Smoking under acceleration - valve guides.

If you need technical information or help with your BOSCH ignition squarecase Ducati 900SS - Darmah engine - post your FAQs, comments & questions here.
Post Reply
andybaggies
Mariana
Posts: 39
Joined: Thu Nov 01, 2018 12:52 pm

Smoking under acceleration - valve guides.

Post by andybaggies »

I'd be grateful for any input people would have on a smoking issue I have with a Darmah after a top end rebuild.

The motor fired up fine on it's first attempt with no or a little smoking but after a gentle 5 mile shake down run oil was seen seeping from the rear exhaust collar. Further investigation showed a good coating of sticky burnt oil in both front & rear exhaust ports - see pics in viewtopic.php?f=9&t=4893&p=23624#p23624. A small puddle of oil was also seen in the inlet manifold on the rear with oil on both spark plug threads.

So thinking this must be valve guide seals I removed the heads and replaced the O rings in the inlets and the 'top hats' on the exhausts. When apart oil was seen sitting in the piston valve cavities and a good coating was on the bore lining (above the piston).

The new seals made no difference and after another shake down run, less gentle this time, it looks to be exactly the same i.e. oil in the rear inlet manifold & oil seeping from the rear exhaust collar. A good burst of blue smoke is seen under firm acceleration (from a steady throttle) and a firm throttle blip when stationary with a barely perceptible haze when on a steady throttle. A compression test shows pretty good numbers of 165/175 rear/front hot or cold with a 10 increase with a squirt of oil in the plug.

So is this rings then? And if so why oil in the inlet manifold?

Btw the piston/bore clearance on initial assembly was measured at a touch over max at 0.05/0.06 and a new set of 86.0 rings was installed. Again the new ring end gap was at the upper max limit at ~0.48/0.50. The barrels were vapour blasted so could the bore have been glazed? The bore showed no wear lip at the top.

Additionally I have installed an uprated high flow oil pump and put a K&N filter on the crankcase vent tower.
Last edited by andybaggies on Wed Sep 23, 2020 9:25 am, edited 1 time in total.
User avatar
Craig in France
Paso 750
Posts: 917
Joined: Tue Mar 23, 2004 3:58 pm
Location: Montpellier, France

Re: Smoking under acceleration.

Post by Craig in France »

Blue smoke under acceleration is normally rings, sad to say, Andy ...

But first check the engine breather is working. (I admit I don't understand why (or even how ...) you've fitted a K&N filter. The original system is perfectly adequate for its task ...). You could be pressurizing the crank cases, forcing oil past the rings.

A possible mistake was being too gentle on your first outing. To get new rings to bed, it can be better to run the engine short, but hard. Also, what oil did you use? Something cheap, nasty and mineral I hope? A good synthetic oil can stop rings bedding.

Let's see what others say ...
andybaggies
Mariana
Posts: 39
Joined: Thu Nov 01, 2018 12:52 pm

Re: Smoking under acceleration.

Post by andybaggies »

Thanks Craig. Your advice is always welcome and appreciated.
Blue smoke under acceleration is normally rings, sad to say, Andy ...
I agree but what I don't understand is why there is oil in the rear cylinder's inlet manifold?
But first check the engine breather is working. (I admit I don't understand why (or even how ...) you've fitted a K&N filter. The original system is perfectly adequate for its task ...). You could be pressurizing the crank cases, forcing oil past the rings.
I've fitted cone filters to the (original 40 mm) carbs and junked the airboxes to make space for a proper re-wire and Electronik Sachse ignition system.

See http://forum.bevelheaven.com/viewtopic. ... 257#p23257

I had thought that but an update on the situation has seen no oil been burned in the front pot which means the new guide seals have worked and helps me think the crankcase pressure is ok. But it is good advice I've heard from others so will check.
A possible mistake was being too gentle on your first outing. To get new rings to bed, it can be better to run the engine short, but hard. Also, what oil did you use? Something cheap, nasty and mineral I hope? A good synthetic oil can stop rings bedding.
I used an old can of Castrol Product 351 which was a straight 40 I used to use. It was certainly short with only a couple of trips totaling 30 miles or so. I certainly wasn't bimbling e.g. ran it up to 70 and biffed past a few cars but oil was seen bleeding from the exhaust even after the first 5 miles or so.

My new theory, ho hum... is that the new oil pump with 50% more flow is overwhelming the heads with oil which is unable to drain away quickly enough. This would cause puddling around the rear cylinder valve guides and, especially with the inlet using the internal O ring seals, allow much more oil down the guides. Which would explain the oil in the inlet manifold.

I'm presently running with this and fitting the old pump to see if it anything changes.
ducadini
860 GT / GTS
Posts: 277
Joined: Sat Jul 31, 2004 9:54 am
Location: Antwerpen

Re: Smoking under acceleration.

Post by ducadini »

Perhaps drilling the drains to (IIRC) 10 mm instead of 8 mm (don't forget the dowels) would increase the draining and solve the problem.
Did a previous owner use some RS bearings on the camshaft-bevel side ? that could prevent/decrease oil flowing to the bevels and raising the level in the head.
You say the guide on the inlet are (original) O-ring inside and the exhaust with outside seal (so modified ?) is there anyhow You could test head/guide interference ? Perhaps oil is seaping here ?
On several Darmah and 860 heads, we found there was a crack between the exhaustvalveseat and the exhaustport. We think because the rear head is shielded a bit too much from cooling air. Never found a crack that runs up to the oily side though.
And on that 150% oilpump : I don't remember if Kevin Bracken ran a original pump or uprated one, but there were signs of running without oil on the bigends (at high to very high revs) so I'm wondering if this pump isn't a bit overkill ?

ciao
ducadini
Nego i ricordi peggiori
Richiamo i migliori pensieri
User avatar
Craig in France
Paso 750
Posts: 917
Joined: Tue Mar 23, 2004 3:58 pm
Location: Montpellier, France

Re: Smoking under acceleration.

Post by Craig in France »

ducadini wrote: Thu Sep 17, 2020 9:37 am <snip> And on that 150% oil pump : I don't remember if Kevin Bracken ran a original pump or uprated one, but there were signs of running without oil on the bigends (at high to very high revs) so I'm wondering if this pump isn't a bit overkill ?
Been having much the same thought ...

I'm no engine tuner. But as I understand it the issue (if indeed there is one in the first place ...), is not how to get the oil UP into the engine. And if you've ever seen a bike running with a gear gazer, you'll know what I mean. The oil flows like a fire hydrant ... The problem is how to get the oil back DOWN fast enough into the sump.

This was the potential problem that Kevin Bracken found. And it's also seen on Spaggiari's (and others) singles with all their external oil drain lines.

But these are race bikes, often endurance race bikes, intended to run at full chat for hours on end. A road bike never meets these conditions.

You may just have gone OTT with your oil pump, Andy ...? :?
andybaggies
Mariana
Posts: 39
Joined: Thu Nov 01, 2018 12:52 pm

Re: Smoking under acceleration.

Post by andybaggies »

Again thanks for all the replies guys - it helps clear ones thoughts when brain storming...
Did a previous owner use some RS bearings on the camshaft-bevel side ? that could prevent/decrease oil flowing to the bevels and raising the level in the head.
You say the guide on the inlet are (original) O-ring inside and the exhaust with outside seal (so modified ?)
I bought the bike when it was 3 years old in 84 and the engine had a Tony Brancato refurb sometime in the late 80s. But I wouldn't know if or how many of the bearings he may have replaced. He certainly replaced both exhaust guides for the later versions and also machined the closing rockers to accept the external seal.
You could test head/guide interference ? Perhaps oil is seaping here ?
On several Darmah and 860 heads, we found there was a crack between the exhaust valve seat and the exhaust port. We think because the rear head is shielded a bit too much from cooling air. Never found a crack that runs up to the oily side though.
During my recent refurb I had the heads vapour blasted and obviously inspected them. I wasn't specifically looking for cracks but would like to think I would have spotted something untoward.

Head guide interference... hmmm I was hoping nobody mentioned that as I don't really have the means to test it. And it's a guide replacement job if faulty. The only thing I can say is that it wasn't smoking when it was laid up in 95. I have, and don't shoot me down here, put a tiny smear of Permatex Aviation brown around this union as some form of (desperate) insurance.
And on that 150% oilpump : I don't remember if Kevin Bracken ran a original pump or uprated one, but there were signs of running without oil on the bigends (at high to very high revs) so I'm wondering if this pump isn't a bit overkill ?
The original pump looked a little worn, but not totally knackered, so as I was in there I decided to replace it. From what I recall there were only unrated pumps available which seemed to me ideal especially after reading much regarding these engines needing plenty of flow.
The problem is how to get the oil back DOWN fast enough into the sump.
You may just have gone OTT with your oil pump, Andy ...? :?
Ho hum, yes that does appear to be the case but only if the old pump cures the smoking... :)

So it seems we may have consensus the inlet valve guides are allowing (too much) oil flow hence seeing oil in the inlet manifold. However is there consensus it's the O ring stem seals that can't cope if the oil level is above the top of the guide?
andybaggies
Mariana
Posts: 39
Joined: Thu Nov 01, 2018 12:52 pm

Re: Smoking under acceleration.

Post by andybaggies »

Well.... ain't it an arse when reality disproves a theory.

With the old oil pump fitted it's still smoking and just revving him up on the stand it actually seemed worse!! I quickly whipped off the rear carb and again there was plenty of oil in the manifold and also a drip was seen on the outside of the guide.... :(

Hmmm... that does seem to indicate the guide/head joint. Can these fail after many years sitting? perhaps the heat of the restart 'loosens' things... :?

Either way, in addition to the bitter pill of disappointment I've got a bitter pill of hindsight with a side order of humble pie to swallow. Even though the guides/valves measured out ok during the stripdown, albeit close to the upper limit, I should have replaced them first time round.

Hey ho, we live and we sometimes learn.

Thanks for all the replies guys. Btw must the valves also be replaced when replacing the guides?
robax
Cucciolo - the Lil Pup
Posts: 7
Joined: Mon Jul 06, 2015 4:50 am

Re: Smoking under acceleration.

Post by robax »

There's always oil sitting in the upper inlet on a bevel. It would be there in the lower as well if it were able to pool. There might be a little more oil there than usual due to your smoke issue, but it's always going to be there, so don't take it as a fault.
Rob
Rob - NZ
-------------------------------------------------
1982 Ducati 900ss
ducadini
860 GT / GTS
Posts: 277
Joined: Sat Jul 31, 2004 9:54 am
Location: Antwerpen

Re: Smoking under acceleration.

Post by ducadini »

So the exhaust guides were changed for the later ones and the inlet stayed the old (inner o-ring) type.
I remember fitting new o-rings in those guides, only to find a tiny piece of it coming out of the guide when I pushed the valve through. Not the top of the valve but the cutout that houses the two half-rings (sharp edge) took a piece of the o-ring.
So I changed the o-ring AGAIN to find the same problem.
Then I gave up and added a drip of 747 to the gas, smoke a little and smells great :-D :-D
One thing I did do was getting rid of all obstacles the oil could encounter going back to the case, head, cylinder and cases.
Basegasket of the cylinder correct fitted ?

ciao
ducadini
Nego i ricordi peggiori
Richiamo i migliori pensieri
andybaggies
Mariana
Posts: 39
Joined: Thu Nov 01, 2018 12:52 pm

Re: Smoking under acceleration - valve guides

Post by andybaggies »

Ducadini, yes that's correct only the exhausts were upgraded to the later guides with the inlets remaining as the older O ring type. And as you say great care must be taken to not cut off a little bit of the O ring when re-inserting the valve stem. I used plenty of lube and a pressing twisting movement and I think I got away with it. But they are are right royal pain I agree.

However all that is by the by as I've now bitten the bullet, removed the head and given it to a local well respected specialist automotive engineers for guide/valve replacement. They do all sorts of work e.g. cylinder, valve, crank etc for all sorts of classic cars and bikes and can be trusted.

They have already heated the head and removed the guides and a small puddle of oil also came out (of each). So it does appear they where leaking through the guide/head interface. They also said the holes where noticeably out of round and will be reamed out to accept the new guides.

Quite why it has started to leak after sitting for 20 years I don't know... perhaps the vapour blast clean removed years of grime that was actually doing the sealing :-D

Andy B
User avatar
81mhr900ss
Parallel Twin
Posts: 146
Joined: Tue May 31, 2016 3:49 pm

Re: Smoking under acceleration - valve guides.

Post by 81mhr900ss »

Interesting thread. I think the single hardest job during my rebuild last year was getting the old O rings out of the guides, the new ones back in and the valve stems pushed through the new O rings. I'd read about someone making a little epoxy cone "hat" for the stems to facilitate the job. I used oil and even the I had trouble. Once the valves were in, they were tight to the O rings; the O rings held them in place. I don't see oil in my exhaust so I guess they are OK.
andybaggies
Mariana
Posts: 39
Joined: Thu Nov 01, 2018 12:52 pm

Re: Smoking under acceleration - valve guides.

Post by andybaggies »

I found the easiest way to fit the o rings was to insert the valve into the guide from the bottom until the top of the stem is level with the bottom of the groove and hold it there.

You can then fold and push the lubed o ring in using a blunt shaft and it'll pretty much pop into the groove of its own accord.
Post Reply

Return to “Squarecase BOSCH Ignition Engines > SD, SSD Darmah, late 900 SS & 900 GTS”