Topic: Honda CB350f to 393

[oldscoot]

Hello.  I recently had my bike built to a 393.  It needed a rebuild and I figured I would go with all new parts and try to maximize whatever I could get out of it.  Hence the 393.  Complete top end rebuild head completely redone. New valve guides, seals, the whole 9 yards.  I got it back...still smoking.  The mechanic told me it needed to be ridden 500 miles bit I thought that was garbage, especially since I know i was burning oil because I had to replenish.  So i took oy back.  He had the machinist recheck the head....all good. More agressive cross hatch put on cylinders.  Got it back, still smoking, but less.  Still having to replenish oil.  Mechanic says its residual oil in pipes.  There is some but its if it wasnt  burning oil i wouldnt need to replenish.  noticed I had a leak at the stator cover so I replaced the gasket.  Now oil light is on and wont turn off.  Related?  Not sure.  Will bad oil pump cause oil to burn?  I wanna ride it but I dont want to make the smoking issue worse.  Does anyone have experience with these kits?  Any issues with rings?  Compression seems to be good.  Anywhere else I should be looking for oil burning?  Sorry its a lot, i know.  Thanks for reading

[MrMoist]

Hey Mate, I've just gone through the rebuild of mine woth the 393cc kit also, did your smoking clear up?

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[Trad]

It could be too large a piston to cylinder clearance. What pistons are you using and do you know the clearance your machinist used?

[faux fiddy]

There are several threads from years back and it's a tough question to answer if it's unknown.

If it is the case, I'm sorry to bring you this news.

Did you orient all of your piston rings with the marks topside?

I think there are a few people here  that fixed their smoking rebuild by going in and flipping rings.

[Bodi]

How are the plugs and pipes? If #1 and/or #4 are oily and 2/3 are good... I would suspect the oil orifice valve seals are leaking oil into those cylinders past the head gasket. I have seen that after someone used sealant around them to avoid the usual oil seepage out the ends of the head/cyl join. If all cylinders are smoking then your scraper rings might be upside down? Or the exhaust valve guides are badly worn: these do not have seals and loose tolerance lets a fair amount of oil creep down the valvestems. The intake valve guides do have seals but those - and the guides/stems - may be worn out. A loose intake guide lets the stem move around which can damage the seal especially when 40 years old and crusty. Other than inspecting them, there's no diagnostic to tell if guides are loose - it just shows up as smoking and excessive oil consumption, sometimes excessive engine vent gas.