Problem with front cylinder on 900 Darmah

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dessmo
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Problem with front cylinder on 900 Darmah

Post by dessmo »

The forward cylinder has caused me trouble during the years. It does not run clean on low rpm, and is occasionally “puffing” out from the carburettor. The plug is running black, and the same is with the exhaust pipe. From 3500 RPM the problem seems to disappear. I have tried to adjust the mixture, but this cylinder prefers a rather fat mixture. A mechanics I spoke to suggested that there is an oil leak into the cylinder from the top. What do all you expert think???
Magnus
Norway
83 900 SD Darmah
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Craig in France
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Rich running on Darmah front cylinder

Post by Craig in France »

Hi Magnus

It could be a leaky guide like your mechanic friend suggests, especially if the black on the plug is oily. A leak down test might help test for this, but otherwise it's not a big job to remove the head and check the valves, their guides and seals.

But if the soot isn't oily, it's much more likely to be a faulty carburettor, for example:

1. The drilling that delivers air for the idle is particularly prone to getting clogged, especially with modern fuels. This will result in rich running at low throttle openings (remember, with carburettor faults, it's throttle opening not RPM that matters).

2. The rubber seal on the end of the enricher piston also gets hard with age and then fails to close off the jet properly - again, the cylinder will run too rich.

3. If the float height is wrong or if the inlet valve has got hard and isn't sealing - too much fuel.

So you might want to get the carb stripped, properly cleaned and re-built by someone who knows what they're doing - if you can't find someone in Norway, our very own Steve Allen offers this service, for example.

HTH

Ciao

Craig in UK
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BevHevSteve
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oil

Post by BevHevSteve »

Thanks Craig, along with what you said, it might even be *just* a bad valve seal. The forward cylinder typically gets a puddle of oil sitting there and not draining back all the way, so if the seal is bad you get oil into the cylinder.
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Craig in France
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Faulty running Darmah front pot

Post by Craig in France »

Hi Steve

Yeh, thanks, you're right, of course - I wasn't being specific enuf ... :doh:

Magnus - as Steve says, the seal on the top of the valve guide can/does break up and come off, and the excess oil flowing down the guide will foul the plug.

This often shows as blue-ish exhaust smoke on start up.

Ciao

Craig
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Geoff
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Post by Geoff »

Based on the observations from my SS rebuild I'd go with either guide seals or rings. Trouble with rings is you can't tell really if the oil ring has gone based on the leak down test; in my case the leak down was fine, but the new rings and a deglaze hone did wonders! I think when I lifted the cylinders off completely and replaced them the old oil ring couldn't bed back down again properly; so if you're lifted yours at some point perhaps the same problem?.

Having said that it's probably the guide seals, and at least you've got a problem with your front pot, and you can take that on and off at will (mine was the rear pot so I did everything in one go as I couldn't be bothered with having the engine in and out twice); so a quick renewal of the guide seals to see if it improves is no problem; then if no good you can always move on to rings/ degalze hone (I'm guessing the Darmah it has those neat external seal which I think are easy to replace; on my old SS they're the old hard internal O-rings in the guides - a nightmare to replace!)

You may have done this already, but during my 4 weeks of investigation onto my oily plug/ oil dripping from the exhaust and rough low rev running I stripped and cleaned the carbs vigorously twice. And SWOPPED them round to see if the problem transferred to the front; it's possible to do this though of course you don't get quite such a clean routing of cables of easy access to the adjusting screws! But ok for check. Of course my problem didn't go away hence I knew the rear carb was in fact ok.

good lick.
Geoff
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dessmo
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Post by dessmo »

Thanks for quick replies an useful answers :)

I have already had the carbs overhauled by TL Veteran ( www.tl-veteran.com ) in Øland/Sweden. According to Torbjørn the carbs should be good to go. It was him who suggested that the problem is an oil leak.

I am not sure that I know what a leak down test is :? , coul you please explain?

I have not removed the cylinder head before, but I have the workshop manual. Is there anything to be aware off before I star to “rip of the head”? :?:
Magnus
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Geoff
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Post by Geoff »

A leak-down test is where you check the compression by pumping up and the combustion chamber to about 100psi at TDC (typically) with all valves closed. You maintain that input pressure to the chamber with a regulator and measure the actual chamber pressure using a second gauge. You can search for leak down test and leak down testers to see what we mean. My only caveat (as others have said) is that will not necessarily show the condition of the oil scraper ring, so you can have excellent leakdown results (mine came out at approx. 95%) but they can still leak oil).

Taking the front head off is easy - you don't need to drop the engine! Follow the manual, make sure you renew the head to barrel o-rings. Stuff the crankcase openings with rags to make sure you don't drop anything in there and protect the con rod from crashing against the crankcase (if you lift the barrel as well). Replacing those external guide seals is easy (though I've never done it; on the old SS they're internal and MUCH harder to shift). Removing and replacing all the valve gear to do it is a little more time consuming, but quite straight forward. If it's too intimidating, once you've gotten the head off drop it at any competent ducati service shop and they can do it for you; while they're about it they can service it too (shimming, lapping, cleaning if required).

If you do pull the cylinder barrel, change the rings and de-glaze hone the barrel as well (check the piston/bore tolerances). Only hassle here is getting the circlips & gudgeon pin out of the piston. Sometimes a little general, gentle heat on the piston (don't recommend naked flame, to much fuel around;hot air gun better) helps. Same for reassembly.

Actually if you're confident the piston wear is in specification don't even remove the piston from the con rod, just change the rings in situ (don't forget those stuffing rags in case you break one and drop the bits into the crankcase!)
Cheers
Geoff
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dessmo
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Post by dessmo »

Thanks for sharing your knowledge and experience Geoff.

I used 1st of May to remove the cylinder head, and as you said it was quite easy.

My immediate conclusion is that the problem is caused by oil leaking into the cylinder. As you can se from the picture below, the piston is oily on the top surface.

Image
From the picture it can also look as the clearing at the bottom of the cylinder is tighter than at the top.

I am not quite sure where the oil leaking into the cylinder is comming from, and would be grateful for your advice.

As you can see the “exhaust valve” is brown, but the gas/air valve is rather greasy.

Image

If you look at the up left corner of the picture there I a canal that I guess is either is feeding oil to the head or returning it from the head. This is the larger of the two holes, and there was a white damaged rubber sealing inside it. You can see it in the picture if you look closely. This hole is on the down side of the cylinder, and as you can see the cylinder was rather greasy. Should there be O-rings or some kind of rubber sealing in these two holes? An do you think a leak from here could spill over to the inside of the cylinder?

Image

As you can clearly see from this picture there is a substantial oil leak. There was no gasket between the head and the cylinder, and due to the oil pressure I guess the oil can spill into the cylinder even if the leak is on the down side of the cylinder. Do you think this can explain the problem I have experienced with this cylinder?
Magnus
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BevHevSteve
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oilk leaks

Post by BevHevSteve »

On the bottom photo I can clearly see what remains of a valve seal stuck down in a hole - that green thing in the lowest hole. THis was your problem, or, at least most of it.

THere is not supposed to be any gasket between cylinder and head. But, there are supposed to be orings, which can go bad also causing all that oil spilling............... Time for a top end gasket and seal kit

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Now THIS is specifically why I set this forum up! All it takes to figure these things out is a couple helpful souls and technology!
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Craig in France
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Oil in front pot

Post by Craig in France »

Wow, Magnus, that's quite a leak! I especially like the valve guide seal stuck in the oilway!

Hopefully, like Steve says, new seals and o-rings and you'll be up running clean!

Good Luck!

Craig in UK
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Geoff
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Post by Geoff »

Great work Magnus! I'm with the guys all the way here; that's your late-type guide seal that's trying to exit the head area via the oil return pathway! Not recommended! Nothing that can't be fixed with a new guide seal then; best to change the others (on the front cylinder at least)while you're about it. Nothing wrong with the head to cylinder seal that a couple of new O-rings won't put right (you must use the correct type, not normal nitrile O-rings; Steve has them).

You were lucky; that could have caused some damage....
Cheer
Geoff
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dessmo
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Post by dessmo »

Hello guys, and thanks for all help so far. I spent a couple of hours in the garage today as well, trying to find out how to dissemble the cylinder top to be able to replace the valve seal. After taking of the covers I found that one of the valve seals was missing (exhaust valve) and the other still in place.

Image

Image

I also removed the upper spanner on the exhaust valve, but am a bit concerned regarding the lower due to the spring. Do I need special tools to get the valves, cam, and spanners back in place? I guess it is easier to get it apart than putting it together. I think I have to remove both the upper and lower spanner to be able to take the valve apart and replace the sealing??

If I understand you right I need to replace the valve seal and also some O-ring between the cylinder and head. Is this only the O-rings for the oil canals, or does it also include a large O-ring around the cylinder?

A last question; by accident the wheel on the bike was moved while I gear. I am a bit concerned for the synchronisation. When I removed the head I aligned the marks on the bevel head, but I found out that you can turn the shaft 4 times before it comes back to the same position. Due to the shape of the shaft it would therefore fit in 3 other positions than it was when I removed the head. How do I make sure that it is right when I put it together?

Thanks again for the help so fare, I really appreciate it!
Magnus
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Willemd
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Great stuff

Post by Willemd »

Great pics, Marcus.
Big learning curve (for most of us I reckon) so can't help at this stage.
Good luck
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Geoff
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Post by Geoff »

Ok Magnus; good work! I've been out, so wasn't able to reply immediately. Read all of this before you start - and your workshop manual too. And then run it through in your mind looking at the head before you actually commence furthe disassembly. Clearly I'm offering you this advice without warranty and you follow it at your own risk.....

First on the subject of head O-rings/ gaskets etc. Yes, your must replace the oil supply and oil return O-rings between the head and cylinder. There is no other large O-ring seal on the head, only metal to metal between the head and the cylinder itself; so make sure this metal seal area is clean and undamaged before reassembly. And torque it down correctly. Make sure you get the correct O-ring seals for a reliable supplier (they are not off the shelf rubber O-rings); Steve @ Bevelheaven has them, also others more local to you in Europe (notably Andy @ desmo-ducati.de). I think you should also replace the O-rings that seal the chrome bevel shaft cover to the engine block and head respectively too.

With respect to the 'spanner' as you call it (we call it a 'rocker'), while the guide seal is different to the one on my old SS, looking at your picture I think you can actually replace it without removing the lower rocker (you don't strictly need a special tool to handle the hair-spring - keeps the valve closed to aid starting- but it does help if you're completely disassembling; again Steve has them).

All you need to do is remove the opening shim (on top of the valve stem), unhook the hair spring from under the closing rocker (you can lever it off with a screw driver), rotate the bevel shaft to drop the rocker and take the upwards pressure off the closing shim (see the manual), remove the closing shim and the half collets that locate the on the valve stem, and drop the valve. Then you should be able to get enough clearance to slip on the new guide seal (you may need to roate some more to make sure you've enough clearance between the bottom of the rocker and the top of the guide - in fact check this is likely to be the case before you disassemble).

Reassmbly is the reverse of assembly, taking care to ensure the closing shim sits firmly against the half clollets that locate it on the valve stem - sometimes a little tap with a hammer on the end of the valve stem with the spring back in place before you put the opening rocker back on helps (check visually before disassembly what a correctly seated shim/ collets looks like). You should be able to slip the spring back into place under the closing rocker easily with pair of pliers. Put the opening shim back on the end of the valve stem.

When you replace the upper, opening rocker make sure you get put the shims on each end back in the same places, or if you've lost their order, make sure you take up the end float on the rocker as it sits on its shaft, while centering the rocker arm over the valve stem.

Timing? Bet you wish you've left the bike out of gear?! I hope you set the upper bevel gears to their respective timing marks before disassembly, so that when you put the head back on (to the correctly timed engine) it's set up correctly? Provided you put the head timing back where it was before disassembly this should be straight forward. I'll refer you to an excellent article on the docv.org website by Peter Shearman: http://www.docv.org/articles/timing.htm. Unfortunately the website looks like it's down right now, but if you google the url and follow the link to the cache you can see it that way. (I just made a pdf of the cache so if that fails let me know and I'll send it to you).

Hope this helps and good luck. Ask more question if you need more help.
Cheers
Geoff
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dessmo
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Post by dessmo »

Just returned after an hour in the garage, and thanks Geoff you saved my day! :-D

The article regarding CAMSHAFT TIMING GEARS was very useful, and I am now back on track! :-D

I also managed to lift of the spring, and as you said it is no need to take out the upper rocker. All I need to do is to get hold of some new O-rings and put things back together. I think I will try to get hold of them in Europe, since importing things into EU sometimes can get very expensive.

Hopefully this will fix the problem, I really look forward to put it together and take the bike for a ride.
Magnus
Norway
83 900 SD Darmah
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