nx650 engine probs

[mick]

Hi guys,i have a dominator with a smoking problem.I have fitted a overbored barrel and wiseco piston and it runs fine but smokes heavily.I have stripped it down and found oil sitting on top of the piston.I bought the parts used and was led to believe it was all good,the piston is new and the barrel looks fine.I guess it can only be the bore size or the rings,well i checked with eastwoods (wiseco supplier)and they said the rings can be fitted any way round.I am taking the barrel to an engineering shop today to get the size checked.Does anyone have any other ideas what it could be?
thanks mick.

[GB500nz]

Valve stem seals?

[peterj]

Memory (hence dodgy) tells me that some wiseco rings are OK either way round, others are not. I think you may find some markings near the gap, and if it matters, these should be topside. Other than that, did you check/adjust the ring gaps (probably won't cause your problem, but if you didn't, do it before you put it back together this time)? Also did you follow the instructions for staggering the ring gaps (memory says 9 o clock 3 o clock for the top two, 12 for the oil ring, but check the fitting instructions).

The engineering shop should also tell you if the honing looks OK.

Experience says you can expect fairly high oil consumpt while running in, but not smoking. Don't try to run it in using synthetic I have been told.

And yes, agree that it could also be the valve stem seals - this usually shows up particularly as smoking on the overrun from memory. If the seals are gone, there's a fair chance the guides are worn too.

Good luck tracking it down and fixing it.

[guest27]

Agreed.

I would check the end gap on the rings - lets you have a good idea if the rings are wrong or the bore worn, but oil on the piston sounds like it is coming down the valves - it is settling there after the engine has stopped burning fuel etc else it would be burnt of in the combustion? Oil is not going to force up the barrel and onto the piston at stand still but could drip down the guide?

Was it in a particular place - puddle or all over?

R

[Ken]

As stated you need to remove and gap the rings. if its smoking as bad as this something is very wrong. If the parts were used are you sure you have piston that is the correct size for the bore. Has it got good compression? I would say check the valve guides and seals but if it never smoked before this should be OK.
Do you have a manual and parts list?

Ken

[mick]

ok thanks for all your suggestions,the valve seals are fine as it never smoked before fitting the new barrel and piston.it was only replaced due to water damage in the old barrel.i will check the ring gaps tomorow,does any one know what they should be (min and max)had a surprise yesterday as both the engineering shops in surbiton that i have used in the past have been demolished.can anyone recomend any workshops in surrey?
thanks mick.

[peterj]

I'm pretty sure ring gap is mentioned somewhere on the wiseco box or installation instructions, but the figure I've been told before is a minimum (well actually should be set to) 0.004" per inch of bore, eg 100mm bore ie approx 4" = 0.016" (don't know your engine's bore offhand).

The only reason I can think of that it would be significantly higher than that (in answer to your max question) would be if the piston clearance is too big (ie the bore is too big for your piston). Wiseco specify the piston clearance for each type they supply (and importantly where to measure it), but it's usually of the order of .003" to .005" measured 1.3mm below the oil ring land on most (but not all - some are 90 degrees to the gudgeon pin at the skirt level) types from what I've seen. Whoever bored it for you should have sorted that out for you, but not all shops do things right.

My SRX runs a fair bit more than it should have though, and it doesn't burn excessive oil. The ring gaps on mine were bigger than the required gap by a fair margin.

I have also heard that wiseco specify a different end gap on some pistons for top and second ring, so it might pay to email them at

questions@wiseco.com

and ask for all the specs if you can't find the figures.

[mick]

ok i took it to an engineer who measured everything for me and said everything seems to be ok size wise,although it could be better.he also found i had the two top rings the wrong way round.luckily i have a spare barrel so i am going for a rebore and a new set of rings and the engineer is going to do the ring gaps for me.
will let you know how it goes.
regards mick

[bikeseamus]

  Make sure your intake valve is smooth with no scars anywhere that will cut the new seal you will install, and make sure the valve isn't worn and wobbling around in the guide.
The exhaust seal is less critical, but is still important. A large piston will generate tremendous vacuum on the downstroke, and will suck oil if you have poor sealing, and you will have accomplished little and be looking at more down time, smoking, and another teardown.    Seals are critical to clean running, and make sure your crankcase ventilation is open and clear or you will pressurize your crankshaft and smoking and leaking will be in the future.   New seals are cheap and easy to install, since you are in there anyway. Teardowns are a little more troublesome and expensive, as you are finding out.    Happy motoring.

[mick]

hi guys i am pleased to say the dommie is now running fine without smoke.the new rings came with proper instructions and i think that was my main problem. thanks for all your advice.
regards mick.

[themoudie]

Aye mick,

Pleased to read it's sorted.

Cheers, Bill