drops to around 2, then up to around 24, and back to 20, or 18 at lower idle. This is normal behaviour I understand. When it comes to the rapid needle shake, I'm wondering if this follows the sound of one of the valves. There's still a light tapping from the valves og course. The rocker assembly has not been changed.

Well, anyway, I can live with it now and will drive it to see how things turn out. I'm certain too, that unleaded petrol makes a big difference. After all, last time I drove a crab daily it ran on leaded petrol. So I suppose one will have to take this into account when demanding these engines to run like a sewing machine at idle and pull like a train on the road today:-)

Updates to come:-)

Regards, Tommy

Thanks! Great link! Yep, it's the same head as used earlier. I suspect a sticky valve too, at least some of the valve guides and valves were changed on this head when it was reconditioned. I seem to recall though, that all valves fell nicely into the guides. Things could be a lot different when really hot though:-) I'm not sure what kind of guides were used. Interesting too, the vacuum gauge is steady at faster idle, I suppose a sticky valve will be most evident at lower rpm, so this could be an explanation perhaps. Perhaps the vacuum gauge is ok when engine is cold? I'll check later.

This seems to match the sound of the valves too, sometimes at least one of them wil tick, other times they are all almost completely silent. Perhaps I've adjusted the clearance a bit to tight?

I'm afraid I don't have a colourtune, I'll definetely get one.

Anyway, I'm not really up for a head job again at the moment so I guess I'll drive it as it is now and watch it carefully. At least there are no problems on the road, and I don't regard the problems as a potential damage to the engine.

Regards, Tommy!

Hi again!

As mentioned earlier here, I have suspected a sticking valve on the rebuilt head I'm currently using. I suppose I could have overtightened the valves a bit earlier, too..

I've now installed a new complete rocker assembly and adjusted the valves correctly, at least they are not too tight. The rocker shaft improved the valve ticking a lot, and as I hoped, I would now be able to at least try to single out any abnormal sound from any of the valves. I took it for quite a long run the other day and the symptoms are still the same, hesitation driving steady at around 70-75 kmh and also when rolling downhill in gear. After going downhill it will hesitate a bit when accelerating again, too. Above 80 kmh it behaves very well. Anyway, what leads me to a valve playing up is that the hesitation is accompanied by what seems like an abnormal and irregular valve tick.

By the way, I've now got the mixture right and found an ignition setting which gives no pinking, yet steady acceleration, except the hesitation. It was set to 10 degrees at 600 rpm, I believe this is reasonable when running unleaded, as it is stated 12 degrees in the manuals from the days of leaded petrol.

During the longer run I stopped, checked the mixture which was fine and it idled well for about 10 minutes. It was a hot day, and when setting off the hesitation was more noticeable, as well as the ticking noise. So, I'm almost sure a valve is sticking when it gets really hot.

I've now taken the head off:-) Thank God I have a long holiday:-)

Nothing unusual at first sight, only I now saw that one new guide had been installed, the inlet on cylinder 3. All the valves moved freely in their guides though, but who knows when it's really hot in there? Actually cylinder 3 was the one I suspected. By all means, I know these engines make valve noise, however this noise is abnormal in my opinion and irregular, and actually more noticeable when hot. It stands out from the "normal" light ticking.

To see if it makes any difference, I'm putting in another cylinder head tomorrow. It has not been rebuilt, milled or anything. It's from a low mileage car.I've cleaned it up very well, I think and will grind the valves tomorrow. I'm a bit uncertain when it comes to valve guide/ valve stem wear, so any feedback here is welcome. There's some sideways movement of the valves in their guides, however not noticeably more than on the overhauled head, which they claimed was within specifications. All the heads I have seem to have the same movement here, so I suppose it's not critical? I have no equipment for checking this accurately. I'll fit new valve stem seals of course, and give it a go. Fingers crossed, again:-)

By the way, have anyone experienced alternative valve stem seals as discussed on various MGB sites?

Well, update to come. God knows what to do once this car is sorted? If it ever will be.. It sure keeps me occupied:-) At least I'm motivated again:-)

Regards, Tommy

Cylinder head changed today, and so far it seems to have improved things. There's no noticeable miss at 70- 75 kmh now, the same goes for rolling downhill, with throttle closed:-) It pulls better and smoother up hills too and sounds more healthy. Idle is quite stable too, and there's no smoke at idle or when running.

I had to advane the ignition a bit as well as richening the mixture. There's no pinking now. I'll re- torque the head and check valve clearances again tomorrow and take it for a longer drive. By the way, I had a look at the brake servo vacuum valve. It seemed a bit loose and The seal was somewhat hard. It's the type with three lugs on the valve. I made a new seal and it made the valve sit more tightly. I've checked there for an air leak 100 times or more, but the valve is tighter now at least.

So who knows if the cylinder head or the servo valve made the difference:-) I'd rather not know.. I was a bit amazed by the carbon build up on the piston tops after only some months, so Ok to have cleaned them anyway. Perhaps it's letting some oil in through the guides anyway? At least after a run tonight all plugs were biscuit brown.

Hopefully it will stay this way now, fingers crossed:-) To put it mildly I'm quite nervous when approaching a steady 70 ish km pr hour still:-)

Regarding the sports coil I haven't got one, but perhaps it would be a good idea to get one? The Lucas DLB 101 I'm running now still gets a bit hot at idle in my opinion. Cools down when running though.

Updates to come:-) Regards, Tommy:-)