Author Topic: Rattle  (Read 3761 times)

Offline muskrat

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Re: Rattle
« Reply #30 on: 27.07. 2010 21:08 »
Maybe I got it wrong, it's 6am here
Cheers
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Offline Goldseeker

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Re: Rattle
« Reply #31 on: 28.07. 2010 09:20 »
Having not seen a barrel other than on a complete engine I haven't a clue what the enclosed bits look like but the article only mentions one drain hole that is blocked.  *conf*

Roger has been doing this mod for a long time, apparently without problem.
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Offline MG

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Re: Rattle
« Reply #32 on: 28.07. 2010 09:31 »
There are two drain holes directly in front of the cam follower block, I'd say these are the ones to block.
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Offline Goldseeker

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Re: Rattle
« Reply #33 on: 28.07. 2010 15:59 »
I checked the mag article and the oil drain is mentioned in the singular as in "Oil normally drains down from the rocker boxes through a passage at the rear of the cylinder barrel. I block it off with a threaded plug". Are there different barrels with different drain holes?

I would have thought that for this mod to work as intended all drain holes would need to be blocked to ensure oil did flow through the cam follower grooves.

I suppose to definitively answer the accumulation of oil question you would need to know the volume of oil passing down the pushrod tunnel in relation to the cross sectional area of original drain holes compared to cross sectional area of the four slots in the cam followers. Anyone got a calculator handy  *smiley4*.

EDIT: Image below:- is this the blanked hole mentioned?
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Offline MG

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Re: Rattle
« Reply #34 on: 28.07. 2010 16:29 »
Regarding the tiny tube for the rocker box oil feed and the rather small amount of oil being pumped up there at low pressure, the volume draining past the slots in the followers shouldn't be a problem imho. And mind you, there's also oil draining past the followers themselves.

But I would definitely not block the drain hole(s) of the exhaust rockers, as this would mean the front part of the rockerbox will fill with oil to the level where it can overflow into the rear part and drain down from there. That oil in the front rockerbox compartment is very likely to cause trouble, either by passing through the ex valve guides or leaking past the rockerbox-head joint, not to mention the mess when taking off the rockerbox.

Re-using my picture again, I've marked where the drain holes are on my barrels. These are two drillings with approx. 5mm in diameter. If you stick a piece of wire up you will see it coming out through a passage directly over the followers top end (where the recess for the pushrod is).
What you have marked on your photo is the locating pin for the ex followers.


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Offline Goldseeker

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Re: Rattle
« Reply #35 on: 28.07. 2010 17:02 »
Thanks for that Markus, I'm learning more about A10's every day.  *smiley4*

It would make sense that the holes you indicate are those that should be blocked. I think it must have been a journalist error talking in the singular rather than plural.

Col.

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Offline chaterlea25

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Re: Rattle
« Reply #36 on: 28.07. 2010 22:36 »
Hi All,
As MG says the quantity of oil draining down the follower tunnel is small.
My opinion is ,
This drains anyway into the cam trough and some will be thrown back up to the followers via the cam
BSA didnt see the need for this mod and neither do I
The main supply for the cam and followers comes from the pressure relief bypass and I think it can be accepted by all of us that if this supply fails or is reduced drastically  the cam and followers fail in short order (no matter how good they are *ex* *ex*)
The most common cause of worn cam's / followers is that the main T/S bush is worn or the pump is fkd! (porus)
Also all the oil in the world will not prevent wear on crap pattern parts!!!

End fed crank conversions eliminate the loss of oil pressure at the T/S main and in my opinion (again) therefore increase oil supply to the cam and followers *smile*

Cheers
John O R

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Offline coater87

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Re: Rattle
« Reply #37 on: 29.07. 2010 11:03 »
 So what he did here, if I have this right...

 By blocking off both oil holes, the oil level will rise to the top of the follower- then HAVE to drain down the new grooves catching the follower faces, the lobes of the cam, and still getting to the trough.

 20 thousandths wear was mentioned as a benchmark. Are we talking about the depth of the wear on the follower faces?

 Lee
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Offline MG

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Re: Rattle
« Reply #38 on: 29.07. 2010 11:21 »
Quote
By blocking off both oil holes, the oil level will rise to the top of the follower- then HAVE to drain down the new grooves catching the follower faces, the lobes of the cam, and still getting to the trough.

 20 thousandths wear was mentioned as a benchmark. Are we talking about the depth of the wear on the follower faces??

Exactly


Quote
The main supply for the cam and followers comes from the pressure relief bypass and I think it can be accepted by all of us that if this supply fails or is reduced drastically  the cam and followers fail in short order (no matter how good they are  )
The most common cause of worn cam's / followers is that the main T/S bush is worn or the pump is fkd! (porus)
Also all the oil in the world will not prevent wear on crap pattern parts!!!

Absolutely agree to all of the above.
But the main benefit I see in this mod is the direct and continuous supply to each single follower and cam lobe even if the oil level in the camshaft trough should fall enough to let the cam run dry (imagine a hot engine idling at low oil pressure, relief valve not opening). So I see this more as a matter of emergency lubrication.
Another positive aspect could be the direct lubrication of the oncoming lobe. I expect most of the oil picked up in the trough will be flung off the (very smooth) lobe on it's way up. A higher amount of oil means better hydrodynamic lubrication.
Probably you are right and the whole discussion is academic, and I wouldn't pull a good engine apart just to do this mod, but otoh it can be done quite easily and if it doesn't help, it definitely won't hurt either.



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1955 A7 Shooting Star
1956 A10 Golden Flash
1961 Matchless G12 CSR

www.histo-tech.at - Restoration, Repairs, Racing

Austria