The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: BigJim on 04.09. 2019 22:51

Title: Engine breather
Post by: BigJim on 04.09. 2019 22:51
Hello,
Have zero endfloat on my breather but have sideways movement of approx 3mm as it is loose on the locating peg. this is evident with the inner timing case in place. Should i be concerned about this and try to stop sideways play?
 Have an oily top end and some oil exiting through the breather hole, might the sideways play be contributing to this?
Cheers
Title: Re: Engine breather
Post by: Rocket Racer on 05.09. 2019 06:02
if your cork gasket shim is doing its job the breather should be firmly held and not able to rotate on the pin.If its rotating as you indicate you still have excess breather clearance and that may contribute to oil loss via the breather. 
Is the smokey motor due to excess oil in the motor or just wear in rings/valves? excess blowby could cause crankcase pressure.
Quite a few variables there.
Presumably the motor isnt wet sumped at start up as that will definitely give you grief.
Title: Re: Engine breather
Post by: Swarfcut on 05.09. 2019 07:37
Jim, The breather will be driven OK by the peg, but will obviously be running  slightly "retarded" for optimum operation of the timed breather as designed. Replacing the worn breather and cam wheel is the easiest and most expensive option. If just the peg is worn it can be replaced, or a new hole for the peg drilled in the breather flange opposite the original, depending on your skill and engineering facilities. The breather also needs to be a good close fit in the inner timing case, where it rotates, and the cork washer thickness chosen to be under slight compression to ensure an airtight seal between cam wheel and breather flange, when the inner cover is tightened into place. Too thick a washer will put a lot of load on the parts and wear the timing cover and breather flange.

 At least changing the parts and correct assembly will eliminate a poor breather as a source of the oil problems.

Swarfy.
Title: Re: Engine breather
Post by: Klaus on 05.09. 2019 08:22
The cork washers are a pain, and have to be grind to correkt thickness. So I convert to use a spring to held the breather in place. Running in seval engine since thousands of miles with no problems.

cheers Klaus
Title: Re: Engine breather
Post by: BigJim on 05.09. 2019 08:34
Thank you gents. Will see what i can do with a slightly thicker cork rubbed down to fit. Have little engineering abilities Swarthy so replacement with new is more likely but not for a while. No wet sumping Rocket R and clinging to hope it's not blowby as engine build is only 2500 (approx) old.
Will also be trying to ride a little more gently!
Thanks again.
Title: Re: Engine breather
Post by: duTch on 05.09. 2019 10:11

 Jim- due to lack of cork thickness options, to pack it out, I used gasket paper shims behind the cork I had- you could probably use any oil resistant material to do same.... and if the hole is out of shape, maybe possible to drill it round and use a short snug sleeve over the peg to reduce any movement- just a thought ?  *dunno*..
Title: Re: Engine breather
Post by: Sluggo on 06.09. 2019 02:43
The cork washers are a pain, and have to be grind to correkt thickness. So I convert to use a spring to held the breather in place. Running in seval engine since thousands of miles with no problems.

cheers Klaus

Klaus is correct of course, but amusing people still using cork washers, along with other Colonial pursuits.  However,,,, *eek*  If you wish to truly master proper end float, shimming and use of proper materials than nothing can compare to shop notes from the Hurley Pugh collective, especially those shims & washers!.....to wit:

" With the crankshaft in the correct position, remove the six bolts that secure the magneto to the top side of the crankcases. You will notice that all of the bolts are different lengths - it is crucial that these are replaced in the correct holes otherwise you will lock the gearbox solid. Underneath the magneto you will almost certainly find one or more thin shims, fitted by previous owners. Hurley-Pugh itself did not actually shim the magnetos when the engines were originally manufactured. Instead, Bill "Masher" Stubbings precisely adjusted the magneto's mounting points by the careful application of a large hammer. If you look closely, you'll probably still be able to see the dents in the top of the crankcase where "Masher" skilfully wielded his scarred hammer. As Hurley-Pugh did not shim the magneto it didn't produce any shims; again, the Hurley-Pugh Enthusiasts Club can oblige with a set of paper shims for a reasonable 280 pounds complete.

Inspection

With the magneto removed, examine the teeth on both the gearwheel and the conrod for signs of distress. Any evidence of chipping, bending, burring or missing teeth will require replacement of both the magneto gear and the conrod, as well as a complete engine strip to remove the debris.

The leather friction washer can be found between the gearwheel and the magneto. To inspect this, use a blowtorch to heat the gearwheel to cherry red and use a 400lb press to ease it off the shaft. The heating process usually destroys the leather washer so it will need to be replaced regardless. Note that the washer is made from treated rabbit skin; some unscrupulous suppliers are selling washers made from inferior cow leather but these parts will not impart the correct amount of friction so should be avoided. The easiest way to test if a washer is from cow or rabbit leather is to send it off for DNA testing.

Adjustment of Friction Washer

The precise amount of friction that the washer imparts on the magneto shaft is crucial to ensuring correct alignment of the gear teeth in operation. Adjustment is obtained by moving the gearwheel slightly in or out on the shaft. The friction is at the correct setting if, with the magneto at operating temperature (60 degrees centigrade for European models, 70 degrees for Empire models - pad the magneto in clean towels and put it in the family tumble dryer until it is at the correct temperature) you should be able to ease the ungummed edge of a Rizla Green King Size cigarette paper - note, NOT Rizla Red - between the magneto body and the washer. If there is insufficient clearance, allow the magneto to cool then prise the gearwheel away from the magneto with a large tyre iron. If there is excessive clearance, tap the gear with a hammer.
Title: Re: Engine breather
Post by: BigJim on 06.09. 2019 08:18
Thank you Sluggo,has cheered me up, now off to work.
Title: Re: Engine breather
Post by: Swarfcut on 06.09. 2019 09:19
Sluggo.  Hurley-Pugh were in the vanguard of engine development, prototypes featuring the first hand carved connecting rods, the material chosen being the pallet wood that came with deliveries of fine Chinese Silk Wiping Rags. Nothing was wasted, any material to hand was used, hence their great commercial success and world leading innovations.
  Cylinder bores were honed and finally the pistons were lapped and the bores polished to a mirror, low friction surface finish with a compound said to comprise 1/8" gravel, road tar and workshop floor sweepings. The fine metallic, mineral and hydrocarbon residue from this process was stirred "in vaccuo" with poxy resin and  used to treat the rabbit skin friction washer, as detailed above, producing a highly prized, rare and variable quality component, the benchmark for today's so called "pattern parts"
 

 Other Forum members may have more information and this thread may even merit a section of its own before the original breather post gets diverted.

Swarfy.
Title: Re: Engine breather
Post by: muskrat on 08.09. 2019 09:14
G'day BJ.
I like duTch have used 0.4mm oil jointing behind the cork to space it out a tad.
Cheers
Title: Re: Engine breather
Post by: morris on 10.09. 2019 22:36
G'day BJ.
I like duTch have used 0.4mm oil jointing behind the cork to space it out a tad.
Cheers
Ah... there’s another oil thread... *yeah*
I use Penstrol 20/100 high bollocks content for that...
Title: Re: Engine breather
Post by: Swarfcut on 12.09. 2019 16:54
Morris, that grade is a little light for the riding you do. White Star Line Lubricants do a grade that may be more suitable, covering temperatures from the Tropics to the Poles.

Swarfy.