PCV Valve Source?

I'm not really in a position to argue about the advantages of a vacuum in the crankcases and any subsequent improvement in power. I have no reason to doubt it. My experience of thrashing Commandos is principally with Mk111s and they do apparently have better joint faces but I have to agree with the statement that a pcv valve should not be necessary to achieve oil tightness in the Commando engine. I'm puzzled by the assertion that pressure causes oil mist to pass to the primary. Surely a garter seal works more efficiently as the pressure on the lips increases (unless it's the wrong way round ) ?

My Mk111 is thrashed mercilessly. It has to be. I'm a fundamentally slow rider who 'bottles' it in nine out of ten bends, invariably scrubs too much speed off and has to go like the clappers to stay with the group.

That my Smiths clock is built with a red line-less Trident dial and that I thought for years that the safe max was 7500 rpm is only an aside. It has been regularly taken above seven through the gears and on occasion, along the Cronk y Voddy for example, taken past 7500 in top. It doesn't leak.

This is not some engine built by a top-level tuner or time-served engineer, it's been put together using the simplest of hand tools by me learning the hard way. It has been assembled to the best of my ability and if I haven't got it right then I'll do it again.

I find the imperative to treat the Commando like the 1970's hooligan tackle that it is far stronger than any urge to save a mass-produced machine for posterity

ludwig said:

pvisseriii said:

.. take a pill.

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Taking pills is like putting a PCV valve on a leaking engine ..

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Please explain the 72 crank pressure issue and the steps needed to properly remedy the problem. I you are unable to offer this info, can you link me in the right direction?

Thank you.

My engine is does not leak a drop. I did have blow by into the primary from the crank seal. A 6 dollar part fixed it 2 years and 10,000 mile ago. Is that so wrong?

And PLEASE read the original post and take a pill.[/quote]


How pvisserij (dutch ??) I do not want to upset you and definitly am not on pills
But do you have an opinion why your crankcase seal is blowing ? The engine I use in my special is also a 72 so I am familiar with the badly placed breather and oil-pick up . Yet even before I modified the cases it did not blow past its seals
Just to show it an be a pain somethimes to achieve what you want I rebuildt my engine 5 (five) times this winter before realising that the oilleak came through a blowhole in the cases wich was opened by the milling for the new oil-pickup .
I then installed the engine in the frame .Before the start up I wanted to drain the sump to find the small sump-plug had enough and shred its thread so nr 6 was in order . But I am taking hr to Colombres in oktober for a run with the friends on the Dukes and am not prepared to take any crap about oil-leaks
Perhaps I should be better off with the pils

lynxnsu said:

Perhaps I should be better off with the pils

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...You're better off with a decent top-fermented ale rather than that fizzy lager stuff...

http://www.witkap.be/witkap/witkap/Home.html

How pvisserij (dutch ??) I do not want to upset you and definitly am not on pills
But do you have an opinion why your crankcase seal is blowing ?

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I do not know why it blew. I change the seal and added the checkvalve. It is possible that I could have stopped at changing the seal.

Thank you for your kind reply and my apoligies for any ill tone. These Nortons can be so emotional.

FWIW, I do not have big leakage issues with my 72 Commando, although there was a slight drool coming from the front where the cylinder and head meet that a new head gasket has cured at least temporarily.

I have read the posts on breather location issues on 72' models. The PCV vlave is an easy installation and helps control crankcase pressure which helps prolong the life of the seals so there is no downside to installing one.

Anyway, I've got a friend ordering one of the MikesXS valves for me, thanks for the offers to help.

pvisseriii said:

How pvisserij (dutch ??) I do not want to upset you and definitly am not on pills
But do you have an opinion why your crankcase seal is blowing ?

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I do not know why it blew. I change the seal and added the checkvalve. It is possible that I could have stopped at changing the seal.

Thank you for your kind reply and my apoligies for any ill tone. These Nortons can be so emotional.

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Reports are that the new seal only helps for a while.

pvisseriii said:

Google the "Motormite Power Brake Check Valve pt #80190. It is available at discount auto part stores like AutoZone and Advance Auto in the "HELP" section.
The best part....$6.00. For what we are asking this to do, it should last a lifetime. For this price and effectiveness, you could buy all you can get and give them as gifts and be thought of often with good regards.

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Interesting how prices vary internationally, when i looked into it a year or so back the Mortormite was, from memory, about $30 in NZ!!!

$6 dollars was 2 years age but after a look around here in US, it is still 4 to 6 dollars.

pvisserij for any-one who is having oil-leaks from a 72 engine this is the cure or when your breather is pumping more oil than your oilpump .If you run your breather into your oiltank then there is no problem either.

block the original oil pick-up



mill a space so the oilpump can suck it up . the bigger the better




the black stuff is where i found a blowhole after the milling

Do not forget to drill a few holes in the timing side crankcase 11 mm if memory serves me right

Yes, I have read much of this mod and have seen many photos to document. i read also of the right side venting to the timing side and breathing through an Old Britts blanking plate added to the old mag area. Do you agree with this or is it over kill due to the new scavaging ability.
Although this procedure is a little ambitious for me, next winter will be my target. I do have a small mill in the basement and the few special tools will have to be required.

With regard to the oil pickup and breather modification to a 72 Commando, I would not bother with drilling the holes through to the timing case. Keep the original breather and route through a reed valve back to the oil tank. This is rather better.

I did drill through to the timing case and now regret doing this as going back to the 72 breather got rid of the last remaining oil weep from the head-barrel joint (only happened at >4000 rpm, but not any more).

Phil.

pvisseriii said:

Yes, I have read much of this mod and have seen many photos to document. i read also of the right side venting to the timing side and breathing through an Old Britts blanking plate added to the old mag area. Do you agree with this or is it over kill due to the new scavaging ability.
Although this procedure is a little ambitious for me, next winter will be my target. I do have a small mill in the basement and the few special tools will have to be required.

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I don't agree with the Old Britts approach for a road bike. Not when a simpler approach of a reed valve will work better. Although if I was running high RPMs for racing I'd probably look at changing the pickup.

lynxnsu said:

pvisserij for any-one who is having oil-leaks from a 72 engine this is the cure or when your breather is pumping more oil than your oilpump .If you run your breather into your oiltank then there is no problem either.

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I would prefer to not have ANY oil going up the rear breather tube as trying to push oil up the tube could increase crankcase pressure to an unacceptable level. this is the way I do the oil pickup relocation. this way you have a screen of sorts to stop larger debris from reaching the oil pump. I also like to leave the dam so as to stop the crank roatation from trying to push the oil to the breather port.

I removed the weir when rerouting the oil pickup on my '72. However, when taking the engine speed up to around 5000 rpm or so no oil makes it to the tank through the breather. This is unlike what was happening beforehand, when oil would spurt through the breather line a few seconds after achieving 4000 rpm.

Fully agree with CNW that the rear location is, after all, good for the breather. Perhaps ideally it should a mite higher with a crankcase reed á la two-stroke, but it's not bad.

Phil.

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I do not think drilling these holes is a good idea The pump has now the choice of 2 areas where to suck from If there is a possibility off sucking air thats what it will do . The oil has to cover the highest hole defore it will suck any oil up .If you only mill your cases than ALL the oil there will be sucked up because thats the lowest part AND protected from that big rotating mass in the concavity of your milled hole Indeed keeping that dam is a good idea