Valve seals
- Thread starter Paul W
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Check to see if you have cast iron or bronze guides. The old atlas cast iron guides did not have seals. We are talking inlet valves here. If you have bronze then then they probably took an intake seal. It may have been updated to bronze but if stock, them probably cast iron.Paul W said:
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Paul W said:
Inlet guides with seals were supposedly fitted from 149670 which relates to a date of manufacture around September 1971, however, there is an earlier service release that states inlet guides with seals were being fitted from about May 1971.
I don't think it's that easy Steve. He will have to get new guides if he wants to add seals. My RH1 had cast guides and I needed comnoz to change them out and seat the valves. I then could apply the inlet seals that he sent back, along with the head.SteveA said:
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Wonder how many owners investigated to determine why Dominators ran for DECADES perfectly well without valve seals and did so without pretending to be Ariel Arrows leaving a convoy protecting smoke screen behind them when as soon as you did tuning mods like fitting the 6 start worm drive to the pump then ones motor began smoking badly?
Personally I changed rings to 'these will cure it mate' Twiflex oil control rings which had no effect ...bored out the oil return hole back to the crank cases.....which had no effect......then Tommy Mortimer(ex AMC race shop friend) suggested we look in the inlet rocker area with the motor running.............oh my gaud....... at not much above tick over the oil level in the inlet valve side was filling the area well above the guides and not only flowing down the guides but also flowing over the hump into the exhaust side(along with the rockers throwing oil over us and the rest of the bike . I dread to think what was occurring at max revs!!......
That must have oil pump 6 start worm tuning mod was responsible. I personally fitted an additional external oil return from the side of the head just below the top of the inlet guides running it back into the timing chest and hey presto no more smoke screen and no need for oil seals. I understand from friends that many fit an external return from the floor of the inlet area between the inlet guides back to the rear of the crank cases.
I can only assume that by the time Commandos (or Atlas Mk3s as they were shown as on the drawings..well they were only a two year stop gap bodge model after all) were well into production there were no Engineers left at AMC / NVT capable of sorting the problem and valve seals were the cheap and only way around the problem they could come up with.
Later in life I learnt that the ONLY reason for the 6 start worm in the first place was because on the Domirace engines they employed positive pressure fed oil to the camshaft lobes (to stop them very quickly wearing out as occurs on Commandos!!) they had to increase the oil supply so the crank did not run out of oil!! If memory is correct one attempt to cure cam and follower problems on the 3s Triumph introduced a timed pressure supply to the cams which was quickly removed from production as the crank suffered from lack of oil......Did NVT do NO testing before introducing that modification just as AMC or whatever they were called by then had failed to do previously.....??????.
Personally I changed rings to 'these will cure it mate' Twiflex oil control rings which had no effect ...bored out the oil return hole back to the crank cases.....which had no effect......then Tommy Mortimer(ex AMC race shop friend) suggested we look in the inlet rocker area with the motor running.............oh my gaud....... at not much above tick over the oil level in the inlet valve side was filling the area well above the guides and not only flowing down the guides but also flowing over the hump into the exhaust side(along with the rockers throwing oil over us and the rest of the bike . I dread to think what was occurring at max revs!!......
That must have oil pump 6 start worm tuning mod was responsible. I personally fitted an additional external oil return from the side of the head just below the top of the inlet guides running it back into the timing chest and hey presto no more smoke screen and no need for oil seals. I understand from friends that many fit an external return from the floor of the inlet area between the inlet guides back to the rear of the crank cases.
I can only assume that by the time Commandos (or Atlas Mk3s as they were shown as on the drawings..well they were only a two year stop gap bodge model after all) were well into production there were no Engineers left at AMC / NVT capable of sorting the problem and valve seals were the cheap and only way around the problem they could come up with.
Later in life I learnt that the ONLY reason for the 6 start worm in the first place was because on the Domirace engines they employed positive pressure fed oil to the camshaft lobes (to stop them very quickly wearing out as occurs on Commandos!!) they had to increase the oil supply so the crank did not run out of oil!! If memory is correct one attempt to cure cam and follower problems on the 3s Triumph introduced a timed pressure supply to the cams which was quickly removed from production as the crank suffered from lack of oil......Did NVT do NO testing before introducing that modification just as AMC or whatever they were called by then had failed to do previously.....??????.
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J. M. Leadbeater said:
A Commando should not flood the rocker box if the correct spindles are installed and the rocker arm to spindle fit is good.
Of course scrolled spindles or non-scrolled spindles installed backwards will flood the intake valve area quickly with a 6 start pump. Jim
Nater_Potater
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Out of fear of derailing this post: assuming bronze guides, how about intake seals (runs cool, always under some partial vacuum attempting to draw oil into guide), and no exhaust seals (runs hot, pressure always trying to blow oil out)? I ran that way on an air-cooled 650 of dubious origin, and never saw oil smoke or consumption. The bike was sold before needing a top-end, so I don't know how the guides and stems would have looked. Has anyone else gone this route?
Nathan
Nathan
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Nathan you have described the standard 6 start oil pump Norton practice so every Cdo came that way unless altered off standard. Its kind of interesting -self monitoring when engine condition is such that its rings seal good so no smoke on wet sump initial fire up till after ~15 sec there a dozen or more seconds of blue smoke as oil pressure hits head to flow then clears up I guess from heat swell sealing seals and guldes gaps better. Exhaust side can never allow oil in while running but could drool into chamber if stopped w/o being full seated.
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