It's taken a very long time, but I finally put the Mighty Falcone back together today. I don't have any heating in the garage, and I'm far too old for working in sub-zero conditions these days...
Here's a summary of what was done:
The valve gear was very noisy, not so much at tickover, but at mid engine speed it sounded like a battalion of dwarfs hammering on steel anvils. The bike ran well enough, and didn't use any oil.
When I took the rocker box off, I discovered a large flat on the rocker - valve face.
inrocker2 by
bancquo, on Flickr
As we all probably know, lubrication to this face is poor, and relies on oil spraying up from a slot in the rocker end face. According to the Paul Friday archives, oil is supposed to be delivered via a slot in the rocker spindle.
However, mine didn't have any slot, and instead, the bushing inside the rocker had a groove to deliver oil to the slot.
slot align by
bancquo, on Flickr
arm slot by
bancquo, on Flickr
This is probably an improvement, as you don't need to worry about aligning the spindle slot with the slot in the rocker. However, it clearly didn't work. I had foolishly decided that as I do very small mileages on the Mighty Falcone, I didn't need to bother with an oil feed. The bike has only done 21,000 km since I got it in 2002, and it was some surprise to see so much wear with such low use.
The standard fix is to add a second oil feed to the banjo fitting on the right side of the head. However, I have always thought this very ugly, and devised a new system where the spindle is drilled from the left side, so only a short copper pipe is required. See post:
http://nuovofalcone.createaforum.com/engine-and-transmission/alternative-inlet-rocker-oil-line/Of course I broke an exhaust stud, and there was no way it wanted to come out, even after soaking for a week in Plus Gas...
plus gas by
bancquo, on Flickr
The valves were in good shape with hardly any wear or burnt faces. A serious decoke was required though, and it's clearly running quite rich...
combustion chamber by
bancquo, on Flickr
crown2 by
bancquo, on Flickr
My troubles didn't end there.
On stripping the head, I discovered significant wear in the valve guides (and I believe that this is a precursor to stuck valves and catastrophic failure, as we never hear of dropped valves on new or recently rebuilt engines). I could have simply replaced the guides, but decided to have the head professionally rebuilt with smaller valve stems (8mm and 9mm), oil seals on the guides, and lighter springs. The smaller stems are supposed to be better, but dropped valves have occurred also with them, so they're not bulletproof (according to Huub, who has experience of that). However, the lighter springs reduce loading on the camshaft and cam followers, so it seemed to be the way to go. I was fortunate to have a good friend, who organised having the head rebuilt.
This was the end result - better than new!
head top by
bancquo, on Flickr
Ports were polished
exhaust port by
bancquo, on Flickr
inlet tract by
bancquo, on Flickr
The new valves are a little shorter, so caps are supplied to extend them to the correct length:
stem caps by
bancquo, on Flickr
You can just about see the oil seal in this photo, and the lighter springs:
double 2 by
bancquo, on Flickr
The mating face was skimmed flat:
face detail by
bancquo, on Flickr
New exhaust studs and flange plate:
exhaust stub by
bancquo, on Flickr
I did consider twin-plugging the head, but was advised this was pointless unless the engine was tuned for performance, and I have no interest in that.
IMG_0858 by
bancquo, on Flickr
With the head off, I discovered the cause of an oil leak since I first got the bike. Whoever assembled it had fitted the pushrod tunnel oil seal incorrectly, so it had been squashed over the top of the head gasket, damaging both seal and head gasket:
macro by
bancquo, on Flickr
removed by
bancquo, on Flickr
I also removed the cam followers, and found pitting on the faces that bear on the camshaft:
Inlet left Ex rt by
bancquo, on Flickr
I bought a pair of NOS followers to replace these.
lifters by
bancquo, on Flickr
I didn't want to pull the camshaft, but was able to inspect through the cam follower tunnels:
Not much sign of wear on the peaks:
cam2 by
bancquo, on Flickr
cam4 by
bancquo, on Flickr
For the bore, it was obvious that the barrel was rusted on the base, and had probably been lying in a pool of water since 1972, until I bought it 30 years later...
bore by
bancquo, on Flickr
I now think I could have rebuilt without changing anything; the engine wasn't burning oil, and I think the rust was secure in the pits, and forming a good seal. However, I made the decision to give it a light hone (on advice from the Engineer) but this made the situation worse, lifting the rust out of the holes, and opening up the pits. A rebore was required then, but I couldn't buy a piston until I knew how much needed to be removed to clear the pits. I had the work done at Engine Resource in Dundee (the owner is a member of our classic bike club, the SCMC) and we ended up with 88.4mm. This was good, as although NOS pistons are available in all four oversizes, not all of the rings are available. 88.4mm is available as a pattern piston from Gandini, and it comes complete with gudgeon pin, circlips and all rings, reducing the number of order lines.
domed by
bancquo, on Flickr
piston by
bancquo, on Flickr
I've often wondered if gapping rings is really important, but this photo of the oil scraper ring shows why it is; jammed solid in the bore, with no gap at all. I used a diamond file to adjust. The compression rings didn't need adjustment, and actually the top ring gap was over spec.
scraper gap by
bancquo, on Flickr
I decided to fit the piston on the bench as being easier than fitting it after the piston was fitted to the con-rod:
barrel-piston by
bancquo, on Flickr
piston fitted2 by
bancquo, on Flickr
Then align the piston so the larger valve cutout for the inlet valve is at the top:
valve cutouts by
bancquo, on Flickr
Then fitted the barrel to the cylinder studs, warmed the piston with a hot air gun, fitted gudgeon pin and circlips:
base gasket by
bancquo, on Flickr
gudgeon pin by
bancquo, on Flickr
Circlips are conventional type; not the wire ones as fitted to the original Mondial piston
circlip1a by
bancquo, on Flickr
3 by
bancquo, on Flickr
That was it for the day:
barrel fitted2 by
bancquo, on Flickr
New gasket and pushrod tunnel seal:
head gasket by
bancquo, on Flickr
Torque head to 45 N-m
torque by
bancquo, on Flickr
Fitted pushrods (inlet is nearest the crankshaft and exhaust nearest timing side:
pushrod alignment by
bancquo, on Flickr
head fitted by
bancquo, on Flickr
Fitted the valve caps with grease to hold them in, then fitted rocker box:
valve caps by
bancquo, on Flickr
Good view of oil seal on this one:
oil seal by
bancquo, on Flickr
Bit of a fiddle locating pushrods into rockers:
pushrod-rockers by
bancquo, on Flickr
Added the new oil feed:
oil feed by
bancquo, on Flickr
After that, it was just fitting exhaust, carburettor, spark plug etc. and set the valve clearances (I use 0.1 and 0.2mm)
I kicked over the bike a few times to get some fresh oil through the system, and was pleased to see oil being delivered from the new feed to the inlet rocker: note position of end float spring on inlet rocker shaft to left of engine; exhaust is on the right side:
oilfeed proof by
bancquo, on Flickr
And that's pretty much it. I'm not a confident engine builder
so I won't be happy until I've done a few hundred miles on it, but on the plus side, it did start second kick. A bit smoky at first, as all the assembly oil burned off, but that soon cleared. Fingers crossed that I haven't screwed up on anything, and that we have a few thousand miles before the next time...