Author Topic: Ignorance : PHOTO ADDED Why A10/A7 engines have no breather pipe?  (Read 976 times)

Offline worntorn

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Now I know why my enclosed chain always looks freshly oiled when I peer through the inspection hole!
Also, next day after a 50-100 mile run there might be a few drops of oil coming from the bottom of the chain case joint at the rear sprocket.
No need for an O or X ring chain on this bike. Road grit can't get at the chain and the crankcase breather keeps things nicely oiled. The chain will last a long time.

Glen

Offline trevinoz

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Glen, how does oil get into your enclosed chain? If I am reading this correctly, you have a fully enclosed rear chain.

Offline worntorn

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Looks to be a tube fitted into the breather hole , then a short bit of rubber hose and an elbow thru a hole in the chain case.
I guess all modifications by some previous owner?
It seems to do the job!

Glen

Offline bikerbob

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Worntorn the oil may not be coming from the breather pipe, I have an A7 which has a fully enclosed chaincase which at times leaks the odd drop of oil from one of the drain holes in the bottom section. My bike does not have a pipe from the breather to the chaincase like yours and the chain always seems well oiled, so the oil in my case I believe is coming from the back of the gearbox leaking along the main shaft and running down the sprocket lubricating the chain then dripping into the chaincase. This is a job that I intend doing over the winter lay up SRM supply a sprocket nut with an oil seal that helps prevent this type of leak. I am a bit surprised to have this leak as when I overhauled the gearbox a couple of years ago I replaced the bushes in the constant mesh gear.

Online morris

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Worntorn the oil may not be coming from the breather pipe, I have an A7 which has a fully enclosed chaincase which at times leaks the odd drop of oil from one of the drain holes in the bottom section. My bike does not have a pipe from the breather to the chaincase like yours and the chain always seems well oiled, so the oil in my case I believe is coming from the back of the gearbox leaking along the main shaft and running down the sprocket lubricating the chain then dripping into the chaincase. This is a job that I intend doing over the winter lay up SRM supply a sprocket nut with an oil seal that helps prevent this type of leak. I am a bit surprised to have this leak as when I overhauled the gearbox a couple of years ago I replaced the bushes in the constant mesh gear.
I had the same issue on the SA. In spite of changing the bush, with minimum shaft tolerance, it still leaked.
The SRM nut cured that completely.
For the record, the nut won't fit a plunger engine/gearbox though. Not enough space between primary case and sprocket.
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Online duTch

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 wornie and b-bob, have a sniff of the drips; g-box/tranny oil has a distinctive aromatic effect on your olfactory senses- as you are probably aware but forgot to mention  *beer*


 
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......For the record, the nut won't fit a plunger engine/gearbox though. Not enough space between primary case and sprocket.

 That's really handy info, thanks- I had wondered  *good3*
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
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Online JulianS

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Some sprocket splines are a poor fit on the constant mesh gear splines and oil seeps along them and drips onto the chain.

Offline muskrat

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G'day fellas.
I always put a good dob of silastic in the sprocket splines. The new nut from SRM also works well. Had one for years made locally.
O ring chains and heavy duty chains (our bikes only produce 40HP) may be too wide and rub on the case, and rob valuable power.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
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Muskys Plunger A7

Offline bikerbob

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Thanks for those tips Julian and Muskrat will have a look when stripped down over the winter.

Offline muskrat

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Wots winter???  *roll*
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
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Muskys Plunger A7

Online bsa-bill

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Quote
Wots winter???

in the UK anytime before and after the random week of  sunshine *sad2*
All the best - Bill
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Offline Peter Gee

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Interesting I have run my rebuild now for like 20 miles....I added a breather pipe stub and a pipe exiting below the gearbox....no oil drop  from this feature so far.

Never seen the like of it in decades of Brit builds! :-)

Offline Sluggo

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The topic of breathers comes up from time to time.  The truth is, for most people who motor about gently its not as much of a problem but truth is the stock breathers are woefully inadequate and contribute greatly to oil leaks.   This can be tested on any engine easily enough, But the Norton people seem to take the obsession to the next level.  However real results have proven that improved breather systems, especially with a check valve does improve performance as well as eliminating oil leakage.

Especially on a long stroke vertical twin, Uncorking it and then measuring the sheer volume of air going in and out, will show this.  There is also a correlation between pressure and volume, as in, the greater the capacity, the less the pressure exerts force.  Triumph, and late BSA engines tried to exploit this by sharing crank case pressure into the primary and then venting with a much larger pipe.

Ideally, the best system was developed by a clever fellow in Wisconsin named Erik Buell.  Other designs have since followed suit, But this can work on a British Vertical twin as well Although on some models the passage to the crank case is constricted via the pushrod chamber, But the attch picture shows the concept,

Used to be much press on a design called the BUNN BREATHER, and the ideas have evolved, what was relevant was if its possible (And proper check valves can make that happen) going from positive, to neutral and then ideally to negative pressure can really benefit any motor, especially long rod twins. (lots of huffing and puffing)

So what are the benefits?
A) Oil leakages will almost be eliminated
B) Slight boost in power
C) less oil fouling and contamination, as the rings seal better under a negative pressure.

Now,,, a modern Automotive LS motor is a total universe removed from these old engine, the benefits are measurable and demonstrable.  However, percentage wise may not seem worth it.

Horses for courses. 

However this article, which just came out demonstrates this concept quite well.  Many of the guys running vintage race bikes are using these same techniques, and guys like Herb Becker, and Alp are proving it at the track while racing 1950s and 60s vintage Britt Iron.

See: https://www.enginelabs.com/news/efi-university-finds-out-how-much-power-a-dry-sump-system-is-worth/?utm_source=rss&utm_medium=rss&utm_campaign=efi-university-finds-out-how-much-power-a-dry-sump-system-is-worth

"  “From 3,000 rpm to 6,000 rpm, on average, the engine made 17 lb-ft more torque and 14 horsepower more… Everywhere. Some places made more than that, some made a little less, but there was an increase everywhere.”

In addition to power, Strader also recorded crankcase pressure on the dyno pulls to be able to illustrate how hard the scavenge pumps are working. “We had no pan vacuum with the wet-sump system all the way across [the RPM range],” says Strader. “With the dry-sump, we had about 6.5 inches of vacuum at 3,000 rpm, and by the time we got to 6,000 rpm, we had almost 10 inches of crankcase vacuum in the engine. That improves the ring seal and helps with the windage, and that’s where that extra power came from.”
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Offline Peter Gee

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Amazing stats above! Whodathot it?

Offline Sluggo

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I cited the engine tech article as it proves a point, and while the main point was comparing a wet sump vs a dry sump system it indirectly proves my point about drawing a negative pressure (VACUUM) and how that aids ring seal and performance.  It shows as well, that inadequate breathing is rather counter productive both from a performance perspective as well as oil leakage.

While it should be obvious,, the engine in that Dyno testing I linked to is a LS based auto engine and the performance specs clearly in scale are impressive but you wouldnt see those numbers on a 500 or 650cc engine, but scaled to application, you WOULD see results. 

2 schools of thought always seem to endure. 

A) Pipe smoking tweed jacket types who insist 1940s and 50s technology is the top of the game and no reason to change.  AKA Factory knows best.

B) Those who enjoy optimizing old technology while enjoying the character of these old steeds.

Neither are really wrong, Horses for courses,, but at least acknowledge they exist. *smile*
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