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Author Topic: Banquo's Mighty Falcone top end rebuild  (Read 960 times)

banquo

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Re: Banquo's Mighty Falcone top end rebuild
« Reply #15 on: March 16, 2019, 11:48:49 am »
Not sure why you've said this banquo since you were in on another conversation in which a forum member  replaced his valves with thin stemmed examples and promptly had the brand new plot drop another valve. Or perhaps you've forgotten? He came to the conclusion that tappets gaps or rather lack of were the cause. One size of  the volkswagon flat four Beetle engine was also known to do this in the very late 60s early 70s,  To rid themselves of the problem Volkswagon changed valve clearances from .004mm to .006mm. NLM used to set their valves to no gap whch seems ok as long as the engines aren't worked hard, but continental advice has always been that the valves are fine as long as the valve clearances are correct. Since these engines have very heavy valve gear and the engine unshrouded by the fuel tank, the tendency is to run them tight to quieten the valve gear, Big mistake, standard these engines should always sound very tappety, somewhere between an industrial sewing machine and a concrete mixer..... with gaps set at .010 and .0.20mm respectively for inlet and exhaust cold engine I think. Perhaps you can advise?

Memory's not what it used to be Cloggy; I do remember someone (Huub) saying he's dropped a valve after an 8mm conversion, but don't recall it being on a new rebuild. I don't see valve clearance being related to the problem. M-G show two different clearances, 0.05-0.10 and 0.10-0.20. The tight clearance is much quieter but I've found a loss of compression on a hot engine, and reverted to the larger clearances. My theory, FWIW, is that excessive guide wear allows the valve stem to tilt far enough to jam in the guide, preventing closure, and with the inevitable collision with the piston following. If it were related to clearances, surely the problem would occur immediately, but certainly most of the issues I've heard of occurred after significant mileage. The stock valve springs seem ridiculously heavy, resulting in excessive camshaft wear, and my guess is the Mandello beefed them up in an unsuccessful attempt to overcome a known issue with dropped valves? Just a guess, and I'm no expert...  ;)

cloggy

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Re: Banquo's Mighty Falcone top end rebuild
« Reply #16 on: March 20, 2019, 09:56:21 am »
Huub's engine was low miieage when the valve broke, with no wear or galling on the valve stem. My theory, recently given more weight by the volkswagon experience is thus.
The pushrods are massive. As the engine heats up they are slow to warm [I've noticed tappet noise goes up and then drops back as the engine warms]. As the engine cools down they are the last to cool. Thus the need to run  big clearences. If the tappets are too tight both the valve seat and the valve have flame constantly over their surface. The seat thus can warp or be forced/drop out by expansion and the valve stem gets very hot causing the metal to lose strength. Thus when the valve cools down sufficiently to hit the seat again it can then break. Huub came to the understanding that the clearances were crucial, even with lighter valves and springs. Loads of old hands in Europe say the same. Keep an eye on the valve clearances and the engines will run and run.
 I guess the cam doesn't incorporate quietening ramps [or it may just be the disparate metals neccessatating large clearances]  so the valve does get far more of a hammering than say my M21 whch will happily glow in the dark and still not break a valve with it's soft springs. The volkswagon problem was confined to one engine size wherein there had been a slight change of head design that had an unforeseen negative effect on heat dissapation.
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randall

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Re: Banquo's Mighty Falcone top end rebuild
« Reply #17 on: March 21, 2019, 10:32:50 am »
I completely agree with what my colleagues  said

and I add that to avoid malfunctions we must first get in tune with the  NFalcone, understand it,  and above all love it;

The NF prefers to tide on the consular roads, possibly full of curves, in the hills and in hours without traffic,

carefully avoiding cities and highways, so as to be able to enjoy and listen to the rhythm of his engine, changing gear as less as possible and avoiding high revs of the engine,

you will see ,you will never have mechanical problems and the NF will reward you with many pleasant kilometers
 ;)
« Last Edit: March 26, 2019, 03:59:37 pm by randall »
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