Dommie cylinder lubrication

Well, I did it my way and put it back together, and it's cured the left cylinder smoking issue. Success!

But now the right cylinder's smoking worse than the left one used to!

I don't know what's going on. But I've only ridden 20 miles so I'll try it a bit longer and see if it improves. Otherwise all I can think of is to tear it down again and re-hone the right cylinder, or stop messing about and have a rebore.

A few facts to follow up on some previous replies:

Oil pressure, taken from the plug on the rear of the timing cover: 80-90 psi cold. 30-40 psi hot, 20 psi idling.

Valve guides replaced in February, inlet guides Commando type with seals. Inlet rocker shafts changed to plain type. Valve stems max. wear 0.0005", within acceptable limits according to manual.

Fuel: Murco Super. This particular batch seems to be ethanol-free according to a water extraction test, but their technical man tells me they're being forced against their will to change their plant to add ethanol to all their petrol. He's been inundated with enquiries about ethanol from classic car, bike and lawn mower owners.

Compression test: 12 bar/175 psi both sides. Warm engine, without oil squirted down the plug holes, which would give a higher reading still. Healthy enough?

then its not the bore, the oil coming for some were else like at the back of you valve guides , have you clean the oil ways in the cylinder head and at the back of the barrel in to the timing chest , these get blocked up and can mimic a oiling problem as all the oil ends up round the top of the valve guides and down the pushrod tunnels

yours anna j

Wassell stocks the "Hepolite" rings which are made in the USA by Hastings (see: http://www.hastingsmfg.com/ )& are of an excent quality & are offered in .010 incriments from stock to .060 oversize. If you cant find a dealer in the UK, PM me & as a Wassell dealer myself, I can get them for you also (I am in the USA).

Hepolite pistons and rings are after market products and are not the originals pistons and rings,

Previously anna jeannette Dixon wrote:

hello why have you got pain rocker shaft spindles have you fitted the 6 start oil pump, as you have not said, and if you have that amount of compression

then its not the bore, the oil coming for some were else like at the back of you valve guides , have you clean the oil ways in the cylinder head and at the back of the barrel in to the timing chest , these get blocked up and can mimic a oiling problem as all the oil ends up round the top of the valve guides and down the pushrod tunnels

yours anna j

It's still got the original 3-start oil pump. I fitted plain inlet spindles when the smoking first appeared, in order to limit the amount of oil in this area, inlet guide seals for the same reason, in case this was the source of the oil causing the smoking. There still seems to be plenty of oil getting into in the inlet rocker box though. I did check the rocker box and barrel drain. Valve guides were replaced by an engineering shop as I wanted them to re-cut the seats afterwards, and they said they were a good fit in the head.

After 75 miles of riding the smoke from the right exhaust seems to be reducing and the plug isn't wet and oily any more, so maybe it's just that the oil rings are bedding in a bit slower than the compression rings.Now you say it well you need the scrolled spindles in and Clean OUT the oil ways from the inlet valve side near were the spring fits and check all the oil ways down from there too the time side were it come out , the is a dog leg oil way in the crankcase like a L shape this gets blocked ,so then if this is blocked the oil ends up running down the valve stem as there are on rubber valve stem seals on Dominator's

Maybe just maybe your crancase mouth is not parralel to your crankshaft. I have never found a 750 Atlas, Commando or G15 with the cases paralel with the shaft. The worst ones were 15 thou out left to right at the barrel flange. The engine would barely turn over with no rings once I tightened down the barrel. The cases were not mismatched. One set had never been apart. It's easy to check with the top off the engine, all you need is a piece of precision ground bar to go through the little ends and a set of feeler guages. Worth a try!

Bill

I have the same trouble on my commando 850 MK3.

First tightening after rebuilding engine (new oïl pump etc..) : 

At 400 kms in very hot weaher in steep but short climb of a small pass (1250 m)

After 8000 kms news pistons and rebore and tightening at 400 kms in the same conditions ! !

Carburation and timming do by a good enginer.

Control with oïl gauge cold and hot = OK

I will contrôl conicity of the cylinders.

I search the cause….

I sorry for my poor englisg luangage but I am french member.

Do you have pictures of the seized pistons.

What colour were the gudgeon pins after the siezure.

What silencers do you use, what size main jets are fitted. 

In days of yore when bikes were needed for work,we did not have the luxury of time to speculate.A friday night strip ,A saterday visit to the spares shop,rebuild Sunday,ride to work monday. A tight piston was "eased" with a swiss file. Problem solved.(more or less!). Hudson advised me to use at least 41/2 thou clearance . I would not dream of ignoring his advice.I suspect this longstanding problem has more than one cause. I too have spotted a step at the case mouths ,had mixture bias, low fuel levels, overheated oil on long motorway blasts. Its clear that the DS is less well lubricated than the TS so that when the motor is highly stressed  this is the weakest area. Replace the timing cover seals, hone out the DS another thou or get the piston releaved.Put up with a little cold piston slap. Rudge Ulsters always siezed solid when piston makers recommendations were followed.If you doubled  the clearance it worked!!..

I have gone the speed up the pump route and created more problems  than I had before. If I was Rob I would (at this time) just increase the DS bore clearance and check for mixture bias.  If starting from scratch I would consider building a big bore 88  with lightened and balanced(99?) pistons and "adjust" the oil flow to the TS big end to encourage more to the DS .I would also correct any machining errors  to the case.A good  88 is a better engine than the 99 for motorway use in my opinion.I used to run an 88  at over80 mph for hours with little problem. It also just occured to me that with the case step you will have unequal valve timimg too!.

Hello,

It is the same like picture Rob.in front of and behind,in "corner".

Pilote jet 230,on the 2 amal.The jet holder was half to unscrew but after 2500 miles,when I defused :! ! !

Silencers peashoter.

Gudjeons nickel,no trace.like the right piston.

FRONT -BEHIND - LEFT PISTON after 2500 miles,oil consumption 1L for 1000 kilométers the oïl ring was stuck in his dwelling

One well smeared piston. Not enough clearance.

I found this:

https://www.memoparts.com/img/cms/Documents/Piston%20Failure.pdf

Page 21 shows examples.

Back in 2013, the first picture looks to me like insufficient clearances with 45 degree seizure marks.

The last picture from Francis (above) looks to me like 'lack of lubrication' since it is on the skirt.

Hello,

It is GPM and their document said 11/100 that is what was done,I going to go to 0.60 and now I am going to put 12/100 with JP pistons,it is good ?

Thanks Robert for your anwer

I cannot read the link.

Thanks David for your answer.

Put the link into google and then select the first thing it finds.

It is an excellent document and well worth a read.

Tony

It is OK with google,thanks Tony and very instructive this like.