Topic: Advice please - exesive amout of oil coming out of breather on CB550 race motor

[vintage_racer]

Started my newly rebuild race motor, new pistons, bores, valve guide seals etc ...

Also replaced crankshaft bearings and oil seals, and all gaskets.

Motor started second kick and sound OK but there is an excessive amount of oil coming from breather in the valve cover and I'm talking at idle (2000 RPM), not at race conditions. This motor never showed anything significant (will collect 30ml over a full season) coming out of the breather even when being seriously worn out.

What should I look at?

Thanks,
Dan

[turboguzzi]

mmm.... not good.... pressure building in the cases usually means rings not sealing, would do a compression/leak test. hope you didnt snag a ring while putting it together.

are you running stock pistons?

TG

[bwaller]

I went back and read these are stock H. pistons & rings. Sounds like TG's prognosis must be right....tough luck.

Did this begin from start-up?

[vintage_racer]

So did I fear.
This are brand new (of e-bay) aftermarket pistons/rings made in Japan. Stock dimensions.

The oil started coming out of the breather right away.
Will have to do a compression test. I examined each bore after machining by inserting a ring and measuring the gap and it seem to be within spec.
May had broke a ring during assembling but that's quite unlikely since the pistons went into the bores really easily this time (and over the last 7 seasons I used to replace rings and do some honing every winter or two).
In any rate, don't have the time to dissemble and inspect everything before the race so will probably be running at Mosport with this problem  

Well, if compression is low across all cylinders, will be able to advance ignition a couple degrees to compensate, what do you think?

Thanks,
Dan

[turboguzzi]

if a boken ring is the case, would expect just one cyl to read low. was any of the plugs more oily than the rest? (though that would be more related to an oil ring rather than compression which seems to be your case)

would think twice about racing like that, you dont want a well oiled tire, do you?

maybe do a few laps and see how much oil collects?

my 0.02

TG

[bwaller]

Or ruin a piston/bore and whatever else. 

[vintage_racer]

Took out the spark plugs and did compression testing (by jumping on the kickstart like an intoxicating monkey while holding the carbs wide open after warming up the motor).
There wasn't any oil on any of the plugs so oil rings are intact.
All cylinders showed EQUAL compression of about 120 - 125 psi. this is about 25-30 psi less then I was able to obsreb after past rebuilds using exactly same method (and gauge) of measurmet.

At the past this is the reading I will get on pistons with broken compression rings (happened once before) but this time I belive it's just the tolerances my machinist used. Also in the past I always used Honda rings, this ones are aftermarket.

Assuming the rings aren't broken, is there a chance that after braking the rings in, sealing will improve significantly enough?

I'm also out of 550 cylinder blocks so boring a new one isn't an option right now.

One more thing - the motor is running VERY rich at low throttle opening, I took care of the main jet for full throttle and also drooped the needle one slot but for lower throttle opening (idle to say 20% opening) what should I do? The carbe are stock CB750 K2 with velocity stalks.

Thanks,
Dan

 

[turboguzzi]

Yes, the chance is there, if you dont have time to take it to the track for running it in, then a 6-10 pulls on a dyno is good too. maybe try that before tearing the engine? rings like some load on them to settle down.

never tried this, but in theory low rpm mixture is related to slide cutaway height. wanna file them a bit? am not taking any responsibility...

TG

[vintage_racer]

Thanks for the advice TG,
will brake in the motor on the track in practice on Friday to be ready for heat races on Saturday.
Interesting point regarding filing the bottom of the carb sliders, should increase air flow and make mixture leaner or may just slow air flow...
May try it at some point.

dan