Head / barrel oilway o-ring

[themoudie]

Aye Geordie,

I rebuilt mine with no gasket between the two crankcase halves, only used a thin film of Yamaha non-setting gasket that I use on the SRX's. Honda sealant is equally as good and shimmed accordingly.

I cleaned everything up then nipped the mounting bolts up. 650km since rebuild. Added another 25km and it hasn't reappeared.

That is what is making me feel queasy. You appear to have squeezed the crankcases together and closed a gap between their mating surfaces by tightening the engine mounting bolts and not by tightening the cap screws holding the cases together! Case faces may not be true, either due to warping or butchery?

The 6mm cap screws are only torqued to 7ft/lbs (9.45Nm).

Good health, Bill

[Geordie]

Aye Geordie,
You appear to have squeezed the crankcases together and closed a gap between their mating surfaces by tightening the engine mounting bolts and not by tightening the cap screws holding the cases together! Case faces may not be true, either due to warping or butchery?

The 6mm cap screws are only torqued to 7ft/lbs (9.45Nm).

Good health, Bill

There are four bolts between the upper screw and lower forward screw. They perform the function of the screws (absent in that section of periphery) as well as stabilising the crankcase mouth and attaching the engine to the frame. They require a higher torque than the screws.
In my case (literally) I have sleeved the cases at the mounts to obviate one of the week spots of the Ducati motor: the tapered holes in the casing mounts. This gives a greater bearing surface on the bolt shanks. The racers bore straight through and use a 3/8" bolt to achieve the same. I also increased the mount thickness and bolt shank length to suit. Nipped up there is now a completely dry joint. Got to 750km today.

Happy with that. Still to sort the head o-ring.

[Geordie]

Almost 2 years on and several O-rings later and the leak is fixed! I removed the flow restrictor in the cam. As that is at the end of the pressurised system, it was raising the oil pressure sufficiently to overcome the O-ring ability to seal the pressure feed to the head.

The cam was one I sourced during restoration and came with the restriction fitted. Now on 2000km since rebuild: any downsides to running with no restrictor?

[blethermaskite]

Conversely, if there is no restrictor in the bevel end of the camshaft I fit one! the restrictor vastly increases the oil flow to the rockers preventing premature wear, I have yet to experience any leaks at 'that' head barrel O ring due to fitting a restrictor. Cheers George

[Duccout]

Hmmmm, not what I would do, but to each his own!

I solder up the hole in the end of the cam in order to get max oil flow to the rockers and cam, a practice that is used by several aftermarket cam makers, who do not drill the oil feed right through the cam. Brook Henry of Vee Two recommends the blocking of the end hole in the cam and I respect his advice, as well as having personal experience of Ducati 750/900 engines that experienced no cam wear on the front cylinder (which does not have the hole as standard) and the rear cam (which does) which wears rapidly.

I can't see that there is going to be any appreciable pressure generated in the cam feed, as the oil has two quite large holes to exit from.


Cheers,

Colin

[Geordie]

Having had several attempts with new O-rings and meticulous prep and assembly, the only cure for the leak has been with the flow restrictor removed. I conclude that there is a pressure threshold at which time the seal fails. As the O-ring is in a countersunk and not a parallel seat as modern practice, it less able to seal. With no flow restrictor, the pressure is below the threshold. All those that have posted here about that same nuisance leak may be pleased to know that.
As the oil pump is near enough fixed displacement, allowing greater flow from the cam end will obviously reduce flow to the cam lobes and pressure overall.
I have read that some have used a roll-pin as a restrictor.
It was yesterday I removed the restrictor (not a roll-pin) and today I tested the result and had the success.
Now I know the cause of the leak on my bike and which may well be bike specific, I can fairly easily experiment with restrictor bore size and avoid O-ring replacement.

[Duccout]

Well, I have two Mototrans bikes with countersunk o ring holes and neither leak, so there must be something going on with your head/barrel joint.

Hopefully you have found the solution.

Cheers,

Colin

[Geordie]

My head barrel joint doesn't leak so there is nothing "going on" with it.

[Geordie]

Solved
Solution as per Mr Nigel Lacey on the "Checking Engine Oil Pressure" thread. Slug in the cam (bevel) end with a 2mm diameter oilway. A successful proving ride this morning and a cafe ride this afternoon after I have a quick nap.