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ET: Engine (Twin) Push rod tubes

paulgoodson

New Website User
VOC Member
I am in the process of removing the cylinder heads from my Black Shadow, which I’ve never done before. I’ve unscrewed the nuts holding the pushrod tubes in place but they are all completely stuck. I can’t shift them at all. Any suggestions gratefully received.
 

Marcus Bowden

Well Known and Active Website User
VOC Member
Never had a problem of sealing standard pushrod tubes but prefer the TT PR tubes as they save the hassle of extracting the tubes before head removal takes place, seals can be renewed without head removal. Can cope with miss alignment it compression plates are fitted. IT ALSO STOPS THE EARS BRAKING OF THE K1 AS THEY ARE NO LONGER REQUIRED. ! Having had the privilege of campaigning LRO 993 (ex-works big port Grey Flash) back in the 60's so adopted the mod for my bikes and have made several sets for other people too.
bananaman
AN OLD PHOTO as having digital gauges now makes it far simpler than trying to count the little dials & hold in memory.
P1050281.jpgHOTO
 

Bill Thomas

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VOC Member
I have had a pcv valve on my L/ning, For few years now, And had a bad leak, Where the Alternator goes ,
I am always playing, So can't blame The Bike, And I run pistons very loose !,
Just for a laugh I fitted a big breather on the chaincase filler, Like I had years ago !!,
Went out and it's fine ??, Didn't go as fast as normal, But what I am saying, Looks like the PCV is not big enough for MY ! Bike.
 

greg brillus

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VOC Member
Thanks Norman....... I was exhausted by the time I got home, but I couldn't be happier with the bike overall. Still a few small teething problems to sort out, but nothing over the top. I got 4 out of 4 great starts even though I was 7th on the grid, and was easily able to catch up to the front runners by the first corner.......Some of them are just much better riders than me. It is by far the most powerful British single I have ever ridden.
 

timetraveller

Well Known and Active Website User
VOC Member
Regarding the pushrod tubes being stuck in the cylinder heads; This is common and, in general, there is not a mechanical problem there. I find that the best way is to get something which will grip the tubes without marking them and then rotate them gently. Make sure that the upper nuts are lowered so that they are out of the cylinder head. It is probably a combination of soft washers, old oil, ? sealing compound, carbon etc. at the top which causes the problem. Once you have them rotating then you can start and wriggle them downwards. Lift the heads just a little before you start to do this as that will try to alter the angle of the tubes and help to loosen them at both top and bottom. The biggest problem I generally find is to get something which will grip the tube securely without marking it.
 

MartynG

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VOC Member
Greg, I understood that PCV valves will remain open when there is positive CC pressure and close when it is zero or negative. If you suspect that the flow rate thru the valve is not sufficient why not install one or two more in addition to the single one now in place, all operating in parallel. All you would need do is to modify the generator blanking plate to take additional outlets. I recall in Tuning for Speed PEI saying it was important for the breather to go straight up (or as close to as possible) before arcing down.

I can recall seeing another bit of advice that said PCV valves work best when they are horizontal, so the ball or flapper in them is not influenced by gravity or centrifugal force when cornering.

just some thoughts.

Martyn
 

BigEd

Well Known and Active Website User
VOC Member
VOC Forum Moderator
Never had a problem of sealing standard pushrod tubes but prefer the TT PR tubes as they save the hassle of extracting the tubes before head removal takes place, seals can be renewed without head removal. Can cope with miss alignment it compression plates are fitted. IT ALSO STOPS THE EARS BRAKING OF THE K1 AS THEY ARE NO LONGER REQUIRED. ! Having had the privilege of campaigning LRO 993 (ex-works big port Grey Flash) back in the 60's so adopted the mod for my bikes and have made several sets for other people too.
bananaman
I have never seen a TT pushrod tube "in the flesh" so don't quite see how how they are adjustable other than the smaller section being able to slide up and down in the crankcase seals? Does the the smaller diameter tube slide in the larger diameter part that screws into the head? If so is there a seal in the larger diameter part. A drawing would help explain the setup if someone has one.
 

stu spalding

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VOC Member
Regarding the pushrod tubes being stuck in the cylinder heads; This is common and, in general, there is not a mechanical problem there.
If I can repeat a previous post, the tubes that Peter mentioned, as made by Maughans, can be shifted by removing the adjuster and pushrod and tapping the tube down with a piece of round bar through the hole in the end of the rocker. Cheers, Stu.
 

vibrac

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VOC Member
I have a set of TT push-rod tubes but I found that the angle is more fixed than the standard tubes I found that with one of the last engines I built I could not screw into the head inserts without changing the compression ratio (cylinder height) I wanted.
I think the comment about producing your own tubes with thicker walls flanges (and perhaps a more pronounced lead in to the seal to help insertion?) is the best solution Its an easy lathe job as I believe the supposedly leaky series D tubes were not due to them being made of aluminum but more to do with the holes in the crankcase being wrong. Anyway if this new tube,new seals, no glue method fails thats what I shall try next.
You have to admit this is all fun the owner of a 2020 motorcycle will never enjoy......
 

Cyborg

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VOC Member
Having just spent three days this week at a state championship classic race event, I found the rear inlet pushrod tube lower "O" rings leaked quite a bit after each race........ I had added a PCV valve to the breather which came from the hole where the generator normally goes (this on a Comet engine)........The leak occurred for 2 reasons, one is the PCV valve is too restrictive causing too much crankcase pressure, and the second is with the extra added oil pump feeding the cam and followers, there is much more oil being flung around in the timing chest.......Added to that issue, I have not done enough to baffle the outlet from the breather to the vertical line back to the catch tank........The catch tank is quite small with a capacity of about 300 ml and after 2 race events, the tank was near full of oil..........Having said that, the cam and followers are showing no signs of wear, with no visible signs of any metal at the bottom of the timing chest. This proves that if the crankcase pressure is too much, then leaks will occur, no matter what you do. For those interested I came 2nd in my class in a field of about 22 bikes of various kinds and sizes. Cheers for now....... Greg.

Try tossing the PCV valve and install a reed valve. You should be able to source one from from the local junk yard. The upside to the junkyard ( or rather motorcycle breaker) is you get to see what different manufacturers are using and could buy the accompanying puke tank which might simplify separating and returning oil. Or maybe order one of the aftermarket ones for a Ducati. If it moves enough air for a big twin, the should be more than enough for the Comet. Maybe it’s time to explore the world of vacuum pumps. Lots of challenges for a M/C. You could also try what some of the old school drag racers (and current aircraft folk) did and plumb the breather into the exhaust. The vacuum created pulls air out of the engine. The drag racers originally did it to reduce oil escaping, but subsequently discovered it created a little extra HP as well. Just not sure if it would upset whatever pipe/meg you are using. Plus you would still have to separate the oil or risk becoming unpopular. If you are running any sort of silencer, then it won’t work. Again... the old school drag racers discovered that when the noise restriction folk moved in. Once they were muffled, the vacuum pumps started to evolve.
 
Last edited:

davidd

Well Known and Active Website User
VOC Member
I have never seen a TT pushrod tube "in the flesh" so don't quite see how how they are adjustable other than the smaller section being able to slide up and down in the crankcase seals? Does the the smaller diameter tube slide in the larger diameter part that screws into the head? If so is there a seal in the larger diameter part. A drawing would help explain the setup if someone has one.

The drawing is very helpful. 609 MPH, page 18.
Capture.PNG
The adaptor becomes part of the head, in effect, and the bottom of the adaptor is angled and flanged to mate with the tube, at an angle, if necessary.

See MPH for the full set of drawings.

David
 

BigEd

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VOC Member
VOC Forum Moderator
The drawing is very helpful. 609 MPH, page 18.
View attachment 38617
The adaptor becomes part of the head, in effect, and the bottom of the adaptor is angled and flanged to mate with the tube, at an angle, if necessary.

See MPH for the full set of drawings.

David
Thanks David. That explains how it works to allow for a different angle and deck height.
 

Marcus Bowden

Well Known and Active Website User
VOC Member
The reason that your TT tubes do not have the movement the standard tubes have for alignment is that I only had 1" diameter alloy to make them from and the hole in the nut is too tight a clearance, The real TT PR tubes have a radius at the bottom of the head adaptor and a bigger diameter funnel at the top of the tube under which there should be a conical washer sealing the very thin funnel against the radiused adaptor and a square form under the washer that the nut seats against. I just used an "O" ring grooved into the taper the very dumpy PR tube fitted against. Sorry, my handsome I shall endeavour to make another pair for you and myself when I get suitable material.
bananaman.
 

greg brillus

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VOC Member
The 2 parts that make the stock tubes become difficult to remove from the head is.......If the flange atop the tube is a snug fit in the head, and the lower sealing washer that sits bellow this flange and the gland nut........If you assemble the washer on to the tube, then linish the OD of both on a belt sander or similar, so the assembly slides easily into the head recess.......This makes assembly and future disassembly much easier.. Just quickly on my racer........I am going to make a shroud to sit over the breather inlet in the timing chest to stop excess oil being flung at it from the timing gears........ I will look at some form of reed type valve to reduce the build up of pressure in the cases, and this should stop the leak at the lower pushrod tubes........It is easy to see from this why the lower seals on a twin can easily leak in service with the tiny stock engine breather system........I have double "O" rings on each tube that normally seal with no problems, and the pressure is forcing oil out of them, especially the rear inlet one.
 

vibrac

Well Known and Active Website User
VOC Member
I had to turn a small amount off the OD of one new pushrod tube flange as it was catching on the head thread . I also made sure that the push rod nuts ran up into the head. one of the nice shiny chrome ones was a bit stiff I dont have a 1"X20 tpi plug tap (after all only the pushrod tube nuts have that size thread on a Vincent) so I selected an old brass coulored one which went in a treat I also assembled the head with the head nuts finger tight so there was a smigin of movement while the pushrod nuts were being run up. I then brought the head nuts up to 27ft lbs and tighted up the push rod nuts fully I shall bring the headnuts up to 32 today there is a lot to compress with the top hat 600 to 500 conversion plug and two gaskets.
 

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