Mystery cause of sticking inlet valves on Mk II engine.

[paul.jameson]

The eagle eyed amongst you will note my Healey at the Ace Cafe last Wednesday but no sign or mention of it on the actual London - Edinburgh run. What happened was that she ran perfectly down to London and to the Ace Cafe. It was stop at most of the traffic signals going in to London on the A5 in hot conditions and stop start for a good mile or so on the North Circular before the Cafe. But she went there with no issues at all.

We had a drink and stayed for about 40 minutes then decided to go the 400 yards or so the the overnight hotel. First kick there was a bit of a spit and clunk. Second kick she started, running awfully, misfiring and sending out lots of sooty smoke. She would not keep running so I pushed her to the hotel. There, with Rob, Roger Gwynn and Jim Haydock, we found sooty plugs but the inlet valves on the two rear cylinders were stuck wide open and could not be closed by suitable application of a screwdriver. The pushrods for them had jumped out in the process of trying to restart the bike.

It was all too clear that to free the valves would be a cylinder head off job so I was recovered home (efficiently, but then I was in London to begin with).

I was previously aware that the slow running was slightly rich but reluctant to alter it before the long run, simply because the bike has been running superbly. All ideas of possible causes are welcome. Curing the problem should be easy enough, but I would prefer to avoid a repeat performance.

[markus.nikot]

Paul,

had similar problems on my SQ4 MkI and II.
Making it short, I think the oil was the problem. I'm using 20/50 as recommendet but different makes having a different point of burning (flammpunkt in german). If the oil gets too hot - and some places in a SQ4 engine are very hot as we know it burns and produces carbon deposits which could build up in the valve guides. The one I've used had a very low point, now I'm using LiqiMoly with a much higher number.

Hope this helps.
Markus

[paul.jameson]

Many thanks for that Markus. I think there is every chance you are right. I spoke to the technical people at Morris Oils this morning as I am running on their Golden Film 20-50 in the Healey. They confirm it could well be the problem, coupled with diesel particles in the air along the North Circular Road in London. It seems pretty clear that all was well when the engine was hot, but that cooling down led to the sticking valves as the alloy / phosphor bronze in the head and guides would shrink more than the steel valve stem.

I will advise further when I have taken the head off but the Healey is currently No4 in the queue for repairs so it will be a few weeks before I get to it.

[wade.edwards]

Is it evil to add a filter and oil cooler? Motorcycles are so much fun to ride but worrying about reliability and the inevitability of short term overhaul periods killed or at least greatly diminished the British trade.

[paul.jameson]

The Healey was fitted as standard with a filter and oil cooler. The oil filter is well concealed between the rear engine plates but the cooler is obvious as it forms the front mounting system for the petrol tank.

That said, the oil cooler is not connected on my Healey. But, there again, the one on my previous Healey was also disconnected, even when I rode 2 up into Kracow at a temperature of 36.5 degrees C, stopping regularly at the traffic lights, with no problems at all.

[paul.jameson]

Having now taken the head off, I am pretty sure that Markus's theory of the problem being burning oil is correct. All 4 inlet valves had to be removed by means of a hammer and punch. The exhaust valves came out by hand but also have deposits on the stems. For all the world, the inlet valves look as if something has flowed down them and then set, mainly on the head of the valve. In one photo you can see this curling up off the stem - almost like glue. There was plenty of oil about inside the rocker covers but a lot of carbon in the combustion chambers. Whether this is due to a rich mixture (I know it was slightly rich) or whether this is bits of burnt oil, I don't know. I am fairly sure that, once valves and guides are cleaned and ground in again, all will be well. I shall weaken the mixture and check the ignition timing on reassembly but the bike was running perfectly prior to going to London. I shall not be going there again.

The photos should enlarge enough for you to see the details.

Stuck Inlet valve before removal:

Deposit flaking off valve stem

Note the ridge on the left side which looks like something has flowed onto the valve head in the photo below

[attachment=1]IMG_86809.JPG[/attachment

[Paul Slootheer]

Paul I have also read tales of over oiling from the valve stems/guides in a SQ head and the mods they tried to prevent this problem. (waller). In that case it might a be a combination of a hot running engine and over oiling. Just a thought…

[JohnnyBeckett]

hi i found the rear cylinders on square fours run a lot hotter than the font i think it doesn't with your legs blocking the air getting around the rear cylinders as well , i tend not to let the bike sit around when it's running

[nevhunter]

Some thing is turning into GUNK you don't want and it's heat related. Some oil additives can do that , but it usually shows most on the exhaust valves in my experience. Are you moving this thing along at sustained high speed? I think I would give a "synthetic 'oil a try for better high temp performance. . something like a 20-40. These oils will mix with the small amount remaining after you drain it all and perhaps a bit less oil going there would help. Nev

[Mick D]

Hi

I'm not sure I'd be so keen to subscribe to the 'oil burning' theory, if that were the case surely the exhaust would be greater affected. The visible oil in the rocker box photo shows signs of carbon deposits which could have originated in the cylinders from reported rich running. If sufficient debris has been generated to gum up the valves I'd be checking the sludge traps, (the debris on the valve stems bears a marked resemblance to the fine carbon like paste which accumulates there). Another thought, is detergent oil performing a deep clean on your oil galleries and producing the black debris?

Regards Mick