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Posted: Sat Jun 03, 2006 1:55 pm
by Guest
Moved 3-6-06

I've spotted a few unusual changes one of them is in the timing side crankcase there are two new .63" dia bosses cast either side of the tappets that are drilled .2402". Into these holes is fitted "Tappet Bearing Strip Pin Q71-4481" .246/.244" dia and over these pins slides the "Grommet-Tappet Guide Q60-4603". There is no drawing but there has to be a part called, something like "Tappet Guide plate" to fit between the inlet and exhaust tappets, it is allowed to float/self align due to the hard rubber grommets. If you also look at the "Camshaft drg Q71-4341" you will see that change number 1 was to increase the gap between the two cam profiles from .08" to .115/.120 presumably this was to make sure the Tappet guide didn't come into contact with the camshaft. This I think was one of a number of changes to make the engine quieter such as the changing of the rocker arms to line contact on the valve tips and also drilling the head and barrel to fit snub rubbers. It would be interesting to hear a P92 running with these changes as it would have had a really quiet exhaust note with the two Norton/Triumph black cap silencers of the day fitted.


valve clearance

Posted: Sun Jun 04, 2006 8:38 am
by Canberra
Anyone found a comment on associated valve clearances? Most top end noise is from the large standard BSA B50 clearances.


Posted: Sun Jun 04, 2006 7:21 pm
by b5070
John -- do you really need to run such big clearances????
We run Megacycle cams, and basically wind the adjuster in until the pushrod binds up, then back off until it will rotate.
Started doing this on the sayso of Ed V.
Have you ever pulled the rocker caps off with the engine really hot -- whilst using stock clearances?? It is scary !! :roll: You'd swear the pushrods had shrunk --- there is so much lash there!!!
If you use this method, just make sure you warm it up before giving it a lot of "welly" :lol:

Posted: Mon Jun 05, 2006 9:33 am
by JB

That minimal clearance is that with Cr/Mo pushrods?

I can understand running small clearances with steel pushrods but what about the std ally ones.


Oops, I forgot to sign in when I moved this post :oops:

Valve clearance and cam timing

Posted: Mon Jun 05, 2006 12:22 pm
by Canberra

I fitted lash caps along with a new valve after the top of a valve chipped off its edges. I have reduced clearance on my B50 and did a few 1000kms since EdV suggested it. I am running his chrome moly push rods and the engine sounds and seems to run sweater. I suspect that even with standard alloy pushrods you could reduce clearances as like you said when you open the inspection caps the high clearance is still there on a hot standard engine.

I guess the effect of reducing the clearances is that the valve opening is advanced a few degrees and closing retarded so valves are open longer. I wondered if the P92 cam was designed to run with reduced valve clearances and the profile changed to retain the same valve opening and closing degrees as the previous B50 engines.

Going back over the threads on this site it was suggested that with the MX cam it ran better if the cam timing was advanced so it seems to have covered two birds for me.


Posted: Mon Jun 05, 2006 8:16 pm
by b5070
John --- don't think the tighter clearances make that huge a difference, valve timing wise, as the lash is still pretty gnarly with a hot engine.
Sure, it's got to be better than running the stock clearances, as the valve timing has to be affected with the lash somewhere aroung 40 thou !!?? :shock:
I'm pretty sure Ed V said it made a bit of difference power wise, on the dyno.
It would be a bit tricky trying to check the valve timing with a stinking hot engine -- OOh AAAH Singe F*+k Goddamit, so it is a bit of an unknown quantity.
Nicest thing though, is the fact it quietens it down a good bit.
I used to use earplugs when I ran straight through mega's, and never really noticed the clatter. Then we went to a Cannondale quad, Bg Gun muffler, which was half as loud -- stopped using earplugs, and thought the thing ws falling to pieces when hot !! ;-)
As mentioned, I think the important thing is to always warm it up before riding hard. Try it and see !!

Posted: Tue Jun 06, 2006 5:54 am
by B4450Paul
Rupert Ratio says the same with aluminum pushrods .
ie. just enough clearance for push rods to turn .
he says clearance grows as engine heats up .
my B50 ss still clatters abit when hot .

Posted: Thu Jun 08, 2006 7:53 am
by ghislain
:grin: Clatters ?????
Mine sounds as if someone was moving a lot of empty bottles just between my legs....quite a difference with my B 40 (iron cylinder) wich is smooth as silk (but lazy). :mrgreen: