Author Topic: crankcase pressure etc  (Read 6634 times)

Offline bikerboy

  • Valued Contributor
  • ****
  • Join Date: Dec 2011
  • Posts: 336
  • Karma: 4
Re: crankcase pressure etc
« Reply #30 on: 25.09. 2017 02:02 »
I feel qualified to comment on this post for sure because I had exactly the same problem after my rebuild you people might remember.

I had the bores resleeved, used old heppolite pistons and new rings. The work was done by an old engineer who really knows his stuff and he passed everything as suitably sized no problem. A plce called teh rebore shop very highly respected in the south of england so I have been told.

3 times I had that engine back apart due to oil and smoke out of the breather. Burning oil. Smoking quite badly out of the exhausts at times. I replaced the guides even tho they did not seem that bad, as I was doing guides I fitted new valves as well. I done rocker box breathers etc etc. There was a long running post on this over the course of months as we all tried to fathom the problem.

In the end in desperation I bought new pistons and took them back to the rebore shop as they were metric just to make sure.

On fitting the new pistons everything was cured instantly.

I came to the conclusion that the new rings nowadays just dont suit old pistons. I can think of no other explanation.

Out of curiosity what colour are your spark plugs after running a while? Mine were always black from burning oil. 30 miles after the new pistons went in I checked a plug and much to my joy I saw this biscuit brown colour.

3 strip downs and about 8 months it took me to cure the problem

https://www.a7a10.net/forum/index.php?topic=9198.0

 

Offline Scott and Jay

  • Moving Up
  • **
  • Join Date: Mar 2016
  • Posts: 76
  • Karma: 0
Re: crankcase pressure etc
« Reply #31 on: 25.09. 2017 22:32 »
I can second this conclusion, but it took us 4 years to put the same solution in place. I had a thread called "Timed breather, what is the actual timing". Our reconditioners had also advised that the old pistons were ok, with only a hone to the bores. To compensate I went the Total Seal Gapless rings way, but I think that just exacerbated the crankcase pressure. So, we were distracted from the underlying excessive-blowby situation. I lengthened the breather valve holes, and narrowed the valve clearances by inserting K-liners. These weren't bad mods. The last time I had oil over the back wheel it turned out pressure hadn't pushed out the drive side oil seal (like it had in the past). But there was too much oil coming out of (where it should, in such a case) - the breather exit pipe, and high consumption. My oil was always black, though - indicating blowby contamination.
My engineer had detected an imperfect part of the bore (caused by rust from 30 years being left), but he was more insistent on new "decent" pistons. I believe the only ones up to the quality he was after are IMD. Adrian Wright, the proprietor, dealt with me personally, with all the specs. The rings that go with them are a big part of the advantage. They are deeper and narrower, and come with their own 3-piece oil ring. He said "you don't gap them" and I didn't - because I couldn't get them out. My compression isn't as low as the pistons are rated because there was barrel and head skimming involved (some of it unavoidable), in my rebuild. It's probably about 8.1:1, lower than the 8.5:1 my old domed pistons were rated at. It kicks over easier. I did the "stationery" running in procedure that Klaus described. From my first ride the bike was much smoother-running and more powerful than before. The plug colour is light brown - from idle through to full throttle.

Offline t20racerman

  • A's Best Friend
  • ***
  • Join Date: Feb 2011
  • Posts: 227
  • Karma: 7
  • Keep it nailed!
    • The T20 'Super Six' Suzuki website
Re: crankcase pressure etc
« Reply #32 on: 02.10. 2017 18:12 »
Thanks for the continued comments - appreciated.

Interesting tale about the pistons - I guess old designs aren't as good as new ones! My oiling problem is nothing like bikerboy describes though - its just a bit leaky at prolonged 4000rpm+ . Its fine at 3700rpm though, so I guess I just need better breathing. My plugs are lovely sandy brown by the way - with no evidence of excessive oil burning. I had inlet valve guide seals fitted when I had the head gas flowed and new 'unleaded friendly' valve seats fitted, and that definitely reduces oil burning.

Update to my earlier post: I fitted a breather to the rear rocker cover, with a tube out to the mudguard stay to catch the air flow. This seemed to make little difference, but my tube was too small a diameter I thought. I put a bigger tube on (about 8/9mm diameter) and that definitely helped to make it less oily - even when thrashed. However, the breather spigot I made only had a 6mm bore, which in hindsight is way too small. Topdad - what internal diameter is the breather you made?
I'll make a bigger one when I'm next working on the bike. I'll report back as and when

Re the tacho cable drive leak - this is STILL chucking out oil at 4000rpm+, despite me taking off the cable mount bracket (inner timing case kind) fitting a new gasket, and resealing it. The cable outer has a split in it at the bottom though, and I'm now sure this is where the oil is coming from - despite me putting silicon goo on it. I've just ordered a new tacho cable, and will ensure it is all sealing nicely.

I'll let you know how it goes.
1961 A10 - somewhat modified :-)
1980 TZ350 - lunatic Classic Race machine
1967 T20 Suzuki - heavily modified Classic Racer
1967 T20 Suzuki - pretty standard road bike
2007 KTM 660 SMC - fast and furious supermoto
Triumph 675 Speed triple
Ossa 250 and yet another T20 racer in bits both being built up

"If I had all the money back that I've spent on motorcycles... I'd spend it all on motorcycles!"

Online JulianS

  • 1962 A10
  • Resident Legend
  • *****
  • Join Date: Mar 2017
  • Posts: 915
  • Karma: 19
Re: crankcase pressure etc
« Reply #33 on: 02.10. 2017 19:02 »
The oil leak in tach drive will be coming from between the drive spindle and cable fixing bracket. If not sorted it will get into the tacho head which will do it no good.

If your setup is the original one there will be a tiny and flimsy o ring and later a ground spiral on the spindle which hoped to keep the oil in. It was no too successful because there are a 3 factory service bulletins on the leak.

The current pattern ones take a more substantial o ring on the inside of cable bracket, like the A65 setup, which is more effective.

Photo is an original drive from a 1962 Rocket engine.

Offline t20racerman

  • A's Best Friend
  • ***
  • Join Date: Feb 2011
  • Posts: 227
  • Karma: 7
  • Keep it nailed!
    • The T20 'Super Six' Suzuki website
Re: crankcase pressure etc
« Reply #34 on: 02.10. 2017 19:15 »
Thanks for that JulianS - very interesting, and undoubtedly correct. Mine is all pattern stuff - I got the tacho drive shaft from SRM about 30 years ago I think. My bracket (also a pattern) was bought at the same time - not sure where from. It doesn't have an O ring of any kind..... I've always had a well oiled tacho cable though!  ;)

As the shaft spins so quick, I didn't think an O ring would be a good idea, but would be very interested in a diagram or picture of how it should be - or how people have modified theirs. I was looking at this at the weekend and wondering if there was an oil seal small enough to fit in the bracket.

Is there anywhere nowadays selling modified brackets with an O ring or oil seal?
1961 A10 - somewhat modified :-)
1980 TZ350 - lunatic Classic Race machine
1967 T20 Suzuki - heavily modified Classic Racer
1967 T20 Suzuki - pretty standard road bike
2007 KTM 660 SMC - fast and furious supermoto
Triumph 675 Speed triple
Ossa 250 and yet another T20 racer in bits both being built up

"If I had all the money back that I've spent on motorcycles... I'd spend it all on motorcycles!"

Online JulianS

  • 1962 A10
  • Resident Legend
  • *****
  • Join Date: Mar 2017
  • Posts: 915
  • Karma: 19
Re: crankcase pressure etc
« Reply #35 on: 02.10. 2017 19:47 »
First photo shows an A65 cable bracket left and pattern item right.

Second photo same with dimension of diameter of recess in inches into which the o ring fits..

Third is the spindle fitted to my A10 together with the A65 bracket and O ring above.

Keeps the oil in.

Offline t20racerman

  • A's Best Friend
  • ***
  • Join Date: Feb 2011
  • Posts: 227
  • Karma: 7
  • Keep it nailed!
    • The T20 'Super Six' Suzuki website
Re: crankcase pressure etc
« Reply #36 on: 02.10. 2017 20:08 »
Those pics are really useful - thank you so much.

Mine is the same, but has never had an O ring. What size is your O ring - do you know?
1961 A10 - somewhat modified :-)
1980 TZ350 - lunatic Classic Race machine
1967 T20 Suzuki - heavily modified Classic Racer
1967 T20 Suzuki - pretty standard road bike
2007 KTM 660 SMC - fast and furious supermoto
Triumph 675 Speed triple
Ossa 250 and yet another T20 racer in bits both being built up

"If I had all the money back that I've spent on motorcycles... I'd spend it all on motorcycles!"

Online JulianS

  • 1962 A10
  • Resident Legend
  • *****
  • Join Date: Mar 2017
  • Posts: 915
  • Karma: 19
Re: crankcase pressure etc
« Reply #37 on: 02.10. 2017 20:43 »
Think it is 2 mm cross section x 6 mm inside diameter x 10 mm outside diameter.

It fitted better in the genuine item than it did in the pattern one.

Online chaterlea25

  • Wise & Enlightened
  • *
  • Join Date: Jun 2009
  • Posts: 3108
  • Karma: 45
Re: crankcase pressure etc
« Reply #38 on: 02.10. 2017 21:01 »
Hi All,
To sort the tacho drive oil leak I eventually made a complete new housing
I shrank a sleeve over the drive spindle and machined the outside to be a tight push fit into
a pair of sealed miniature ball races that are fitted in the new housing
The new housing needs longer screws to hold the lot in place  *wink2*

John
1961 Super Rocket
1963 RGS (ongoing)

Online JulianS

  • 1962 A10
  • Resident Legend
  • *****
  • Join Date: Mar 2017
  • Posts: 915
  • Karma: 19
Re: crankcase pressure etc
« Reply #39 on: 03.10. 2017 09:18 »
Rocker box breathers assisting the timed breather are limited by the 4 drillings , 2 by cam followers and 2 from exhaust valve compartment which allow the oil to drain to the crankcase.

Any breather in the rocker will suck air in as well as blow it out.

Seal a plastic freezer bag or similar to the rocker breather tube, run engine and see what happens to the bag - it does not inflate as a thought it would.

Offline t20racerman

  • A's Best Friend
  • ***
  • Join Date: Feb 2011
  • Posts: 227
  • Karma: 7
  • Keep it nailed!
    • The T20 'Super Six' Suzuki website
Re: crankcase pressure etc
« Reply #40 on: 03.10. 2017 17:24 »
Charterlea - that is definitely the best long term solution, and something that I will look into. In the meantime I'll try fitting an O ring.

JulianS - I know it moves the air both ways, but removing the peak pressure each cycle is the idea behind my breather. I'm looking into a one way pressure release valve to keep the peak negative pressure (sucks oil in!) and let the peak positive pressure out each cycle. That would blow your bag up - albeit slowly as it's pressure peaks I'm trying to reduce, not huge amounts of air flow.
1961 A10 - somewhat modified :-)
1980 TZ350 - lunatic Classic Race machine
1967 T20 Suzuki - heavily modified Classic Racer
1967 T20 Suzuki - pretty standard road bike
2007 KTM 660 SMC - fast and furious supermoto
Triumph 675 Speed triple
Ossa 250 and yet another T20 racer in bits both being built up

"If I had all the money back that I've spent on motorcycles... I'd spend it all on motorcycles!"

Offline Scott and Jay

  • Moving Up
  • **
  • Join Date: Mar 2016
  • Posts: 76
  • Karma: 0
Re: crankcase pressure etc
« Reply #41 on: 03.10. 2017 20:59 »
I'm glad Julian pointed out what I believe too. I also had a vent in my rocker cover at one stage. I know it's common and have met other people who did it. It certainly didn't seem to alleviate crankcase pressure for me. With the narrow crank cavity on the A10 (not open to the primary like A65s) - it seems to need the vacuum created on the piston upstroke. That means it's not having to push much air out of the breather exit, when the (standard) breather valve opens, on the downstroke. You won't get such a vacuum if it sucks air in through the rocker vent and there will be more pressure to be relieved..

Offline t20racerman

  • A's Best Friend
  • ***
  • Join Date: Feb 2011
  • Posts: 227
  • Karma: 7
  • Keep it nailed!
    • The T20 'Super Six' Suzuki website
Re: crankcase pressure etc
« Reply #42 on: 03.10. 2017 22:31 »
I'm glad Julian pointed out what I believe too. I also had a vent in my rocker cover at one stage. I know it's common and have met other people who did it. It certainly didn't seem to alleviate crankcase pressure for me. With the narrow crank cavity on the A10 (not open to the primary like A65s) - it seems to need the vacuum created on the piston upstroke. That means it's not having to push much air out of the breather exit, when the (standard) breather valve opens, on the downstroke. You won't get such a vacuum if it sucks air in through the rocker vent and there will be more pressure to be relieved..

That's why I'm trying to get one of these:

http://www.ebay.com/itm/Stoney-Racing-Oil-Catch-Can-One-Way-Non-Return-Check-Valve-PCV-Breather-Hose-/182462713511

Unfortunately out of stock. ☹️
1961 A10 - somewhat modified :-)
1980 TZ350 - lunatic Classic Race machine
1967 T20 Suzuki - heavily modified Classic Racer
1967 T20 Suzuki - pretty standard road bike
2007 KTM 660 SMC - fast and furious supermoto
Triumph 675 Speed triple
Ossa 250 and yet another T20 racer in bits both being built up

"If I had all the money back that I've spent on motorcycles... I'd spend it all on motorcycles!"

Online orabanda

  • Resident Legend
  • *****
  • Join Date: Nov 2008
  • Posts: 973
  • Karma: 21
Re: crankcase pressure etc
« Reply #43 on: 04.10. 2017 03:40 »

Online duTch

  • Ricketty Rocketty Golden Flashback
  • Wise & Enlightened
  • *
  • Join Date: Oct 2011
  • Posts: 4517
  • Karma: 40
Re: crankcase pressure etc
« Reply #44 on: 04.10. 2017 03:49 »
 
I'd be more confident if it were called a 'PCV', instead of a 'PVC' valve
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia