SOHC.co.uk Forums > CB750

smoke, stem seals, rings or oil pump?

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Graeme77:
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?

Trigger:
Even though the engine has been rebuilt you can still get glazed bores due to too much gentleman riding. 

Graeme77:
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.

Graeme77:
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?

Trigger:
you will soon know if you take it apart.

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