Blue smoke !!

[shoebone]

Just bought a 1960 Minor, standard 948 engine coughing blue smoke. Bodywork and underside is very good condition so I used the smoke to get the price down, expecting to rebuild the engine. Head off and bores still show cross hatching from a +20 re-bore, pulled a piston to find it in similarly excellent condition, had a look at the head and discovered no valve seals fitted !! Valves have a little wiggle in the guides but I don't think its excessive so my expected engine rebuild may start/finish with a set of valve stem seals .... Bargain. !! Mini Spares sell Dupont Viton seals .... http://minispares.com/product/classic/LJQ101160.aspx would these work for my engine?[frame][/frame]

[bmcecosse]

IF you can get them to stay on these guides - they are intended for guides with a little groove near the top to retain the seal. And only fit them to the inlet valve guides - the exhausts need the lubrication. You can clean the guides and remove all traces of oil - and fit them with a spot of Superglue - that may work. Otherwsie - possible there is pressure in the crankcase - check breathers are clear, and maybe the oil rings have been fitted wrong way up?

[philthehill]

As you have the head off why not replace the valve guides (with wiggle) with the valve guides suitable for the DuPont seals.
http://www.minispares.com/product/Class ... ssic/valve guides.aspx|Back to search
Phil

[shoebone]

Thanks for quick replies, yes, I think I will get hold of some new guides with grooves. So ... Oil rings .. The pistons are made by AE and have two oil control rings in the one groove, they can spin independantly, no springs or spacers. The rings have a profile like this ...[frame][/frame] Tough to get a picture but here you go ...[frame][/frame] I've not seen this type of oil ring before, what do you think?

[bmcecosse]

They should have a wavy 'spring' ring between - at least any I have seen are so equipped.... I think you have found the problem. Is there any trace back to whoever did the engine 'refresh' ? I suspect these loose rings are just pumping oil up the bores. Although these ones are not for your engine - you can see the wavy ring there... http://www.ebay.co.uk/itm/GY6-50cc-Pist ... SwP~tW4h5w

[shoebone]

After much searching on the web and finding no information about these pistons, I finally found a reference in the 'vizard bible' .... "if you are looking for a high performance piston for either an 850 or 948 engine, the Sprite flat topped, Powermax piston from Hepolite, part number 18519/KR is a pretty good bet. The piston is of a somewhat dated design in that the rings are a little wider than is ideal and a double rail, cast iron ring is used rather than a 3-piece stainless ring for oil control. However, in spite of this its still a good working piston in this size of engine"

So .... Looks like this is what I have .. double rail and no wavy spring! I had not seen this design before. No history on the engine work carried out so maybe I should pop this piston back in and replace valve guides and seals and see what happens

[bmcecosse]

That picture doesn't look like 'double cast iron' oil rings..... Just the springy and slightly concave normal steel oil control rings - missing the wavy backing ring. There is also a correct way to fit these rings (due to the concavity) but I can't remember which way round it is.......no doubt a search will bring that up. The 'double cast iron' oil rings refers to another ring and groove below the gudgeon pin. Since I used to machine off virtually all the piston below the gudgeon pin to minimise weight, I obviously just had the one oil ring above the gudgeon pin. Since it was a 'race' engine that was fine - but it certainly didn't blow out blue smoke ! You need to find the correct oil ring set for the pistons you have there.

[shoebone]

So .... I fitted eight new valve guides and new valves with DuPont seals on the inlet valves. Its cured the smoking. Thanks for the advice

[oliver90owner]

Assuming, here, that you recut the valve seats concentric with the new guides and at the correct angles?

RAB

[oliver90owner]

Assuming, here, that you recut the valve seats concentric with the new guides and at the correct angles?

RAB

[bmcecosse]

I can't believe the oil rings will work like that for long.....

[shoebone]

Nothing wrong with the double cast oil rings, they are a snug fit in the groove when compressed and no wavy spring ever fitted or required, not like there's anything flapping about loosely !! i'm no expert but that's how these Hepolite pistons came and they appear to be doing the job. No I didn't cut the valve seats and not sure why I would need too, I got good results lapping them in with a consistent ring at the mating faces. Engine is running great now.

[bmcecosse]

Good luck with it! These are NOT 'double cast rings' - and Hep pistons DO come with a wavy spring behind the two steel rings to hold them in place - but if it's working for you as they are - happy days !

[philthehill]

After fitting new valve guides it is not always possible due to engineering tolerances to get the valve to sit square to the valve seat and that is why it is always better to run a valve seat cutter round the seat to ensure that the valve sits absolutely square to the guide.
Use engineers blue to check the seating before lapping the valves as lapping may not show up any low/high spots as the size of the particles (even fine) in the grinding paste will mask those low/high spots.
Phil