Oily Head ~ 1970 250 Springer Scrambler WC

[insanity]

Ahh the saga continues.

So, head is off again, as oil was leaking ~~ and the source of course was indeterminate, even after de greasing pressure washes and applications of talcum powder. It seemed to leak from behind the bevel tunnel tube junction with the underside of the head, onto the fins then away to anywhere it could go.
I did think it was the exhaust valve rocker cover, but NO. So my intent was disassemble a fit a fat paper gasket between the tunnel and the head, the smear of expensive aeroplane gasket goo didn't cut the mustard, not keen on polymers squishing and leaking into oilways so I may have been a lot less than liberal with it.

And "lo and behold" as the great sage once said, I found oil puddled in the valve recesses of the head ! though it started and ran so well.

Screenshot from 2025-01-04 15-23-37.png

As alluded to in the parent post ("Head Repair Springer 250 bevel drive pass through hole") all was eventually well.
And I did replace all perishables and use once bits , such as circlips and head O ring etc, AND valve stem seals too.
Though the stem seals are a Phil@R+R substitute. I did a quite MILD reseat grind before re fitting the valves.
The valves felt nice in the guides and the dial gauge showed bugger all slop and slap (shafts wet with oil).

Right now I don't know what my valve clearances should be either - nor do I know what cam I have as there is no green or white paint on it. I have shim type, not screw and locknut type valve rockers.

Haynes says intake 0.005/0.13mm exhaust 0.010/0.25mm
Clymer says intake 0.010/0.25mm exhaust 0.016/0.04mm

What I have is Intake 0.007/0.178mm Exhaust 0.016/0.040mm sadly I didn't measure before I disassembled the head, which
would have been a good thing to do so as to confirm or otherwise correct reassembly on my part.


Another question, given my 250 has a350 barrel (going by fin count and tunnel and cam gear driveshaft), is it a 250 or a 350 ?
It is a rocket what ever it is.


Later the same day
Hmmmm,

Could I have been foiled by crook substitute parts ?

Would the wrong O ring cause oil egress?

I put a long stick cotton bud into the exhaust outlet (where the header goes) no oily residue , carbon black though
I put a long stick cotton bud into the inlet (where the carb goes) no oily residue

I measured the 6 replacement o ring I bought OD 12mm Thickness 2.2mm ID 8mm
I measured the original used o ring OD 11mm Thickness 1.8mm ID 8mm

OhRings.png

[attachment=1]

I measured the oil feed @ the barrel – OD 8mm Height 6.5mm

I measured the oil feed @ the head
-- lip 10mm Dia 1.3mm Deep at the recess the o ring is supposed to fit in
-- 7.12 Dia & 8mm deep for the recessed bit

[Bevel bob]

No leaks at all on my NC 250. Do remember issues with the top of the tunnel ,having to make a gasket and also getting the clearances right on the angular bearings and holding the steel bush down. Valve clearances dont seem critical I run around 5 and7 thou . Books say more.

[Duccout]

Could the puddles in the valve seat pockets be unburnt fuel? I would have thought that any oil getting on top of the piston would have burnt off.....

The sealing of the top flange of the bevel tunnel is a problem, allied to keeping the bearing sleeve clamped in place. It seems to me that there are two methods of securing this, Eldert's where the flange is bolted up and the gap measured and a gasket is cut from the correct thickness paper, perhaps sealed with a smear of silicone, or Nigel's method of filling the gap with silicone, which guarantees that the bearing sleeve is clamped tight.


Cheers,

Colin

[LaceyDucati]

The original head 'O' ring is imperial 5/16" bore 1.78mm section.

The sealing of the bevel tube and holding the bearing housing tight is a flawed design and unlike the lower assembly it cannot be shimmed. This issue has been discussed in detail many times before on this forum, and there are a few different opinions of how to resolve the issue. I've given my opinion before but here are a few pics to show my solution....35 years on, still working flawlessly for me. The sealant I use is an RTV Loctite ultra black, but other setting sealants would work too. Don't use semi-setting sealants as they are the ones potentially that may cause blockages. Like all sealants used sensibly they will work without issue. Remember using the original gasket and method is the reason your head was damaged and was the start of your saga...

PXL_20231213_115617230.MP.jpg

PXL_20231213_115723862.jpg

PXL_20231213_115859470.jpg

PXL_20231213_122249308.jpg

As for valve clearance 7 thou inlet is large and 16 thou exhaust is massive! Mostly manuals are misinterpreted, by reading valve clearances for checking cam timing rather than running clearance. Aftermarket manuals are not always clear or correct, certainly not for all models. The actual clearance will be dependant on the cam, but if in doubt 6 thou inlet and 8 thou exhaust is a "reasonable starting point. Most original cams if in good condition can be easily identified by simple measurements across the cam lobes. If you compare those measurements with the cam data that someone posted on this site somewhere then you will most likely identify the cam. All the different cams have quite distinct base circles and lifts. From there you can set the checking figures as per the original spec and then confirm cam timing. Though do remember the ducati timing figures are +/- 5 degrees....if you are lucky. This is mostly because the figures are at initial lift and at that point of the acceleration is very slow and errors are to be expected. Checking at higher lifts are far more precise, but that's not what was specified.

Aside from all of this, from your picture I would suggest that the head face would benefit from lapping or machining. Small errors can be corrected by lapping with the cylinder (dowel removed), beyond that a lap or machining. use engineers blue to check the sealing surface....it may be okay. If you do end up lapping the face do this with the head stripped and make sure you wash any grinding paste thoroughly.

Hopefully this helps

Regards Nigel

[insanity]

No leaks at all on my NC 250. Do remember issues with the top of the tunnel ,having to make a gasket and also getting the clearances right on the angular bearings and holding the steel bush down. Valve clearances don't seem critical I run around 5 and7 thou . Books say more.

Hi BB,
Thanks, I thought I had it worked out the same way, ended up with quite a thin home made gasket from paper I had from Triumph days.
BTW I bought the single because I thought kicking over 1 cylinder might be easier than two !

[insanity]

The original head 'O' ring is imperial 5/16" bore 1.78mm section.


Hopefully this helps

Regards Nigel

Hi Nigel,
Thankyou,
If i were in England I think it would be in your shop by now. I will try the sealant and do the bluing test out of interest. I used a finger smear of Loctite MR 5923 on the thin gasket around the outside as you do. When I had the triumph I would just use grease.
It has a sasche ignition and 12 volt system on it, which from what I have read is very forgiving on timing, possibly why it is a rocket. I am finding there are a lot of variables associated with Ducati Bevel as opposed to other brands I once had (that were not bevel).

I do appreciate the time and knowledge you and the people in this group share.
Keep Well Folks
Thanks

[insanity]

Could the puddles in the valve seat pockets be unburnt fuel? I would have thought that any oil getting on top of the piston would have burnt off.....

The sealing of the top flange of the bevel tunnel is a problem, allied to keeping the bearing sleeve clamped in place. It seems to me that there are two methods of securing this, Eldert's where the flange is bolted up and the gap measured and a gasket is cut from the correct thickness paper, perhaps sealed with a smear of silicone, or Nigel's method of filling the gap with silicone, which guarantees that the bearing sleeve is clamped tight.


Cheers,

Colin

Hi Colin,
I didn't consider fuel, but as there were no snail trails of oil into the cylinder likely you are correct !
I sort of applied both methods, tested fitment on the bench without the gear installed so I could be sure the carrier didn't spin, I must check to see I didn't over do it and warp the tunnel tube face.

Thankyou,

[Duccout]

I am not sure that it is possible to distort the flange faces as it is a substantial casting and very strong. On both of mine I trimmed down the lip slightly on the lathe and even though they are fifty years old and have been through God knows what, neither were distorted. I do not think that much pressure is needed on the two screws to keep the steel sleeve clamped.


Cheers,

Colin

[themoudie]

G'day insanity,

Just a wee bit of info, I use a torque wrench to torque the two cap head screws securing the drive shaft tunnel to the head, set to 8 ft/lbs, 10Nm, or 1.1kg-m.

I also use this torque for all the other 6mm cap screws in the engine, making sure that the threads in the holes and on the screws are clean, before applying a wee smear of copper grease to the threads of the screw, not a blob on the end of your finger, using a small, cheap artists paint brush. Just to give a little lubrication, prevent galling and possible electrolytic corrosion that I get from our wet and often salty roads/climate.

Good health, Bill

[insanity]

Hi Chaps,

I will respond in order lest I run away verbally.
Colin – probably correct unburnt fuel, I took the opportunity to invert the head and loaded it with fuel, it didn't leak away so confident the valves are fine. Flange not distorted, just my paranoid thoughts – Anthropomorphism, it lies I wait to ambush me !

Nige – I used a smallish artists paint brush to apply loctite sealant as per your excellent illustrations, Leak Gone from the tunnel interface Thanks Heaps, Else I will just leave things as I found them the wait I went through for the head repair and ferrule was exasperating, I don’t have the sanity to go through it again. I got new O rings locally viton high temp, again no leaks, there are some confusing posts out there on sizes, I like your straight forwardness.

Bill – I read on the forum somewhere some sage advice “to never use an Allen key over two inches in length” My tension wrench doesn’t go down that low, but it is oil tight right now. And I do use copperslip.

Graeme – Yes, two leaks – the shaft tube and the front rocker cover, the cover was once chromed I think, I have a inherited model engineering stuff, among it a flat steel disc 1 ½ inches thick and in a custom carrier so it is my flat sanding surface. A bit of leveling and the artist brush again and no leaks.

RockerCover.png

I love the 12v conversion and Electronic ign on this single.
Better then the boyer on the Triumph, as heretical as that may sound, first kick wakes the electronics, second kick starts the bike up Ab’ Fabulous !

And It must be said Many thanks to our host, the fine man who provides this forum