Mystery cause of sticking inlet valves on Mk II engine.

[david.anderson]

I do think that overoiling in this case is at least part of the problem. And the inlet valves are the ones that are most affected due to the very strong suction of the induction stroke. The exhaust valve stems generally only show signs of carbon when there is excessive wear and are not affected by the strong suction of the induction stroke. That is why many engines only fit valve stem seals to the inlet valves.
After building my 4 I became aware of the overoiling of the top end after just a few thousand miles when I looked in the inlet ports. At that time I investigated positive seals which were good for 600F, but would have had to remove the guides to machine them to fit the seals. So I decided to wait until the guides needed renewal.
There have been a couple of threads on this forum regarding the fitting of valve stem seals so it may be worth investigating a little more. From memory someone used Harley seals.
Have you fitted the original steel umbrella seal used in the last couple of years the 4s were produced as I cannot see them in the photo.
I would also change the brand of oil. Mobil V-Twin 20w 50 will withstand the high temp of the 4.
David

[David Smith]

Paul there seems to be an awful lot of oil getting down the stem and onto the valve, Fours are not my territory at all, but on the KH i restricted the oil flow to the top end by feeding it off the return and use cast iron guides which presumably run less hot clearance. The high temperature cooking point of the oil would seem also to be critical,

[nevhunter]

It just occurred to me that the 4 with one carburetter has suction to all inlet valves with part throttle which is why slide carburetters don't work well and a lot of oil may go down the guides. Inlets don't need much clearance in the guides and rarely jamb in my experience. Nev

[markus.nikot]

This week I've had to dismantled the MKI head because of a migrated valve seat ring. The coking was pleasantly low. Quite different from the times when the valves got stuck. So the new oil seems to work.

Btw it is MOTUL 3000 20W-50 4T, point of burn 240deg C.

Markus

[paul.jameson]

I have done a little basic research, with interesting results on the flash points of oils:

Mobil 1 V-twin 20W-50 (Suggested by David Anderson but apparently unavailable in the UK at present) Flash point 214 degrees C

Motul 3000 4T 20W-50 (Suggested by Markus Nikot and available in the UK at present) Flash point 240 degrees C

Morris Golden Film 20W-50 (In the engine on the day of failure) Flash point 210 degrees C

Morris Golden Film SAE 40 (Previously used but recently changed for the 20W -50 version, regrettably) Flash point 224 degrees C

Reading the sales literature on the Mobil 1 V-twin 20W-50 it appears ideal, being designed for use in air-cooled motorcycle engines such as Harleys which have a rear cylinder fairly well shielded from air flow. It is fully synthetic. The Motul 3000 4T 20W-50 is also advertised as being to Harley specification but is a mineral oil. Clearly, the oil in the engine on the day of failure, Morris Golden Film 20W-50 was the worst option of these 4 and it was a mistake to change from the SAE 40 which has a flash point between those of the two suggested oils. There is nothing to tell me whether Golden Film is mineral or synthetic but I assume it is mineral.

When I was riding into London on the day of the failure I was reminded of the trip into Kracow. The main differences between the two journeys were that on the London trip the weather was a lot cooler and I was solo instead of two up. The traffic light stops in Kracow were longer and long enough for me to stop the engine regularly whilst waiting. The Kracow trip did not finish with about a mile and a half of walking pace movement like the London trip.

The oil used on the Kracow trip was initially Morris Ring Free 20W-50 but as the bike was using oil it had a significant amount of oil in it which I had bought at a Shell filling station in Hungary so an unknown product.

Both bikes were Healeys, but the Kracow one had low compression pistons and a Mk I type camshaft. The London one has standard Mk II type pistons (although ex BMC, modified by Healeys to Mk II spec) and the high performance Healey camshaft. In terms of condition, the Kracow engine had seen extensive use but the London one, particularly the cylinder head and valves, has done less than 4000 miles from new at Selly Oak.

I took a pair of the valves to the Summer Rally last weekend and showed them to anyone who would listen to me. Perhaps the most interesting comment came from Peter Kent who referred to a problem he had encountered at work due to mixing of 2 types of oil which caused the formation of "a lacquer". That is a perfect description of what seems to have formed in my engine. Geoff Brown kindly came round yesterday to look at the engine. He has seen nothing like it before in his extensive experience but agrees with the description of "a lacquer". He agrees with me though that I need to take the cylinder off to check that the rings haven't become jammed in the pistons.

So far I have cleaned up one inlet valve very successfully. The corresponding valve guide is proving more difficult to clean so far but I have both an adjustable reamer and a flexi-hone to use if needs be.

Any further thoughts and advice would be welcomed.

[Sean.O'Brien]

Paul,

Morris Golden Film SAE 40 is based on highly refined minerals oils. See section 12.2 on the material spec.

https://www.morrislubricants.co.uk/prod ... a78aee.pdf

Interestingly, they quote two different closed fash point temperates, the material spec says 229, whereas the technical specification says 224... It will be interesting to see what the pistons/bores look like.

[David Smith]

Paul
Do you run an oil cooler?
Experience running Honda cb72 engines( notoriously hot running in race condition) in the classic Manx GP on Catrol R30 Castor oil broke the oil down to something resembling vinegar with brown lacquering all over including the bores. The following year bored out to a full 350 so greater heat load, with an oil cooler and on Mobil 1 triumph mcle 10 / 40 resulted in no oil breakdown and a perfectly clean engine, The standard centrifugal oil filter was in place both timesl. I run a Panther 650 outfit which gets round the problem by converting oil to smoke at an impressive rate! However they run 0.004 and 0.006 inch clearance on he guides MINIMUM!

[david.anderson]

During our hot summers I had a couple of oil brands clearly fail (black and thick) when overheated in my 4, although I did not experience sticking valves. Mobil 1 V-twin was recommended to me by a fellow historic vehicle club member and Harley dealer/mechanic. He spoke about the very high heat of some of the Harleys, particularly overbored and high compression engines and he stated Mobil 1 V-twin was his go to oil. I tried it and no breakdown due to heat when run in my 4 so I have run it since then and been happy with it. I subsequently came across a follower scar testing of various oils and the Mobil 1 V-twin came out as one of the better oils having a high load capacity and relatively low total heat from friction. This is a link to the oil testing results https://www.accessnorton.com/Oil-Tests/NortonOil.php and this thread gives 59 pages of info regarding the testing https://www.accessnorton.com/NortonComm ... 018.25898/
Clearly the better oils listed are for flat tappet engines and are suitable for Ariel twins and 4s.
An interesting note during the testing is that many of the oils did not protect well until at operating temperature so the old saying is true.
So hopefully there is a suitable extreme protection oil that is available in England and that will not break down at high temperature.
A further note is that my current neighbour is a retired industrial chemist from an independent oil industry testing company who was most impressed by the information and testing listed above. He spoke very poorly about certain oils that I should not name on forum, although two are listed in the “oil might cause excessive wear …” table in the first link.
David

[Mike Nash]

Paul,
I fear the flash point is little guide to high temperature breakdown in lubricating oils. (But are you thinking of spontaneous or auto ignition?) All fluids have some vapour (even molten metals, some at room temp like mercury) and if the fluid is flammable then with the right test it will ignite when a flame is presented to it (which is done under specific conditions to give the "flash point"). Poking about the interweb I can only find a figure of 375C for auto ignition temperature of lubricating oil, but which type of lubricant and under what conditions isn't given.
I'm sure the best guide in the choice of oil is to do as you have done, to look at recommendations for Harleys from reputable companies. As an aside, I'm doing the same for my VB (don't laugh) 'cos I've found that the area of the cylinder near the exhaust port and in the same zone the piston and its rings have lacquered and carboned much the same as your SQ4; sidevalves too, have their problems if they're ridden in a spirited manner.
Regards from MikeN.

[nevhunter]

Side valves do have heat and bore distortion problems and NEED the best of exhaust valves The area between the exhaust port and the cylinder gets very hot. It's not as efficient an engine as the OHV and the combustion chamber shape is far from ideal. (Too much surface area for the volume and worse gasflow). They got popularity for their low height, safe when valve stems break and cheaper cost of manufacture (simplicity). Nev.