Bad luck David, That's a new one on me, All in 400mls !. What's the inside of the adjuster cap like, Sounds like something has put pressure on the pivot, Did TT say "has the top of the lower valve guide been shortened, For mk2s." Cheers Bill.
Valve piston clash
- Thread starter davidjoyner
- Start date
Probably not David's problem but decades ago I made a mistake which didn't fail for hundreds of miles. I managed to insert the rear inlet rocker arm too low. It flicked the collar ET35 upwards off the step and operated the valve by working just on the increased diameter until the forked end cracked and jammed on the larger diameter holding the valve open. I was two up on the way home from a Liphook meet when, to steals David's description, it sounded like a Comet but with the power of an allotment wheelbarrow! David may have overestimated the power of a twin running on a single cylinder.
Although adjustment will show the experienced assembler that the rocker adjuster is screwed in too far, (it may need the locknut moved to under the rocker) the rocker may contact the top of the lower valve guide earlier than the collar would.
It is something else to check out before lifting the heads.
Although adjustment will show the experienced assembler that the rocker adjuster is screwed in too far, (it may need the locknut moved to under the rocker) the rocker may contact the top of the lower valve guide earlier than the collar would.
It is something else to check out before lifting the heads.
Look on the bright side. You now know what it is but you still have to find out why. However the solution should be quick and cheap so it could have been a lot worse. However, now the head is off you can see if there are marks on the piston and if not then it sounds like the lower valve guide need cropping.
I can't remember ever changing ET 26 After I have built my bikes, And that is lots of years, + racing, And they were old bits anyway !. Like somebody said it is best to turn the engine over by hand after a rebuild, It will be interesting to find out what it was, Good Luck, Bill.
I cut the top off the adjusters, And grind two flats on the sides, To miss the inside of the cap, But you can buy allen key type adjusters, I think from the Club Shop, Cheers Bill.
My standard MO 17 shows the standard set up for rocker bushes ET26/1 held down by the rocker feed bolts ET100. One of the first things I learned when building my twin was that if the tunnels were worn longer ET26s could be fitted. If the tunnels were not worn, the best way to preserve them was to fit locking rocker feed bolts ET100/1? which held the ET26s up against the roof of the tunnel by screwing into a “top hat” nut inside the bush. Could loose tappets without locking feed bolts allow the bushes to rattle up and down causing the pinion ET28 to wear on the bushes?
Sounds to me like a cam has slipped in it's wheel, being retarded the exhaust valve is clipping the piston because of the late timing. Also if you have installed Mk 2 cams, the extra lift could be binding on something....if you installed new followers, a big one is the ball ends on the pushrods not fully seating into the cup of the new followers, which then wear quite rapidly, and then eventually sink down the hole giving odd tappet settings and poor adjustment........Ahhhh, like everything on a Vincent, it all needs checking and then double checking when you change something.
Here's a long shot- check that the locking rocker feed bolts are not protruding the locknuts and baulking the rocker arms movement. Happened to me recently! Gives a similar effect to valve/piston bothers.
Been domestic pressure - haven't had time to have a good look but the rocker pinion is fast in the rocker !
Sorry if it looks like I'm hijacking the thread, but I have Mk2 cams and had new guides fitted a couple of years back.
After this thread I went out and checked the clearance at max valve opening, exhaust is fine, but the inlet has 1- 1.5mm additional movement at the push rod end, is this sufficient.
JimR
After this thread I went out and checked the clearance at max valve opening, exhaust is fine, but the inlet has 1- 1.5mm additional movement at the push rod end, is this sufficient.
JimR