Scrambler 350cc leaks and tightening torque

[Rocla]

Hello everybody,

My 350cc Scrambler 1974 engine has been renewed last year (crankshaft+bearings) and after 800 kilometers of running in, there are some leaks on the engine in a normal use (despite 5000 rpm max). It seems to come mainly from the bottom of the cylinder, on the left side (opposite side of the bevel gear). I've just checked the tightening torque of the 4 nuts with a torque wrench but the torque was ok. So, are leaks an unavoidable problem ? Do you recommend to tight significantly more than the 4 to 5 daN mentionned in the owner manual? Many thanks again for your help

[themoudie]

Hello Rocla,

Not being an engineer I didn't know about the use of daN to measure the torque applied to fasteners. I have always used ft/lb or Nm.

However, I note from 'Google' that 1 daN = 1.019716213 kgf

And that 1 kgf = 7.23301/lb

So, the minimum that I would tighten the cylinder head bolts, would be 25 ft/lb or 3.45637 kgf, or 3.3895410861 daN

The maximum torque for the cylinder head bolts, would be 28ft/lb or 3.87114 kgf, or 3.7962915081 daN.

If you need to apply more torque than this, to effect an oil tight seal, then there is something wrong with either the crankcase mouth or the bottom of the cylinder barrel mating surfaces and these should be checked with a straight edge and or a surface plate. Just increasing the torque to the cylinder head bolts will only either stretch them or pull the threads from the crankcases!

Have you used a new cylinder base gasket when assembling the cylinder onto the crankcases? Lacey Ducati can supply them individually.

I apologies if my torque unit conversions are not correct! But, the ft/lb units that I have given, are those that I always use and are recommended in both the Clymer and Haynes workshop manuals for the widecase models that I assume your 1974 350 scrambler is.

Good health, Bill

[blethermaskite]

The oil feed to the cylinder head runs up a passage in the cylinder barrel on the left side and can leak at the cylinder base at this point and more usually at the same place between the barrel and head where there is a rubber o ring seal. As Bill has said further tightening of the head bolts are more likely to cause mechanical damage rather than fix your leak either the gasket at the barrel base is faulty or the joint faces are damaged......usually with someone trying to lever the barrel off the crankcase with a big screwdriver ...hope its just the gasket for you.
Cheers George

[Rocla]

Thanks very much Themoudie and Blethermaskite. The torque recommended in my owner manual is 4 to 5 mdaN = 29,5 to 36,8 ft-lb. Maybe the leak comes from elsewhere, I've tighetened all the nuts including the exhaust pipe. Wait and see. If the leak remains, that means it is around the oil duct on the left side of the cylinder...

[Rocla]

Hello again,

But is it possible to lift the head+cylinder few milimeters (in order to add some mastic on the seal) without dismounting the distribution? Under condition to keep the piston on the lower position and not spinning the camshaft, there is no risk. But I don't realize if there is something to unscrew around the bevel gear in order to free up the engine from its cases...

[Duccout]

Hi Rocla,

Do not be in too much of a hurry to lift the head, there are other areas that can leak and the oil can then very quickly run anywhere. After 50 years of working on Ducatis I have never had an oil leak from the cylinder head O ring, although it can happen. Are you sure that the leak is not coming from the camshaft end cap and running down? There is a lot of pressure from the oil feed in the end cap and this can leak at the gasket surface if it is not perfect.

I would not put silicone around the O ring unless you are sure that it is the cause of the leak, and then only if you remove the head and put just a smear on the O ring. Have you tried washing the engine thoroughly and then starting and running it for a few minutes and then looking all over the head for the leak?

Good luck,

Colin

[ranton_rambler]

My 175 leaks from both the cam end-cap and the joint between the bevel tube and head. Head will be coming off with a hope of fixing both soon.
Ian

[themoudie]

Gentlemen,

Rocla specifically describes oil leaks as

and after 800 kilometers of running in, there are some leaks on the engine in a normal use (despite 5000 rpm max). It seems to come mainly from the bottom of the cylinder, on the left side (opposite side of the bevel gear).

No mention of oil leaks from the cylinder head!

Rocla asks, I suspect through translation, if he can lift the head and the barrel, without disturbing the timing ("distribution"), so that he can apply

some mastic on the seal

to the base of the cylinder/ crankcase mouth gasket.

I do not have oil leaks from my 450 MKIII engine, after at least 3,500 miles running, I can have a dust attracting mist stain from the front edge of the camshaft end cap, the kickstart shaft and the gearbox sprocket shaft, but no oil leaks. If the widecase engine is assembled correctly, it will not leak oil! Snowies we Ducati 350 after being thrashed for 3 laps of the TT circuit in the Manx GP and setting a race average of over 99mph, did not have any oil leaks or misting marks on the engine.

Whilst the cylinder head can be lifted in situ, without disturbing the timing, removing the barrel will require more care. Removing the barrel can be done, without affecting the timing, providing the lower camshaft bevel drive from the crankshaft is locked in position at BDC, before the cylinder head is removed, using the appropriate tool. If you don't have the tool then a nylon wedge will do the job, but it is not as secure. Be sure to stuff the crankcase mouth with clean, lint free rag or paper towels, so as not drop debris into the crankcases.

I do not use silicone sealant on my cylinder base gasket, but use a very thin smear of grease to settle the gasket. On other engines I have used Honda or Yamaha engine assembly sealant, without problem, providing it is applied with a small paintbrush as a thin film. It is the big blobs applied with the large finger tip that cause the problems of blocked oilways etc.

I hope that this helps Rocla and if I have misunderstood and/or misrepresented what you are trying to say I apologies. Would a Google translation of our advice help?

Good health, Bill

[Duccout]

You are right Bill, I have noticed before on the forums where someone asks a question and somehow as the answers come in, the subject changes!

Re-reading the original post, I think that Rocla IS asking if the barrel can be lifted enough to put a smear of silicone around the crank case/barrel joint, and I don't see why not. What about if the head was removed, with the engine at TDC with the camshaft dots lined up, and the barrel lifted enough to allow it to be supported on two small blocks of wood? It may be possible to degrease the area around the oil way, and apply a smear of silicone.

Colin

[themoudie]

Aye Colin,

That might work. I am just concerned if debris gets inside the crankcases, or that the gasket is damaged, especially around the oil feed to the head and applying silicone doesn't cure the leak.

An alternative that I have seen work is the Captain Tolley's remedy! Here is a link to the product website. I should also say that they produce a 60ml bottle, as well as this 250ml bottle: Captain_Tolleys_creeping_crack_seal_website

Rather than stripping the rocker covers on my wifes Honda Bros, I applied some of the sealant around the rocker cover flanges and they have been leak free since. Including after removal for servicing!

My regards, Bill