Author Topic: smoke, stem seals, rings or oil pump?  (Read 3221 times)

Offline Graeme77

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smoke, stem seals, rings or oil pump?
« on: May 28, 2015, 03:22:43 PM »
My 750f1 smokes when you start it up.
I know smoke on start up/over run is normaly valve seals and smoke when accellerating is normaly rings.
Mine smokes when you start it but sometimes a little and clears quick and sometimes alot for ages.
It did used to wet sump alot but going over the pump seems to have sorted that.

the longer it sits the more it smokes on start up.
Ive never had the motor apart but someone did (I have reciets), 12 years ago but its only done a couple of thousand miles since then.

I have just put the bike back together after restoration.

If this is stem seals, no big deal I guess. Rings more of a pain and im sure its not that, but does it sound like its still wet sumping enough to smoke? Can I get pump seals etc to cure it?

If parts were cheaper and access was better id just go through the engine but I dont want to take engine out if its just the pump, not sure there is anything I can do to the pump anyway.

Tempted to just ride it as is but its also a pig to start if its been left a week (oiling plugs?)

Any thoughts?

Offline Bryanj

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Re: smoke, stem seals, rings or oil pump?
« Reply #1 on: May 28, 2015, 03:27:42 PM »
What you describe is more likely stem seals or rarely a cracked valve guide if it ha been mishandled during rebuild, rings are less common but if you take the head off to do the seals it is false economy not to lift the cylinders as the base gasket will probably leak later as the same studs clamp both

Offline Graeme77

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Re: smoke, stem seals, rings or oil pump?
« Reply #2 on: May 28, 2015, 04:32:30 PM »
I would have left head on to do the seals.
Otherwise as you say, might as well remove cylinders, do rings, may as well open bottom end and to primary chain as its almost on the limit.....


Trying to avoid all this at the moment hence wondering if it sounds more like its burning oil from wet sumping.

Offline Graeme77

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Re: smoke, stem seals, rings or oil pump?
« Reply #3 on: May 28, 2015, 04:33:31 PM »
Are the stem seals in the gasket sets any good?

Offline steff750

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Re: smoke, stem seals, rings or oil pump?
« Reply #4 on: May 28, 2015, 08:06:36 PM »
 ;) i have to say id be very surprised if wet sumping is your problem,
 all my cb750's wet sump if left long enough but not all of them smoke .although the old britt bikes are a prime example of what you are experiencing
 i would try a compression test first and you will probably get your answer   ;)

Offline Graeme77

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Re: smoke, stem seals, rings or oil pump?
« Reply #5 on: May 28, 2015, 08:40:15 PM »
You suspect rings then?

I know they were replaced by a previous owner. I know he was a professional mechanical engineer. I have a hand written table of measurements taken at various depths of the bores from when the motor was rebuilt.

This all leads me to think he did I good job and its done hardly any milage since, but that doesnt mean the rings arent stuck, carboned up or broken.

I dont have a compression tester or id have done this already. I was hoping to ride it this summer and rebuild the engine next winter.

If the smoke was a ring issue wouldnt it smoke all the time or on acceleration?

Offline Trigger

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Re: smoke, stem seals, rings or oil pump?
« Reply #6 on: May 28, 2015, 08:44:04 PM »
Even though the engine has been rebuilt you can still get glazed bores due to too much gentleman riding. 

Offline Graeme77

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Re: smoke, stem seals, rings or oil pump?
« Reply #7 on: May 28, 2015, 08:54:09 PM »
Thats true. It was rebuilt about 2003, bought by my wifes uncle in 2005. It was ridden gently a couple of times doing only a couple of hundred miles over the next 6 years.
I bought it in 2011 and its always had this issue although it was worse when I first got it.
Ive put about 1000 miles on it but I tend to ride it hard. Im not shy to wind it up.
Its not turned a wheel in the last 2 years though.

Its not enjoying being idle.
Its reasonably smoke free and starts super easy if I run it every day but leave it a couple of days or a week and its a pain.
Ive not run it for 3 weeks. I know ill have to make sure the battery is fully charged and either drain the float bowls or use loads of easy start to get it going again. I know it will fill the garage with smoke but if I then start it every day or every other day it will start without you even hearing the starter spin and will run great.

Offline Graeme77

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Re: smoke, stem seals, rings or oil pump?
« Reply #8 on: May 28, 2015, 09:03:35 PM »
Thinking about its symptoms, with the hard starting combined with the smoke (they seem to go together) maybe its the stem seals leaking and the oil accumulating in the bores is oiling up the plugs?


Offline Trigger

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Re: smoke, stem seals, rings or oil pump?
« Reply #9 on: May 28, 2015, 10:59:27 PM »
you will soon know if you take it apart.

Offline Graeme77

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Re: smoke, stem seals, rings or oil pump?
« Reply #10 on: May 28, 2015, 11:17:38 PM »
:)
Lets face it, its only going one way isnt it.
Im off work tomorrow. Ill start it and if it smokes (which it will lol) ill take the motor out.

Offline billy192

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Re: smoke, stem seals, rings or oil pump?
« Reply #11 on: June 03, 2015, 09:43:41 AM »
sorry to sound stupid but what the heck is wet sumpping? and how des this get oil into the combustion chamber ?
Thanks
Billy

Offline Bryanj

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Re: smoke, stem seals, rings or oil pump?
« Reply #12 on: June 03, 2015, 09:47:49 AM »
Wet sumping is where the oil tank empties into the engine sump (which is not designed for that amount) and crancase pressure and /or vacuum pumps/drags oil past the rings into the combustion space

Offline billy192

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Re: smoke, stem seals, rings or oil pump?
« Reply #13 on: June 03, 2015, 03:17:55 PM »
thank you Bryan
Thanks
Billy

 

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