Dominator 99 problems

Peter. You have completely changed the ignition system, so it would seem unlikely that it is an ignitioncomponent fault unless very coincidentally the same problem is manifest on the new part as the old part. You say there are signs of crankcase excessive pressure. To check the breather, fit a long plastic pipe to enable you to sit on the bike with the pipe in your mouth. Remove the plugs and slowly turn the engine over, with the kickstart and blow hard into the extended breather pipe. If you have a normal breather system which is working correctly you should be able to feel by the pressure in your mouth that air is being allowed to blow into the crankcase and then firmly stops as the disc valve rotates. If you can feel this timed operation then the breather is working normally.If not, it could be that the rotating disc has become damaged. (The driving "ears" have become worn off...unusual but possible).

The breather, if not working, will not cause a misfire though, but what can happen is that the crankcase pressure blows oil past the oil seal in the distributer shaft, and the oil travels along the internal parts and gets onto the points. An easy check is to see if oil is on the points.

You have reasonable compression (but not that good) with both sides equal, so the valves are probably seatingquite well.

Back to the ignition, are you sure the low voltage connections on the coil have not been reversed? Make sure the CB terminal does indeed go back to the points. Although a coil will work with the connections reversed it will only work well with them correctly connected, so you may well have a weak spark if reversed. Just as it is so easy, it would be an easy thing to change the spark plugs again for another new set, it just might be bad luck that one of them is the culprit.

Although unlikely as you say you have cleaned the petrol tap, it could be fuel supply problems. Check the fuel delivery rate from the tank at the fuel pipe at the carb end. It could even be the petrol cap air hole is blocked.

Les H

Have you checked the charging system and battery to make sure you are getting 12V at the coils without any breakdown from AC to DC due to a dud rectifier?

Dominic

If it was a fuelling problem it would manifest with a more difinite surging/hesitation. What do the plugs look like after a short ride?

Dominic

Previously wrote:

Hi Dominic

Don't think it's fuel unless something is causing an intermittant blockage. The strange thing is that it takes 20 miles of normal riding before the problem shows. If it was fuel I would expect it to happen hot or cold. One thing I forgot to mention, on the return journey with the bike missing badly particularly when trying to pull away fron lights (sods law stated that I hit every red on the way home), I reved the bike far beyond what I normally would in sheer frustration and the problem cleared for the mile I had left..!!.

I tried it again today with the breather reconnected and sure enough it started to misbehave at the usual mileage. When it was idling badly I pulled off the breather pipe and the idle settled down to near normal. Unfortunately running with the pipe removed from the tank results in oil going everywhere. I checked the vent in the oil tank and it is clear.

Peter

The pipe you are removing is the one from the motor to the oil tank? if so there should not be much if any actual oil coming out of that pipe. It should be vapour mostly. How much pressure is in that pipe when the bike is running? ie if you were to put your finger over the open end.

The return to the tank from the oil pump is pumping sufficiently I assume. At idle how does the return feed seem? Is it producing the usual spurt style on and off? it is a pity that one could not drain the sump as soon as the problem manifests to check the oil pump's scavenging function. How do the plugs look? perhaps you should check the plugs when it starts its problem as they may be oiling up. Does the bike smoke at all once the problems manifest?

So many questions. Apologies!

Dominic

Hi Peter.Intermittent faults are a pain. At least you've learned that you have a timed breather system and your one is working normally and no work on it is required.

I cannot see how the breather system can affect the normal firing of an engine apart from keeping oil away from the combustion chamber and interfering with the firing, but I would almost rule this effect completely out, but see note at the end..

You could hard wire the the battery directly to the SW terminal of the coil (you could incorporate a switch in series too with the wire for extra convenience). This would illiminate all chances that your ignition wiring or ignition switch has some form of poor or intermittent connection.

Do this and report back, it will have to be a series of steps to locate the fault, otherwise you will chase around and around and not get anywhere.

BTW I don't know what is causingthe smoke from the crankcases, but you check the plugs for sooting up. I know you say you have reasonable compression, but an engine can still burn oil excessively if the oil scraper rings aren't working well. It would not cause smoke to blow from the engine though.

Les

Previously wrote:

"The return to the tank from the oil pump is pumping sufficiently I assume. At idle how does the return feed seem?"

This seems fine with a healthy flow on idle when engine speed is increased it falls back a little but picks up again.

The feed at idle should be initially continuous and after a short time to spurt. The reason I am asking this is to check whether your scavenging pump is working correctly as a full sump of oil would cause the excessive pressure in the sump and may affect the firing as a result especially as it seems to take 20 mins for the problem to surface. The breather should not push oil out.

When last did you do an oil change? Does your model have the oil strainer at the bottom of the sump? If so is it clean?

Dominic

Hi Peter. Your suggestion of sticking valves is a possibility. The exhaust valves will be the most likely. It can happen if the valve stem has carboned up. I've never know it myself to happen when running, but I've known the exhaust valve to stick open after leaving the bike not running for a long time. You might be able to seethe valve stems by removing the exhaust pipes and getting the valves on full lift. I can only imagine that the crud will be the point on the stem that is only just going into the valve guide at valve closure, and is also exposed to the exhaust carbon. It could be occassionaly causing some binding. If it is this area, there would have been a good chance that some contact has been made by the piston crown at TDC...not nice!

You might, repeat might,be able to,with a suitable tool (perhaps a bent screw driver with sharpened blade) scrape away the crud on the the valve stem. It will only be required at the the one small area as I have just described. I doubt if you willbe able to turn the valve in situ though to to get to the back of the stem.

As I said, I have never known this to happen but I guess it can happen. A full head service will be the best way to ulimately overcome the problem.

If the problem remains and all aspects of ignition and fueling have been totally certified as working normally, then this is a worthwhile check as it is a possibilty.

Les

Just adding aCORRECTION here: I've just thought that if if the sticking is just before the valve fully closes, then there will be less chance for the valve to come into contact with the piston which is a relief. I suggested there was a "Good chance" that piston contact would be made, but as I have justsaid, it is not that likely, so good news!

Les

Previously wrote:

Hi Peter. Your suggestion of sticking valves is a possibility. The exhaust valves will be the most likely. It can happen if the valve stem has carboned up. I've never know it myself to happen when running, but I've known the exhaust valve to stick open after leaving the bike not running for a long time. You might be able to seethe valve stems by removing the exhaust pipes and getting the valves on full lift. I can only imagine that the crud will be the point on the stem that is only just going into the valve guide at valve closure, and is also exposed to the exhaust carbon. It could be occassionaly causing some binding. If it is this area, there would have been a good chance that some contact has been made by the piston crown at TDC...not nice!

You might, repeat might,be able to,with a suitable tool (perhaps a bent screw driver with sharpened blade) scrape away the crud on the the valve stem. It will only be required at the the one small area as I have just described. I doubt if you willbe able to turn the valve in situ though to to get to the back of the stem.

As I said, I have never known this to happen but I guess it can happen. A full head service will be the best way to ulimately overcome the problem.

If the problem remains and all aspects of ignition and fueling have been totally certified as working normally, then this is a worthwhile check as it is a possibilty.

Les

Just adding aCORRECTION here: I've just thought that if if the sticking is just before the valve fully closes, then there will be less chance for the valve to come into contact with the piston which is a relief. I suggested there was a "Good chance" that piston contact would be made, but as I have justsaid, it is not that likely, so good news!

Les

I wondered whether the scavenging effects of the pump were inadequate while the bike was riding which may fill the sump up to unacceptablelevels for riding. It seems odd that oil is being pushed out of the breather while you ride. Either there is too much crankcase pressure or the sump is slowly filling up. I have had the experience that too much crankcase pressure with weak oil scrapers will cause poor running - however the plugs/s would look damp with oil which is not your case. We need Sherlock Holmes!

Hi

had simlar problem on my 500 twin it was down to loose head bolts around the pushrods. leaking combustion pressure into sump through pushrod channels.

causing back pressure pushing oil out everywhere.

also it would only run cool with addative mixed in with fuel. if i didnt put addative in it ran very hot with simlar problem that you describe

it must boil the fuel evaporating then when you stop it all cools down hence return of fuel and off you go again

Baz

Previously wrote:

Hi . i just tightened the head down . when i say the bolts were loose you would have had to use spanner to move them. they simply wernt torqued up right .

the engine would misfire on one pot and throw smoke out on over run .after i tightened head it seemed to cure all. back pressure ect.

i am no means an expert just thought it might help .

Baz

Baz

Thatâs an interesting comment on the loose head bolts and although mine seemtight I will torque them down and see what happens. How did you cure theproblem, did you just tighten down the head or did you replace the headgasket?.

Les

Just before the crash when my last entry disappeared I thinkthat you mentioned that you thought that I had discounted the sticking valvetheory. I am coming to the conclusion that the problem is mechanical as I havereplaced all the electrical components and bypassed the ign. switch, so this isstill a possibility. The fact that there is an increase in oil leaks fromsomewhere near the chaincase after a hard run but not after a shorter run intothe city also seems to indicate a buildup of pressure.

I was also wondering if there were any problems associated with changing theoil pump ( other than the cost ) that I should be aware of. Will pulling offthe cover have any effect on the chain tension?. Speaking of chains I decidedto replace the rear chain but the nearest I can find here is a Japanese size of520 as the distributers here have never come across 5/8 X 1/4 before. The onlything is that the one I got is a full 5mm wider than the 1 1/2 cm on presentlyfitted. I normally buy from Norvil but the weight of a chain makes postageexpensive.

Thanks again,

Peter

Peter. I would now advise you to get a Norton expert to check over your bike,The scavenge side of the oil pump is the more likely side to get damaged (by debris pick up) and thus your pump might have a problem keeping the sump dry. Whether this will be the reason for the misfire looks tenuous though, but not completely impossible if all the other worn engine parts add up in the right (wrong) way. Maybe you now consider a complete engine rebuild?

The oil pump renewal is straight foward and will not effect the chain tension by removing the timing cover but one would imagine you would take the opportunity to adjust the chain tension/slack at this time but you will require a cutaway coverfor better accuracy.

As for the chain, the Jap system expresses the size in eights, so 530 is 5/8 x 3/8 and your new 520 one should be ok at 5/8 x 2/8 (1/4) What you might have is the extra heavy duty one. These have thicker side plates and create a wider chain, (roller width remains the same though)It could be that you have a 525 chain by mistake which is the same as a 5/8 x 5/16 (8/2.5) and thus wider by 1/16".

Les

Hi Peter. Have you checked the dizzy shaft and advance mech for looseness in the bearings. See if point opening varies under under side pressure. This is common in old dizzys.Your problems say ignition ,good even compression rules out valve piston and gasket.