75cc and 100cc oil feed to cylinder head

[chris78jota]

The little 75 and 100 bikes use oil vapour to lubricate the rockers and valves - vapour finds its way out of the engine via small drillings in the barrel and head, then vents out to atmosphere by a grille in the back of the rocker cover.

Putting aside the environmental issues for a moment  :-[ , whilst it actually 'works' this isn't the best solution.  Pictures of the early 75cc racers show the toolbox behind the head caked in oil, so they updated to a breather pipe running from the cover to the rear of the bike fairly smartly.

More interestingly (and I'm finally getting to the point, sorry  : ) the factory race bikes later changed to normal, positive lubrication direct to the cylinder head; the breather vent was bunged up and the breather shifted to the crankcase.
This was surely a far better method of keeping the valvegear lubricated - especially bearing in mind the 1500km endurance rides they were used on.

My question is; does anyone know how the factory did this, or have any photos, or indeed has anyone pondered on the issue and come up with an idea about how to do it?  I'm in the process of getting a really nice 75cc head completed (thanks Maestro) and I'd rather it didn't wear out from lack of oil.

Chris

p.s. I'm proud I didn't use the word "lube" even once - although I'm sure Chris K will slip one in...

 

[DavidH]

Chris, I don't believe what you have stated is correct.
The photos show what I would consider petrol staining from carby blowback.  We have a small collection of photos collected from the intranet and other places, and none of them show the staining of the photos posted.

Both the 75cc and the 100cc bikes have a small diameter breather tube in the oil dipstick.  This is I believe to ventilate/prevent pressure build up in the crankcase.  All do have a small venting disc on the head at the rear - ranging from 1951 thru to 1957 build.  I can't see how a mist would lubricate the top end of a 75 engine, and believe that there is a positive oil feed to the head and rocker area of oil as against mist.
Photos of racing 100's show an engine breather on the lhs towards the back of the lhs crankcase half, but not all such bikes have them.

Our 75cc littl uns are in storage, and the 100 engines out for a spot of work, so I cant investigate at the mo, but the oil residue in the heads after a run would suggest to me that there is positive feed, but I may be entirely wrong.  Somewhere I have a doco showing the lubrication of the littl uns, unfortunately I have not scanned it so will need to find the doco.  I'll have a search this weekend and come back.

Wilfred has a lot of knowledge on the little uns as do several other European members, so it will be interesting to wait for their input.

 

[Gravelroad]

[...]  I can't see how a mist would lubricate the top end of a 75 engine, and believe that there is a positive oil feed to the head and rocker area of oil as against mist.[...]

Well, the Morini vee-twins incorporate just two "drop noses" casted into the rocker box cover (like stalactites in a cave), pointing to the lubrication holes on the rockers, as a sole way of bringing oil to the rocker shafts/valve area by mist. Does work surprisingly well, at least if you wait for the oil to warm up before giving the engine a handful.

 

[Paul Marx]

In view of the chores asked of those small singles for decades with the standard setup whatever it is, our grandchildren will be old before wear gets serious in those engines.

I would think that the extra breather of the race bikes has to do with the 11 000 revs they were subjected to.

Paul

 

[sfcpiet]

The mist lube works quite well, as does the primitive breather, my 100 didn't throw out more than a drop or 2 over the 1600km of the 2015 Milano-Taranto event.  The valve gear was very oily when I checked valve clearances after day 3.  The clearances were also spot-on, with no adjustment necessary.  Ignition timing is another story...

Yes, the rockers and push rods do wear, but I don't think it is down to of the hit-or-miss lube system.  More down to maintenance neglect, like changing the oil every 9-10 years and not bothering to adjust tappets. :  I think considerable mileage would be required for the wear and tear I've found in the tiddlers.  They're generally not on the 4th or 5th over-size piston for nothing.

I have seen a road engine with the positive feed to the valve gear, not totally convincing actually.  The rocker gear was just as worn as the ordinary stuff.

Unless you're going all-out racing, the stock set-up seems quite adequate. 

piet

 

[DavidH]

Very interesting Piet,
I'm more than happy to be wrong in this case.

I based my opinion on the amount of oil on the valve gear after I started our 51 Tourismo and checked it.
Amazing that anything gets up there.

As for wear and tear, I agree, caused by continual use and very little maintenance.  The 57 Sports Lusso had what appeared to be molasses/treacle in it when we got it.  The head had quite a deposit on all internal surfaces which was hard to remove.

Chris, I have sent you an e-mail.