CB750 F1 smoking like a b*****d.

[MCR]

Hello Lads,

Just joined your site and I have question to kick off with.
My overbored CB750 F1 with CR oil cooler has started to smoke like a B****d.

My concern is that the smoking is down to wet sumping due to fall back from the extended, external oil line from the return outlet to the oil cooler. I say concern, that would be the best scenario I think. Either that or it's seepage from the valve seals.....although I did replace them in the rebuild.....Gut instinct says its a bad seal or valve guide.

Relevent spec: 836cc overbore / Dyna S ign / CR carbs / Accer coils / rebuilt engine by me 8 mths ago (I take any blame) / CR oil cooler and extended oil lines / High flow headers and pipe / non standard oil box..etc....

Starts first kick then aprox 30 seconds later comes the heavy blue / oil smoke which clears when warm, then she runs smokeless and very strongly as a rebuilt engine should. Stop for half hour or so and same problem.
I note that there is aprox three quarter of oil in the sump, never known what amount should rest there?

I had a similar problem with a Ducati 900 Bevel, turned out to be a combination of valve seals and crap valve stem tolerance.
Oh yes, it started smoking just after a routine oil and filter change, I used Silkolene semi 10/40...relevant??

I will have to work out how to reduce the kb size of my build pics to show engine detail.

Thoughts welcome...Cheers.

[Bryanj]

Try going back to a 10/40 straight mineral oil first, its cheaper and no matter what type you use it still needs changing every 1500 miles

[MCR]

Bryanj,

I historically change the oil every 1,000 miles max, however this rebuild hasnt done that many miles as yet.
I notice that this semi synthetic stuff is much thinner than straight 10/40, oil I normally use by the way.

I will drain off the semi and refill with millers and post the results.

Cheers

[Bryanj]

Honda used to say if you don't do the mileage change annualy. As to the other post I rarely get to any meets as I work nights driving now.

Merc commercials use 3 times the ammount of oil if you run synthetic !!

[Waggles]

Agree with above advice. If its a valve related problem you usually get smoke on the overrun even when hot.