Timed breather, what is the actual timing?

[KiwiGF]

I'm asking this on behalf of a friend who has had endless problems with crankcase pressure including the primary side crankcase oil seal repeatedly blowing out.

He has measured the timing (at the crank) of the the timed breather and told me that he got these results below, the question is, are these values "normal"?

Open  90 degrees before bdc
Close 45 degrees after bdc

If anyone has the dimensions of an unmodified breather (hole) I guess that that would also help.

[duTch]

 

   Open  90 degrees before bdc
                Close 45 degrees after bdc   

 Seems reasonably logical, @ 90 degrees before bdc(90º atdc), the piston will have built enough C.C pressure to blow out, and closing @ 45º abdc (135º btdc) as the piston goes up again will inhibit back-sucking through the gallery. As you say though, maybe those figures are not quite right-

 

primary side crankcase oil seal repeatedly blowing out.

  do you mean it literally and physically blows out  ?

 

what is the actual timing

     I think I started to work it out but gave up on the  basis of 'suck and see'

[BSA_54A10]

How is the cork.
If the gasket is too thin it will not make a seal so the breather becomes effectivly useless.

[TT John]

I'm asking this on behalf of a friend who has had endless problems with crankcase pressure including the primary side crankcase oil seal repeatedly blowing out.

He has measured the timing (at the crank) of the the timed breather and told me that he got these results below, the question is, are these values "normal"?

Open  90 degrees before bdc
Close 45 degrees after bdc

If anyone has the dimensions of an unmodified breather (hole) I guess that that would also help.

I don't think there is any set timing, as long as the marks line up on the crank, idler sprocket & magneto, as these only line up after about eighty revolutions. I know I had the same problem but found that the return pipe was blocked with, most probably old silicon gasket material, I use an air line to blow all the old crap out.

[KiwiGF]

Thanks for the replies, I think what Scott is trying to do is establish whether he has a non standard breather eg hole in wrong place or wrong length, he has investigated all other known reasons for excess crankcase pressure.

Scott glued the crankcase oil seal in place and it still blew out!

Its had a rebore and has gapless rings but still burns far too much oil.

[chaterlea25]

Hi,

Its had a rebore and has gapless rings but still burns far too much oil

Sort this out and all will be well
More than likely the bores have glazed, what oil has been used?
Or a loose or worn valve guide(s)

John

[KiwiGF]

Sorry it was not rebored just honed. Scott has just had the top end off to check the bores rings and guides etc. He Fixed a small end issue; but still the oil burning issue remains. He is reluctant to rebore what is an  in tolerance barrel until he is certain the timed breather is not at fault.

SAE 50 oil is used. Penrite, I think.

[Rocket Racer]

Sorry it was not rebored just honed. Scott has just had the top end off to check the bores rings and guides etc. He Fixed a small end issue; but still the oil burning issue remains. He is reluctant to rebore what is an  in tolerance barrel until he is certain the timed breather is not at fault.

SAE 50 oil is used. Penrite, I think.

let me know if you want a spare breather, I've got a stack of them 

He does live in NZ in the North Island ..., whats wrong with 40 weight. 50 is into big singles territory with roller big ends. too heavy an oil IMHO for plain big ends in the summer.
 But drop me a pm if you want a breather or two.

[KiwiGF]

Hi Tim, careful this might turn into oil thread 

I use cheapo castrol gtx 20/50 myself 

I'll ask Scott to get in touch with you then; in the mean time could you plesse measure the breather slot next time you visIt your shed full of breathers (and rocket 3 you lucky s_d).

Scott is obviously checking the non obvious as he has checked all thd obvious. He had a bunn breathet fitted to the breather  exit at one stage and that did not work either, albeit he had the std breather as well.

[Rocket Racer]

If he gets in touch I can stick one in the post.
I recall cake street classics recommend modifying the hole to extend the breathing.
Will try and find a couple. Being in a rental temporarily, I struggle to find anything or progress the bikes. Need that new big man cave 
Busy sorting out the electric leg on the R3 

my track A10 runs Bunn breathers, they're great 

[BSA_54A10]

otting gapless rings requie  few mods and willput a bit more pressure on the breathing system.
First thing is to sit behind him while he throttles on and then downchanges,
Smoke when throttleing on = bad seal on the rings
smoke on the over run = oil being sucked down the inlet valve guide
And as it is summer, check that the breather outlet is clean and dose not have a mud plugger of some sort stuck in there.
Also check the oil tank breather for the same problem.

[duTch]

 

I recall cake street classics recommend modifying the hole to extend the breathing. 

 Wouldn't one need to take care doing this- might be OK on the blow side, but on the 'suck' side,might sick too much

 I'm inclined to go with TrevorTrevs line of thinking, you (he) should be able to poke a bit of wire up the gallery each way and blow air through (out)

[KiwiGF]

I've a copy of the cake street article and their mod was intended to increase performance rather improve breathing I reckon, they suggest elongating the hole in the breather to commence it opening earlier before bdc. The article does not give standard dimensions of the breather unfortunately.

Scotts bike uses in the region of a pint per 150 miles, more when the seal has blown out (mine is nearer 300 miles per pint and does not smoke) and whilst his bike doesn't smoke much it does smoke pretty much all the time (not great to be following behind it!), it's performance is good and it's mechanically quieter than (dammit).

If the breather is standard then he might have to try new rings, maybe a rebore, but the possibility that the excess pressure is causing the oil consumption is worth thoroughly investigating first.

[duTch]

 But is the passage clear, and the tank breather too?

[KiwiGF]

Hi Dutch, I'll ask about the tank breather and if it's been checked, but I'm puzzled as to why the oil tank breather could cause the engine to burn oil? If it's blocked, could it cause oil to build up in the crankcase?

Wouldn't  this also show up as a highly pressurised oil tank?

 Or would the rockers get too much oil? or what?

Edit: the breather exit has been checked and it's not blocked